capacitors on motors

[John Gutmann]

i dont know if t his should be here or not but when ever i see a motor from a r/c car it has a couples of capacitors between the leads on the motor, and i was wonder what is the purpose of them?

[Quatitos]

Originally Posted by sparksandtabs

i dont know if t his should be here or not but when ever i see a motor from a r/c car it has a couples of capacitors between the leads on the motor, and i was wonder what is the purpose of them?

Capacitors are usually used in dc motors to try and smooth out electrical "noise" created by the motors. This noise, if not smoothed out by the capacitors, could cause some of the other electronics hooked up to malfunction.

[billbo911]

Originally Posted by sparksandtabs

i dont know if t his should be here or not but when ever i see a motor from a r/c car it has a couples of capacitors between the leads on the motor, and i was wonder what is the purpose of them?

I believe that is a fair question.
Those little caps perform a very specific function, one that is important in the environment that those motors are used. They are filters. Their purpose is to suppress, or at least reduce, high frequency noise and RF interference generated by the making and breaking of the connections between the brushes and armature.
Considering that these are used on Radio Controlled vehicles, this is a good thing.

[mechanicalbrain]

they also can be used to cover over momentary power drains in your system (like i used a camera and there were power drops but the capacitor covered it right up). speaking of which can WE use capacitors to smooth out noise

[Hutch]

Originally Posted by mechanicalbrain

speaking of which can WE use capacitors to smooth out noise

Definitely - my team did it this past year because our rotary encoders were being stupid. They are also good for digital logic circuits (gate state changes can cause big current drops).

[Denman]

and they are also used in flashes in cameras

Important for pretty much everything really....

[Andy A.]

I am not entirely sure as to the legality of using capacitors on motors, since that could be construed as modifying an electrical component. My gut reaction is no, it is not legal.

Nor is it really necessary. Most of our motors probably already have capacitors mounted inside the case. Besides that, the Victors undoubtedly prevent any back emf from leaking into the rest of the bot, and unless the radio is right next to a badly arcing motor the radio noise produced won't be enough to interfere with the link. Motors can, and do interfere with sensors. But, capacitors probably won't cure your problem. It's much more effective to shield the sensor and/or move it away from the motor.

Also, the capacitors on motors will not in fact help with momentary power drops. Typically, the capacitors are in the range of .1 micro farads. Thats very, very tiny, not enough to even make a big motor twitch. It is possible to use capacitors that way, but it wouldn't be useful to us, nor legal.

The capacitors are important on R/C cars because the radios are A: relatively cheap AM/FM deals, and B: Are inches away from a motor that is designed to be powerful, not polite. On top of that, many motor manufactures never bothered to solder their own capacitors on, so it was up to the hobbyist. Thats changing though, and most motors now ship with presolderd caps.

-Andy A.

[mechanicalbrain]

you misunderstand me not to power the motors to power sensors!

[Hutch]

Yeah, when I said yes I was talking custom circuitry and sensors and the such - on motors it's completely unnecessary.