The do's and do not's when shifting

[Joe G.]

Originally Posted by WesleyK

So would placing an encoder on the output shaft of the gear box and limit the motor power based on that be enough to prevent overdraw or would we have to monitor the rpm and current draw of each individual cim using a CIMcoder and a current sensor on each motor?

You could infer the stress on your motors with a single encoder value per side compared to the commanded motor speed, over a sustained period of time (you don't want to shift down for a fraction of a second just because you accelerate hard). Doing the same thing with the built-in current monitoring functionality of the new power distribution panel is a lot more straightforward way of doing it though, since you get the actual value (the current) which causes bad things to happen.

[MetaEngineer]

So would placing an encoder on the output shaft of the gear box and limit the motor power based on that be enough to prevent overdraw

This is a crude but potentially effective way of estimating motor load, using the commanded motor power, the motor speed, and the current gear ratio.

or would we have to monitor the rpm and current draw of each individual cim using a CIMcoder and a current sensor on each motor?

All CIMs on the gearbox will turn the same speed, so you can use a single encoder as part of the gearbox to get both wheel speed and motor speed (taking into account what gear is selected). Talon SRX motor controllers have built in current sensors for individual motors, which can be accessed through CANbus.

This can allow code that can automatically shift gears based on both speed and motor load. Related code can back off the drive motor power and even shut down other motors such as the air compressor to stave off a brownout (with its subsequent total cutoff of motor power).

Auto shifting needs hysteresis and possibly a time delay to prevent rapid cycling when right at the threshold of low gear and high gear. Keep very close tabs on wear and tear, as the gears will get torn up much faster when driven hard with automatic shifting.