RoboRIO MXP Breakout

[Jaci]

Originally Posted by Greg Needel

I don't want to directly speak for FIRST here, but I will share our experience putting a few boards last year through the process (and maybe some new ones for this year ). The main concern that FIRST has is when a robot is disabled, nothing moves. Inside the roboRIO this is taken care of and if all PWM lines are just passed through they don't have to worry about any problems. If there are any active or passive components on pwm lines between a motor controller and the RIO, there is a chance that the robot will keep moving when disabled. Things like pots and capacitors can cause motor controllers to read false signals and even a twitch of a motor can be very dangerous. Some of the motor controllers on the market even have this twitch problem with nothing more than a bad Y-cable in the mix, so you can see why FIRST is cautious.

All that being said, if you wanted to do a trim Pot on a motor controllers, why not just plug it into an analog port and modify the pwm signal in code? I figure it would have the same results with probably a more predictable outcome.

I can see FIRST's concern, but if a schematic for something as simple as a Trim were to be sent in and put through approval (i.e. a direct passthrough, but will be blocked when an external signal is active, therefore no auxiliary signal generated for the PWM), I would hope it would be at least possible

I'm not saying this is something I'd do, I'd just see it as a good theory to use in upcoming boards. I guess it's more a principal than anything, although I have no intention of running PWM on the board I'll be making, 10 ports is more than enough