[DougJensen]

Thanks Folks. We are using the hardware limit switch inputs of the talon - no software is involved in limiting the motor. The config page is set to normally open.

Again, the switches STOP the motor properly in the appropriate direction. However, they Affect the motor when traveling in the other direction. Very simple test we do:
1.) Drive the motor in the FWD direction (continuous CAN throttle value which happens to be 100%.)
2.) Motor moves normally at high speed in FWD direction.
3.) Using a toggle switch to short the REV limit switch input to GND:
a.) Every time the switch shorts the REV input to GND, the motor stutters(like it is being rapidly modulated on and off - think of a multicylinder engine missing a few cylinders).
b.) Open the REV switch and the motor returns to high speed.

Repeating for emphasis: Opening/shorting the REV limit affects the motor when traveling in the FWD direction. (and vice versa.)

Although I haven't put a scope on it, it's almost like there is a high capacitance on the limit input and the weak pullup is causing the input threshold of the micro in the talon to get confused as the pullup yanks the signal through the Vih level. I have not tried a stronger pullup to test this, and I'm puzzled why the input signal is not pulled higher than about 2.3V - I assume the micro is running at 3.3, so I would expect the input to be pulled to that rail, not some 'soft point' like 2.5V.


It's great to hear some input from a CTR dude (thanks Omar) - in this case, I cannot explain how the FWD/REV limit input is affecting the REV/FWD operation. In cases where limit switches have short travels before the mechanism stops, they spend very little time actuated when transitioning at end of travel locations - and 'what we see' would be masked by the short time/travel required. In our design, we have a mechanism with lots of momentum that cannot be stopped quickly, even with braking enabled. This means our limit switch has considerable overtravel required. This requires the motor to travel a 'considerable' amount before the limit switch de-actuates - and during this portion of travel, the motor's operation is hampered by something in the talon/limit switch operation.

Sadly we are abandoning the hardware limit to go to the software limit operation through the dio ports on the rrio...But I'd really like to find the problem here. Thanks to everyone for taking the time to offer help.