Today I wrapped up assembly of the two OSMC's for my robot. I don't think I've introduced my robot yet. That's still to come, I guess. ;) For now, let's stick to the motor controller. I mentioned in the last post, I omitted a few components to save money. Some of those were things like the 10 pin ribbon cable connector. Nice, but adds cost with virtually no benefit in my mind. Another thing I omitted was the onboard 12v regulator. The chips for that regulator were $5 each, and then the inductor that it used was out of stock for months. I found an equivalent, but it was almost $10 each. So I saved a fair bit just skipping the onboard regulators completely. Instead I'll just pick up a pair of chinese DC-DC converters that'll take anything from 15-75v and give me a nice 12v output, and run both boards off the single power supply.
When it came time to install the mosfets, I had to plan ahead for the heatsinks I had purchased. This board wasn't originally intended to have heatsinks, just a fan blowing down over the bare mosfets. Meh. Bare TO220 packages will rise 63C per watt dissipated (watts dissipated is based on their internal resistance). That amount of heat rise would seriously limit how much current they could supply the motors with. Well I found these great heatsinks on Mouser for 21cents each, and according to their site, these are 25C/watt. That's a seriously epic improvement, especially for 21 cents.Anyways, as you can see in the picture above, I had to put half the mosfets on the bottom of the board to make room for the fins on these heatsinks. Not a real big deal, but it did make assembly harder.
I also had to notch one on each board to clear one of the TVS diodes.
You can just make out the notch going around the diode in the above picture.
There they are. All 32 heatsinks installed. Heatsink paste behind each one. I wasn't sure about which ones could and couldn't touch each other, so I just assumed they couldn't ever touch, and arranged the heatsinks/bolts accordingly. I also arranged it so that nothing hung over any edges, so I can still put the whole thing into an enclosure. I forgot to order nuts/bolts with the heatsinks, so I had to do some serious scrounging to come up with enough for the whole thing.
With heatsinks on both sides, I'll have to put fans on both sides, but I'm ok with that. Oh yeah, I omitted standoffs for the fan from the purchase when I bought the components for this board. I'll have to improvise something else.
Stay tuned, I just might wire these up and test the robot base next.