BOB update Posted at: Wed, Mar 17th, 2010 | 4:55PM UTC By Josh Ashby

Half the time, something works, the other half of the time it doesn’t, and the other half of the time, it just goes up in smoke. As such was the case with my V1.5 Rev. 1 quad motor controller.Problem #1:

The supply trace going from ground to the MOSFETs source was _way_ to small, as a result, it could just barely handle one motor at 10A, but as soon as two motors kicked in, those 10As jump up to ~20A. BOOM!!… well not really, just a lot of white smoke and that o-zoney smell. So now there exists a 14G wire running from ground to the MOSFETs ground pad, and that little trace is no more.

Safety under thought #1:

When working on the MOSFET gates I discovered that I was not pulling them low when not in use. I was relying on the MOSFET driver to do this as the inputs on the driver are pulled low; However, just for safety, for right now I want both the gate and the driver input pulled low (mostly because this is going to be in my room and I don’t feel like patching a 2X3 foot hole in the wall :) ) So I added in a 1k pull down to each gate.

Stupid error #1:

To avoid the variable i from overflowing when the motors ramped down, I programmed in a simple safeguard that prevented i from reaching 0, however this backfired and now if that code is used, the MOSFETs will not turn off.

Stupid error #2:

I forgot about a fan, luckley me and my grandpa picked up a small >2 inch fan to go over the MOSFETs which works perfectly now. Stupid error #3: When designing the board I forgot that the MOSFETs have the tab as the drain, and my design has all the tabs touching, which means one MOSFET turns on, and the whole board does. as a fix I bent the leads on the MOSFETs to make a stacked pattern on them, which also works and increases air flow so one bird with two stones.

I’ll try to get some pictures up of the changes this week.