Anyone want some ridiculously powerful motors?

Hello all,

FIRST alum from '07 here. I sort of fell out of the scene after high school, but I’m glad to see that it’s grown so much (what is this cRIO and Jaguar shenanigans?!). I have a few things I’d like to hawk to the community - not being too sure which category this kind of post belongs in, so I put it in “chit-chat” for now.

A few of us builders of rideable things up at MIT recently commissioned a custom order of very large R/C model motors. The minimum order was more than we could ever reasonably use, so I figured I would return here and see who else is into building wacky moving contraptions.

Basic specs: “C80” type brushless outrunner, 80mm OD, 110mm length, torque constant Kt ~ 0.053 (or 180RPM/V). 0.021-0.024 ohms line to line resistance. 12mm shaft on both ends. Weighs about 6 pounds.

These things are scarily powerful - typically up to 5-6000W peak mechanical output and more than 90% efficiency. Many electric bikes and go-karts have been made with this type of motor. People have rewound them and pushed 10kW through them for short periods of time. In ground usage, they will not do this kind of power forever because there is no cooling implied. They are “rated” for 7kW in aircraft use where you’re pretty much guaranteed a stiff breeze. Now keep in mind this is a typical R/C industry spec, but this motor has plenty of traction usage behind it.

We have like 5 more of these and would like to see $200 each - PM or email charlesg@ (that 3 lettered university I mentioned) .edu.

Some questions you might have, since I hate leaving people dangling with a cool picture:

What controller do I use with such a thing?

Typically you’d use a >100A R/C aircraft type ESC, but because the motor is really capable of drawing several hundred amps, those without current limiting or torque control capability (basically all of them) are risky to use. The Castle Creations HV160 is a good example of one which can handle both the current and has protection.

Alternatively, if you pursue a sensored controller, the Kelly KBS is about the smallest you can use. They have current control, but just rather low current, so you wouldn’t be using the motor to full potential. Their KBL series (bigger) in 200 or 400A config is better suited.

How do I couple it to a load?

In its intended use, you bolt a prop spinner to the rotating can of the motor directly. This motor has a mounting face (stationary) and tailshaft which is useful for mounting sprockets/belt pulleys, etc. It’s 12mm and smooth, so optimally you’d bore out your pulley/sprocket and fasten via pin or large-set-screw-with-flat.

How would I mount Hall sensors onto it if I wanted to use sensored commutation?

The motor does not come with sensors or encoders, etc. since it’s designed to be used essentially as a synchronous AC motor in an aircraft application. You will need to strategically place 3 Hall Effect digital latch sensors to use it with a sensored controller. One good place to look and ask is the Endless Sphere forums ( , where many people chop R/C model parts into ground applications

Alternatively, we also made (3d printed) a sensor PCB mount for this motor, and also had several Hall sensor carrier boards made. There are a few of these boards left too and the mount can be 3DP’d on demand. Here’s a picture:

If you get a motor I’ll print off a sensor ring and pitch in a pre-assembled Hall board (add your own 5 pin cable though) for $20. These get sandwiched between the motor’s conical face and its mounting plate and is adjustable 120 electrical degrees to let you find your motor’s best timing.

I don’t have an immediate use for these, unfortunately. Wish I did. But I will attest to the fact that Charles makes some very wild stuff and these are serious motors.

No, they are not and probably never will be FRC legal :slight_smile: But if you have a monster off-season project you might want to contact him.

Ooh, i could do some pretty neat stuff with it. Maybe make a little motorized cart or something.

Oh how I wish we could use brushless motors…

By the way, as a random hook to hopefully inspire more of you guys to build off-the-wall rideables (perhaps literally) in the off season, I’ve more been into writing up resource and instruction guides for small electric vehicles lately:


are two of the examples.