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Post by danielquinn on Jul 28, 2014 8:46:57 GMT
My PT runs of a maxon DC motor with brushes .
DC motors fall in two categories - brushless and brushes . Brushless are apparently superior in terms of torque , reliability , speed stability but require expensive controllers to make them work .
Anybody know anything about brushless motors - is rpm variable with voltage and usually done via the controller ?
Ta . |
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Post by danielquinn on Jul 28, 2014 10:01:56 GMT
Well Ive answered my own question the answer is yes .
so another question anybody know a calculation/formulae that works out the required rpm of a motor to turn a platter at 33.3 ?
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Post by pre65 on Jul 28, 2014 10:14:14 GMT
I built a belt drive turntable from bits of a DM-101.
The motor I used was a DC video drive motor (off e-bay) and initially I powered it with a variable bench PSU. Just adjusted the volts till the RPM was near enough.
Later, Nick Goreham loaned me a proper PSU with two independent (and adjustable) settings for 33 and 45 which was much better. 
EDIT the bench PSU was 0 - 12v
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Post by danielquinn on Jul 28, 2014 10:24:21 GMT
I currently use a bench 0-12v for my PT it is head and shoulders above the origin live I had .
I am keen to investigate the difference between brushless and brushed as the latter require maintainece and degrade over time and the possibility of a motor and control unit at 10% of the original very expensive price , but info is vague so I am trying to eliminate the possibility of buying it and it not being fit for purpose .
hence the formulae on rpm's
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Deleted
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Post by Deleted on Jul 28, 2014 10:47:55 GMT
The brushless motor controllers I have experience of are very noisy electrically.
This is an a different application though - RC Helicopters. The RPM requirement is slightly different.
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Post by danielquinn on Jul 28, 2014 10:48:40 GMT
They vary - some are very quite and vibration free .
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Deleted
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Post by Deleted on Jul 28, 2014 14:04:16 GMT
Are you talking about the motor or the ESC?
My comment was in relation to the speed controller. They are high amp throughput though.
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Post by ChrisB on Jul 28, 2014 17:15:00 GMT
How about this:
Motor speed = 33.33333 x Y / X
Where Y = platter diameter (or inner platter diam.)
And X = pulley diameter
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AlexM
Rank: Duo
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Post by AlexM on Aug 7, 2014 18:40:08 GMT
Are you talking about the motor or the ESC? My comment was in relation to the speed controller. They are high amp throughput though. Yay! another model heli flyer. I have been flying crashing and rebuilding 450 model helis for four years or so. a brushless motor controller (ESC, or electronic speed controller) operates the motor by building a rotating magnetic field by varying the voltage in each coil winding in turn to induce motion in the rotor. they can be quite complex in Helis and deliver huge power outputs even from small motors (my 450 heli motor can pull 40amps from the speed controller!). I would expect that a multi-pole brushless motor could be used to provide low noise/cogging, and good speed stability in a turntable or other application. I suspect it would have to have a hall effect sensor to allow the ESC to maintain timing (as opposed to back EMF). The performance of the system would be determined by the controller and the motor together. A programmable speed controller would be inefficient and not 'smooth' at low speeds due to the PWM modulation of the output having a very small duty cycle at light loads. There are others that use sinusoidal output waveforms, I don't know anyone who makes one for very low power output/rotation speeds, so unless you can create a bespoke speed controller a staight-forward brushed DC motor is the way to go.. Regards, Alex |
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