Just about the only thing I don’t love about the Open ReVolt motor controller is the case.
As cool as an Open Source Motor Controller is, it’s just not shown off with a basic metal cover. In fact, I actually drilled through the original cover (and put clear packaging tape over the holes!) to see the power and troubleshooting LEDs through the lid.
Recently, the Milwaukee Makerspace got itself a laser cutter. It’s not all that powerful, but more than capable for cutting plastics. One of the Makers posted a blog entry about making a wood box on the laser. He used a program called BOXMAKER which helps you layout the size of your box, including overlapping cut edges to put the whole thing together.
This got me started on the idea of building a clear plastic case for my 500 amp Open ReVolt controller. But I had never even used the laser before. I sat down with the member who owns the laser, and he took me through the basics of importing files, exporting to the laser, and modifying power and speed settings. With that, I was able to start making a few test items on the laser. I figured that since I already had the Open ReVolt logo as a vector file, it couldn’t be easier to try out etching some plastic with it.
I used the laser to make a few small test pieces on various materials. The two logos turned out pretty well. They were both etched AND cut out with the laser. On the orange medallion, I mirrored the image, so it would be a design on the “back” of the piece. That keeps the upside nice and shiny and clean.
Plastics cut on the laser
After practicing a bit on the laser, I started wondering what else I could cut, mark, or etch with the laser. Last night, I forgot something at the Makerspace, so I had to return there this morning to retrieve it. And I am NOT a morning person, so I had my trusty travel coffee mug with me. It’s stainless steel with an anodized dark gun metal finish to it. “I bet that would laser engrave nice!” I though to myself. Sure enough, it only took a little tinkering to figure out how to keep the mug from rolling sideways inside the laser before I could engrave it.
Also, when I came in this morning, all the lights were off, except for one – Tom’s LED lit plexiglass desk drawer. I asked him for some advice last night about how to engrave and then edge-light in clear plastic. He plugged in his project to show me a sample, and had left it on. It was eerily awesome to see the Makerspace lab lit up by green LED power! It’s a good example of how I would like to engrave the top of the controller case and light it up.
Well, that’s it for now. Next, I’ll have to take careful measurements of the controller, lay out the box, find some material to work with, and figure out where and how big the cuts in the end plates will need to be for the bus bars.
When I arrived at the space Sunday, I had planned to work on a circuit board design in DipTrace. After I left, I had spent six hours rewiring a golf cart. Allow me to explain…
It all started when I went to take the trash out. I used the golf cart with the flatbed to ferry the cans out to the dumpster. After emptying the cans, I rode back and decided to charge the cart’s batteries. Tom and Rich had just returned from lunch and Tom suggested we swap out batteries instead. While swapping them out, we decided to also rewire them. While rewiring them, part of the cart broke. There’s a small white plate under the driver’s seat. It’s about 4″ x 6″, likely made of asbestos, and holds a series of copper contacts that a lever attached to the gas pedal slides over to select the speed of the cart. And it broke in two when we tried to tighten fix a wire on it.
We had a few options: try to mend the old, brittle plate, replace it with something new, rewire the whole thing, or scrap everything out for a solid state motor controller. Not wanting to adopt a new project or sacrifice a motor controller that could be better used elsewhere, I volunteered to try and fabricate a replacement for the broken part.
First I documented everything just the way it was. I labeled wires, took photos, scribbled down notes, etc. Next I went about removing the broken plate. There was probably more rust than metal on those bolts. Then I took a pair of digital calipers and a ruler and measured the locations and sizes of holes for each component. I considered using the CNC router or drilling a plate by hand, but the laser cutter seemed to be a much faster and precise approach. I drew up my replacement plate in CorelDraw and found a scrap of 1/4″ acrylic that matched the size and thickness of the old plate. After some tinkering with the printer driver and a dozen passes with the laser, I had a copy of the original in plastic form.
The next few hours were spent migrating the old parts over to the new one and wiring it back in. Right around 7:00 PM, I tied some batteries together and the thing leaped forward. A few more tests and it should be as good as new. Someone suggested that maybe the plate was asbestos to avoid heating issues so we’ll keep an eye on that too.
My electric Dodge neon uses an AC motor and an industrial motor controller. I upgraded from m 1984 motor controller to one less than 25 years old (actually less than 5.)
The new controller does much more than the old one and has the ability to do some fancy tricks. At the moment I am running it in “sense vector” mode. The controller senses the position of the armature by monitoring the current in the field coils. This works great… as long as the motor is spinning. From a stop it tends to get out of sync, but there is a cure!
The controller can use a quaderature encoder so the encoder can read the position of the armature at any speed.
To add an encoder to the motor I decided to try a chip amde by Austrial Microsystem AS5040. This chip senses a magnet near the chip and calculates the position of the magnet and can generate multiple output: PWM, binary via I2C, and quadurature!
I bought a few of the chips and built a surface mount board to hold the chip and a few LEDs to display the output. The first two version had a few problems but the 3rd time was the charm.
Thanks to Royce for working out the process for surface mount PCBs.
The final version had to be small enough to fit in a depression in the end of the motor cap. The sensor centered and the whole board insulated (clear enamel) since this is a grease pocket
for the rear motor bearing.
The magnet is mounted to a bolt that is threaded into a tapped hole in the back end of the armature. It took a while to the position right (it needs to be within a few millimeters of the sensor) hence the nuts and washers.
The cable is brought out of the motor through a small threaded hole (it was an alternate location for the grease fitting.) The hole is filled with epoxy and the wires go to a DB9 connector. I built a small test board that shows the quadurature signals (4 round LEDs) and the status outputs from the chip (the two rectangular LEDs)
The motor controller puts out 15V to power an encoder and wants A and B as well as inverted A and B signals. The circuit includes some NPN transistors along with a voltage regulator and a few capacitors to tie it all together. I put the schematic for both the sensor and test board on one schematic so I could make both boards at the same time.
I installed it in the car today, but still need to put a few more parts together to run it.
It doesn’t work!
Ok, so the electronics work fine, it talks to the controller.
But it tops out at 256 pulses per revolution and the controller needs 1024. It was a minor confusion between terminology. The sensor detects 1024 positions, but to generate quaderature it uses 4 positions per pulse output.
Back to the drawing board.
I picked up a commercial shaft encoder on ebay for 50 that outputs 1024 PPR but it only works at 5V, so I’ll need a level shifter board and connector adapter.
Oh, yea, and I need to put the motor again, take out the old encoder, bring a shaft extension through the back grease pocket, add a grease seal and couple it to the encoder.
At home, I have a small LED light that is designed for use under cabinets. I use it mostly to illuminate one side of my aquarium, and I occasionally pull it out to use it as a light for filming video.
The problem is that it is quite a bit brighter than the other LED light I have on my aquarium, and for video use, it would be nice to be able to adjust the brightness of the light as well.
However, LEDs just CAN NOT be dimmed with a regular old light switch dimmer the way an incandescent bulb can. I had heard that they can be dimmed through PWM – pulse width modulation. I was already familiar with the term, as that’s the same technique used to control the speed on the motor of my homebuilt electric car.
So, when I was in at the MILWAUKEE MAKERSPACE I asked Tom G if he had any suggestions for me to start learning electronics by building a simple PWM dimmer for my fish tank LED light. As a hobby, he has built a fair number of robots, and pointed me to the Dallas Personal Robotics Group web page, where they had a number of tutorials posted. Sure enough, they had atutorial on building a simple motor speed controller, using a 555 timer chip. It also included a very nice explanation of Pulse Width Modulation. It’s really a simple thing that is sometimes hard to describe. I don’t think I have ever heard it explained so clearly as in the DPRG tutorial.
Part of the fun of the Milwaukee Makerspace is just having lots of odds and ends around handy, instead of having to take a trip out to the hardware store or electronics warehouse. A 555 timer, a few resistors and capacitors, and a bread-board were I all right there, ready for me to prototype this simple circuit. Even with nearly no electronics experience, it was pretty easy for me to follow the tutorial and connect up the 555 and other components into a working circuit.
After some playing around with it, I found that this circuit could not only control the speed of a DC motor, or dim an LED light, but somebody else suggested I hook a speaker up to it. Sure enough, I could generate various frequencies of sound as well! (Although since it’s a square-wave, none of them sounded very nice!)
So, the next time I was going past Radio Shack, I stopped in and picked up some “Perf-Board”. It’s sort of the step between a breadboard and a custom circuit board – just a board with a bunch of holes in it, all evenly spaced, ready for you to insert electronic components and solder them together.
I then recreated my original breadboarded circuit on the perf-board and soldered it all together.
I also grabbed a used plastic case from the Makerspace parts pile to use as an enclosure for the circuit-board. A bit more scrounging meant that I had a power connector for it that matched the power supply for the LED light. I’d be able to use the same power supply whether I was using the LED with or without the dimmer.
A bit more soldering (only ONE soldering iron burn!) and installing the board in it’s case, and I now officially had a PWM Light Dimmer for my aquarium!
But here’s where it gets more interesting. I really built this not so much out of need for a dimmer, but as a learning experience to find out where theory and practice come crashing together in the real world. After assembly, I already noticed a few ways to improve the final version of the device. (I’m still thinking of this as a proto-type or first run!)
Ideas for future improvements include:
1) A power indicator light. If the PWM is turned all the way down, it’s hard to tell if the device plugged into the dimmer is even on or not.
2) A volt-meter display. It’s pretty neat to be able to see that the perceived output voltage of the dimmer is. I have several 12V devices that I would like to run from a large 14.4V battery. With a volt-meter built in, I could set the dimmer to send exactly the correct output.
3) Battery Operation. The surplus case that I used as an enclosure already has a removable cover. It shouldn’t be tough to fit some AA batteries in there to make the whole thing run without requiring a power cord to the wall.
Recently, we through a birthday party for a friend of ours. She requested a Disco Ball at the party. My sister found a disco ball at the clearance table at a store, but no matching disco ball motor.
Aha! Here’s my chance to not only save a few bucks by not PURCHASING one, but also learn about motors and gear reduction! Next time I was in at the Makerspace, I dug through the bin of scrap motors on the “Hack Rack”. An AC motor? No that’s no good, it has to run on batteries.. Stepper motor? I have no idea how to run one of those…. Hmmm. What’s this? I eventually found not one, but two motors, both connected to to some gearing and a pair of tiny square drive axles. The motors were marked as 24V DC, and I knew that if I drove them at a lower voltage, they would still work, but not spin as fast. I tested them both with a benchtop power supply and saw that they worked. The one was geared to a much faster speed than the other.
I later tried running both directly from a 9V battery, as it is the simplest power supply I could think of. The one motor, through the gear reduction, would spin the driveshaft at exactly 2 revolutions per minute at nine volts. That’s almost PERFECT disco ball rotation speed!
I bent a paper clip through a connector on the end of the drive shaft to hold the ball, and added a carbineer to hold the motor to the ceiling. POW – top-notch disco ball rotation!
For the party, I let it run on just the 9V battery. It got left on overnight, and was still running the next afternoon. What a nice, efficient motor!
But what if I wanted to spin that ball a bit faster or slower? Either motor was designed to run up to 24 volts. My PWM “dimmer” was really a motor controller anyways after all. That was all set up for 12V. I connected the dimmer to the more quickly geared motor, hung it up, and strung the disco ball from it. Sure enough, by varying the potentiometer on the dimmer, I could make the ball spin from way too slow to nausea-inducing quick!
I even noticed that at very slow speeds, the motor made a little bit of a high-pitched whine. Remember how I said an audio speaker could be hooked up to generate a tone? At slow speeds, the pulses of the motor controller can actually be heard – the frequency is within the range of human hearing. The first time I ever heard a Chevy Volt, I noticed that it made a quiet, yet distinct noise right as it accelerated away from a dead stop. That’s the sound of the car’s electric motor controller picking up frequency as the car increases speed.
So there you have it. From dimming a light, to spinning a ball, to driving an electric car, Pulse Width Modulation is a simple, yet useful, trick that’s all around us. If you would like to build your own basic light dimmer/motor controller, check out the info at: http://www.dprg.org/tutorials/2005-11a/index.html
If you are anything like me, you like to learn new things, and find it fascinating how various areas of industry and science are all related. It’s far more fun to build and design something yourself then it is to just purchase somebody else’s.
Back in college a friend of mine built a small demonstration model of a vibratory conveyor. Basically it’s a ramp covered in grip tape and a motor. When tuned properly, you can send small objects like coins up the incline almost magically. I’d like to build one myself for fun.
So today Ben brought over the kit sent by PaulHolmes for their OpenReVolt open source motor controller. The plan is to build the controller and use it in my EV Motorcycle I’ve been working on for several months. Today I accomplished a few things. First, I got a brief soldering lesson from TomG; I’ve never done any small electronics, usually only car audio/misc. wiring. Second, I started soldering in some of the resistors and capacitors into the control board. I took a few photos/short video clips of the progress i was making for reference for others wanting to make their own home build OpenReVolt. Once they are posted online I will post them here. This controller is very nice as it’s almost like paint by numbers, all the components are labeled in bags and their corresponding numbers (R23) are on the control board making it very easy for an amateur like myself to build. So far I’m having a lot of fun; more than i initially thought i would have! I’m very excited and motivated to finish this motor controller as soon as I can so I can get my bike out on the road in time for spring! Check back for periodic updates!!
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