Quote:
Originally Posted by Jaci
As something to keep me busy during the offseason, I've looked into possibly making some circuits for the RoboRIO's MXP Breakout Port.
Unfortunately, upon reading this article, it seems that PWM devices MUST be a direct passthrough. I suspect this will bear some issues regarding sensor based response (i.e. a Trim) for the PWM port.
While I can see why FIRST is doing this (in the interest of safety), I was wondering if there's a way to interface with the PWM on the breakout without passing it directly to a motor controller, i.e. putting circuitry inbetween. While there is an approval process, there is nothing in the article that I can see stating it as being coherent enough to include this type of control.
Additionally, approval process states that the report must be in conjunction with a company as a vendor, and all information disclosed at kickoff. I see the MXP board as an extremely powerful tool, but for some teams they may want to keep this interface board private, or just not have to deal with manufacturing for other teams (i.e. build for their own usage). I hope to see FRC make this interface legal for single-team use, as Electrical Engineering in FRC hasn't really delved much further than 'plug the thing in the thing'. |
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.