Using a belt or gears to slow this down...

[LostBoyNZ]

I needed something to turn quite slowly as part of a computer case mod, so I've hacked up a pc fan that runs at 700rpm and need to use it to make something turn at about 1/20th of that speed.

The "something" is two small cardboard drums so they're very light. But how ever I get them to turn needs to be as quiet as possible. The reason for using a fan instead of a small motor was noise; the little motor I have that already spins at the right speed is too loud.

I'm so new to all this though, I don't really know what to try. Looking around online it seems gears or a belt are options, although I wonder if gears would be quite noisy.

Any advice or thoughts at all would be a HUGE help. Thanks! :up:

[Diamon]

Under-volt the fan motor. It's probably designed to run at 12 volts so running it at like 1 volt would make it spin very slowly. The problem with that is that the fan motor needs more power when it's starting then when it's running so it will probably not start if it's wired to 1 volt. What you could do is buy a potentiometer (quite expensive) and use that to lower the speed after it has started.

You said you already had a motor spinning at the right speed. Have you done all you can to fix that one? Greasing it etc etc to make it quieter?

[x88x]

The problem with gearing down a motor is that it usually introduces more noise sources. That's probably why your slow motor is so loud. Also, a problem with running a belt off a fan is that they're not designed for any kind of torque, so it might not work at all. Adjusting the voltage after it starts is a thought...I can try that at home tonight if you like, see if it works. I know a lot of fans require a certain voltage to start; idk how they would behave if you drop below that threshold after it's already started. Pots don't have to be expensive; it all depends on what you get and where you get it. Just make sure you hook it up as a potentiometer, not a variable resistor, or you'll probably burn it out.

[mDust]

Light machine oil or pure mineral oil will likely help with mechanical noise in your motor. If it's 'air noise' from an internal fan effect then you're probably out of luck with it.
If the loud motor can't be fixed, then under-volt the fan motor to the point where it still starts on its own. Then you can step it down further with a rubberband, a small drive pulley, and a large pulley on the driven side. If the 1/20th speed was an exact figure based off the 700rpm (35rpm), then you'll need to do a little algebra to figure out what size pulleys to use depending on the under-volted rpm. If it was just a rough estimate, then it's much easier to ballpark it.

[Oneslowz28]

Time to go Arduino and a small DC gear motor. Or just a cheap DC gear motor and a $0.99 potentiometer. Check our electronic Goldmine or solarbotics for the gear motor and pot.

[blueonblack]

I've used this gearmotor (http://www.solarbotics.com/products/gm7/) from Solarbotics and I was very impressed with it's size, torque and noise level. It's reversible simply by pushing the shaft out the other side of the motor, and though it's rated at 75 rpm at 3 volts, it will start with less than that.

Hope it helps.

(You might be tempted to get this one (http://www.solarbotics.com/products/gm17/), because it's only 12 RPM at 3 volts, but if quiet is what you want this is not the motor for you.)