RoboRIO MXP Breakout

[philso]

Originally Posted by Jaci

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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'.

Why do you feel that directly interfacing with the PWM signals is necessary? It is much, much easier (and safer) to manipulate the PWM signals in software as Greg suggests. Much more can be done in software than can be done in hardware. Some teams use co-processors, as Micheal indicates. It would be difficult to find a co-processor with enough horsepower and speed to put in the path of the PWM signals that would not compromise the PWM signals in some way. There are other ways you can apply your creativity without endangering yourself and others.

By directly manipulating the PWM signals, you will be adding complexity to a safety critical system. That complexity can lead to an unsafe condition if not tested very, very thoroughly. This is likely why FIRST wants to see a company as a vendor. It is also likely that they will want to review the company's policies regarding making and documenting design changes. Otherwise a system that was deemed to be safe can become unsafe.