Gear Tooth Sensor FIRE


This past friday, our robot caught on fire in a catastrophic failure of the gear tooth sensor. The way we hooked it up is as follows (I know its wrong):

PWM cable from the J1 (12 v and G) solder connections on the sensor to     digital input 1..

No connection to the breaker panel.

This configuration caused the wire to heat up so that it combusted. Today, with the remaining gear tooth sensor, after realizing it was originally connected in the wrong fashion, we connected J1 Black to Ground and White to the Positive side of the breaker. We connected J2 Black, Red, and White, respectively, to digital input 3. This caused one of the speed controllers for our drive motors to trip the breaker panel. Somewhere in the process, the pwm cable going to the robot controller heated up again and melted, but did not ignite since we caught the problem earlier. Does anyone have any clue as to what might be wrong? Also, the wire that melts is always the ground wire…
Thanks in advance

Did you hook it up according to this datasheet:

If you did, it’s possible that you just have a faulty gear tooth sensor.

EDIT: Make sure that you didnt accidentally get some solder between the wires on the other side of the board, that’s happened to me. Also, if you are bolting it to your frame, make sure you put electrical tape on the side that’s being bolted so you don’t short out the leads on the frame.

I don’t know what would be causing that; I hope you didn’t fry your RC’s digital I/O ports!

The white wire is the signal wire, so what you did was tie the digital input of the RC and the signal output of the sensor to +12 volts through the sensor. What might have occured at this point is anyone’s guess. As to the ground wire heating up, it is taking all the current that is passing through both of the other wires so it will heat up faster. The RC inputs are fairly well protected but this may have killed them and the sensor as well.

I went back and checked the sensor paper again after Chris posted and it is very misleading…
“c. Generally, the “B”, “R”, and “W” connections connect to ground, +5V and signal respectively.”

The connector marked J1 has 12V on the white wire, and return on the black. It sounds like you hooked the sensor up correctly (the second time), unless the PWM signal cable was plugged in backwards on the RC. I don’t know what the GTS would have to do with making another breaker trip, unless you have something funny going on in your software.

this has been probably noted else where and before but here goes. Make sure that you do not have a positive side short to your chassis. This can be very subtle and not always obvious. During the 2003 build our team discovered this problem when the RS 232 cable from the tether port to the OI flamed. The short was discovered at the 120amp breaker as the positive battery side cable was shorted directly to the breaker mounting bolt next to it. The on-board electrical circuits were otherwise isolated from ground so the only time the heating occurred was when the robot was connected to an external ground via the RS 232 cable. We did not sustain any on robot damage from this but learned a good lesson anyway. LRU.