DC Gear Motor

I've got a pretty simple question about DC gear motors. I understand the relationship between torque, motor speed and Hp. Typically when I see a spec for a motor it list all three values. Are the torque and speed both attainable at the same time or are those the peak values? Because when I try to calculate the Hp from the listed torque and speed, I never the Hp listed.

If I wanted a dc motor to have a torque of 2 ft-lb and a speed of 60 rpm, then the motor would have to be able to put out 0.023 Hp. Correct?

But as the speed is reduced, the motor can supply much more torque and like wise as the speed in increased, the motor cannot supply as much torque.

Is my understanding correct?


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Often, the HP listed is the motor shaft output, not the gear box output.

Let me check. The torque of 2 ft-lb refers to the ability of the gearbox to produce a force of 2 pounds at a distance 1 foot from the axle. But one turn of that axle will pull that 2 pounds through a distance of 2*pi*1ft=6.28 linear feet. So the work done by the 2 pound force per rotation will be 6.28*2=12.57 ft-lb of work. Multiply that by 60 rotations per second and you get 754 ft*lb/min or about .023 of a horse power (1 HP=33,000 ft*lb/min). Check.

Sounds pretty good to me. A DC (permanent magnet) motor has some zero load speed at a given supply voltage, and that speed falls pretty linearly to zero at stall torque. The peak horsepower usually occurs at about half no load speed (half of stall torque and half of no load speed).

Reply to
John Popelish



it's probably best to look at the data sheet which will give all the details, rather than relying a summary from a catalogue.

Bye. Jasen

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Jasen Betts

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