I have stripped down the electric motor off a lawn motor. It is a real piece of engineering. The brushes are mounted such that the position of them can be adjusted (by rotation) to one of four fixed positions relative to the fixed windings. The brushes always remain at 180 degrees to each other but can be rotated by about 5 degrees at a time - relative to fixed windings. The adjustment can be made from outside the motor.
Any ideas?
On what?
Either what is the purpose of being able to make the adjustment - or why you are retarded - take your pick.
The retard is you,whichever way you position them they'll wear down faster and also alter the performance of the motors speed till they get a halfmoon shape. ps they can also shatter the brush completely...so much for the "real piece of engineering"
I assume you have not understood:
What do you mean "Whichever way you position them they will wear down faster" - faster than what?
What will shatter the brush completely?
And finally - why would there be such an adjustment which can be made from outside the motor - when would you use the adjustment - what is its purpose?
I recall from college days having a motor with a similar adjustment (the brush wear comments show they don't understand the axis of the adjustment). Presumably it will effect the power and efficiency of the motor - but not sure why it would be on a lawnmower where you would expect the maker to have optimised it.
As the Universal Motor will run on DC or AC, I wonder if it needs the adjustment on the brushes to optimise it for DC?
Again, I am assuming you are rotating the brushes around the armature axis.
Can you adjust them far that the motor reverses? If so, it could be a multi purpose motor with a reversing feature to suit other applications.
Or a speed or voltage adjustment? Phil
Well done Sir, I think that you are spot on - I have had a look at the plate on the motor and it is indeed AC or DC. - and yes the brushes can be rotated around the armature axis in to a different position - ie relative to the field poles (see below)
The firm which made it was the Electric Motor Development company.
As I said - it is a real piece of engineering.
From the web:
As Electric Motor Developments the company became an internationally recognised leader in the design, development and manufacture of permanent magnet commutator electric motors, gearboxes, differentials, electronic controllers and a wide range of induction motors. The company was established at Halstead, England, in 1962 and built it's reputation for creative design with a new type of electric motor for domestic grass cutting equipment, achieving sales of over 5 million units.
I have also found for DC motors: On DC machines with commutators proper positioning of the holders in relation to the field poles is critical. The brushes should be equally spaced around the commutator.... The brushes must also contact the commutator within the neutral zone where voltage levels are near zero. When the holder position allows the brush to make contact outside the neutral zone there will be higher bar to bar voltages under the brush, circulating currents, bar edge burning, and damage from arcing.
Thanks to the positive responders - much appreciated.
When I have cleaned it up and reassembled, I will experiment with the different positions and see what effect they have.
Odd coincidence.... I was talking on the phone today to a colleague about this, and have the book open at the right chapter.
Best commutation and minimum sparking. If the line between the two brushes is at right angles to the poles they are at the g.n.p. or geometric neutral position and will spark as the brushes short windings. However rotating the brush line slightly, to a place called the m.n.p or magnetic neutral position, produces best commutation and minimum sparking.
The other method of improving commutation is to leave the brushes at the g.n.p and use what are called interpoles, which are small magnetic poles between the main poles.
many thanks
When tuning brushed motors for model aircraft we set them for max RPM and minimum sparking.
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