4QD Motor Speed Controller
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4QD Motor Speed Controller
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A tacho generator is a precision generator used to sense mechanical speed of rotation of a motor.
Motors have 'stiction' - or static friction. A moving surface, such as a motor bearing, has higher friction when it is stationary that when it is moving. The result if this is that it takes a significant voltage to start the motor, but it will then run at some speed. A tacho will automatically compensate for this effect by giving the motor more voltage to start it turning then automatically reducing the voltage to keep the motor just turning.
Without a tacho generator, a speed range of maybe 10:1 may be accomplished. With careful setting up, maybe even 15:1. But speed range is heavily load dependant.
With a tacho generator this speed range can be extended easily to 30:1 or even 50:1 speed range and this can be maintained under varying load.
True tacho generators are, however, expensive - so the facility is normally only found on expensive industrial controllers.
4QD's controllers of the Pro-120 can however be fitted with tacho feedback and the same system can also be used with the VTX series.
This is done by means of a small, inexpensive additional board which plugs into the expansion connector on the Pro-120 or VTX controller.
It is also quite possible to use a much cheaper small permanent magnet as a tacho generator. See Speed stability and Tacho generator feedback in our FAQ sheet.
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