Automotive Starter Motors as Drive Motors

[dtengineering]

Okay... first of all, this is not for an FRC application.

A colleague of mine has suggested using recycled automotive starter motors as drive motors in an application not entirely different from how we would use CIMs on our FRC robots. In fact, my suggestion was that we use CIMs... but my colleague liked the "recycled/maker/DIY/low-cost" vibe of the starters. I thought I'd seek out some more information before getting too fixated on CIMs... I really like CIMs, but want to keep an open mind on this.

Here's what I'm thinking.... I'd appreciate advice from anyone with practical experience using starter motors this way.

It appears that many late-model starter motors are permanent magnet DC motors with a planetary gear drive reduction. Sounds promising, especially the internal gear reduction. Even 3:1 helps.

They tend to be more powerful than CIM's (one guestimate is that a starter motor will be about 1/50th the power of the engine it is starting) and thus draw higher currents. This is not only likely to cause a problem with overheating, but also for motor control circuitry, batteries and wiring. I expect most starter motors to pull over 200A on start up and 100A under load. I may be able to dial that back with a motor controller and put a soft limit on current draw.

Older, series and shunt wound motors can be converted to forward/reverse operation, or even for use with a speed control. Should be able to do the same, but even more easily, for a permanent magnet one.

Mounting the starter motor and putting a useful gear on the end of it will be a bit of a pain relative to a CIM, but we do have access to a full machine shop including CNC lathes, mills and a waterjet. (Yeah, sucks to be me... )

So it seems like there aren't any insurmountable problems with going with recycled starter motors.... but I'm worried that something weird is going to pop up... something like having them timed so that they don't run well in reverse or... well, I don't know what.

I know starter motors work great with car batteries in on/off applications for relatively short bursts, like bar stool racers, but has anyone used them with speed controllers in forward/reverse applications? Any reason why they wouldn't work? (Edit: and alternatively... any success stories where they do?)

Thanks for your thoughts!

Jason