I'm looking for a source for a motor that is 1/2" thick or less, can run from AA or AAA batteries, and has a decent amount of torque. I need to pull a pin from a spring loop that is under tension. I don't think the little motors that run toy cars have enough oomph to do the job. It's the torque that I'm not sure about. How do I determine what I need so I know if I've got a motor that might work?

Ed

I don't think there is a motor that small. Anyway, my local hobby shop does not have them. You may have to go the electro magnetic method of pulling the pin. I know Roydon's Shooting Thru a Girl illusion used this type of device to pull a pin back into the coil of wire.

As far as torque, you would need the advice of an electrical or mechanical engineer, or just trial and error with each size of motor.

Also you would need a clutch and/or break on the motor to have it idle or shut off after the pin is pulled.

Have PM-ed with an idea

Hi Ed! I think you will have to go with a bit larger moter, but, as I have looked for these high-torque small moters for myself, I have come closer to getting what I was after by going to the surplus places out there...can't remember the specific names though. Check with surplus outlets though. I will be interested to hear what you come up with.

Thanks...Michael

Use a DC gearmotor. You need to have some idea of the force you need to pull the pin. You can hook a fishing scale to it and get a rough idea. You can also add a spring assist to the pin. You should also think that the line to pull the pin can be run around guides or pulleys to increase the leverage or change directions.

Lots of ways to go here.

Richard

High torque DC motors are everywhere. The trick is finding one only .5" thick. This one is 1.5" thick:

http://www.virtualvillage.com/high-torqu......ing_feed

Or maybe http://www.goldmine-elec-products.com/pr......r=G18706

Why not use a battery solonoid... they have significant push/ pull capabilities.. and some of the ones I've seen are TINY

Search on "dc gear motor" for lots of examples.

http://www.ebay.com/sch/i.html?_from=R40......tegories

There are a lot of small ones listed that are less than 1/2" thick, and various gear reduction ratios are available. If you could measure or at least estimate the pull force required on your release mechanism, you could work out the torque required for your motor. (Basically, force x lever arm = required motor torque.)

Another option would be to use a hobby micro servo. These can be really tiny and already come with an output arm that you can attach your pull pin to, assuming the pull force and stroke meets your needs. The rub is coming up with the electronics to drive the servo. Or you could hack the servo to just run like a gear motor.

Instead of a motor, can you use a shape memory alloy (SMA) wire? These heat up and contract when you pass current through it. Perhaps you could use this to pull the pin directly. I've seen some that will generate about an ounce of pull force for under 100 mA, which is well within the capability of the batteries you are considering. The actual setup is dependent on what pull force and stroke your mechanism requires.

As Richard says, lots of ways to go here.

Regards,

Ross

Looks like my comment on the Royon trick was in error, it was a Solonoid not an electo magnet, I am only guessing. It was a pin that was pulled back into a coil of wire with no housing around the coil.

Thanks to all for the quick feedback and suggestions.
I think I've got enough to get me forward a little bit more.

Cheers!
Ed

I was going to suggest a solonoid, too, but makeupguy beat me to it.

I use a music box to pull pins. Works for me....

I like the control with a windup music box. It give better control of the start and stop.

Bob