Older blog entries for Chuck McM. (starting at number 2)

16 Apr 2002 (updated 16 Apr 2002 at 08:21 UTC) »

Progress and none too soon. Firmware development on the PIC is fun and sometimes slow. Pictures are up at my site with pictures of the official speed controller board.

Some folks who have built OSMC boards have done some testing and have run them at 160 amps. I hope they knew what they were doing, because if they did then my board should stay at nearly room temperature doing 200A.

Another month. Wow.

So how do you build a truly competition grade high current speed controller? Answer: Carefully :-). I've got what I believe is the final layout of my speed controller and its off to the PCB house for a prototype run. Things that I've learned are: 2 oz copper means holes get smaller. 4 layer boards have weird layout requirements The strangest was theiving.

Theiving is a technique where small squares of copper are added to a layer (away from other features) to create a better copper/substrate ratio so that plating is more even. Strange! The PCB house guys added it for me so I didn't have to worry about it but it was news to me.

The second thing I've learned is that FETs are cheaper than copper. My original design used 16 FETs (4 per leg) and that meant dissipating 240 watts of heat when fully loaded. Not impossible, but it was a challenge. So taking a cue from Victor and others, I ran the thermal analysis with 32 FETs, dissipation drops to 60 watts. A whole lot better. Now I need only a fan and my water cooling system is surplus. (not that I looked forward to having a radiator hose blow in my battlebot!)

Building them up next Friday, and then its off to melt steel (crowbars make a great dummy load for a 200Amp speed controller :-)

Whoa, this is a very cool site and I am extremely honored to have be certified at Master status. Lately I've been building a 200 amp speed controller for very large motors.

The current design is going to use two 16F628 PICs as the basic control mechanism (servo code reception and PWM generation). I could use a PIC16F87x but its actually easier to do the multiprocessing thing. The guys at Microchip really make it easy.

So projects on the way to this goal include:
Pulse Measurement -- This uses the PIC's input capture to measure pulses in the "servo" range.

And a project for generating the PWM. Now since the PIC only has one bit of PWM my circuit has the PWM output pin driving four AND gates whose other inputs are being fed by four GPIO pins. The four GPIO pins hold the "command" for the bridge and the PWM pin pulses it.

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