Spikes and CIM?

[Superllama12]

We were trying to use a spike to control a CIM on an old robot we're repairing. We blew a couple of fuses and talked to some mentors until finally someone said to try a Vic. The Vic worked, but does anyone know if we're able to use a Spike to control a CIM? The PD board was putting out 30 amps, and the Spike had a 20 amp fuse, is that the problem, or are they physically incompatible? Thanks!

[electron]

Originally Posted by Superllama12

The PD board was putting out 30 amps, and the Spike had a 20 amp fuse, is that the problem, or are they physically incompatible? Thanks!

Yes, that would be the problem. I've seen CIM motors draw about 40 amps. The Spike is limited to 20 amps, and (as you saw) the fuse will just continue to burn out.

[Rosiebotboss]

To answer your question: RTM. More specifically the wiring schematic. It will clearly show that controlling a CIM with a spike is verbotten.

[ebarker]

The CIM draws vastly more current than the spike can handle. Spike is verboten.

[Russ Beavis]

Regardless of the rules (it sounds like you're trying to repair on old robot that won't be used in competition), a very important factor to keep in mind when pairing motors and motor drives is that, for a short period of time, DC brush motors will always draw stall current when starting from zero speed. Brushless motors can also draw high currents depending on the drive design.

The CIM's stall current when driven with a perfect 12V battery, wiring and motor drive is over 100A. A Spike cannot tolerate those 100A peak currents. Hence the 20A fuse/breaker that is often used on the Spike and why you keep tripping that overcurrent protection device.

Spikes and CIMs don't play nice which is why the rules generally (always?) do not allow that combination. Spikes will work well with most smaller motors, though. You'll just need to learn how to interpret the datasheets for the motors and Spike and select appropriate breakers and fuses.

Russ

[Al Skierkiewicz]

Guys,
A spike is only designed to handle 20 amps max. That is the rating on the contacts in each internal relay. When used with the compressor, you can change the fuse to a 20 breaker as the compressor start current exceeds 20 amps for a very short time.
A CIM motor on the other hand, has a stall current of 133 amps. That is the current it draws every time you apply current to it and it is not moving or everytime you are in a full throttle push with another robot and going nowhere. It will draw that current even if you put a 20 amp circuit breaker in place. Breakers do not limit current.
For FRC robots:
<R48>
A. Each CIM motor and Fisher-Price motor must be connected to one and only one approved speed controller. These motors must not be connected to relay modules.

[Ether]

Originally Posted by Al Skierkiewicz

A CIM motor on the other hand, has a stall current of 133 amps. That is the current it draws every time you apply current to it and it is not moving

Just to be clear, that is the current it draws at 100% PWM with a 12volt supply when the motor is not moving.

[Al Skierkiewicz]

That would be what it draws if connected to a Spike and turned on.

[Ether]

Originally Posted by Al Skierkiewicz

That would be what it draws if connected to a Spike and turned on.

Sure enough :-)