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-   -   Dynamic Brake/Coast Modes? (http://www.chiefdelphi.com/forums/showthread.php?t=142175)

MoistRobot 28-01-2016 13:46
Re: Dynamic Brake/Coast Modes?
 
I know we had dynamic brake/coast in our drive train on the 2012 robot, however I believe we used a spike to control the state on the jaguar jumper pins.
Don't believe it was even questioned during inspection at 2 regionals.

Thad House 28-01-2016 14:05
Re: Dynamic Brake/Coast Modes?
 
Quote:
Originally Posted by MoistRobot (Post 1531574)
I know we had dynamic brake/coast in our drive train on the 2012 robot, however I believe we used a spike to control the state on the jaguar jumper pins.
Don't believe it was even questioned during inspection at 2 regionals.
It had been assumed to be legal, including I'm pretty sure Al had used it and suggested it in the past. But if they found a hardware issue where high current could end up running though a legally allowed to be 28 AWG wire, it's absolutely the right call to make it illegal. Thats a good way to start a fire really easily.

GeeTwo 28-01-2016 17:39
Re: Dynamic Brake/Coast Modes?
 
As promised previously, here's the Q&A so that when someone reads this in 2020 they can see the content:
Quote:
Originally Posted by Q646
  • Q. In this post: http://www.chiefdelphi.com/forums/sh...81&postcount=3 and following, it is suggested that the brake/coast pin of a PWM-controlled motor controller may be wired to a control signal from the RoboRIO's DIO port. I read this as a violation of R68, and as a modification beyond the wording of R66, especially bullet I. Others there see it as legal. Is this practice permitted? If allowed, I suggest providing clarification in the rules as to how to wire this safely.
  • A. You are correct, this practice is a violation of R68. We acknowledge that this has been a common practice, and we will review this with Inspectors.
As for a simple way to do this safely (but not currently legally), an optoisolator could be used to act as a virtual jumper. Assuming the outputs of the isolator can handle the current that passes through the jumpers, this should only need a ballast resistor for the LEDs to be enough. If more current is needed, a few transistors and resistors would be necessary to supplement. One could even do the double isolation and use a totally COTS relay module. Repeat: this would be safe, but not (currently) FRC legal.

s1900ahon 28-01-2016 18:23
Re: Dynamic Brake/Coast Modes?
 
Quote:
Originally Posted by GeeTwo (Post 1531681)
Assuming the outputs of the isolator can handle the current that passes through the jumpers, this should only need a ballast resistor for the LEDs to be enough.
Virtually no current passes through the brake/coast jumper.

On the Jaguar (I cann't speak for the design of others, but I can for Jag) the current involved is that in charging the MCU's GPIO input. The GPIO input uses an internal (to the MCU) pull up which is on the order of 50 kohms. The isolator would only have to pull the input below VIL.

Note that this opto isolator, like the one on Jaguar's PWM input, is inverting.

GeeTwo 28-01-2016 21:20
Re: Dynamic Brake/Coast Modes?
 
Quote:
Originally Posted by s1900ahon (Post 1531696)
Virtually no current passes through the brake/coast jumper.

On the Jaguar (I cann't speak for the design of others, but I can for Jag) the current involved is that in charging the MCU's GPIO input. The GPIO input uses an internal (to the MCU) pull up which is on the order of 50 kohms. The isolator would only have to pull the input below VIL.

Note that this opto isolator, like the one on Jaguar's PWM input, is inverting.
If there is virtually no current, couldn't you just move the resistor and output tap to the ground (emitter) side and re-invert passively?

In any case, I was thinking of using the phototransistor side directly as a switch between the center pin and the brake/coast pins. To do this, you would only need to know whether the jumper pulled the B/C pins up or down.

Al Skierkiewicz 29-01-2016 07:27
Re: Dynamic Brake/Coast Modes?
 
I have received reports from independent testing that jumper current is well under 10 ma in all controllers but it does vary from manufacturer to manufacturer.

GeeTwo 29-01-2016 08:04
Re: Dynamic Brake/Coast Modes?
 
Quote:
Originally Posted by Al Skierkiewicz (Post 1531881)
I have received reports from independent testing that jumper current is well under 10 ma in all controllers but it does vary from manufacturer to manufacturer.
Thanks, Al. I'll file this one away as a post-season control project.

ozrien 29-01-2016 23:55
Re: Dynamic Brake/Coast Modes?
 
Quote:
Originally Posted by seg9585 (Post 1527029)
...I have not used CAN control on the Talons before, so I wasn't sure if the Talons could be programmed with this functionality...
As mentioned by GeeTwo, CAN Talon SRX supports this and is in the Talon SRX Software Reference Manual.
Quick example here also...
https://github.com/CrossTheRoadElec/...bot/Robot.java


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