A long road…
Hi Jay,
Its been a long road of experimentation, trial, and a helluva a lot of error. But, my latest revision is based on the now famous BOA Bridge (catchy aint it BOA?).
Some quick highlights of the history :
1. Ended up ripping all of the “brains” and safety controls out of the chair, because they did not agree with my plot of enslaving humankind.
2. Tried a large variety of homebrew electronic circuits to control the very hefty wheelchair motors from a digital source - put them all through a variety of tests - all went POOF in flames and mushroom clouds of silca
3. Tried a commercial (robot power) simple H bridge - POOF (that was expensive - not doing that again)
4. Talked with BOA at length about the mystries and benefits of manly MOSFETs - helped a little describing why a gnd on the gate is needed to turn off the MOSFET
5. BOA comes up with the BOA Bridge - a fabuloso simple electronic design
6. Robologist suggests a gate driver - turns out in my case he was right
7. So after much frustration and dead MOSFETS here is the latest revision of the controller circuit. It has not gone through ALL of the tests, however, the ones it has gone through it has not heated up at all. So I beleive this circuit can drive a 200 lbs heavy duty electric wheelchair without a problem - (more to come)
* the schematic is missing the IGBT gate driver
*Ugly free form circuit - I love wire nuts !
On the digital control front :
1. had computer PWM control wheelchair motors through parallel port - found this jerky an not reliaible due to task scheduling and interrupting cpu with a variety of "other tasks"
2. got a cheap DIO card from ebay - to try instead of the parallel port - card did not support pwm - or at least I could not figure out a way to do it
3. got a cheaper Arduino - hooked it up to the computer - Works Brilliantly
4. working on software for the computer & Arduino so that the Computer does heavy number crunching of video image processing from webcam and Arduino is kindof a dumb slave - but a very good dumb slave. I think of it like the dinosaur Stegosaurus - it had two not very big brains - or like the coretex and the cerebellum - a big brain and something that is responsible for reflexes and "staying alive"
5. Setup is Computer -> Arduino -> BOA Bridge -> Wheels . The nice thing about a regular computer it that it is extremely powerful and easy to do things we already expect. For example wireless. So I can do this “My Computer” --(wirless)–> Computer -> Arduino -> BOA Bridge -> Wheels. My computer can use a keyboard or joystick or game paddle etc. so this is pretty easy “Joystick” -> “My Computer” --(wirless miles away)-> Computer -> Arduino -> BOA Bridge -> Wheels… get my drift?
Here is some of the gui portion of the code I have been working on …
Too much info?