Static Motor Speed Under Dynamic Load

[omalleyt]

Hi. For a project of mine, I need a motor that can dole out and pull in a wire at a constant speed under a dynamic load. The load will be anywhere between 20-500 lbs. The speed will be about 1 ft/sec. Any idea about how I can achieve this effect? Is a motor even the right way to go or should I be looking at hydraulics? Thanks for any help!

 

[Phrak]

I have a suspicion weight will be an issue.

AC induction motors turn at fairly constant speed. But a brushless DC motor can be made to rotate at a constant speed using an electronic speed control and is far lighter.

 

[omalleyt]

How much (approximately) would the DC motor weigh, and would it be able to withstand the 500lb load?

 

[Phrak]

At one foot per second, the motor will need to be geared down. The question is not how much weight, but how many horsepower. This happens to be one horsepower, or a little more, for your one foot per second requirement.

 

[FredGarvin]

Many industrial motors can operate on this kind of condition. For example, think of a motor on a lathe. The loads are drastically changing but the speed remains constant. The combination of motor and controller will dictate how the motor runs.

 

[Bob S]

Some motors driving fluctuating dynamic loads use large flywheels as temporary energy storage to smoothe out the torque requirements; e.g., air compressors. For larger energy storage, hydraulic systems use compressed air reservoirs.
Bob S

[edit] The reservoirs are actually called accumulators. They have a bladder in them to prevent direct contact between air and fluid.

 

[Phrak]

You can get one horse power out of an outrunner DC brushless motor 2" diameter and 2" long. It isn't cheap, and will need to be geared down like any other motor selection. If affordable, it would be the way to go to cable lift for the batman thing.