Talon SRX Missing Encoder Counts in Labview

[TylerStaudigel]

Originally Posted by ozrien

Chris, I figured out what is wrong, the problem is your LabVIEW app. Without revealing the details of your project, the brief description of the problem is that "Motor Enable" is being called every loop. Every time "Motor Enable" is called, a frame is sent to the Talon to "set" the current encoder position. Since the caller has wired the position signal to the last received position, it has the negative effect of constantly setting the position to the last received position [not ok]. So changes in encoder position in the Talon firmware are being stepped on by the RIO's request to reset the encoder position.

I reproduced your exact symptom by creating a new Labview project and dropping in your VIs. I teleop'd enabled, moved the encoder to the zero position, marked it, moved it forward one rotation and then back. Encoder pos was no where near zero [not ok]. Then I deleted the call to "Motor Enable" in ElevatorPositions.vi and redid the test, encoder went back to zero successfully [ok].

Long story short, do not call motor-enable continually. If you want to kill the motor drive set the throttle to zero or change the control mode of the Talon object.

What do you mean by the motor enable vi. Is it the motor set output or something in the begin category?

[Chris_Elston]

Originally Posted by TylerStaudigel

What do you mean by the motor enable vi. Is it the motor set output or something in the begin category?

In my student's code, when a limit switch was hit, he has a true/false condition that "disable the motor" then it would "enable the motor".

What Omar is saying is inside this VI, it writes a SET Position of "0" each time this VI is called. Here is the screen shot Omar sent us to check. We will check this tonight.

Omar recommends NOT USING Motor Enable/Disable in this method because the VI write the SET POSITION in the back ground, I assume for safety reasons...it writes a set position of ZERO so the PID won't take off when the motor is enabled. You don't want a "run-a-away" motor condition on power up.

[TylerStaudigel]

Originally Posted by Chris_Elston

In my student's code, when a limit switch was hit, he has a true/false condition that "disable the motor" then it would "enable the motor".

What Omar is saying is inside this VI, it writes a SET Position of "0" each time this VI is called. Here is the screen shot Omar sent us to check. We will check this tonight.

Omar recommends NOT USING Motor Enable/Disable in this method because the VI write the SET POSITION in the back ground, I assume for safety reasons...it writes a set position of ZERO so the PID won't take off when the motor is enabled. You don't want a "run-a-away" motor condition on power up.

So we don't even have that vi in our code. We are just using the motor set. To make sure we have the same problem, the encoder counts up correctly but when we try to return to zero it doesn't return to the same point. This is the problem you guys are having right?

[ozrien]

TylerStaudigel, check the Self-Test to see exactly why the motor movement isn't matching your expectation.