Subject:
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Re: 2 Motors -> 1 axle
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 10 Jan 2000 14:23:36 GMT
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Original-From:
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simon_jensen-fellows@avid/NoSpam/.com
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Viewed:
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691 times
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I have to agree with Jack Gregory, Tilman Sporkert and others that
there is no 'differential force' causing motors to 'fight' each other.
A commonsense understanding of the way an electric motor works should
make it clear why this is the case.
An electric motor consists of a series of coils around a bobbin on
a central axle. Surrounding that is a circle of magnets - usually one
for each coil.
The coils are electrically connected to a commutator. The magic of the
commutator is that it controls the supply of electricity to the coils
depending on the rotation of the axle/coil assembly.
This is why two coupled motors will not fight: if motor A is more powerful
than motor B, then the commutator in motor B will ensure that electrical
power is switched at the appropriate time for motor B to rotate at the same
speed as motor A.
(The commutator supplies the 'logic' of the motor. By sensing the position of
the rotor it energises a coil at precisely the right moment to pull it towards
the approaching magnet.)
This is somewhat of a simplification: coupling two motors puts a load on
both motors. Thus, two coupled motors will not rotate at the free wheeling
speed of the faster uncoupled motor. On the otherhand, the power output of
the two coupled motors will certainly be greater than the output of a single
motor.
There is one danger: an energised coil heats up. The constant switching on
and off (some motors reverse polarity and coils both push and pull against
magnets)
allows some refraction. Conceivably, radically slowing down the rotation of
a motor might cause overheating and burn out the coil. I think that you're
more likely to see this in a stall condition rather than a coupled state.
Your homework for tonight is to consider the situation where two otherwise
similar motors are coupled with step up/down gears: say an 8 tooth gear on one
motor and a 24 tooth gear on the other.
-Simon
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