# Setting a Motor so that it spins at a certain RPM [closed]

I'm making a record player for a school project and I'm having trouble with the motor that will spin the platter. I'm using a belt drive system, so I have two circles connected by a pulley system. Using the velocity ratio and pulley formula (knowing that the platter had to have a diameter of 100mm and spin at 33.3 RPM, and the motor spindle would be 5.55mm diameter) I worked out that the motor would have to spin at exactly 600 RPM.

I have no knowledge in electronics so any help would be massively appreciated. Could you please suggest a way I could buy a motor online and a way to control the motor so that I could get it to spin at exactly 600RPM? I've been looking at motors like these and adjustable motor speed controllers like these but I am unsure what motors would have the right voltage and amps, and whether the variable controllers would be compatible with them?

If anyone could suggest a combination of motor, and an adjustable motor speed controller and possibly even a way to put them together I would be so grateful. This is for a school project to finish.

• how do your power your whole project? I certainly hope you're not plugging in mains. Dec 1 '16 at 11:40
• You need to define "exactly". "Exactly 600RPM" is not meaningful, does it mean 600RPM ± 10RPM or 600RPM ± 0.0001RPM? Dec 2 '16 at 18:35
• Note that LP records spin at $33\frac{1}{3}$ RPM, not 33.3. Dec 3 '16 at 16:42

## 1 Answer

You have basically three options.

1) AC synchronous motor (example): the speed of these is governed by the mains frequency. They don't require any other electronics, just power it on and it goes at that speed. Since they're mains powered you have to take appropriate safety precautions in wiring.

2) Stepper motor / Brushless DC + driver. See Difference between Brushless Motor and Stepper Motor

3) Simple brushed DC motor like the one you've linked + active closed-loop speed control.

Both of these options will require programming on an Arduino or similar, unless you can find a pre-build board designed for constant speed control.

• Thanks very much pjc. For a simple brushed motor, would this speed control be suitable? amazon.co.uk/1-8V-Adjustable-Motor-Speed-Controller/dp/… Dec 4 '16 at 18:35
• If used with appropriate motor and power supply, probably. Dec 4 '16 at 19:59