DC Motor Brush Angle

I repaired the rusted shell of a small 12V DC PM motor, but forgot to note the position of the brushes relative to the magnets. After
putting it together, it seems to run at the same no-load speed with a wide variation in brush angle and I can not apply a load and adjust the brush angle at the same time. This is a low cost Japanese motor (20mm 6-pole rotor, copper-graphite brushes on 6-sector communtator, and two thin ceramic magnets inside the shell). Where should the brushes be for maximum power or how can that be determined? (Note: subtract 69 from listed email for actual email.)
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You didn't say how many brush locations there are around the commutator but I think what your describing is a 2 pole motor with 6 slots on the rotor. There would be 2 brushes, 180d apart. I believe that the brushes should be place so as to draw the minimum current when operated as a motor. This would be half way between the poles more or less depending on how the commutator is connected to the winding. This probably is not the same as the physical half way point between the magnets. Fine adjustments should be made to minimize sparking under load. Someone who has studied DC motors more recently than 40 years ago should confirm this.
The angle of the brushes on the com is another problem that needs someone skilled in brush voodoo.
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Fred Lotte
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...
Thanks Fred, motor current does seem to have a minimum over a smaller range than maximum speed.
I can't see the commutator when it is in operation, so I don't know about sparking.
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Bob,
Sorry I don't know the answer to your question other than trial & error mapping the rate of change etc etc. Why not email the company & explain or possibly, if replacements are available, phone the supplier & just ask, sometimes tech people will go to all sorts of lengths to help out. Another thought, if you have similar motors hanging around your workshop, see whether there is a "typical zone" into which brushes are generally placed. I must say that over the years I have had a bit to do with DC motors & getting optimum designs etc has always seemed a blcak art. Good luck.
Pete

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