A few of us worked on a car for The Power Racing Series and somehow we got it done at 3:15am on Thursday night after about a week of intensive nights cutting wood, and trying to weld metal, and scrounging for batteries. We then took it to Maker Faire Detroit and raced it.
The car is modeled after Noah’s Ark, supposedly dimensionally accurate, scaled down, of course. It runs at 24 volts and uses one 250 watt hub motor meant for a bicycle. It was not fast. It drives like a boat, maybe because it is one.
We didn’t break down until the last few minutes of the Endurance Race when we popped a tire, so we just kept going on the rim. (Our qualifying lap was 40.40 seconds. Also our car is #40. Amazing!)
We built this in about a week, and made a lot of compromises to get it done on time. Originally we were going to use two 250 watt hub motors for the rear wheels, but… compromises.
The good news is you can spin around in a super-tight radius by turning the wheel 90 degrees and then going full throttle. The bad news is, you might puke afterwards.
Anyway, we’d love to see more people build cars for The Power Racing Series event that will be happening at Maker Faire Milwaukee. If you start now, you’ve got 60 days, and since we built this in about 6 days (and rested on the 7th) it should be totally doable.
Remember, you don’t have to be fast if you’re awesome. You do need to go, and stop, and not take it too seriously. If you can do those things, we’ll see you at the races!
Will Milwaukee Makerspace have a functioning car? Will there be a RAGE BUILD today, and every day this week? Will we pull it off at the last minute and continue our long-standing tradition of racing in Detroit?
This 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.
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.
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…
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 showing core inserted into jig.
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.
Finished plunger removed from the mold. The mold had to be broken off by design.
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!
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:
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.
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…
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!
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.
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!
At Wisconsin State Fair Park, the same weekend as Harvest Fair. Admission is free. Thanks for a great 2015! See you next year. A joint presentation by the Makerspace and the Betty Brinn Children's Museum.
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