Talon SRX Missing Encoder Counts in Labview

[Chris_Elston]

Was hoping to bounce some ideas off of others on CD since these Talon SRX motor controllers are kinda of new and we are just learning about them.

So like most, our application is a PID position based application. Our current feedback sensor is a US Digital S5 shaft encoder that is 1000 PPR. It's coupled to the output shaft of a gear box.

Working with my lead programmer student today, we was able to setup a fully closed loop control method around our mechanical linear elevator. We spent some time tuning the PID and the result is fantastic. The rate is aggressive with a nice accel and decel right at the end of the setpoint.

That part works wonderfully well....kudos to the Cross Road Guys, we like how user friendly the controller is so far.

What we are having problems with is accuracy or what looks like we are missing encoder counts. That's where I wanted to bounce some ideas of some people to see what methods we can use for troubleshooting our problem.

Here are some thing we are sure are OK.

1. Wiring for sure is ok. The closed loop method works great and the position response is wonderful. We don't have an reverse or out-of-phase condition because we are able to set up setpoint commands and everything works great there.

2. The encoder is not slipping on the output shaft of the gearbox. The follower gear is tight and everything seems like it's mechanically coupled ok.

As a test, we used velocity sampling to see if we are missing some counts. In looking at the waveform, it does appear that some skips are happening because as we accelerate a "wave form" is made and there are horizontal flat spots then a rise in the step when we look at the wave form, small ones. I wished we would have grabbed a screen shot....

So here are my troubleshooting thoughts to try on Monday.

1. The obvious, switch out the encoder. Making sure we don't have a bad one. We don't have brand new one, but I have three more to try and see if we can repeat the problem.

2. I am wondering since the encoder is wired directly to the Talon SRX, what methods of debug do we have to see about missing encoder counts? Right now we have a 1000 PPR encoder. I was thinking about trying a 250 or 360 PPR encoder. Is our 1000 PPR encoder too much for the Talon SRX interrupts?

3. The while loop that my lead programmer has is a 50 millisec loop in it's own VI. So every 50 msec, it's samping the count information via CAN BUS of course to his VI. I don't think there would be an software issues, because if we can't get a repeatable count from the get count, then the problem is not software, it gotta be something up with the two above conditions...

Any other suggestions for troubleshooting to understanding here our encoder counts are going?

I am also going to stop by AndyMark in the morning and pick up a couple of MA3 analog sensors along with the analog breakout board and see how that works. Anyone tried the MA3 analog sensor yet with the Talon SRXs?