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EDIT: I feel I might have placed the emphasis wrongly in my original question so I'll try to revise it here.

In the video cited the demonstrator can be seen spinning a small "hobby" motor with her fingers and lighting an LED. Can anyone suggest what the specifications of that motor might be ? Or an actual motor which I could buy online. (I have tried reading the model number off the screen but no joy ;-). I am also interested in more general information but that's the main thing I would like to know. Thanks


In this video an LED is lit by spinning the rotor of a "hobby" electric motor.

I have tried doing just that with a number of motors and not seen the same effect (tried with LED in both polarities).

A couple of the motors used were ones I had lying around and I've no idea of their specs. Another one was this one the specifications of which can be seen on the 'specifications' tab of this web page.

The description of the motor used in the video and provided by the video maker is "Small hobby motor, 6-12 volts" but I suspect that's an insufficiently detailed description of the motor used to ensure the effect shown is seen.

What are the specifications of a motor that would work as shown ?

Secondarily, what is a useful text which outlines all parameters of such motors and what their effect would be when using the motor as a generator ?

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  • \$\begingroup\$ Are you looking at permanent magnet motors or motors with field windings ? Look at motors with inbuilt gears so that you can rotate the shaft slowly and the armature will rotate fast enough to generate enough voltage. \$\endgroup\$
    – AJN
    Aug 9 '20 at 7:07
  • \$\begingroup\$ Thanks for your comment. I take your point about the gears and that would certainly seem to be one way forward however the "hobby motor" shown in the video is, I'm almost certain, just a plain old motor with any gearing so I am still quite interested in knowing what that is. The project shown in the video would, due to the small windmill in use with it, not generate enough torque to turn a geared motor .... this is speculation on my part as I'm not knowledgeable in the field but I do think that's so. Thanks again for your thoughts. \$\endgroup\$
    – glaucon
    Aug 9 '20 at 22:31
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A motor is a backwards generator. So flip all the specifications around.

That motor has a no-load RPM of 13500RPM when 6V is applied. So for you to get it to produce 6V, no-load, you must spin it at 13500RPM. Spin it at 1/3 the speed and you will produce 1/3 the voltage. Can you pull that off manually? Probably not. Pick a motor that spins the lowest possible speed at the highest possible voltage.

You are going to a bigger motor, since bigger motors have the tendency to run slower for the same voltage. If you have 6 diodes to make a 3-phase rectifier, an outrunner motor is your best bet (it is a brushless motor so has no brushes to rectify the current in the coils to DC. It will end up as 3-phase AC so you need a 3-phase rectifier).

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  • \$\begingroup\$ Thanks for your response. It's really useful, I wasn't aware of the straightforward relationship between the "acting as a motor" and "acting as a generator" specifications you described. I take your point about a bigger motor but I am still quite interested in how the demonstrator appears to have a very straightforward "hobby motor" and is able to produce enough voltage to light, momentarily, the LED. \$\endgroup\$
    – glaucon
    Aug 9 '20 at 22:28
  • \$\begingroup\$ I don't know about the motor in the video, but honestly, you have no idea where the motor came from. It could have been designed to run off a much higher voltage or whatever and still look the same from the outside. What LED are you using? \$\endgroup\$
    – DKNguyen
    Aug 9 '20 at 23:23
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    \$\begingroup\$ To me it looks like a coreless motor, which has no cogging so it is easy to spin at high speed. Perhaps similar to this? \$\endgroup\$ Aug 10 '20 at 1:24
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    \$\begingroup\$ If you need a small low rpm motor, here's one that only needs 263rpm per volt (should light a white LED at ~900rpm) \$\endgroup\$ Aug 10 '20 at 1:34

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