Need Help With Motor Selection

I don't have answers for you but you will often get better responses from CR4 if you register. We have a lot of mixed experiences with people named "Guest".

For lower prices of surplus/used equipment you can try:
* Skycraft on Fairbanks in Orlando
* Astro Too on NASA in Melbourne
* Astro on Vicky Circle in Melbourne
* Panik's Electronics on Industry Drive in Melbourne
* EBay

Also ask around. There is a lot of high technology from Tampa thru Orlando over to KSC. Thousands of engineers have very useful stuff that has been "discarded" from closed projects at their jobs. Many modern companies/contracts require sale or destruction of surplus equipment. In the old days anything that was not classified/sensitive was usually only required to go out the door at the end of the project/contract.

Also, the people that pay the server bills for CR4 are at http://www.globalspec.com/. They have motors and almost anything else you can think of listed on their web site.

Register and let us know how things are going.

Wouldn't a ceiling fan motor fall into this range? I haven't checked any spec's, but they run off 110 VAC, probably can spin at 240 rpms, and are reversible. Don't know the torque req's, but 20 in-lbs doesn't seem very high so they might meet that range. You can get one at your local big box diy store for under $200.

Also check out Parvalux.

Theoraticaly the DC motor is considered as ideal for changing speeds however it is usually neglected that torque is not the same at all the speeds and condition for maximum power (gross mechanical power) is when back emf is equal to half the applied voltage.

Further you will need to convert AC to DC and since you seem to directly couple the motor to the load, the size and rating of the D.C motor will be large.

Your need is somewhat consistant speed under budgetory constraints, A.C. motor is more readily available at an affordable price (even you can buy used one).

Since your are having mechanical background I suggest DIY - set of different dia pulleys coupled by means of steel chain coupling (like in a bicycle) to achieve desired speed, plus you have the advantage that as the speed is reduced you will need a smaller A.C. motor proportionately.

Formulas for the above calculations are the same as you would have used if a mechanical drive would have existed in place of electric motor.

Try a brushless DC motor and ESC for RC cars. They will do everything you want and can be had for $100.

Not in Zimbabwe, they can't!

Front load washing machines use about 10:1 spin to wash speed ratio. For multiple spin speeds brush type motors are standard. However squirrel cage motors with ten pole (wash) windings were common, particularly European models.They meet your spec if a shade large. The control panel will also have the speed and reversing gear.

For your cencern regarding "backdrive" a very commomon foolproof application I have seen at costruction sites is to use a grooved wheel alongwith a sturdy hinged metal flap arranged so that when the wheel is turning in the right direction the flap just slides across, on reversal of the wheel the flap engages to lock the turning of the wheel.

A hand operated lever brake system is used to lower the weight cautiously (Now the locking flap is disengaged manually).

Also please do not undermine the AC motor, my experience with spillway gates of mega dams which weigh several tons are powered by AC motors of just few KW rating (since the gates slide upword a few inches per minute).