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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 7th Dec 2017, 11:05 pm   #21
Refugee's Avatar
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 3,569
Default Re: Mini-drill; Speed Controller Problem

Just get any DC motor and connect a low value resistor in series with it and a low value capacitor across it.
On a scope you will see something like an unregulated DC signal.
Pick off the AC with a coupling capacitor into a high gain amplifier so that it clips to a square wave.
If you can get a PWM chip to track it to match a variable oscillator you should be able to get a wide range of loading at a constant speed that is adjusted by varying the oscillator.
If you can find a drum motor board off an old VCR you might be able to reverse engineer it should work. It will work like a DC servo.
Another solution would be an F to V converter and a POT on regulated DC driving a PWM chip.
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Old 7th Dec 2017, 11:26 pm   #22
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Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 2,078
Default Re: Mini-drill; Speed Controller Problem

I remember helping a friend to get his treadmill working again after the motor burned out. It was an old machine made by 'York' and we managed to buy the very last replacement motor of its type in the UK, think it was about 100. They are powerful motors! We had to replace the SCR and the FET which controlled it and that got it going again. We never had a circuit for it, so not sure how it was controlled.

We know there are known unknowns. But there are unknown unknowns ones we don't know we don't know.
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