1MHz DC-DC Converter Test

dcdc1mhzThis week I tried out a new DC-DC converter, the RT8293BHGSP, for my singing pumpkin controller. The issue I had with the old converter was that it was pretty expensive to get a 100uH coil that was rated for 4 or 5 amps. The most recent spin of the board only has about a 1.5 amp coil on it. This new converter runs at a little over 1Mhz as opposed to ~300kHz for the old converter. As such it can use a much lower value coil (10uH) that can be obtained in the 4 to 5 amp range for a reasonable price and with a reasonable package size.

This tester board seemed to work pretty well. It got plenty warm pushing around 2 amps, so it may need a heat sink. Still I’m pleased to have a solution that lets me get all the way up to the 3 amp limit of the converter.


First Ever Test of the 3.5 Liter Syringe Extruder

My last post showed how I made a plunger for a 3.5 liter syringe.  Today’s post is the results of the first ever test of that syringe assembly including the plunger.  The goal of the test was to determine if the syringe pusher would be able to push very thick, viscous paste (sort of like melted chocolate) out of the 1/4″ syringe nozzle.  It was also a test of the ability of the previously made silicone plunger to maintain a seal even against whatever pressure develops inside the syringe as it is pushing.

I mixed about 1 liter of extra thick pancake batter to a consistency that I thought would be much thicker than molten chocolate (pancake batter is much cheaper than chocolate) and shoveled it into the syringe, then bolted on the pusher and hooked it up to a power supply:

Looking back, I probably should have loaded the syringe from the other end.

Syringe loaded with super thick pancake batter.

Syringe loaded with super thick pancake batter.












Here’s the actual test.  It gets especially interesting about 1 minute in:

The syringe continued drooling after power was removed due to air that was trapped inside the syringe.  As the plunger pushed, the air was compressed.  When the motor stopped the compressed air continued to push out the batter.  I will have to be careful to eliminate air bubbles in the material when it comes time to use this in a printer.

It only took a couple minutes to clean out the syringe after the test was done.

The pusher did its job much better than expected, and the plunger held up just fine, too.  I feel confident that this device will be able to extrude chocolate.   Now the real work begins…

Making a Plunger for a Chocolate Syringe

My latest project is a 3D printer that will produce chocolate objects.  Like many other chocolate printers, it will include a syringe to dispense the chocolate.  Unlike those other printers, the syringe in my printer will have 3.5 liter capacity to enable printing large objects.

The syringe is made from PVC pipe using mostly standard fittings.  One piece that wasn’t standard was the plunger that fits inside the syringe tube and pushes on the chocolate contained therein.  I had to design and fabricate the plunger.  PVC pipe isn’t perfectly smooth or perfectly round inside, so I needed something compliant enough to ride out the pipe’s bumps and constrictions while maintaining a seal.  The seal needed to be tough, yet safe for use with food because it will be in contact with the chocolate inside the syringe.  I found some food-grade silicone casting material and ordered it.

While waiting for the silicone to arrive, I designed a 3D printable core for the plunger and a mold and jig.  The core fits on the end of a linear actuator that will provide the push.  The jig centered the core a few mm above the bottom of the mold.  The mold was tapered and the widest part -the bottom- was a few mm larger diameter than the pipe, and several mm larger diameter than the core.  The silicone envelops the core and is locked in place by holes that connect top and bottom side of the core.  The plunger squeeze-fits into the pipe to maintain the seal against the uneven inner surface of the pipe.

Mold, jig, and core for syringe plunger

Mold, jig, and core for syringe plunger

Mold, jig, and core for syringe showing core inserted into jig.

Mold, jig, and core for syringe showing core inserted into jig.










Mold, jig, and core assembled for silicone over-molding.

Mold, jig, and core assembled for silicone over-molding.

I measured and mixed the silicone, coated the core with it and then set the core and jig in/on the mold and let it cure for 24 hours.  Then I removed the jig and broke the now silicone covered core out of the mold.  Result: a perfect, tight fit inside the syringe tube.

Core in mold with silicone.

Core in mold with silicone.











Finished plunger removed from the mold.

Finished plunger removed from the mold.  The mold had to be broken off by design.












Plunger mounted on linear actuator.

Plunger mounted on linear actuator.













The assembled syringe.

The assembled syringe.

All Officers to the Bridge!

Starship Bridge

In preparation for our Artemis Simulator that’s going to be at Maker Faire Milwaukee, we’ve partnered with Betty Brinn Children’s Museum to build a realistic starship bridge. Here’s what we’ve got so far.

Starfleet never produced an episode of How It’s Made, so we’re going to have to do a little guessing along the way when building our bridge. Obviously we still need to install the EPS conduits, Tribble-proof everything, and get the self destruct system up and running. But we’ve got nearly 80 days to get it all done.

Don’t forget to bring your phaser to Maker Faire Milwaukee to check out the final build!

Experiments in optics and image processing

After successfully mating a web cam with my microscopes (http://www.thingiverse.com/thing:216821) and telescope (https://www.youmagine.com/designs/web-cam-adapter-for-meade-telescope-eyepiece), I decided to design and print adapters to mount my Droid Turbo phone on the same scopes (https://www.youmagine.com/designs/microscope-adapter-for-droid-turbo-phone and https://www.youmagine.com/designs/droid-turbo-phone-to-telescope-adapter) so I could shoot higher resolution stills (21 Mp) and 1080p (and even 4k) video.   The telescope adapter fits over a Meade 32mm focal length Super Plössl eyepiece and provides about 47X magnification with the telescope.  I printed a similar adapter for my surgical microscope.














The telescope adapter firmly grips the phone and the eyepiece.















Initial tests were a little disappointing.  The combination of the phone’s camera and the telescope’s optics has significant pincushion distortion.  The image has only been mirrored L-R and scaled down (original is 21 Mp).  Note the lack of contrast (looking through 1/2 mile of humid air) and the curves in the power line and pole, and even the grass line:

pinch test original










A quick search found that the Gimp has built in transform tools to correct (or create) lens distortion.











It only took a couple minutes of messing around to get acceptable results.  Here’s the same image with the pincushion distortion corrected (whole image), contrast stretched and white balance corrected (rectangular area).  The pole, power line, and even the grass line now look straight.

pinch test corrected










And here’s the final image with all corrections and cropping applied:












Next step: photograph known square grids through the microscope and telescope and then create and save some preset corrections to apply with Gimp.

I wonder if something like this exists for video.  Hmmmmm…






Flaming Lotus is…

Flaming Lotus

Our Power Racing Series team is back for 2015! But, well.. we’re a little smaller. Right now it’s just Ed C. and me (Pete!)

But as you can see from the photo above, we have a body mostly primed. It’s actually been painted a bit more since this photo from two days ago. It’ll be ready to go for Maker Faire Kansas City in (less than) two weeks!

I can hear you saying “Yeah, a body is a great, but where’s the frame, the motors, wheels, controller, brakes, and all that jazz!?”

I present you with this CAD drawing. Everyone knows designing a thing is 95% of building a thing. So we’ve completed 95% of the work… now we have (less than) two weeks left to put it all together. Easy!

CAD Lotus

See you in Kansas City!

Fix Your Symbols


This Saturday I continued with the commissioning of my unified singing pumpkin controller. I got all the sub-systems working except for the power amplifier. In the picture above, on the left is the pumpkin controller. On the right is a (normal) Arduino amplifier shield using the same amp chip.  That shield works. If you look carefully you can see that the chip pins are mirrored between the two boards.

Mirroring pins is an innocent enough mistake. It happens to everyone once in a while. The problem is that I made the EXACT same mistake on the first round of that amplifier shield. (Notice the R2 on the right hand silk?) Apparently I fixed that problem manually without correcting my library symbol. That was many months ago and I forgot about it, thus resulting in a repeat of the same error on the unified pumpkin controller. Dumb mistake! It would have taken 10 mins at most to fix the symbol.

Don’t be like me, fix your symbols the moment you notice the mistake! You may not get back to it for a while and may not remember there was a problem.


Son of MegaMax Enters Instructables 3D Printing Contest

Many 3D printers being given away as prizes!  If I win one I’ll be donating it to my son’s school or other school or library that would like a machine and doesn’t already have one.  To do that I need your votes!

Son of MegaMax

Son of MegaMax

Please see my Instructable here:  http://www.instructables.com/id/An-Almost-Reliable-High-Precision-3D-Printer-Son-o/and vote for me by clicking the little red “vote” ribbon in the upper right corner of the start page.



Maker Faire, as easy as 123…

Maker Faire Countdown!

Last August Brant asked me to add a countdown to Maker Faire Milwaukee on the MMPIS, so I whipped up some code on a remote server and he got it running on the MMPIS display at the space.

Seeing as planning for this year’s event is in full swing, I figured it was time to start the countdown again. Yes, we are counting the days, and the Call for Makers is now open! Got a project, or something you made, or things you want to show off? Submit it, and share it with the world!

Singing Pumpkin Controller

pumpkins pcb smallA few years ago I made animatronic singing pumpkins using an Arduino Uno, a Wave shield, a 16-channel servo/pwm controller, and some DC-DC power converters, all from Adafruit. I designed a single PCB that unified all of that and included a 15W amplifier. Today I completed assembling that board and began its commissioning. I used solder paste and a mylar stencil cut on our laser. Its the first time I have ever soldered a TSSOP package with no shorts.

Anyway, I managed to forget to bring a microSD card, but the program loaded into the AVR OK and is running. All the various power supplies are outputting the correct voltage.  6 volts for the servos, 5 volts for the AVR, and 3.3V for the microSD card and buffer chip. The amplifer gets the raw 12 volts. So, I’m hopeful that over the next week I’ll be able to bring the board completely online.