Tag Archives: 3D printing

Transitioning from TinkerCad to Blender with CAD Sketcher

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Posted 6 August 2022

I have been been doing 3D printing (a ‘Maker’ in modern jargon) for almost a decade now, and almost all my designs started out life in TinkerCad – Autodesk’s wonderful online 3D design tool. As I mentioned in my 2014 post comparing AutoDesk’s TinkerCad and 123d Design offerings, TinkerCad is simple and easy to use, powerful due to its large suite of primitive 3D objects and manipulation features, but runs out of gas when dealing with rounded corners, internal fillets, arbitrary chamfers and other sophisticated mesh manipulation options.

Consequently, I have been keeping an eye out for more modern alternatives to TinkerCad – something with the horsepower to do more sophisticated mesh modeling, but still simple enough for an old broke-down engineer to learn in the finite amount of time I have left on earth. As I discovered eight years ago, AutoDesk’s 123D Design offering wasn’t the app I was looking for, but Blender, with the newly introduced CAD Sketcher and CAD Transforms add-ins, may well be. Blender seems to be aimed more at graphic artists, animators, and 3D world-builders rather than for the kind of dimension-driven precision design for 3D printing, but the CAD Sketcher and CAD Transforms add-ons go a long way toward providing explicit dimension-driven precision 3D design tools for us maker types.

I ran across the Blender app several months ago and started looking for online tutorials; the first one I found was the famous ‘Donut Tutorial’ by Blender Guru. After several tries and a large amount of frustration due to the radical GUI changes between Blender 2.x and 3.x, I was able to get most of the way through to making a donut. Unfortunately for me, the donut tutorial didn’t really address dimension-driven 3D models at all, so while the tutorial was kinda fun, it didn’t really address my issue. Then I ran across Maker Tales Jonathan Kobylanski’s demo of the CAD Sketcher V0.24 Blender add-on, and I became convinced that Blender might well be a viable TinkerCad replacment.

So, I worked my way through Jonathan’s CAD Sketcher 0.24 tutorial, and as usual got in trouble several times due to my ignorance of basic Blender GUI techniques. After posting about my problems, Jonathan was kind enough to point me at his paid “How To Use Blender For 3D Printing” 10-lesson series for $124USD. I signed right up, and so far have worked (and I do mean worked!) my way through the first six lessons. I have to say this may be the best money I’ve ever spent on self-education (and at my advanced age, that is saying a LOT 🙂 ). In particular, Jonathan starts off with the assumption that the student knows absolutely NOTHING about Blender (which was certainly true in my case) and shows how to set the program up with precision 3D modeling in mind. All lessons are extensively documented, with video, audio, and all keypresses fully described. At first I was more than a little intimidated by the deluge of short-cut keys (and still am a little bit), but Jonathan’s lessons expose the viewer to slightly more bite-size chunks than the normal fire-hose method, so I was able to stay more or less on the same continent with him as he moved through the design step. I also found it extremely helpful to go back through the first few lessons several times (very easy to do with the academy.makertales.com lesson layout), even to the point of playing and replaying particular steps until I was comfortable with whatever procedure was being taught. There is a MakerTales Discord server and a channel dedicated to helping academy students, and Jonathan seems to be pretty responsive in responding to my (usually clueless) comments and pleas for help.

Jonathan encourages his students to go beyond the lessons and to modify or extend the particular focus of any lesson, so I decided to try and use Blender/CAD Sketcher for a small project I have been considering. My main PC is a Dell XPS15 laptop, connected to two 24″ monitors via a Dell WD19TBS Thunderbolt docking station. I have the monitors on 4″ risers, but found they still weren’t high enough for comfortable viewing and seating ergonomics, so I designed (in TCAD, several years ago) a set of riser risers as shown in the image below

My two-display setup. Note the red ‘riser elevators’ under the metal display risers
Closeup showing the built-in shelf for my XPS 15 laptop

As shown above, the ‘riser elevator design incorporates a built-in shelf for my XPS15 laptop. This has worked well for years, but recently I have been looking for ways to simplify/neaten up my workspace. I found that I could move my junk tray from the side of my work area to the currently unused space underneath my laptop, but with the current arrangement there isn’t enough clearance above the tray to see/access the stuff in the back. I was originally thinking of simply replacing the current 3D printed risers with new ones 40mm higher, but in an ‘aha!’ moment I realized I didn’t have to replace the risers – I could simply add another riser on top. The new piece would mate with the current riser vertical tab that keeps the laptop from sliding sideways, and then replicate the same vertical tab, but 40mm higher.

Doing either the re-designed riser or the add-on would be trivial in TinkerCad, but I thought it would be a good project to try in Blender, now that I have some small inkling of what I’m doing there. So, after the normal number of screwups, I came up with a fully-defined sketch for a small test piece (I fully subscribe to Jonathan’s “When in doubt – test it out” philosophy), as shown:

CAD Sketcher sketch for the test piece. Same as the final piece, except for height

I then 3D printed on my Prusa MK3S printer. Halfway through the print job I realized I didn’t need the full 20mm thickness to test the geometry, so I stopped it midway through and placed it on top of one of the original risers, as shown in the following photo:

Maybe not completely perfect, but still a pretty good fit

After convincing myself that the design was going to work, I modified the sketch for the full 40mm height I wanted, and printed 4ea out, as shown:

CAD Sketcher sketch for the full-height version
4ea full-size riser add-on pieces

After installation, I now have my laptop higher by 40mm, and better/easier access to my junk tray as shown – success!

Finished project. Laptop higher by 40mm, junk tray now much more accessible

And more than that, I have now developed enough confidence in Blender/CAD Sketcher to move my 3D print designs there rather than relying strictly on TinkerCad. Thanks Jonathan!

16 August 2022 Update:

Just finished Learning Project 7: Stackable Storage Crate, and my brain is bulging at the seams – whew! After finishing, I just had to try printing one (or two, if I want to see whether or not I really got the nesting geometry right), even though each print is something over 13 hours on my Prusa MK3S with a 0.6mm nozzle. Here’s the result:

Hot off the printer – after “only” 13 hours!
Underside showing stacking groove. Printed without supports, just using bridging

Frank

FlashForge Creator PRO 2 IDEX Filament/Color Designator Project

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Posted 29 July 2022

I’ve had my Flashforge Creator PRO 2 IDEX 3D printer for a while now, and ever since Jaco Theron and I got the Prusa Slicer Configuration for this printer working, I have been enjoying trouble-free (as much as any 3D printer is ‘trouble-free’) dual-color printing.

However, there are some ‘gotchas’ that can make using this printer annoying.

  • The way that the FFCP2 filament spools are arranged on the back of the printer means that the filament from the left spool feeds the right extruder, and vice versa, which leads to confusion about which filament feeds what extruder
  • The printer configuration in the slicer refers to the left extruder as ‘Extruder 2, the left extruder temperature as ‘T1’, the right extruder as ‘Extruder 1, the right extruder temperature as ‘T0’, so I’m never sure which physical extruder I’m dealing with when setting up for a print.
  • The filament spools are located at the rear of the printer, so it’s impossible to tell what filament type is loaded without physically rotating the whole printer, removing the spool from the holder, and looking at the label. And, since my short-term memory is about equal to that of a amoeba, I wind up doing this multiple times.

So, I decided to see what I could do to ameliorate this issue. The first thing I did was to use my handy-dandy Brother label maker to label the left and right extruders with their respective designations in the software, as shown in the photo below.

The next thing was to use my newly-acquired Blender super-powers to create and install removable filament color/type tags to both sides so I would no longer have to rely on my crappy memory to know what filament type and color was loaded on each side, as shown in the following photo.

Filament type and color tags for each extruder

The type/color tags slide into slots in the plate holders, and the plate holders are mounted using the FFCP2′ 4mm hex-head front plate mounting screws. I printed up tags for all my normal colors and filament types and store them inside the printer (the red box seen inside the printer on the left-hand side). Then, when I change a spool, I change the tags to match the new filament type & color.

FlashForge Creator Pro 2 Dual Independent Extruder (IDEX) 3D Printer

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Posted 30 August 2021,

For the last year and a half or so I have been struggling to get reliable multi-material 3D prints from my MakerGear M3-ID Independent Dual Extruder (IDEX) machine, and failing. I could get it dialed in for a few prints, but then prints would simply refuse to stay attached to the build plate no matter what I did. I tried everything I could think of, short of ‘hair-spray’ and ‘glue-stick’ options, which I refuse to do. In addition, the web-browser-only operator interface to the M3-ID was more than a little clunky. The printer was set up about 2 meters away from my PC, so I kept having to run back and forth to get simple things done, like load/unload filaments or do first-layer calibrations, or cancelling a print when it, once again, jumped off the build plate.

Eventually I realized I was never going to get it to work reliably in my small home lab, so I started looking for alternatives. In addition to the M3-ID, I have a Prusa MK3S single extruder printer that is completely reliable, almost completely silent when printing, and about twice as fast as the M3-ID. I seriously considered getting the MMU2 multi-material add-on to the Prusa, but there are some serious drawbacks to that option; for one, there have been many reports where running dissolvable and structural filaments through the same extruder causes the printed part to basically fall apart, due to filament cross-contamination. For another, printing a dual material part with the Prusa takes MUCH longer than printing the same dual material part with dual extruders, because the Prusa setup has to go through a complete filament retraction, change, and purge cycle for each material change. For a complex part this adds up to hundreds or even thousands of change cycles.

So, back to the web, where amazingly enough I found that FlashForge had just recently come out with their Creator Pro 2 IDEX model, at a very reasonable price-point. Moreover, I was able to find several YouTube reviews by well-respected 3D printer enthusiasts, and they had very good things to say about the printer. One of the most consistent comments was how easy it was to assemble the printer out of the box and get very high quality prints, and – important to me – get high quality prints using PVA water-soluble support material paired with PLA. In addition, at least one of the reviewers was successful in printing with PETG, even with the 240C extruder temperature limit on the stock extruders. And, even better, there is removable build plate option that works flawlessly (with the addition of a 2mm shim – available on Thingiverse). The build volume of the Creator Pro 2 is about half the volume of the M3-ID, but since I rarely build large items that wasn’t a deal breaker for me.

So, I put my MakerGear M3-ID up for sale on eBay for about a third of what I paid for it, and it sold in about an hour. Then I used the proceeds to buy the FlashForge Creator Pro 2 with a little bit left over – sweet!

When I received the unit, the shipping box looked a little bit beat up, and some of the foam packing material was damaged, so I was worried about printer damage. However, the printer itself seemed in perfect condition, other than a seriously mis-aligned X axis carriage (more on that later). Here are some photos I took during ‘unboxing’ and assembly.

After getting everything unboxed, I started going through the ‘quick start guide’, and rapidly got the extruder assemblies attached to the X-axis carriage, but when I checked the X-axis alignment with the very well thought-out alignment tools (the grey 3D printed parts in the above photo), I discovered the carriage was way out of true, as shown in the following photos:

So, I decided it was time to see how well FlashForge support worked, and I was pleasantly surprised that I got a very quick response to my email. I was connected to ‘Cheery’, who said he would be responsible for getting me going, and he did an excellent job of doing just that. After a couple of back-and-forths, he sent me a link to a video demonstrating how to re-align the extruder carriage. The video showed a FlashForge technician simply reaching into the printer, and brute-forcing the carriage into alignment – wow! Never in a million years would I have tried this without seeing the video – just not something you contemplate doing with your brand-new printer. While watching the video I heard some quite loud clicking sounds which at first I attributed to background noise in the obviously industrial setting, but then realized it was actually the printer itself making the clicking noises as the tech forced the carriage into alignment. I verified with ‘Cheery’ that I too should hear ‘clicks’, and that gave me the courage to apply enough force to overcome whatever ratcheting mechanism is associated with the carriage. I’m a big guy and in pretty good shape for an old fart, and it took some real force to make anything happen. In any case, I eventually got the right number of ‘clicks’ and the carriage was then aligned perfectly – yay!!

Once I got everything put together, I did a couple of the test prints provided by FlashForge, including one they called a ‘Hilbert Square’ that required a support material. I decided to try it with PVA water-soluble material support, and it turned out very nicely.

Not museum quality, but plenty good enough for me!

Although not perfect, this print was SO much better than I had ever been able to achieve with the M3-ID that I almost cried from happiness; out of the box with no real tuning, using FlashForge’s so-so proprietary FlashPrint5 slicer, and bingo – great prints with dissolvable supports – yay!

The next thing I tried was my pill-dispenser design, which features a sliding drawer arrangement to dispense one pill or caplet at a time from a bottle. The sliding drawer requires a dissolvable support to make it work, and again the print worked like a champ on the very first try.

Needless to say I’m extremely happy with my new FlashForge Creator Pro 2 IDEX printer. There are lots of things to quibble about (FlashPrint doesn’t seem to recognize the USB connection, and it’s kind of clunky compared to Simplify3D or Prusa Slicer), but it really, really does a nice job of printing, at least with PLA and PVA support material. I’ve already printed a set of ‘universal filament spool holders’ to replace the FlashForge proprietary ones, and I’ll be doing some more prints in the near future. I have quite a backlog of dual-color, dual-material prints I have been unable to finish while fighting the M3-ID, and I’m looking forward to actually being able to set up a print and walk away, knowing the FFCP2 is reliable enough to leave alone.

28 March 2022 Update:

Since this post was first published back in August of last year, I have been pretty happy with the Flashforge Creator Pro 2 IDEX machine, especially since Jaco Theron and I collaborated (well, Jaco did all the work and I helped with the testing) on a Prusa Slicer config file and post-processing script for this printer, I’ve been even happier.

Unfortunately that all came to a screeching halt about a week ago as I was doing some dual-color test prints to prove out Jaco’s latest changes. First I suffered a filament jam in my right extruder, which I could not seem to clear using my tried-and-true methods.

After a lot of cursing and gnashing of teeth I finally did get it cleared, only to start getting errors about the right extruder not holding temperature. I’ve never heard of this error before, so after scratching my head and searching vainly through the inet, I wound up completely disassembling the right extruder assembly, whereupon I found that the thermocouple cable to the right extruder had broken off where it enters the heat block, as shown in the following photo:

broken thermocouple cable (blue wire) where it enters the heat block.

I had been working with ‘Cheery’ from FlashForge’s After-sales support site through this process, and after verifying the printer was still under warranty, he arranged to have a completely new extruder assembly shipped to my house, from China via DHL – talk about customer support – Wow!

So, the DHL box arrived today, and sure enough, it contained a brand-new extruder assembly, including a brand new stepper motor already attached – wow and wow!

New extruder assy still in its protective foam wrapper, old parts on build plate
Old (left) and new extruder assy – note damaged thermocouple cable on old part

30 March 2022 Update:

I had some time last night, so I installed the replacement extruder assembly. This took a couple of hours and the requisite number of mistakes, including the required “Oh shit – I dropped a screw into the printer and it (of course) went right into one of the gaps in the interior floor and into the electronics space in the bottom – crap!” At first I thought – “no problem, I have spares”, only to realize later that I didn’t have spares for that particular set of two screws – double crap!

And, one last little ‘gotcha’; when the new extruder module was assembled at the factory, the cooling fan was mounted upside down, with the open port for cooling air to the extruder pointing up, and the closed ‘top’ pointing down, as can be seen in the following photo:

red circles show upside down fan mounting. Airflow direction arrow circled at upper right

Anyhoo, after removing the bottom cover of the printer (this turned out to be pleasantly easy, with only four screws vs the 54,225 for normal printers) to find and recover the (literal) loose screw and re-orienting the cooling fan to mate properly with the cooling duct, I finally got everything back together. That was enough drama for last night, so I waited until today to see if my repair worked. After loading filaments and calibrating, I printed a two-color calibration cube using Prusa Slicer for slicing; It turned out pretty nice, as shown below:

two color calibration cube, with ‘draft shield’ enabled

Stay tuned,

Frank

Basketball Shot Make/Miss Recorder

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Posted 27 November 2020

After my recent right shoulder surgery, I have been looking for ways to get back into BBall shooting practice. However, the combination of Covid-19 lockdowns and the oncoming winter weather has drastically reduced my options for shooting practice. Not to be dissuaded from BBall practice, I figured out a way of moving my practice area from my driveway outside the garage inside the garage. As it turns out, our earth-sheltered house boasts an attached earth-sheltered two-car garage with a 12′ interior ceiling and no vertical support beams (I insisted on this in the design, and paid the extra cost, knowing from prior experience that interior support columns in a two-car garage was a bad thing.

Still not quite perfect, as even a 12′ ceiling isn’t quite enough room for a 10′ high BBall rim and enough headroom for practical shooting practice. So, I decided to mount my new practice rim at 9′ vs 10′, leaving 3′ of headroom. Obviously this isn’t ideal, but I figured a lot of practice on a 9′ rim was much better than no practice on a 10′ rim ;-).

As I started to shoot in my new practice gym, I realized I also now needed a way to record hits and misses so I could keep a running ‘made shots’ percentage. My short-term memory degradation due to being an old fart has made it almost impossible to do this in my head, and besides, what could be better than being able to combine my love of BBall, my love of programming, and my love for hardware/software projects? That’s at least a trifecta if not a quadfecta (and that is actually a word!). So, I programmed up a Windows program in C# to display ‘Hits’, ‘Attempts’, and ‘Hit Percentage’, and used an Arduino microcontroller to interface to two push-buttons – one for a hit, and the other for a miss. The arduino talks to the Windows program via a serial port over the USB cable, and the Windows program displays everything in a readily visible way. My idea was to use foot switches for the input so it would be easy to provided the needed hit/miss inputs without having to break out of a shooting rhythm. So, I jumped up on Thingiverse and found a neat, rugged footswitch by ‘vandenmar’. I needed two switches, so I modified vandenmar’s design by adding an additional cable routing trench out to the other side of the switch (so the switch cable can be routed in from the left or right-hand side of the switch).

My very own indoor basketball court (with a few minor restrictions…)
Nice, rugged footswitch design by vandenmar on Thingiverse
The 12 mm switch used here is available from Adafruit

Here’s a photo of the Arduino switch contoller

After getting all the pieces together, this is how it looks in my garage. The red footswitch is for ‘makes’ and the blue one is for ‘misses’.

red/blue footswitches, with cable to UNO and laptop in the background

This setup worked pretty well, but it still wasn’t quite ready for prime time. The UNO & breadboard were, well, breadboards, and not very mechanically robust. I was afraid I would spend more time repairing the breadboard than I would actually shooting, so I decided I needed to move from a breadboard to a more finished project. In addition, the Windows program I was using to display stats needed some work, so both sides (Windows and Arduino) needed some TLC.

I happened to have a Sparkfun Pro Micro module laying around in my parts bin, so I decided I would change out the UNO for the much smaller Pro Micro. With only two pushbutton switches and a Red/Green LED, the Pro Micro has plenty of I/O for the project. Here’s the Pro Micro version of the hardware layout.

So then I opened up my trusty Open SCAD ’rounded box with lid’ script and printed up a translucent enclosure, shown below

Sparkfun Pro Micro translucent enclosure. Photo above shows the ‘Make’ green LED illuminated

Next I updated the Windows program to show Makes, Misses, Percentage makes, and number of shots made in a row, along with the longest run of made shots for this session, as shown below

And here is the ‘final’ setup in my garage:

The two footswitches are shown at bottom left, with the Pro Micro enclosure hanging down from the laptop.

Here’s the schematic for the Sparkfun Pro Micro setup

And here is a short video showing the system in action.

At 0:43 into the above video you can see the green ‘Make’ LED illuminate in the background when I pressed the red ‘Make’ footswitch, and at 1:25 you can see me pressing the blue ‘Miss’ footswitch.

Stay tuned!

Frank

New Wheels for Wall-E2

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Posted 24 August 2020, 1402 days into the Covid-19 Lockdown

My autonomous wall-following robot Wall-E2 is now smart enough to reliably follow walls and connect to a charging station, at least in my office ‘sandbox’ testing area, as shown in the following video

However, as can be seen toward the end of the video, Wall-E2 had some trouble and almost got stuck making the third 90 degree turn.  Apparently the current thin 90mm wheels just don’t provide enough traction on carpet.

So, I decided to see what I could do about re-wheeling Wall-E2.  After some research I found there are now plenty of larger diameter wheels for robots out there, but I couldn’t seem to find a set that would fit Wall-E2 and still allow me to keep the current set of wheel guards.  I needed the same (or maybe slightly larger) diameter for ‘road’ clearance, but something less than about 20 mm thick to fit within the current wheel guard dimensions. Then it occurred to me while reading the specs for one of the wheels (ABS for the wheel, and TPU for the tire)  that I already had two 3D printers standing around waiting for something to do, and I had a plentiful supply of ABS (or in my case, PETG) and TPU filaments – why not build my own?  After all, how hard could it be?  As you might guess, that question started what now feels like a 10-year slog through ‘3D printed wheel hell’

I wanted to create a spoked wheel with a hub that would accept a 3mm flatted motor shaft, and I wanted to fit this wheel with a simple TPU treaded tire.  The wheel would have small ‘guard rail’ rims that would keep the tire from sliding off.

It started innocently enough with a search through Thingiverse, where I found several SCAD scripts for ‘parameterized’ wheels.  Great – just what the doctor ordered!  Well, except that the scripts, which may have worked fine for the authors, didn’t do what I wanted.  and as soon as I tried to adjust them to fit my design specs, I discovered they were incomplete, buggy, or both.

I had wanted to learn a bit more about SCAD anyway and this seemed like a good project to do that with, so I persevered, and eventually came up with a SCAD design that I liked.

I started with bioconcave’s ‘Highly Modular Wheel_v1.0.scad’ file from Thingiverse, and (after what seemed like years trying to understand what was going on) was able to extract modular pieces into my own ‘FlatTireWheel’ scad script, as follows:

Here’s a screenshot of a completed 86mm wheel with elliptical spokes and a hub compatible with a 3mm flatted shaft.  When a TPU tire is added to the rim, the assembly should be about 90mm in diameter.

SCAD-generated wheel with elliptical spokes and a hub compatible with a 3mm flatted shaft. Note extensions to set screw hole through spoke and rim

One of the many issues I had with the original code is it assumed the hub would sit on top of the spokes, and therefore there was no need to worry about whether or not the setscrew arrangement would be blocked by the spokes and/or rim.  Since I wanted a wheel that was mostly tread, I wanted to ‘sink’ the hub into the spokes as shown above. In order to make this work, I needed to extend the setscrew access hole through the spoke assembly and through the rim.  In the finished design, the hub assembly can be moved freely up and down in the center of the wheel, and the hole extensions will follow.  If the hub setscrew hole isn’t blocked by the spokes and/or rim, then the extensions don’t do anything; otherwise they extend the setscrew hole as shown above.

Here’s a photo of separate wheel/tire pieces, and a completed wheel/tire combination on Wall-E2

Separate wheel & tire parts, plus a completed wheel on Wall-E2

2 September 2020 Update:

After running some sandbox tests with my new wheels, I discovered that the new tires didn’t have much more traction than the old ones. However, now that I ‘had the technology’, it was a fairly simple task to design and print new tires to fit onto the existing new rims. Rather than do the tire design in SCAD, I found it much much easier to do this in TinkerCad. Here’s a couple of screenshots showing the TCad design.

Original printed tire on the left, new one on the right. Note more aggressive tread on new tire
Exploded view showing construction technique used for new (and old) tire. Very easy to do in TinkerCad!

03 September 2020 Update:

The increased traction provided by the new tires have caused a new problem; on a hard surface the rotation during a ‘spin turn’ (one side’s motors going forward, the other going in reverse) is too fast, causing the robot to slide well past the target heading. Not so much of a problem on carpet, but how would the robot know which surface is in play at the moment. After some thought, I decided to try and modulate the turn rate, in deg/sec, as a proxy for the surface type. So, in ‘SpinTurn()’ I put in some code to monitor the turn rate and adjust the motor speeds upward or downward to try and keep the turn rate at a reasonable level.

Here’s a video of a recent run utilizing the new ‘SpinTurn’ rate modulation algorithm

And the data from the three ‘spin turn’ executions, one on hard surface, and two on carpet.

Spin Turn executions; hard surface, followed by two carpet turns

As can be seen in the above video and plots, the motor speeds used on the hard surface turn is much lower than the speeds used during the carpet turns, as would be expected. This is a much nicer result than the ‘fire and forget’ algorithm used before. Moreover, the carpet turns are much more positive now thanks to the more aggressive tread on the new tires – yay!

Lab Power Supply

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Posted 30 June 2020,

Almost exactly one year ago I ran across some posts regarding a very nice lab power supply regulator and display called the DPS500x power supply front-end.  My existing linear style supply was getting a little long in the tooth, and ran out of gas pretty quickly above about 12V and 1A.  So, I decided it was time to upgrade, and wound up with a very nice, lightweight well-performing unit.  Unfortunately I forgot to document the project and when I recently wanted to point someone else to this nifty product, I didn’t have anything comprehensive to point to!

So, this post is a belated documentation post for the project.

There are three ‘big’ pieces (big in terms of importance, but not in actual size or weight) used in this project; the controller head itself, an appropriate housing, and a AC/DC power supply that will fit inside the housing

The DPS5005 50V 5A constant voltage/constant current digital controller head

This is a really neat little gadget that takes a DC power supply as input and steps it down to the desired output voltage using a highly efficient buck voltage converter technique, and applying some constant voltage/constant current magic to the output, all in a package that is maybe 40 x 60 x 30 mm.  I got mine from Banggood.com, but they are available everywhere.

DPS5005 from Banggood

A suitable housing

In this case, an aluminum two-piece housing and hardware kit custom designed to house the DPS500x series of power supply controller heads.  The upper and lower halves slide together via a tongue-and-groove arrangement, and is VERY well done.  In addition, the housing has three sets of internal rails that make it easy to align/mount internal assemblies – NICE!

As the second photo above suggests, one suggested layout is to have an external 25-50V power supply connected to this piece, with basically nothing inside.  However, I did some research and convinced myself that I could fit a small open-frame AC/DC power supply inside the housing and wind up with a complete unit, just with lower wattage.

An AC/DC power supply

I wanted one that could fit inside the housing between the front and back plates to provide the ‘raw’ DC voltage to the controller head.  In the past I have used a number of Mean Well supplies and found them to be small, reliable, and cheap, so I started looking for a unit that could deliver 24V at 2A or greater (the most I thought I would need for a general-purpose bench-top power supply) while still fitting into the housing.  After a bit of research, I found that the Mean Well EPS-65-24 24V 2.7A open-frame power supply would do the trick nicely, and was available from Mouser for $13.80

Side view of power supply with model number shown

With all the ‘big’ parts identified and ordered, there some smaller issues that needed to be addressed:

Custom 3D printed back panel:

Because I was planning to use an internal AC/DC power supply rather than an external one, I needed a panel-mounted AC plug instead of DC Banana plugs, and I wanted an AC ON/OFF switch as well.  So using the basic dimensions and layout of the existing back panel, I designed a new one in TinkerCad to meet my needs.  I found some designs for 40mm fan grills on thingiverse and used them to create a cutout directly into the back panel, and took the cutout dimensions for the power switch and AC plug from the manufacturer’s specs for the parts.  When I was finished, I had a nice 3D printed panel as shown below:

TinkerCad back panel design

Custom back panel installed on power supply housing

Power Supply Mounting Rails:

The housing sports three sets of internal rails that can be used for parts mountings, so I designed and printed some ‘runners’ that would attache to the bottom of the power supply and mate with the internal rail geometry, as shown below:

3D-printed runners to mate with housing internal rail structures

Tilt Stand:

The finished power supply worked great, but it was so small and flat that it was difficult to get my fingers on the controls, so I designed and fabricated a custom tilt stand, as shown below

Front view showing tilt stand. Ignore the missing screw 😉

Miscellaneous:

Mean Well AC/DC power supply AC input connector:

Mean Well AC/DC power supply DC output connector:

HP style AC cord panel-mount receptacle:

AC Power switch: KCD3 T85 16A 250VAC, 20A 125VAC.

Here’s a link to the 3D print (STL) files for the tilt stand and the custom rear panel.  If you don’t have access to a 3D printer, there will surely be someone in your local area who can print them for you.

 

Frank

 

IMU Motor Noise Troubleshooting, Part II

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Posted 13 November 2019,

After a month-long diversion to help Homer Creutz investigate some of the many issues associated with the Invensense MPU6050 IMU chip, I’m now back to figuring out how to keep my robots’ motor & driver noise from corrupting the yaw values from my MPU6050 IMU module.  In my last post on this issue, I worked through a number of theories for what might be causing the problem, and eventually decided the issue was more associated with the motor drivers than with the motors themselves.  At the conclusion of this prior study, I was able to demonstrate effective turn control using MPU6050 yaw values, even with the motors running.

However, I have since determined that I basically had gotten lucky; the problem still persists, even after changing back from switch-mode to linear motor drivers.  After a lot more work, I am now convinced that the basic problem is very high frequency voltage spikes on the order of 2-3 V p-p being conducted onto the Mega 2560 microcontroller board via the motor control connections from the Mega to the motor driver.  The result is intermittent and erratic behavior from the Mega and/or the MPU6050 module.

As a potential solution to the problem, I spent some time investigating whether or not I could use a ESP32 module to replace the Mega and it’s accompanying wireless module  (HC-05 BT module on the 2-motor robot, and a Wixel wireless serial extender on the 4-motor model). The idea was that since the ESP32 module is much smaller and has an integrated/shielded wireless module, it might be more immune to the conducted noise issue.  As it turned out though, getting the ESP32 to work the way I needed it to was next to impossible, and so I abandoned ship after a few weeks.

Anyway, now I’m back to working the motor noise problem again.  When I left the problem the last time, I thought that one possible solution to the noise conduction problem would be to use an optical isolator module such as this one, to isolate the motor power circuits from the Mega circuits.

So, I set up an 6-channel optical isolation bank between the Mega 2560 controller and the 2-motor robot’s motor controller, as shown below:

6-channel opto-isolator setup with 2-motor robot and Mega 2560 controller

However, when I tried this trick, I still got lots of high-frequency transients on the control and power lines, and the computed yaw values from the MPU6050 soon became invalid.  After poking around a bit with a scope, I realized that while this cheap 4-channel optical isolator is great for voltage difference isolation and low frequency isolation, the high-frequency stuff I was seeing was going around the optical isolation and capacitively coupling from the output side back to the controller side – bummer!

After getting back on the project, the first thing I did was to refresh my memory on a prior project to test a Sparkfun MPU9250 (basically the same as the MPU6050 but with a magnetometer included) interfaced to a Teensy 3.2 microcontroller.  The Teensy is much faster and physically much smaller than the Mega controller currently on my robots, so I thought it might be less susceptible to motor noise – worth a shot anyway.  So, I got the Teensy/MPU9250 configuration working again, and then did the absolute minimum to get the Teensy to drive just one motor on my 2-motor robot.  Surprisingly, the Teensy/MPU9250 combination went Tango Uniform as soon as the motor started up – wow!

So, now I wasn’t any closer to solving the problem, but I did have some additional information.  Now I knew that the problem wasn’t unique to the Mega 2560/MPU6050 combination – it also happened in the same manner with the Teensy 3.2/MPU9250. This indicated to me that the issue really was high-frequency noise spikes being conducted down the motor control wires and back into the microcontroller circuits.

So, I needed a way to effectively block these transients from reaching the microcontroller.  As noted above, I tried the cheap eBay optical isolator module, but although it clearly isolated the DC circuits, the high-frequency transients still made it through to the controller board. I needed an optical isolator setup with an ‘air gap’ big enough so that there would be no chance for the transient energy to jump the gap.  And, because to a man with a 3D printer, everything looks like a 3D fabrication problem, I figured I could whip something up using IR LED/IR phototransistor pairs, something like the following:

This model is just a small solid piece of plastic with 4 holes, sized so that a 3-mm LED / phototransistor will slide in, with a step to stop if from sliding all the way through.  There is no metal at all, other than the LED/phototransistor leads, so (hopefully) no conductive or capacitive path.

After the required three or four quick and dirty model iterations, I had a model that I could use for a very basic experiment.  In fact, I realized my little 4-hole model was way overkill, as all I really needed was one channel for the motor speed PWM signal – the other two inputs to the motor controller could be tied HIGH or LOW as necessary on the motor controller side for purposes of this experiment.

The setup is shown below:

Teensy 3.2 controlling one robot motor via homebrew optical isolator

Closeup comparing the 3D-printed optical isolator with the commercial 4-channel module

After getting the 1-channel optical isolator working, I used it to control one of the two motors on the 2-motor robot, and found that I could run this setup indefinitely with no data corruption – yay!  Here’s an Excel plot of a 35+ minute run with the robot motor running.  As can be seen from the plot, the MPU9250 responded properly the entire time. The five ‘spikes’ are caused by occasional manual sensor rotation to confirm proper operation

35-minute run showing reliable yaw data acquisition. The three ‘spikes’ are caused by manual sensor rotation to confirm proper operation

For the next step, I plan to expand my homebrew opto-isolator to 2 channels so I can control both robot motors.  If that is successful, I’ll add 4 more channels so I can control both motors completely.  If this all works, then I’ll need two complete 6-channel opto-isolators to control all 4 motors on the 4-motor robot.

15 November 2019 Update:

I added two more optical isolator channels so I could control both the speed and the direction of one motor on my two-motor robot.  Then I modified my Teensy 3.2 test program to run the motor at increasing and then decreasing speeds, both forward and backward, forever.  The motor speed increments and direction changes occur in the same section of code that acquires a new yaw value, every 200 mSec or so.  Here’s the setup

This setup puts about 30 mm separation between the two circuits, with the only connection being via my homebrew optoisolator.

I ran the system for over two hours with the motor running in both directions and with the speed varied across the entire range.  The motor, the program, and the yaw retrieval process worked perfectly the entire time, as shown in the following Excel plot and short video clip.

 

This clearly demonstrates that my homebrew optical isolator works as it should, and effectively isolates motor/driver related transients from the Teensy board.  What it doesn’t do is demonstrate the same capability with the Teensy connected to the same power supply; right now the Teensy is powered from my laptop via USB, and the motor is powered from the robot battery supply.  The next step will be to figure out how to suppress these transients to the point where both the Teensy and the motor/driver can live on the same circuit.

16 November 2019 Update

Success!  I now have the Teensy controller and the Robot running from the same power supply – yay!!  I accomplished this by constructing a two-stage RC filter between the 8.5V battery supply voltage and the 4-6V Teensy power input, as shown below, and modifying the USB cable to cut the red power wire.

Two-stage power supply filter for Teensy

2-stage power supply filter

With this setup, I ran for almost 30 minutes with no problems, as shown in the following Excel plot (the ‘glitches’ at the start and finish are manual sensor rotations to confirm valid data retrieval.

 

Stay Tuned!

17 November 2019 Update

According to this link, Thomas Huxley once said “The great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact.”  Well, my ‘beautiful hypothesis’ has been well and truly slain by an ugly fact! As a last experiment to verify my hypothesis about the need for both an optical isolator and a power supply filter to adequately address the two-wheel robot’s motor noise transients, I bypassed the optical isolator as shown in the following photo, and ran the setup for several minutes.  Unfortunately (or fortunately depending on one’s point of view), the setup did not cooperate with my hypothesis – the setup ran fine, with no missed yaw value acquisitions, as shown in the following Excel plot (the ‘glitches’ in the plot are due to me manually rotating the sensor to verify proper operation).  So, apparently the power supply filter is required, but the optical isolator is not – Yay! (I think).

 

 

 

So then I removed the Female-Female jumpers and wired the motor control lines directly to the Teensy – no problem.  Then I added the three control lines for the second motor, and changed the Teensy program to control both motors.  This ran fine, so it is now clear that all that is required for motor transient suppression (at least for the Teensy setup) is a good power supply filter.  It’s even possible that my 2-stage power supply filter circuit is overkill for the application, and one stage would do fine.  To test this theory, I eliminated the first stage of the filter entirely, and tried again.  This works as well, so it looks like only a single-stage power supply filter is required for reliable operation, at least with the two motor robot and the Teensy microcontroller.  However, one fly in the ointment is that eliminating the first stage causes the power dissipation of the 5V Zener diode to increase to well over its nominal max Pd of 1W.  With a 10-ohm series resistor dropping 3.5V, the current through the zener is 3.5/10 = 0.25A (minus the negligible Teensy current), so Pd = 0.25 * 5 = 2.5W – oops!  I need to increase the series resistor by a factor of 2.5 to get Pd down to 1W.  So, I increased the series resistor to 20 ohms and with the actual power supply voltage of 8V, the zener Pd falls well below 1W.

For a final confirmation test, I eliminated the power supply filter entirely, bringing the setup back to to the original baseline, with the Teensy controlling both robot motors with no power supply filtering or optical isolator.  As expected, this caused the Teensy to lose synch with the IMU within a few minutes.

19 November 2019 Update:

After testing with the Teensy/MPU9250 combination, I decided to try and go back to the Arduino series of microcontrollers.  The reasons for doing this are:

  • The Teensy doesn’t have sufficient I/O channels to control all the required peripherals on the 4-wheel robot.  I does have enough I/O to control the 2-wheel robot, but that’s not what I’m after.
  • Remote programming of the Teensy is not possible without the use of another controller, like a Raspberry Pi Zero W or something like that.  However, this is easy to accomplish with the Arduino UNO or Mega 2560.

So, I started with an Arduino UNO that has been modified by removing T1 so board power is isolated from the USB cable power lead, and hooked up the motor control lines directly to the 2-wheel robot.  This arrangement failed after a few minutes, with or without power supply filtering.

So then I re-introduced my homebrew optical isolator, and found that the UNO will run indefinitely while running one of the two motors via the optical isolator and the power supply filter.  So at this point a reasonable hypothesis is that the Teensy is a bit more robust with respect to EMI/RFI effects than the UNO/Mega controllers, but the combination of the two-stage power filter and my homebrew optical isolator effectively suppresses motor and motor driver EMI/RFI (at least for one motor).

30 November 2019 Update:

I now have my two-motor robot running reliably with an Arduino UNO running my DF Robots MPU6050 module, with both motors running. As far as I have been able to determine, this requires both a power supply filter between Vbatt and the UNO Vin, and a 6-channel optoisolator between the UNO and the motor driver module.  Some photos and schematics are shown below:

6-channel homebrew optoisolator and power filter mounted on an Adafruit ‘Perma-Proto’ half-size breadboard

Optoisolator mounted on two-motor robot. Note DF Robots MPU6050 module in top left of photo

6-channel optoisolator schematic

 

03 December 2019 Update:  The Final Chapter (I hope)

After going through the entire process described above, proving to my satisfaction that the ‘final cure’ to the motor noise problem was to opto-isolate the motor driver control signals and thoroughly filter the power to the UNO, I was once again rudely smacked in the face by reality when my finely tuned setup refused to cooperate. As I prepared to start ‘field’ testing again, the yaw value corruption problem once again reared its ugly head.  This was beyond depressing – I have now spent upwards of 5 months trying to kill this particular alligator, and it keeps coming back.

Based on my philosophy that if I’m having an apparently insoluble problem, there’s someone (possibly many someones) out there in the i-verse that has had (and solved!) that particular problem already, I started over on internet research, googling for ‘motor noise problem’ and similar terms.  One of the hits I got was for an application note on the Pololu site dealing with just this problem (don’t know why I didn’t see it before, but…). In any case, Pololu’s solution was to install one or three bypass caps on the motor body itself.  Since I had already tried everything else, I thought ‘what the heck -it can’t get any worse than it is already’, and installed the three-capacitor arrangement, using non-polar 1 uF caps from each terminal to the motor body, and a 0.01 uF cap across the terminals.

Pololu D20 metal-geared motor with bypass caps installed. Blue caps are 1uF, orange cap is 0.01uF

Lo and Behold! It worked!  I was able to run for 90 minutes without a problem with all three elements in place; the motor bypass capacitors, the power supply filter, and the 6-channel optoisolator.  So, the next step was to bypass the optoisolator and see if that was a necessary component – and it continued to work without problems – yay!  Next, I bypassed the power supply filter circuit, and everything STILL continued to work great – double yay!

Two-motor robot with power supply filter and optoisolator bypassed

So, I wound up back at the beginning of my five-month circular journey, having learned a lot and had a lot of fun, but having wasted half a year.  So, if you are using metal-geared motors like the Pololu D20/D25 models, for Pete’s sake install bypass capacitors before doing anything else!

Stay tuned,

Frank

 

Flashforge Creator Pro 3D Printer Motherboard replacement

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Posted 07 October 2019

I have owned a Microcenter clone of the very popular Flashforge Creator Pro for several years now and just the other day it gave up the ghost and died; the internal LED lighting and the front panel LCD display started flickering, and then went dark altogether. This wasn’t an entirely unexpected event, as for the last week or so I had been smelling burnt insulation every time I used the printer.

So I turned the printer on its side and removed the bottom panel to have a look around. Everything looked normal until I examined the main power connector to the motherboard; this connector looked a bit brown and charred as shown below:

Motherboard power input connector. Note the discoloration and bubbling

If I wiggled this connector with the power to the printer enabled, I could get the display and internal LEDs to light up briefly and then go out again, so it seemed pretty reasonable that this was the problem.  After removing the motherboard from its mounting posts, I was able to get a better look at the connector, as shown below:

 

Motherboard power connector as viewed from the side

As can be seen in the photo, the plastic power connector has melted and bubbled out to the side, and the mating halves of the connector are fused together.  In order to disconnect the power cable I had to physically pry the two halves apart, as shown in the following photos:

Motherboard half of the burnt power connector

Cable half of the power connector

I didn’t know if the connector fried and caused the motherboard to die, or the motherboard died and caused the connector to die (or maybe a little of both?).    Anyway, I decided to try an replace the motherboard with a new one purchased on eBay.

When the new motherboard arrived, I started preparing for the exchange by carefully labelling all the cables, so I could make sure I got them back to the right places after the exchange. The labelling step is critical, as many of the motherboard connectors and the corresponding cables are indistinguishable from each other; without the labels there would be no way to tell which cable goes to which connector. Then I moved all the cables except for the power cable from the old motherboard to the new one, as shown in the following photos:

After moving all the cables, I still had a problem; the cable end of the power connector was so badly damaged that I couldn’t use it on the new motherboard, and without a power connection, there was no way to test the new board.  I solved this problem by temporarily disconnecting my after-market extruder cooling fan from the ‘EXTRA’ connector on the motherboard, and using that cable connector for the power connection to the motherboard.  After making this change, the printer came up normally when I applied power – YAY!!

So, I still had the problem of not having a connector for my printhead cooling fan cable.  After some more web research, I found this link by Aaron Gilliam (on Thingiverse of all places) describing the part numbers for the entire Flashforge Creator Pro in detail – thanks Aaron!

Flashforge Creator Pro Motherboard connector

Flashforge Creator Pro cable connector

The connector I was looking for was ‘2 pin DIGIKEY # ED2779-ND’ So, off I went to Digikey where I ordered several of the cable connectors, and also several of the mating motherboard connectors.  My plan was to first get the printhead cooling fan back on line, and then maybe try and replace the motherboard connector on the old motherboard to see if that was the only problem; if so, then I would have a complete spare motherboard available – cool!

Stay tuned!

Frank

 

 

 

 

Speaker Amplifier Project, Part VI – Second Production Run

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Posted 29 September 2019,

I got an email from Dr. Betty Lise Anderson of the Electrical Engineering Department (I think it’s actually Electrical and Computer Engineering now) at The Ohio State University, asking me if I still had the documentation for the speaker amplifiers I created a couple of years ago for her STEM outreach program.  . Dr. Anderson said these units were very well-liked by her STEM outreach students; so well liked in fact that they apparently walked away on their own!  She asked me if I would be willing to fabricate another couple of amps, and said she would happily pay for all the parts.

Since I never throw anything away, I did indeed have the documentation and even some remaining parts from the original project.  I still had a half-dozen or so of the custom audio level indicator PCBs and at least one Adafruit 20W Class D amplifier left over.  I figured I’d need a couple of wall-wart 12V power supplies and one more amplifier – everything else was already available in my parts bins.  I figured the hundred bucks or so required to get all the parts was not worth worrying about, and besides I could probably write it off as advertising expense for EM Workbench LLC.

The enclosure:

When I made the first set, I 3D printed an enclosure that was a modified version of the nice rounded-corner box design published by Adafruit for just the amplifier.  However, when I tried this trick again, I wound up not liking the result.  Instead, I decided I should be able to create my own rounded corner box.  I searched around on Thingiverse and found a few parameterized rounded box designs, but they all seemed sort of half-baked.  So I broke out my copy of Open SCAD and started figuring out how to do it myself.  I ran across a video that demonstrated the rounded-corner technique using a ‘minkowski’ function, and then I was off and running.  After just a few hours (OK, more than a few, but definitely less than infinity) I had coded a nice, compact Open SCAD module to generate an arbitrary shaped rounded-corner box with an optional companion nesting lid.  The code is available on Thingiverse here.  Using the Open SCAD module, I generated an enclosure and companion lid and exported the result as an STL file, which I then sucked into Tinkercad to add the required cutouts and such for the amplifier project.

Amplifier enclosure as generated in Open SCAD

Amplifier enclosure after importing the STL file into Tinkercad

Amplifier enclosure after modification for the Adafruit amplifier and level indicator PCB

After getting the enclosure design all spiffed up, I started printing it on my trusty PowerSpec 3D Pro 3D printer, only to have it die on me – so much for ‘trusty’!  This was not an entirely unexpected event, as I had been noticing a ‘burnt insulation’ smell coming from it over the last few weeks, and suspected that it might be on its last legs.  So, this batch of amplifier enclosures would have to be single-color (the last one was dual-color red or the enclosure and gray for the text) – at least until my new MakerGear M3-ID 3D printer shows up :-)).  Here’s the result.

Amplifier and Activity Indicator:

In reviewing the documentation from the original project, I saw that the activity indicator schematic wasn’t entirely accurate, so I brought it up to date – mostly cosmetic/lettering, but…

View showing power indicator LED installation before installing power input terminal connector

View showing 2.2K current limiting resistor for power indicator LED

View showing connections between activity monitor PCB and amplifier board

The finished product:

Two complete amplifiers with companion power supplies

A large part of the motivation for this post was to thoroughly document all aspects of fabricating the second run of OSU/STEM speaker amplifiers, so that when I get that next call from Dr. Betty Lise Anderson… 😉

Frank

Alzheimer’s Light Strobe Therapy Project

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Posted 24 March, 2019

A friend told me about a recent medical study at MIT where lab mice (genetically engineered to form amyloid plaques in their brains to emulate a syndrome commonly associated with Alzheimer’s) were subjected a 40Hz strobe light several hours per day.  After repeated exposures, the mice showed significantly reduced plaque density in their brains, leading the researchers to speculate that ‘light strobe therapy’ might be an effective treatment for Alzheimer’s in humans.

The friend’s spouse has been diagnosed with Alzheimer’s, so naturally he was keen to try this with his spouse, and asked me if I knew anything about strobe lights and strobe timing, etc.  I told him I could probably come up with something fairly quickly, and so I started a project to design and fabricate a light strobe therapy box.

The project involves a 3D printed housing and 9V battery clip, along with a white LED and a Sparkfun Pro Micro 5V/16MHz microcontroller, as shown in the following schematic.

Strobe Therapy schematic

I had a reflector hanging around from another project, so I used it just as much for the aesthetics as for functionality, and I designed and printed up a 2-part cylindrical housing. I also downloaded and printed a 9V battery clip to hold the battery, as shown in the following photos

Finished Strobe Therapy Unit

Internal parts arrangement

Closeup showing Sparkfun Pro Micro microcontroller

The program to generate the 40Hz strobe pulses is simplicity itself.  I used the Arduino ‘elapsedMillis’ library for more accurate frequency tuning, but ‘delay()’ would probably be close enough as well.

 

I’m not sure if this will do any good, but I was happy to help someone whose loved one is suffering from this cruel disease.

Frank