# oscillation motion from DC motor (computer fan)

I intend to make an oscillating motion from a simple computer DC fan (say 5V).

My question is: could a signal generator with a sinusoidal signal of (say voltage 5V and frequency of 5 Hz) be used to power such a DC fan to produce the oscillating motion ?

Second question: it is related to Oscillations in motor control systems. Will there be a damage for a low frequency and low voltage input to the fan ?

• How large of an angle do you want the motor to move through, and how big of a load are you putting on it (i.e., what are you putting on it)? – TimWescott Sep 3 '19 at 15:03
• It is lightweight load (e.g. as in a piece of small cardboard), and the angle can be at least 45 degree. – Karsun Sep 10 '19 at 8:37
• Sorry -- could you edit your question with that comment, to complete the question? It's a StackExchange thing. When you do, say whether you mean $\pm$45 degrees, or $\pm$22.5 degrees. – TimWescott Sep 10 '19 at 14:53

computer fans are driven with direct current but contain a circuit which chops the DC into pulses that sequentially excite sets of electromagnet coils inside the motor to make it turn. these motors are called brushless dc motors and cannot be operated the way you want to.

You can instead make a "conventinal" or brushed DC motor vibrate the way you want simply by feeding it AC instead of DC.

A better way to make vibrations out of electric signals is to feed them into the terminals of a loudspeaker.

• could you elaborate more on second part: "feeding it AC instead of DC". Say the signal generator is amplified.. – Karsun Sep 2 '19 at 4:31
• yes, run the signal generator through a small audio power amp (as used for car stereos) and then connect that to the motor. – niels nielsen Sep 2 '19 at 5:44

Yes and no, maybe.

Computer fans are specialized, cheap brushless motors, with their own built-in controllers. The ones that I took apart 30 years ago had 4-pole coil assemblies and an unknown number of poles in the magnets, and a 3-transistor circuit that actually made the rotation happen.

You should be able to convert one to a galvonometer by disassembling it and driving the coils directly, in two pairs, in opposition. Whether this will give you enough rotation is an unknown to me -- it depends on whether the magnet has two poles or six (either of which should work, for a fan).

As long as you don't drive the thing with too much current you shouldn't damage anything -- the two things to worry about are overheating the coils and demagnetizing the magnets.

• Plus for " overheating the coils and demagnetizing the magnets.". – Karsun Sep 11 '19 at 7:23