Labview velocity PID

[mhsrobotics3616]

Originally Posted by Ether

You can use the output of the joystick as the setpoint, and the encoder signal as your process variable (feedback).

that's what confuses me. because joystick output would give me a setpoint between +- 100, how does the encoder correspond to that. because if i gave it encoder value as the feedback wouldn't that make it think that the motors power was what ever the encoder value was which could be 0-infinity.

[Alan Anderson]

Originally Posted by mhsrobotics3616

that's what confuses me. because joystick output would give me a setpoint between +- 100, how does the encoder correspond to that.

You would just need to scale the joystick and the encoder so that they both map to the same range, and would have the same value when the arm was at the commanded position. If it's an arm with a limited range of motion, you might want to use something that provides an absolute measure of the arm angle such as a potentiometer or magnetic sensor, instead of a relative-position measurement such as a quadrature encoder.

[Mark McLeod]

Here's an example of mapping a joystick to the range of a potentiometer.
This would force an arm to a particular setting of the potentiometer.

In this case we have a pot with a minimum value of 1.17v when the arm joint is in the lowest position.
The pot has a maximum value of 3.9v when the arm is in the highest position. (You never want to run your pot right up to it's physical limits, otherwise it can get broken very easily)
The joystick full range gets mapped to the pot's full range in the left box. In other words the joystick value gets converted into pot terms.

The right box applies the PID based on the joystick position (now in desired pot terms), and compares it to the current actual pot value, to produce a motor output that will force the arm in the direction it must go in order to make the actual pot value line up with the desired pot value.