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Tacho Generator Feedback

A tacho generator generates a feedback signal proportional to the speed of rotation, which can be used to provide closed loop control of a motors speed.

Varying loads

If such a ‘tacho’ is used and fed to an appropriate controller, then the controller can maintain motor speed very accurately under varying loads: by responding to the feedback signal, the controller automatically compensates for the varying load and maintains the motor at a constant speed. Without a tacho generator, a speed range of upto 15:1 may be accomplished. But speed range is heavily load dependant. With a tacho generator this speed range can be extended easily to 30:1 or even 50:1and this can be maintained under varying load.

Tacho generators and suitable controllers

True tacho generators are expensive – so the facility is normally only found on expensive industrial controllers.  But it is possible to use a much cheaper small permanent magnet motor as a tacho generator. Our Pro-120 can be fitted with our tacho feedback board which plugs into the optional expansion connector on the Pro-120 or VTX controller. In theory the same system could be used with our other controllers, but the controllers do not have the necessary connections brought out suitably.

PID control

Our newer controllers – the Pro-100 / 160 / 360 have an input and software that can monitor and limit the speed of a motor using an optional speed sensor board. Whilst this does not give accurate rpm control at the moment [Nov 2023] we have prototype PID control software available that is able to do this. This function depends heavily on correct set-up of the P, I, and D parameters and this is something that must be undertaken jointly with 4QD.