brushed DC toy motors - Page 1
Forum section: electronics / general

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 09, 2014, 10:39:26 pm
content: I know I should probably ask over in a hobby forum, but I think I'd get more concise answers here.Small brushed DC motors, like 30x10mm, always come in CW or CCW versions. Is that because the brushes are assembled one way or the other inside ??If I connect a motor the wrong way, I'll get less efficiency because the brushes would bounce off the rotor contacts?

author: amyk
author_rank: Super Contributor
timestamp: September 10, 2014, 03:19:07 am
content: You mean motors like this?http://commons.wikimedia.org/wiki/File:Brushed_dc_motor_assembly.jpgThe brushes on those are symmetrical. Reversing the connections will reverse the direction of rotation.

author: SeanB
author_rank: Super Contributor
timestamp: September 10, 2014, 04:18:26 am
content: Some of the higher power motors do have the brushes at a small angle to increase power and lessen wear on them, so are directional. Tiny little ones though are not done that way, so you can run them in either direction with the same poor efficiency. Add a pair of 10n ceramic leaded capacitors from each terminal soldered to the frame to reduce EMI, and use a 100n across the terminals as well. A ferrite bead in each power wire right by the motor also helps. Some do have internal VDR rings on the commutator to reduce EMI.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 10, 2014, 12:51:00 pm
content: Quote from: amyk on September 10, 2014, 03:19:07 amNo, I mean small coreless ones. But I guess the principle is the same. However if you look at the brushes, obviously one way they sweep "with" the rotor, the other way the brush would chatter, I'd guess.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 10, 2014, 02:13:18 pm
content: Quote from: SeanB on September 10, 2014, 04:18:26 amI guess my mechanical intuition is failing me. I was just wondering why the motors on my quadcopter have color-coded leads to distinguish the CW from the CCW motors.If it's so simple, why don't they just use the same type for all 4 motors and just have the connector on the PCB determine the direction?That was my real question...

author: David Hess
author_rank: Super Contributor
timestamp: September 10, 2014, 04:32:51 pm
content: The brush timing can be optimized if the motor is only intended for one direction of operation at high power.

author: macboy
author_rank: Super Contributor
timestamp: September 10, 2014, 05:15:37 pm
content: It usually comes down to brush timing a.k.a. commutation timing. If you run the motor in the intended direction, you will notice that it runs faster (and with more torque) than in the opposite direction. The brush timing on such a motor is advanced so that the proportion of of time that the energized coil spends pulling toward a fixed magnet is increased. There is a tradeoff of lower efficiency (more heat) so not all motors are built this way. Brushed motors for R/C models often have an adjustable 'endbell' (the part holding the brushes) that can be loosened and rotated in order to select the amount of timing advance desired. Those motors are quickly fading away in favor of brushless motors, whose timing is controlled entirely by the speed controller electronics.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 10, 2014, 06:03:09 pm
content: Quote from: macboy on September 10, 2014, 05:15:37 pmAwesome, I figured there was something going on here. Small brushed motors still make sense for small toys since the weight of the driving electronics would negate any benefit of a BLDC motor.This means I'll have to keep looking for spare CCW motors for my quadcopter...

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 10, 2014, 06:21:42 pm
content: Quote from: macboy on September 10, 2014, 05:15:37 pmThanks, I see it now. I didn't do any scientific test beyond noting that the motors sound different in the wrong direction. I didn't feel like taking the plastic end off since that requires pulling the tiny gear off.