DC brushless motor not getting enough voltage

Thread Starter

x1222

Joined Oct 22, 2011
31
Hello everyone,

I'm building a project where I need a motor to move a small tray along a track, but I can't seem to get the motor to push it. I can push the tray with the flick of my finger. I'd be a bit surprise if it was too weak to push it, since it was from fairly large remote control car.

To test the motor, I connect it directly (no resistor) to a power supply. With no load I can get it to 6v, but as the motor is trying to push the load, the motor cannot maintain it's operating voltage and stops moving. Even if I keep cranking up the voltage dial, the voltage won't go much higher. The current is maxed out. It'll spin with voltage dial at 0.2V without load.

Would using batteries instead of a power supply make any difference? Or does this mean my motor is too weak for the job? Any help is much appreciated.
 

SgtWookie

Joined Jul 17, 2007
22,210
It sounds more like your power supply is weak.

What used to power the motor when it was in the remote control car? Use the same type of power.
 

Thread Starter

x1222

Joined Oct 22, 2011
31
The power supply is at school, so I don't remember the power rating but its dials can go up to 20V and 4A, 80W? The car itself uses 8AA batteries, 12V, but it has two motors, so i'm assuming it only needs 6. I'll have to get a battery holder and check then.

So the inability to get enough voltage, is a power problem and not due to the motor strength?
 

SgtWookie

Joined Jul 17, 2007
22,210
Hmm, then the power supply should not be the problem unless it is defective.

Motors used in model cars usually have a gear train between itself and the wheels; this allows the motor to spin much faster than the wheels, and the torque from the motor is multiplied by the gear ratio.

Did the car originally have gears, and you removed them?

Are the wheels/tires/gears/etc that you are using now too large, so that the motor has no mechanical advantage?

It would help if you could photograph or sketch what your setup is and post it.

Operating a motor in a stalled condition (rotor locked) is very hard on it. Don't allow that situation to last more than a few seconds, and then a long cooling period (several minutes) or you will probably burn up the motor.
 

Thread Starter

x1222

Joined Oct 22, 2011
31
Yeah there were originally gears, which I took out. I guess that explains the weakness. It is attached to a lot larger disc. I ended up getting a new motor and it works. Thanks for the advice.
 

strantor

Joined Oct 3, 2010
5,159
The problem was that you were trying to power with DC current a brushless R/C motor. These motors have 3 cables and you need a Electronic Speed Controller that will output pulsed current to the multiple stator windings in synch.

You can find some DIY designs here:
http://www.rcgroups.com/forums/showthread.php?t=140454

or buy one for a few bucks.

Dimitrios
+1
R/C motors usually do not have the brushless commutation circuitry built in to the motor. the "ESC" (electronic speed controller) is usually located elsewhere in the car. do you still have the car? maybe you can get the ESC out of it.
 
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