Talon SR Help

[Razer0901]

Hello everyone!

We have a problem with one of the four Talon SR motor controllers that came in the KOP. As we were practicing for our upcoming event we noticed that turning left was a problem. After searching all around, we found the culprit, a talon SR. After searching around on the forums, I found nothing similar to our problem. The motor controller spins forward fine but not backwards. It refuses to spins backwards, no matter how we try.

If anyone has any solutions I would be grateful, but it seems like we have to replace it. As a rookie team, we only have 4 talon SRs and since they are discontinued we can't buy them anywhere! Is there anyone in Massachusetts who is willing to sell us one? We would be willing to come pick it up tomorrow.

Another possible solution is a victor sp. Is there anything against using two different motor controllers from the the same PWM (Y cable) to the same gearbox?

Any help would be appreciated!
Thanks in advance!
-Geoffrey Wang

[Jacob Bendicksen]

Sounds like a miscalibrated Talon. Look on page 7 here, and try calibrating the Talon - there's a good chance that this'll fix it.

As far as using a Victor SP, it's generally not recommended to use different motor controllers on the same gearbox. Different controllers have different response curves, so you'll probably end up with one motor doing more work than another. It's not necessarily unsafe, per se, just not recommended.

[Razer0901]

Thank you so much for replying!

I will try to calibrate my Talon. I already tried that twice, but maybe I didn't do it right. Should there be load on it? Or should it just be connected to power?

-Geoffrey Wang

[Jacob Bendicksen]

Shouldn't matter if there's load - what it's doing is comparing the full speed forward/full speed backward PWM input values, then calculating the average as your new zero.

And yes, connecting it to power should help

[GeeTwo]

Answering the second question first because it's easier:

We have wye'd PWM signals to at least two motor controllers in the past when we wanted to control them from the same signal. We saw nothing against it in the rules, and the inspectors either didn't notice or didn't see it as a problem. AndyMark actually sells a cable for just this purpose, though I believe we made all our own.

Back to the first:

• Did you calibrate the Talon SRs?
• Have you tried to isolate the issue as being a talon vice a 'RIO vs a motor problem?
  • You can check whether it's a motor problem by measuring the voltage across the talon's output terminals.
  • If you don't have an o-scope, the easiest way to check the talon is to swap two talons at both the PWM and motor output ends, and see if the problem tracks the talon or the signal.

[GeeTwo]

Originally Posted by Razer0901

Is there anything against using two different motor controllers from the the same PWM (Y cable) to the same gearbox?

Agreed that you should not control different types of controllers from the same signal. In software, you can create a virtual motor controller that basically sends the same voltage percentages to multiple physical controllers; these can be of different types.

[Ether]

I don't have any test data to back this up, but I'd bet that the performance and linearity of the VictorSP is very similar to the TalonSR. There may even be more variation in the CIMs than those two controllers. I'd say go for it.

[ozrien]

I'd expect a Talon SR and Victor SP to have very close response as long as you calibrate.

When your Talon SR is "not going in reverse" what are the Talon LEDs doing? Are they red (solid if 100% reverse, blinking if less than 100%).

[GeeTwo]

Originally Posted by ozrien

When your Talon SR is "not going in reverse" what are the Talon LEDs doing? Are they red (solid if 100% reverse, blinking if less than 100%).

Normally, I'd check these first. However, as OP believed that the problem was in the Talon, I recommended tests that would rule the talon in or out as the issue. If the issue is within the talon, the lights might give the expected results (red/green/blinking) if the problem is on the power amplifier/output side of the LED test point, and unexpected results (I won't speculate) if it is on the PWM/input side of the LED test point. In either case, if it's inside the Talon, it's beyond the capability of most FRC teams to repair.

[GeeTwo]

Originally Posted by Ether

I don't have any test data to back this up, but I'd bet that the performance and linearity of the VictorSP is very similar to the TalonSR. There may even be more variation in the CIMs than those two controllers. I'd say go for it.

Yes, from some clues in the wpilib, the Victor SP and Talon SR seem to use the same nominal timing-to-voltage curves, and you'd stand a pretty good chance at getting away with it, especially if these were two motors on the same gearbox as opposed to two separate mechanical trains you were trying to synchronize with open loops. In any case, do not wye a PWM output between a jaguar and anything else - bad joojoo.

Originally Posted by wpilib documentation

The Talon and Victor controllers use typical hobby RC controller timing of 1ms to 2ms and the Jaguar uses an expanded timing of ~.7ms to ~2.3ms. (link)

[ozrien]

Originally Posted by GeeTwo

Normally, I'd check these first. However, as OP believed that the problem was in the Talon, I recommended tests that would rule the talon in or out as the issue. If the issue is within the talon, the lights might give the expected results (red/green/blinking) if the problem is on the power amplifier/output side of the LED test point, and unexpected results (I won't speculate) if it is on the PWM/input side of the LED test point. In either case, if it's inside the Talon, it's beyond the capability of most FRC teams to repair.

correct. I thought that was obvious when I asked the question.