Gearbox question

Would a 3 cim gearbox still work of one of the motors is shut off or at a significantly lower speed? Also can you have a gearbox with 2 cims and a mini CIM?

A 3 cim gearbox will work if a motor is shutoff or if a minI CIM used in place of a cim. A cim and a mini CIM will lead to significant current draw though, I’d caution against it :slight_smile:

2 Cims and 1 mini Cim per side (4 Cims and 2 mini Cims total) is viable. You wouldn’t want to run one motor at lower power relative to the other two however (Edit: unless I’m wrong?). Someone else will have a better explanation as to why but generally you power each motor equally.

Yes and yes. If you have a motor shut off in gearbox the other motors will continue to turn that motor like a generator. It is inefficient since it adds drag to the system. Also you can add a mini CIM in place of a cim in most scenarios how ever they do run slightly faster, they are often considered 2/3 of a cim.

Would this be bad for the motor that is shut off?

It won’t harm the motor. The other motors just have to work harder to overcome the load of the unpowered motor, especially if its leads are shorted or connected to a speed controller in brake mode.

In 2014 we ran 3 cim ball shifters with 2 cims and a mini cim. The mini cim improved performance and we didn’t notice any strange wear and tear on any drivetrain components.

If your programming includes shutting down one or more motors (but not all) on a gearbox, it is essential that the motors you will shut down be in “coast” mode. Putting a “brake” motor on the drive train will just turn a lot of your battery capacity into heat, unless you brown out or trip a breaker. With the SRX operating in CAN mode, you can change this dynamically, but IIRC with the other controllers this a design requirement.

As stated above a miniCIM can be swapped out for a CIM with no ill effects.
Taking a look at 234’s drivetrain tests will clear up a low of current draw effects with different motors: http://www.chiefdelphi.com/media/papers/3071