Independent but synchronous mechanisms?

[ismail_hasan]

I have two mechanisms that are independent of each other, not mechanically linked, and they both have a CTRE Mag encoder on them. I’m wondering how I would go about synchronizing these mechanisms in software so that they would always be in the same place relative to each other, and their encoder positions are always the same.

Thanks!

[BriFRC]

If they’re run by Talons just put one of them in follower mode. It looks something like this. frontLeft.set(ControlMode.Follower, rearLeft.getDeviceID());

[ismail_hasan]

There could be more load on one mechanism than the other though. Would that make a difference?

[BriFRC]

Can you give me a specific example of what you’re trying to do? That may help. The main reason I’ve used this is for the drive train. We use a 4 CIM drive train, and by putting the front talons in follower mode they’ll always work in sync and you only need one encoder per half of the drive train.

[Basel_A]

Follower mode definitely would not work in the case of different loads. Follower mode sets the input on the follower motor to be the same as the leader, but in this case you’d want different inputs to achieve the same output.

[POWERM]

You can try to take the value of one encoder of a TalonSRX and feed it to the other one as a PID input. It would take a lot of try to fine tune the PID but I think it would work

[ozrien]

You can use TalonSRX closed-loop for differential. We added this last season (for diff-swerve, diff-drive-train, and other similar mechanisms).

Basically you make one master talon calculate PID[0] + PID[1], and PID[0] - PID[1].
The former is applied to the motor. The latter is sent to your AuxFollower (talon set to follow with FollowType.AuxOutput1).

CrossTheRoadElec/Phoenix-Examples-Languages/blob/master/Java/MotionMagic_AuxStraightQuadrature/src/main/java/frc/robot/Robot.java

You could even run a primary PID to servo the difference/sum of the two sensors to maintain level, while open looping the overall up/down of the mechanism.

ArbitraryFeedForward with AuxPID1 not sending FF term to slave TalonSRX

What you can do is use PIDF1-aux to produce essentially a feed forward term. Set the gains for PIDF1 so its kF only. Then whatever target you specify for aux1 will just get multiplied by KF (essentially a feed forward), This works on my setup… Although I’m not sure what physical mechanism this would be useful for. I guess doing a single-axis servo, and then applying an open-loop differential could be useful depending on where the sensor is.

Similar post here manipulating two sensors to produce a sum/difference to servo/maintain.

Talon SRX Motion Profile Manual

RemoteLOS fault is set. That means the Talon is trying to get remote sensor data and its not on the bus. Probably the remote filter is wrong. You have to make some decisions about what sensors you want to use before firing MPs. Some steps … Decide which talon will be running the profile. I usually use the right side, so I’ll treat that as the example. This means the right talon will execute PID[0] + PID[1]. That the other side talon (left) will be setup as an Aux Follower, so it will ap…

MotionMagic with Aux PID[1] would be useful since your target mechanism is profiled along your single-axis, meaning Aux PID[1] maintains the sensor difference just like a turn-closed-loop during an arc.

Whatever you do, start by configuring the peak outputs to be very weak or disconnect motors entirely while you work out direction/phases/etc during hardware-bringup.

Makes sense?

[ismail_hasan]

Yes, it does, thank you very much!