Tag Archives: 3D printing

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

 

Chess Piece Replacement Project

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Posted 15 March 2019,

A week or so ago a family friend asked if I could print up a replacement part for a chess set.  I wasn’t sure I could, but what the heck – I told them to send it to me and I would do my best.  Some time later a package arrived with the piece (shown below) to be duplicated – a pawn I think.

Chess piece to be duplicated

Chess piece to be duplicated

The piece is about 43 x 20 x 20 mm, and as can be seen in the above photos, has a LOT of detail.  I didn’t know how close I could come, but I was determined to give it the old college try!

3D Scanning:

The first step was to create a 3D model of the piece.  I was semi-successful in doing something similar with an aircraft joystick about five years ago, but that piece was a lot bigger, and had a lot less detailed surface.   This previous effort was done using Autodesk Capture123, and it was a real PITA to get everything right.  Surely there were better options now?

My first thought was to utilize a professional 3D scanning service, but this turned out to be a lot harder than I thought. There is a LOT of 3D scanning hardware out there now, but most of it is oriented toward 3D scans of industrial plants, architecture installations and big machinery.  Very little to be found in the way of low-cost high-resolution 3D scanning hardware or services.  There are, of course, several hobbyist/maker 3D scanners out there, but the reviews are not very spectacular.  I did find two services that would scan my piece, but both would charge several hundred dollars for the project, and of course would require a round-trip mailing of the part itself – bummer.

Next, I started researching possibilities for creating a scan from photos – basically the same technique I used for the joystick project.  While doing this, I ran across the ‘Photogrammetry’ and ‘Photogrammetry 2’ video/articles produced by Prusa Research, the same folks who make the Prusa Mk3 printer I have in my lab – cool!  Reading through the article and watching the video convinced me that I had a shot at creating the 3D model using the Meshroom/AliceVision photogrammetry tool.

At first I tried to use my iphone 4S camera with the  chess piece sitting on a cardboard box for the input to Meshroom, but this turned out to be a disaster.  As the article mentioned, glossy objects, especially small black glossy objects, are not good candidates for 3D photogrammetry.  Predictably, the results were less than stellar.

Next I tried using my wife’s older but still quite capable Canon SX260 HX digital camera.  This worked quite a bit better, but the glossy reflectivity of the chess piece was still a problem. The wife suggested we try coating the model with baby powder, and this worked MUCH better, as shown in the following photos.  In addition, I placed the piece on a small end table covered with blue painter’s tape so I would have a consistent, non-glossy background for the photos.  I placed the end table in our kitchen so I could roll my computer chair around the table, allowing me to take good close-up photos from all angles.

End table covered with blue painter’s tape

Chess piece dusted with baby powder

Chess piece dusted with baby powder

Chess piece dusted with baby powder

Next, I had to figure out how to use Meshroom, and this was both very easy and very hard.  The UI for Meshroom is very nice, but there is next to no documentation on how to use it.  Drag and drop a folder’s worth of photos, hit the START button, and pray.

Meshroom UI

As usual (at least for me), prayer was not an effective strategy, as the process crashed or hung up multiple times in multiple places in the 11 step processing chain.  This was very frustrating as although voluminous log files are produced for each, the logs aren’t very understandable, and I wasn’t able to find much in the way of documentation to help me out.  Eventually I stumbled onto a hidden menu item in the UI that showed the ‘image ID’ for each of the images being processed, and this allowed me to figure out which photo caused the system to hang up.

Meshroom UI showing hidden ‘Display View ID’s’ menu item.

Once I figured out how to link the view ID shown in the log at the point of the crash/hangup with an actual photograph, I was able to see the problem – the image in question was blurred to the point where Meshroom/AliceVision couldn’t figure out how it fit in with the others, so it basically punted.

Photo that caused Meshroom/AliceVision to hang up

So, now that I had some idea what was going on, I went through all 100+ photos looking for blurring that might cause Meshroom to hang up.  I found  and removed five more that were questionable, and after doing this, Meshroom completed the entire process successfully – yay!!

After stumbling around a bit more, I figured out how to double-click on the ‘Texturing’ block to display the solid and/or textured result in the right-hand model window, as shown in the following photo, with the final solid model oriented to mirror the photo in the left-hand window.

textured model in the right-hand window oriented to mirror the photo in the left-hand window

So, the next step (I thought) was to import the 3D .obj or .3MF file into TinkerCad, clean up the artifacts from the scanning process, and then print it on my Prusa Mk3.  Except, as it turns out, TinkerCad has a 25MB limit on imports due to its cloud-based nature, and these files are way bigger than 25MB – oops!

Back to the drawing board; first I looked around for an app I could use to down-size the .obj file to 25MB so it would fit into TinkerCad, but I couldn’t figure out how to make anything work.  Then I stumbled across the free Microsoft suite of apps for 3D file management – 3DPrint, 3DView, and 3DBuilder.  Turns out the 3DBuilder app is just what the doctor ordered – it will inhale the 88MB texturedMesh.obj file from Meshroom without even breaking a sweat, and has the tools I needed to remove the scanning artifacts and produce a 3MF file, as shown in the following screenshots.

.OBJ file from Meshroom after drag/drop into Microsoft 3DBuilder. Note the convenient and effective ‘Repair’ operation to close off the bottom of the hollow chess piece

Side view showing all the scanning artifacts

View showing all the disconnected scanning artifacts selected – these can be deleted, but the other artifacts are all connected to the chess piece

The remaining artifacts and chess piece rotated so the base plane is parallel to the coordinate plane, so it can be sliced away

Slicing plane adjusted to slice away the base plane

After the slicing operation, the rest of the scanning artifacts can be selected and then deleted

After all the scanning artifacts have been cleared away

Chess piece reoriented to upright position

Finished object exported as a .3MF file that can be imported into Slic3r PE

Now that I had a 3D object file representing the chess piece, I simply dropped it into Slic3r Prusa Edition, and voila! I was (almost) ready to print!  In Slic3r, I made the normal printing adjustments, and started printing trial copies of the chess piece.  As usual I got the initial scale wrong, so I had to go through the process of getting this right.  In the process though, I gained some valuable information about how well (or poorly) the 3D scan-to-model process worked, and what I could maybe improve going forward.  As shown in the following photo, the first couple of trials, in orange ABS, were pretty far out of scale (original model in the middle)

I went through a bunch of trials, switching to gray and then black PLA, and narrowing the scale down to the correct-ish value in the process.

The next photo is a detail of the 4 right-most figures from the above photo; the original chess piece is second to right.  As can be seen from the photo, I’m getting close!

All of the above trials were printed on my Prusa Mk3 using either orange ABS or gray (and then black) PLA, using Prusa’s preset for 0.1mm layer height.  Some with, and some without support.

After the above trials, I went back through the whole process, starting with the original set of scan photos, through Meshroom and Microsoft 3D Builder to see if I could improve the 3D object slightly, and then reprinted it using Prusa’s 0.05mm ‘High Detail’ settings.  The result, shown in the following photos is better, but not a whole lot better than the 0.1mm regular ‘Detail’ setting.

Three of the best prints, with the original for comparison. The second from right print is the 0.05mm ‘super detail’ print

I noticed that the last model printed was missing part of the base – a side effect of the slicing process used to remove scanning artifacts.  I was able to restore some of the base in 3D Builder using the ‘extrude down’ feature, and then reprinted it. The result is shown in the photo below.

 

“Final” print using Prusa Mk3 with generic PLA, Slic3r PE with 0.1mm ‘Detail’ presets, with support

Just as an aside, it occurred to me at some point that the combination of practical 3D scanning using a common digital camera and practical 3D printing using common 3D printers is essentially the ‘replicator’ found in many Sci-Fi movies and stories.  I would never thought that I would live to see the day that sci-fi replicators became reality, but at least in some sense it has!

Stay tuned!

Frank

 

 

 

 

 

 

 

 

Better Battery Charging for Wall-E2

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Posted 08 February 2019,

After recovering from my bout with #include file hell, I’m back to working on Wall-E2, my autonomous wall-following robot.  In a previous post I described the integration of the TP5100 charger module into Wall-E2’s system, but I have lately discovered that the TP5100 end-of-charge (EOC) detection scheme isn’t very reliable in my application.  The TP5100 uses a current threshold to determine EOC, which works fine in a normal application where the battery pack isn’t simultaneously supplying current to the load, but in my application, Wall-E2 stays active and alert while it’s docked at it’s feeding station; it has to, in order to be able to respond to the EOC signal and detach itself.  So, the current going through the TP5100 never goes below the idling current for Wall-E2, which is on the order of 300mA or so.  This is enough to keep the charging current above the TP5100 EOC threshold, and so Wall-E2 hangs on to the charging station forever – not what I had in mind!

Life would be good if I somehow measure Wall-E2’s idling current while on charge and the total charging current.  Then I could subtract the two values to get the excess current, i.e. the current going into the battery but not coming out – the current actually going into increasing the battery charge level. When this current falls below an appropriate threshold, then charging could be terminated. This scenario is complicated by the need to measure the current on the high side of the charging circuit and of the +Vbatt supply to the rest of the system.

Well, as it turns out, Adafruit (and I’m sure others) makes a high-side current sensor just for this purpose, based on the 1NA219 and INA169 chips. The INA219 module reports current via an I2C connection, while the 1NA169 module provides a open-emitter current source proportional to the current through an onboard 0.1Ω resistor (see this data sheet for details).  My plan is to use two of these modules; one at the charging circuit input, and a second one at the 8.4V +VBatt supply from the battery to the rest of the system. Since Wall-E2 stays awake during charging, it should be simple to monitor both currents and decide when charging is complete (or complete enough, anyway).  As a bonus, I should be able to extend the life of Wall-E2’s battery pack by terminating the charge at less than 100% capacity. See this very informative post by François Boucher for the details.

03 March 2019 Update:

After the usual number of mistakes and setbacks, I think I have the dual current sensor feature working, and now WallE-2 charges by monitoring both the battery voltage and the actual charging current (total current measured at the charging connector minus the run current measured on WallE-2’s main power line).  As a final test, I discharged the main battery pack at about 1A for about 1 hour, and then charged it again using the two-current method. As shown in the Excel plots below, Charging terminated when the actual battery charging current fell below 50mA.

Complete charge cycle, after discharging at approx 1A for approx 1 Hr

Last 20 minutes or so of charge operation, showing detail of end-of-charge behavior

two 1NA169 high-side current sensors mounted in the battery/motor compartment.  Note the 3D-printed mounting plates.

Here is a showing the installation of the two 1NA169 sensor modules in WallE-2’s battery compartment.  The one on the left measures running current, and the one on the right measures total current (charging + running).

The following figure shows the system schematic for WallE-2, with the two new 1NA169 sensors highlighted

System schematic with locations of new current sensors highlighted

Now that I have the current sensors and the new charge algorithm working, it’s time to go back an take another look at the charge/discharge characteristics of the Panasonic 18650B cells I’m using to see if I can extend their life with a more intelligent charge/discharge scheme.  The following plot shows the charge characteristics for this cell.

Charge plot for the Panasonic 18650B LiPo cell

As noted by François Boucher, the red line above is the total energy returned to the battery during charge.  As he notes, the battery acquires about 90% of its total capacity in the first 105 minutes of the charge period, when charged at 0.5C at 25C.  My battery pack is a 2-cell parallel x 2-cell series stack, and currently I’m charging to a 50mA cutoff.  According to Boucher, this is way too low – I’m charging to almost 100% capacity and thereby limiting the cycle life of the battery pack.  Looking at the end-of-charge detail plot above (repeated below), I should probably use a charge current threshold of around 500mA charging current (250mA per cell in the parallel stack) for about 90% capacity charge.

End-of-charge detail with approximate 90% charge current highlighted

On the discharge side, Panasonic’s Discharge Characteristics plot below shows a discharge down to 2.50V/cell.  WallE-2’s typical current drain is about 1A or about 0.3 – 0.5C, and the cutoff I’m using is 3.0V cell.  From the plot, this gives about 3150mAH of the approximately 3300mAH available at 0.5C, or about 95%.  So, it looks like I should raise the discharge cutoff voltage to about 3.2V or about 3000mAH of the 3300mAH available, or about 90%.

Conclusion:

So revisiting WallE-2’s battery management seems to have paid off; I now have much better visibility into and control over charge/discharge of the 18650B battery pack, and at least some expectation that I can use WallE-2’s new found battery super powers for good rather than evil ;-).

Stay tuned!

Frank

 

Dawes Lightning 1500 Stem Bracket

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Posted 13 June 2018

A friend got a new Dawes Lightning 1500 bike, and wants to install a ‘Swing Grip’ handle accessory on the piece (the ‘stem’) that connects the front fork post to the handlebars.   I had printed up a similar bracket for Ray in the past, and so he asked if I could do one for this bike too.

I had him bring the bike over so I could get a good look at the ‘stem’ shape and then built up a prototype in ABS.   I had a lot of difficulty with getting the ABS to print without lifting off the heated bed, and so eventually had to use a raft, which sucked because the raft stuck to the part too well.   When I got the part done I tried it on the bike, and of course it didn’t fit, but it did allow me to see where the design had to be changed.

Printing Notes:

I printed the PLA part with

layer height:   0.2mm

extruder temp: 205 for layer 1, 195 for 3 & up

print bed temp: 70C

speed: 30mm/sec

Z-offset: -0.05mm

I had to work a bit to get the PLA to stick to the bed, and the right combination was the above settings, plus attention to getting the bed levelled properly and the correct Z-axis offset so the first layer was ‘squished’ significantly.

 

 

To a man with a hammer, …

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Posted 17 March 2018,

To paraphrase the saying, “to a man with a hammer, every problem looks like a nail”, “to a man with a 3D printer, every problem looks like a 3D printing opportunity”.   And that’s pretty much what happened when I ran across the problem of adapting some  80mm wheels to my Wall E-2 robot, which came originally with 65mm versions.   The extra 15mm diameter/7.5mm radius doesn’t sound like much, but it makes a  huge difference when navigating over carpet or other small obstacles (like my wife’s slippers).

After a  lot of work, I finally was able to print four reasonable quality adaptors, and thought I was home free.   Unfortunately, I soon learned that despite my best efforts, the printed adaptors were no match for physics; the wheel eventually worked its way off the motor shaft, just as before – it just took a little longer ;-).

After the usual number of curses, imprecations, and woe-is-me’s, I finally decided to use whatever was left of my engineering brain to actually look at the physics of the situation.   When I did so, I realized that my adaptor idea was never going to work.   While the adaptor did indeed (after the aforementioned ‘lot of work’) provide for a better fit between the 80mm wheel receptacle and the motor shaft, it also moved the wheel another 9mm or so away from the robot chassis, which put the wheel center of pressure (CP) well outside the adaptor-to-motor shaft parting plane.   This meant that the wheel would always be trying to pry the the adaptor off the shaft, and it didn’t take all that long for it to succeed :-(.   The following photo illustrates the problem

80mm wheel with 3D-printed adaptor on the left, same wheel directly attached to motor shaft on the right

So, contemplating this problem while drifting off to sleep I was struck by a solution; I could use a small roll pin inserted through the wheel and motor shafts to literally pin them together.   The geometrical physics would still cause the wheel to flex the shaft, but the forces wouldn’t be able to overcome the strength of the metal roll pin.   Because I knew I would forget this insight if I left it until morning, I staggered out of bed and jumped onto the McMaster-Carr site (they have  everything!) to look for an appropriately sized roll pin.   I found a 1 x 6mm roll pin that would be perfect for the job, and if I ordered them now they would probably already be on my doorstep when I woke up in the morning.

McMaster-Carr metric roll pins

However, while I was doing the necessary measurements on the motor shaft, I noticed the motor shaft had a axial hole in it, and so did the wheel; hmm, maybe I could simply run the roll pin through the axial hole, instead of cross-wise?   Then I thought – wait that hole looks to be slightly smaller than 3mm – maybe I could simply drill/tap it for 3mm and use a 3mm screw (of which I had plenty in different lengths) instead of a roll pin?

So, in just a few minutes I had drilled & tapped the axial hole in the motor shaft of one of my spare motors, drilled out the wheel hole for 3mm clearance, and firmly screwed the wheel to the shaft (the right-hand wheel in the first photo above) – cool!

Now all I have to do is modify all four wheel shafts for 3mm clearance, and all four motor shafts to accept a 3mm screw – piece of cake!

As can be seen in the above photos, the 80mm wheels are now much closer to the chassis.   The wheel guards are now much too wide, but I may keep them that way for the moment, as I have already adjusted the charging station lead-in rails to accommodate the (now unnecessary) greater wheelbase – oh well 😉

So, the moral of this little story is:   Just because you have a 3-D printer doesn’t mean the solution to every problem is a new 3-D printed piece; and maybe to keep one’s eyes/brain open for even better solutions as they might come along when least expected!

Stay tuned,

Frank

 

 

 

 

 

 

 

Printing an ABS Shaft Adaptor for 80mm Wheel

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Posted 25 January 2018

Over the last few days I have been struggling with a project to 3D print a small adaptor to allow me to mount some 80mm wheels I bought some time ago to my Wall-E2 autonomous wall-following 4-wheel drive robot.

The original robot came with 56mm wheels and this gave Wall-E2 very little ground clearance.   I found some 80mm wheels that I thought would do the trick nicely, but when I tried them, it quickly became apparent that the shaft receptacle on the wheel was significantly larger than the motor shaft, leading to a very bad wobble and catastrophic wheel departures – oops!

Lightweight 4WD Drive Aluminum Mobile Dolly Car Robot Platform for Arduino

 

original 56mm wheel and companion motor

Ebay ‘Arduino Robot’ motor dimensions

80mm wheel

After some troubleshooting, I discovered that the new 80mm wheels have a shaft receptacle that measures 5.9mm long and 3.6mm wide, while the motor shafts are 5.4mm long and 3.5mm wide.   The width is OK, but the longer length is causing the problem.

After thinking (and cursing) a bit, I decided to try printing an adaptor.   The larger diameter wheels are also considerably thinner (20mm or so vs 30mm), so there should be room for an adaptor part, as shown below

shaft adaptor for 80mm wheel

And threw it on my PowerSpec 3D PRO (Flashforge Creator Pro knockoff).   After just a little fiddling, I got some nice parts, and thought I was done.   A couple of days later, I noticed one of the parts was just a little loose on its shaft, so I said to myself – “I’ll just print off another one”.   Unfortunately, what came off the printer was really ugly, and completely unusable, even though that same printer had produced nice parts just a few days ago – WTF!?   Clearly I had forgotten what magic I had wrought the first time, so now I had to go back and recreate it – bummer.   As part of my penance for this crime, I am writing this post so the next time I want to do this, I’ll have the print settings recorded.

Print Settings for ABS

The significant factors in how to get good prints with ABS on this printer appear to be

  • Print speed
  • Extrusion factor

The first thing I did was slow the print speed down, but this had only a minor effect on print quality.   Going slower helped, but even very slow speeds (like 10mm/sec) didn’t result in clean edges on the male part of the adapter. However, the female portion was very clean, which left me a bit puzzled – why one part but not the other?   I finally realized that the difference was that the female piece was perfect because the hole perimeter was the first thing laid down at each slice, then the outside perimeter, and finally the fill material was added last.   This meant that the hole perimeter had a chance to cool and solidify before the fill material impinged on its outer surface, and this meant that the perimeter stayed in the same shape as originally laid down.   When printing the male part, however, the outer perimeter was laid down first, and then the fill material was immediately added, before the outer perimeter had a chance to cool and solidify, even at the slower speeds.   The material making up the fill was pushing the outer perimeter out of shape.

This led me to focus on the extrusion factor.   Reducing the extrusion factor from 1.00 to 0.95 had a significant positive impact on the print quality of the male portion of the adaptor.   Reducing it again to 0.90 resulted in an even better print, as did a further reduction to 0.85.   However, at the 0.85 value, I started to see some degradation in the quality of the female portion, so I backed off to 0.90 as the final value.   The following image shows the last seven prints.   All were printed at either 20mm/sec or 10mm/sec, and the last three on the right were printed with 10mm/sec and extrusion factors of 0.95, 0.90, and 0.85 respectively.

The last seven prints. the last three on the right were printed at 10mm/sec and with extrusion factors of 0.95, 0.90, and 0.85 respectively

Original and new wheels, with completed adaptor shown

Bottom Line (PowerSpec 3D Pro, Simplify3D):

  • Material: Gray ABS
  • Extruder temp: 230 (not critical 220-240 should be OK)
  • Bed temp: 110 (not critical, 100 should do too)
  • Speed: 20 or 10mm/sec (maybe faster would be OK, but not much)
  • Extrusion factor: 0.95 or 0.90

 

 

 

 

A New Chassis For Wall-E2, Part II

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Posted 17 November 2017

In my ongoing quest to give Wall-E2 a bigger/roomier ride, I am continuing the process of moving all Wall-E2’s stuff to the new chassis, and modifying the charging station to work properly with the new wide-body model.

Second Deck Sensors:

Even with the wider footprint, there’s not enough real estate to easily mount the three distance sensors (LIDAR for forward distance, and acoustic for left/right distance).   I could shoe-horn it all in, but it would look messy and would leave all Wall-E2’s electronics exposed to potential damage from furniture, cats, careless humans, etc.   So I decided to transplant the second deck, complete with all the sensors, to the new chassis.   This looked to be a real PITA, until I let go of the notion that the 60mm stand-offs had to remain in the same locations. Once I did that, things got a  lot easier 😉

IR Homing Module:

This was a straightforward transplant, especially since all the detection/demodulation is being

3D printed spacers for the motor controller PCBs

done by a Teensy 3.2 physically attached to the sunshade. All I had to do was drill the mounting   holes, add two more press-fit nuts, and screw on the module.

Arduino Mega Processor and Motor Controllers:

These two items came over as a group, as that way I didn’t have to disconnect anything – my kind of transplant!   However, while I was at it, I decided to neaten things up a bit by printing spacers for the motor controllers; this isolates the underside of the PCBs from the metal chassis, and provides a nice flat surface for mounting the controllers to the chassis with double-sided tape – a win-win-win (the last ‘win’ was because I got to use my 3D printer some more!)

Arduino Mega processor, motor controllers, rear taillight assembly, and IR homing module transplanted

Charging Station Modifications:

I was  not  looking forward to modifying the charging station to work with the new wider chassis.   The charging station electronics assembly is non-trivial, and it would be a real PITA If I had to reprint the frame and transfer all the electronics. Fortunately for me, this turned out not to be the case.    By a happy coincidence, the distance from the right-hand guide rail to the center of the power receptacle was exactly the same for the new chassis as for the old one, so all I had to do was re-position the left-hand rail to accommodate the wider tread spacing. Well, there was one minor glitch – the charging station has two physical stops, and the one that mated with the left-hand wheel guard on the old chassis now didn’t hit anything, so I had to print a small 5mm thick spacer and double-sided tape it to the front of the existing stop.

Closeup of the spacer for the right-hand charging station stop

Front view showing left and right charging station stops (with spacer added to right one)

18 November 2017 Update:

I’ve got almost everything transplanted over now, as shown in the following photos:

Side view without the sensor deck, showing that all modules are in place

Side view showing the sensor deck in place.

end-on view showing the difference between the old and new chassis dimensions

There’s still a ton of work to be done; The latest version of the charger PCB still hasn’t arrived from Bay Area Circuits, so I still need to do all that, and then wire the finished module into the battery compartment. Also, I’m having to redo the front bumper guards, as I have found they are somewhat fragile due to the way in which they were printed – bummer!   However, it shouldn’t be  too long before I can take the new model out for a spin! ;-).

Stay tuned!

Frank

 

 

 

A New Chassis For Wall-E2, Part I

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Posted 06 November 2017

Back in May of this year I came to the conclusion that I was never going to get my new four-cell battery pack (4ea 18650 3600mAH 3.7V LiPo cells connected as 2ea 7400mAH 3.7V stacks) and its companion charger module to comfortably fit into Wall-E2’s current chassis.   It all fits, but only with a considerable amount of pushing and shoving which has invariably resulted in damage to something – a connector, a wire, or something else vital.

Bottom side view of 4WD robot showing battery packs and charging module

Bottom rear view of 4WD robot showing battery packs and charging module

So, I spent some quality time online looking for a new, larger home for Wall-E2, and found this chassis

Lightweight 4WD Drive Aluminum Mobile Dolly Car Robot Platform for Arduino

This chassis has an internal cavity width of about 14cm compared to 10.5cm for Wall-E2’s current ride.   This extra inch or so make all the difference in the world for comfortable installation of the battery pack and charger.

After getting this chassis on order, I basically forgot about it while I was working on the square-wave modulated IR homing project.   Then when my grandson Danny and his family visited in August, we dug out the kit and assembled it.   Danny wasn’t all that impressed with the quality (well, neither was I, but I didn’t expect all that much for $30 either).   After looking at both chassis (Wall-E2’s current ride and the new one), Danny suggested that maybe we could transplant the motors from the new chassis into the old one and get enough additional space from the different form factors to solve the battery problem.   At the time I pooh-poohed the idea, and put the new chassis back on the shelf to be forgotten again.

However, after finishing up the IR homing project last month, I decided I would actually try this trick and see what happened.   So, I laboriously swapped all four right-angle motors from the new chassis to the old one, and … RATS!!   As the photos below show, no real change in the available room for the charger/battery pack combination.   Well, at least I tried ;-).

So, now I’m back to swapping chassis (wow – plural form of ‘chassis’ is ‘chassis’ – go figure) instead of motors.

One of the major shortcomings in the new model was the cheapness of the threaded holes in the frame components.   The frame metal is so thin that instead of drilling and tapping the material, the holes were punched in a way that left the punched-out metal in the hole, and this material was tapped with the machine thread.   Needless to say, this lasted for about one (or fewer) screw/unscrew cycle before stripping out – bad design!.   Fortunately I knew how to fix this problem, with the help of McMaster-Carr.   I went to their site and ordered a bunch of press-fit nuts (also called PEM-nuts for historical reasons)

Press-fit nuts for my new robot chassis

In case you have never dealt with McMaster-Carr, they are incredibly quick.   I normally tell people that once I click on the ‘order’ button, I get up, walk to my front door, open it, and get hit in the chest by the shipped order! ;-).

Once I got the nuts, I replaced all the threaded holes on the new chassis with these wonderful little gadgets.   I used a #16 number drill to drill out the holes, and pressed the nuts in the new holes with a pair of cheap gas pliers – done!

As seen below, there is a  lot more room in the new model

In fact, there is so much room that now I have to figure out how to keep the batteries and charging module from sloshing around in there.   Fortunately I have a fertile imagination, TinkerCad, and a 3D printer – so I designed and printed up a battery box, and a prototype stand-off design for the PCB, as shown below.

The next part of the puzzle will be to figure out how all that stuff (IR Homing Module, laser and ultra-sonic distance sensors, motor controllers and the main controller) is going to fit on the new chassis.

Stay tuned!

Frank

 

 

 

IR Homing Module Integration, Part III

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Posted 20 August 2017

I’m writing this post from our Kids’ place in St. Louis, which just happens to be in the path of totality for the upcoming solar eclipse.  As usual, I brought my project stuff with me so I can work in the off moments, but this trip has a bonus in that I have managed to suck my 14 year-old grandson Danny into helping me with the robot project.  He also has my old PrintrBot ‘Simple Metal’ 3D printer, so he is able to print up new IR detector holders as required.

So, the first thing we did was to print up a new holder with a 30 º angular offset for the detectors; this is something I forgot to do with the previous model.  With this setup, we got the following results from an azimuth scan.

Azimuth scan for 2-detector model with 30-deg angular offset and center divider

meanwhile, my friend and mentor John Jenkins came up with a set of simulated azimuth response curves (shown below) that showed that the center divider (apparently originally intended to make steering more responsive) was more of a liability than an asset.  Turns out (at least according to John’s results) that removing the divider makes the (diff/sum) ratio curve smoother and more linear in the critical boresight region.

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So, we printed up a new holder with the center divider removed (and in the process made the walls thicker to block IR transmission through the material), and took some more measurements.