help with a motor choice problem and possible alternatives.

Hello, I have a geared ac motor; I'm not sure what the correct term would be but it will only turn one direction regardless of polarity. What I need to accomplish is to reel in a string of about 20" until a set point where it would be automatically fed back out. It will be an elevator of sorts to lift a ball (about 5 lbs) about 20". The end points I know can be determined through simple limit switches which I know how to setup, again its the mechanical aspect which has gotten me thinking. I realize a dc motor would be much more convenient for its reversible nature. It would have to have a gearing that would be able to pull in this string with a load of about 5-6 lbs on it, ideally the full 20" could be taken in under 30 seconds. I'm thinking a simple battery powered reversible drill would serve the purpose well. Does anyone have any thoughts on where to locate one, I know the prices are quite steep on e-bay with batteries included which I would not need. Ideally I'd be able to use my current motor. I am willing to use dc and in reality if a cheep source were to preset itself would be preferred. Any thoughts are welcome. Thanks in advance....

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Just a thought but what about using a windscreen wiper motor, or one of a car window motor.
I think they both have a worm and wheel arrangement and being DC I would expect you to be able to reverse them.
-- Cheers Adrian.
http://www.aphtrading.co.uk/pages/apage1.htm Weekend Workshop

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Visit any Black & Decker Service Center. They'll have barrels full of battery drill motors, refurbished, but with no batteries. They were charging $9 each last time I was in the one local to me.
Uh, just noticed you're in the UK. If Black & Decker doesn't have service centers over there, some other manufacturer probably will.
Gary

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Fit a disk to the end of the motor with a crank pin on the disk at 10" centres. Then fit a con rod to this pin. The end of the con rod will move from bottom dead centre to top dead centre a distance of 20" and raise the string in 1/2 a rev. Following 1/2 a rev will lower it again
No need to reverse but you will probably need a slow speed motor to be controllable. -- Regards,
John Stevenson Nottingham, England.

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Didn't even think of doing that, good thought unfortunatly i'm not sure if the motor will be able to supply the torque needed. Good thing to consider.

Is your motor a capacitor start motor? if so you can reverse it, there shoud be three wires coming out of the motor body, usually two white one black,black wire to neutral, two whites to capacitor, live wire to one cap terminal. To reverse connect live to other cap terminal. If the motor is a shaded pole one, like in old record turn tables you can't reverse electrically. If it has carbon brushes/commutator and outer field coil, like in a pistol drill, sometimes it is possible to reverse the supply to the brushes, but this can be difficult depending on motor construction. I used a £5.00 B&Q/Chinese rechargable srewdriver for a similar job. This had a reversing switch thas was easily hacksawed out and had plenty of torque. hope that helps, Mark.

Hello Krem
In my " useful someday :-) " bin I have two used Philips 9904 120 52814 motors. 13.5 V DC, reversible, at 12V they give 60 rpm, so a 1/4" diameter drum would be needed at full speed. They weigh 140g each, 70mm long +15mm shaft. footprint 40 x 55 mm.
E-Mail ( adjust as signature ) if interested.
-- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
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Hey Krem,
Just an "outside-the-box" thought for you. If this is a constant motion "thingy" you want to make, then consider hooking the "string" to the flat plane on/near the periphery of a wheel or an "arm" driven by what you have already. As the wheel/arm rotates, it would pull in and then pay-out the string. Adjusting the radius of the swing will control the amount of travel of the 5 pound weight, and it will have a soft start and slow down for direction reversal, and the greatest torque at those same points. Door operators on elevators used to work like that.
Take care.
Brian Lawson, Bothwell, Ontario. XXXXXXXXXXXXXXXXX
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Krem Brian as a very good thought. If his description isn't clear think like a crankshaft and a piston in a engine. There are many ways to turn rotary motion into linier motion. Look up some of the mechanisms books in the library or on line. Track down a metal shaper drive system design and work from that. Put a cam on the motor and use the cam to lift and drop a lever arm. Maybe a Scotch Yoke. If you have a motor that cannot be reversed, don't want to buy another, then the above suggestions should allow you to work with what you have. Their not as simple but will achieve the same results. Consider finding an old garage door opener if you can. They would have most of the logic and switches you need. lg no neat sig line
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Krem Rereading Brian's suggestion, if you use it, consider using a counter balance on the wheel/arm so that the motor has less work to do if power is a problem. lg no neat sig line
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Brian's idea is similar to another post.... get an old windshield wiper motor and linkages. DC, variable speed, and plenty of power since the "arm" would only have to be 10" long to pull in a 20" string..... Ken.