CAN Jaguar Encoder Wiring

[Brian Selle]

We want to use an encoder connected directly to the Jaguar for speed control. The jaguar doc shows 5 wires to connect the encoder (5v, GND, A, B, index). The US Digital E4P that we already have just has 4 wires (5v, GND, A, B). Do we need the index wire?

[Jon Stratis]

No, you do not need the index wire.

[Brian Selle]

Thanks. What the index wire used for? Do you need it for position control?

[dyanoshak]

Originally Posted by btslaser

Thanks. What the index wire used for? Do you need it for position control?

Some encoders have an index pulse that happens once per revolution. It is useful for orienting the encoder when its initial position is unknown.

In Jaguar's case, whenever it sees an index pulse, the encoder count resets to zero. This is useful if you want to make an incremental encoder somewhat of an absolute encoder.

-David

[Kevin Sevcik]

The index is a line that pulses exactly once per revolution.

I can't think of any FRC applications that would require it. In industry, you use the index pulse in combination with a home switch to determine an absolute zero location for a motor. Physical switches are notoriously inconsistent, so to zero a location consistently, you set zero at the point when the home switch is on and the index pulse happens. As long as the index pulse happen a reasonable distance from the switch turning on, you have a very consistent zero point.