Need help selecting a motor

What do you guys think of these?

Have you tried improvising using say an electric screwdriver motor ? It's more likely to have the kind of torque you need.

Graham

If you use different gear sizes on the motor and spindle shaft, then other RPM values could work as well.

Mark

"Ed" schreef in bericht news: snipped-for-privacy@z14g2000cwz.googlegroups.com...

Sounds like a job for a gearbox motor. Perhaps an old windshield wiper motor.

Try a motor out of a power window from a auto wrecker. Go for the passenger side as it has had less wear and tear.

Cheap and with the torque and speed you need.

Cheers.

I get 127 rpm, same as Ed. It seems you are using 4 feet for the length of rope, not 5.

The linear speed is:

In terms of inches and seconds (converting from feet and minutes):

(5 x 12 inches) / 4 sec = (pi x 2.25 inches) x (RPM / 60 sec/min)

or

RPM = (5 x 12 / 4) / (pi x 2.25 / 60) = 15 / 0.1178... = 127

Mark

(Not that it matters all that much :-)

The windshield (UK = windscreen) wiper and window motors would be too slow to meet your 4 sec requirement. (Unless, of course, you increased the diameter of the driving pulley.) The screwdriver motor suggested by Graham should be fine though. Mine run fast and with good torque.

Your rpm calculation is just a little high. The required speed would be (4*15*12)/(pi*d*n), where d = diam in inches and n = rpm. So n = 720/(pi*d) = 720/7.068 = 102 rpm

I'd try these methods to connect the cord:

1. Tension it with a small spring (trial and error) and see if friction proves adequate.

1. Extend the driving spindle if necessary and wrap 17 turns of the cord neatly around it. With the clothes line at its mid-point (i.e. with your imaginary wet shirt or whatever hanging 2.5' away), you should then have 8 loops symmetrically on either side of the middle loop. Secure the middle loop to the spindle at one central point. (Several ways of doing that. A simple staple would do.) If you then turn the spindle 8.5 turns in one direction, the line will move (8.5*2.25*pi)/12 = 5 feet, and all the loops will now be to one side of the fixed point. For robustness, I'd make that 19 not 17 loops, so there would be less strain on the fixing. If the cord is say 1/6 inch (4mm) in diameter, the loops would take 19/6 = 3.2", so a 4-5" spindle should be OK. I used the same approach in my curtain opener, albeit with only 7 loops on a 1.75" spindle:
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The method of connecting the motor to the spindle will depend on what motor you use. In the case of my ex-screwdriver geared motor, it came with a removable double-ended 'bit'. I made the spindle from doweling, drilled an undersized hole, and epoxied the bit into it.

Improvisation is the name of the game .

You're right, my mistake, sorry. 4 *seconds*, 5 *feet*!

Thanks to everyone for the excellent suggestions. I'll get this thing to work one way or another using your advice.

Thanks!