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I've become fascinated by Rolling Ball Sculpture (RBS) and plan to start building my first one soon. Typically a RBS uses a low-voltage, low-RPM motor to carry the marbles to the top of the structure where they begin their journeys down the track. I've been scavenging fan and turntable motors from old guitar amps, computers, microwaves, etc., but am at a loss as to how to determine the type of motor (AC v. DC) and operating voltages of these normally-unmarked motors. Thank you in advance for any help you can provide.

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  • \$\begingroup\$ Measure V before removing and write it on them... \$\endgroup\$ – Solar Mike Mar 16 at 4:58
  • \$\begingroup\$ Search amazon for mini DC gear motors \$\endgroup\$ – Sunnyskyguy EE75 Mar 16 at 13:16
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Most modern motors can be differentiated by the color, number and size of their conductors. 2 wires usually black and red for DC motors, black and white for AC, and 3 wires, (red black blue/orange brown yellow)for 3 phase AC motors at low voltages, sometimes with an extra white wire if they are wired in wye for some reason. Extra wires outside these sets may provide individual access to coils of an ac motor, or may indicate a motor with speed or temperature feedback, or provide control functions if they are smaller. The size and color of the additional conductors will often let you identify special motor types like positional motors or steppers. Make your best guess and then carefully apply voltage. Very little is likely to go wrong if you connect it to 1.5V, then 3V then 4.5V DC by adding 1.5V cells in series. If it doesn't spin unloaded one way or the other at 4.5V, it's probably not a low voltage DC motor. Just an option if you don't have a power supply to carefully test with.

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  • \$\begingroup\$ Happy to help. Definitely not a conclusive list, but it should help you narrow down where to research. \$\endgroup\$ – K H Mar 19 at 3:16
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Measure V before removing and write it on them...

But you could try say 12v dc on some of the ones if they are computer cooling fans - geared down they should be ample for moving marbles.

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  • \$\begingroup\$ I'll remember to do that going forward. Thank you! \$\endgroup\$ – gpb14916 Mar 18 at 16:28
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Do you have a multimeter? Easiest way would be to probe the motor while it's running in its original circuit. Aside from that, if it truly is unmarked then it'll be tough to tell. I believe DC motors typically have only 2 wires, some AC motors have more wires for additional phases. I'm not an expert on the different types of motors, but searching your question yielded this thread, which seems to have a lot of relevant info.

The safest way is the buy a motor with corresponding specs so you know exactly how to drive it. Alternatively, the method mentioned in that other thread of slowly ramping DC voltage to see if it works may also suit your needs.

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  • \$\begingroup\$ I do have a multimeter and will remember your recommendation as I scavenge motors in the future. I will also be much more diligent in noting any markings I find, as an EE friend of mine has made me aware of something called "data sheets". \$\endgroup\$ – gpb14916 Mar 18 at 16:27

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