# Brushed DC motor - 4 pole field winding help

#### amilton542

Joined Nov 13, 2010
497
Until now, I had no idea a 4-pole field winding arrangement could complicate brushed commutation.

As a frame of reference, the field windings consist of 4 poles, armature inherits saliency features by which again consist of 4 poles, and now I feel there is a need for another pair of brushes, 2 pairs in total, in order to eliminate any 'dead' coils.

Now, I'm not one to give in easily and after hours of internet research, thinking and drawing I finally fold.

What is the commutator arrangement to connect this up?

Any diagrams or links would be much appreciated, thanks.

#### shortbus

Joined Sep 30, 2009
10,039
If I understand what your saying, this is to run motor in reverse. It is done on "universal" motors, brushed motors that run on AC. Because the AC can't be reverse polarities like DC, to reverse rotate the motor, they use one set of field poles(180* apart) for one direction and the other set of poles (90* from the first set) for the other direction.

#### amilton542

Joined Nov 13, 2010
497
If I understand what your saying, this is to run motor in reverse. It is done on "universal" motors, brushed motors that run on AC. Because the AC can't be reverse polarities like DC, to reverse rotate the motor, they use one set of field poles(180* apart) for one direction and the other set of poles (90* from the first set) for the other direction.
From the YouTube video I've watched, this method is employed in starter-motors.

Please observe the video at 9:45.

This is the same arrangement as the one I'm trying to build but with a 4-pole salient armature.

Last edited:

#### amilton542

Joined Nov 13, 2010
497
No worries, I've done it now. Problem solved

#### shortbus

Joined Sep 30, 2009
10,039