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### Author Topic: How to calculate the brush position for a DC motor  (Read 2089 times)

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#### Spatial

• Newbie
• Posts: 3
##### How to calculate the brush position for a DC motor
« on: October 13, 2014, 03:29:22 AM »
When I look at a brush holder from above I can see that the brushes are set at different angles. I assume this has to do with the diameter of the commutator, degrees between slots, number of slots and brush width?

Is there a formula that calculates the optimum brush position using these parameters?

I am looking at a brush holder on a DC PM with four brushes and a commutator with 29 slots (starter motor) I can see the offset is 20 degrees at the commutator face but wonder how this was arrived at?

#### kam

• Hero Member
• Posts: 1849
##### Re: How to calculate the brush position for a DC motor
« Reply #1 on: October 13, 2014, 08:45:21 AM »
i try to get the image but i cannot. what do you mean 20 degrees at the face? do you have a picture to indicate this?

#### Spatial

• Newbie
• Posts: 3
##### Re: How to calculate the brush position for a DC motor
« Reply #2 on: October 13, 2014, 08:52:22 AM »
I have circled the area I am referring to.  We want to have this motor CCW currently its CW.  When we simple swap the poles we see a drop of 50% in the torque which we do not expect and are wondering if the brushes need to be adjusted on the brush holder but everything I have read says this should not be necessary?
Thanks!

#### kam

• Hero Member
• Posts: 1849
##### Re: How to calculate the brush position for a DC motor
« Reply #3 on: October 13, 2014, 09:01:56 AM »
You talk about 4 brushes, but i cannot see them in this drawing. Note the actual brush position with a green color to see. Also, how many windings are on the motor? 3? Do you have a motor picture?

#### Spatial

• Newbie
• Posts: 3
##### Re: How to calculate the brush position for a DC motor
« Reply #4 on: October 13, 2014, 09:06:21 AM »
Attached is a 3D of the brushes, my interest is in knowing how you determine the correct orientation of these brushes?

Sorry I tried pasting it here but I must be doing something wrong?

« Last Edit: October 13, 2014, 10:19:25 AM by Spatial »