Transmission question

[Gozdom]

The project in question is a motorized lamp, basically a cable car (aerial tram) that moves on a cable with a pulley assembly (a set of 3 pulleys is needed to avoid tumbling), automatically reversing when it bumps at the end (solved). The cables will provide 12V DC. The car body and lighting is easy. However, the drivetrain raises some problems. I do have a recipe I was going to use but someone may have a better idea.

So, the transmission has to fulfill the following requirements:

- Ratio: around 1500:1. It should move slowly, not zipping to and fro. Also, a higher ratio means high torque, thus a smaller motor can be used.
- Low noise. As quiet as possible. You don't want a roaring accent lamp.
- Light weight.

I have a couple old clock movements, but they are bulky, heavy and rather noisy. I also have plastic gears scavenged from VCRs and toys, though matching enough of them may be a challenge. I also spotted a transmission building kit at a vendor which comes with plastic gears, axles and the frame predrilled - this is the route I want to take. It yields 1000:1, good enough.

What else may be used? Belts and pulleys are easier to mount than gears, not so easy to get and construct the whole thing. May also take up more space and prone to failure. I can't build a planetary set, nor do I have the gears for that.

[Thermionic Drew]

Fastest way to get big reduction is via worm drive.  A screw turning on the side of a larger gear.

[Gozdom]

Good one. Too bad I only have a single worm but I think it will be incorporated.

[Eastblock]

Belt drive is the way to go if you want it to be quiet. Pulleys can be made from MDF or ply on an electric drill. O-rings can be used as belts if you don't need loads of torque.

[Steamworkshop]

I used a small geared motor from this place for my motorized USB drive. http://www.hobbyengineering.com/SectionM.html

They have motors in small to medium sizes. They have motors with gearboxes attached and you can pretty much choose the RPM of the output shaft.

I spoke to them when I bought mine and they were very helpfull and knew what they were talking about. I got it fast too.

[Eastblock]

Alternatively you can convert a hobby servo to continuous rotation. Servos are very cheap these days.

[Gozdom]

I used a small geared motor from this place for my motorized USB drive. http://www.hobbyengineering.com/SectionM.html

They have motors in small to medium sizes. They have motors with gearboxes attached and you can pretty much choose the RPM of the output shaft.

I spoke to them when I bought mine and they were very helpfull and knew what they were talking about. I got it fast too.

That looks like an incredibly cool shop, thanks! I may resort to overseas ordering if local sources fail. They got what I need ready made, Tamiya, and cheaper than the bare gear set I had in mind. Except shipping, unfortunately. Still, a great outlet.

In fact, I'm starting to entertain the idea of importing such goods and reselling them. Whatever is available here comes at exorbitant prices, and many are simply unheard of, like chain + sprocket assemblies or pulley kits.

[Arceye]

Try not to mount a worm gear directly on the motor shaft, it will strain the motor bearings with the sideways thrust. Interpose a pinion- that is to say, a pinion on the motor shaft, a layshaft with a second pinion and the worm. And, make sure the worm is well lubricated, they wear terribly otherwise.

[Otto Von Pifka]

this one is a bit big but very slow rpm. search "DC gear motor" for others including mini and micro sized motors.

http://cgi.ebay.com/37mm-12V-DC-4RPM-Replacement-Torque-Gear-Box-Motor-New-/260687050176?pt=LH_DefaultDomain_0&hash=item3cb228b5c0#shId

you could try motors from car doors, older cars sometimes used geared litle motors for the power door locks instead of solenoids. older printers and appliances might have dc motors that aren't steppers. power antennas for cars, old VCRs, headlight actuators for cars, and even cheap motorized toys.

using a motor/gearbox rated for a higher voltage like 24V will turn slower and run much quieter at 12V
and with the giant advantage the gear ratio has, it won't labor much at the lower voltage.

[Thermionic Drew]

Other sources of low speed motors include the turntable drives for microwave ovens and the motors out of old "dropping flap" bedside digital clocks.  My call would be to strip a junked microwave for the turntable motor.

[Arceye]

A very sturdy motor/worm drive unit can be got from the sort of electric wheelchair that has a motor drive to each rear wheel. They are 24V and carved from the solid- almost impossible to break.