Using a star configuation for Jaguars on CAN

[apalrd]

It seems like a star configuration would negate the advantages of using CAN over PWM. Just a thought.

[NickE]

Originally Posted by apalrd

It seems like a star configuration would negate the advantages of using CAN over PWM. Just a thought.

In theory, you could still utilize the current sensing and PID features on the Jaguars.

[Dale]

In our case we needed to use CAN for current and voltage sensing throughout our robot. For example, our front ball magnet would capture a ball and then stall by design with the current held at a constant value so as not to smoke the motor. It could also sense if it had a ball by looking at the voltage being delivered to the motors.

Our kicker would vary it's kicking power by monitoring the current going to the winch as it's being cocked.

We'd love to use the daisy chain configuration if it were reliable. We might give it another whirl next season but be ready to fall back to PWM for speed controllers that don't need all the fancy features.

[apalrd]

Originally Posted by Dale

In our case we needed to use CAN for current and voltage sensing throughout our robot. For example, our front ball magnet would capture a ball and then stall by design with the current held at a constant value so as not to smoke the motor. It could also sense if it had a ball by looking at the voltage being delivered to the motors.

Our kicker would vary it's kicking power by monitoring the current going to the winch as it's being cocked.

Interesting uses for the current sensors. We used a broken-beam sensor and pulsed the roller, although we didn't have any problems with heating (with a FP). It would spin so much that the ball would begin climbing up the front of the machine and get carrying penalties, so we pulsed the roller to keep torque on it while not continuously forcing it. If we back up, the roller runs full.

We used a potentiometer for our kicker. The kicker motor is actually on a Spike, and Spikes don't have current sensors. We had no jaguars at all (all Victors and Spikes), so CAN wasn't a question we asked. (the answer would have been NO unless we needed the current sensors).

[biojae]

Originally Posted by apalrd

(the answer would have been NO unless we needed the current sensors).

The current sensors have a way of making themselves useful.

The original design (in software) of our kicker only used an encoder and a reed switch.
This software was buggy, sometimes it would not know when to return and continue applying power after it reached the hard stop. (I blame the encoder... )

Needing a quick fix, the current sensing feature of the kicking jag was used to terminate the kick if it was stalled (meaning it either reached the hard stop, or got stuck on something else ) .

This fix worked well enough that no more modifications were needed for the rest of the season.

And like Dale, our magnet uses the current to detect a ball.
(This is used mostly for auto)
It stops it if the ball gets too far in, but isn't needed as much to prevent blowing the motor. (Its a CIM)

The use of current sensing was an after thought, but because we had the capability, it was very useful.