Cordless Drill Torque at Speed

[mechengineer18]

Is there a way to find out the approximate torque of a cordless drill at a certain speed? All of the manufacturers I have found only list max torque and then speed ranges. Is the max torque when the unit is stalled?

Thanks,
Mike

 

[scastillo]

This might be what you're looking for:

http://www.uryu.co.jp/english/pdf/07_OTHERS.pdf

You might also look on the web for companies that rent testing equipment, such as:

http://www.atecorp.com/

 

[sreid]

I'd assume that the max torque is at zero speed. Brushless motors usually retain their torque through out their speed range except at the highest RPMs where the motor inductance-resistance keeps the current from rising to maximum.

 

[dcasto]

I thought DC motors had 100% torque at any speed, except for loses due to friction or limits of current as speed increases, so sried is right on. look at

http://www.teslamotors.com/index.php

to see the ultimate torque on a DC motor.

 

[MiketheEngineer]

I know that my DeWalt - fully charged - could break a wrist if you aren't careful!!

 

[mechengineer18]

I am looking at a 28 volt Milwaukee Electric Tool drill: V28 1/2 in. Hammer-Drill #0724-20. The low speed setting is up to 600 RPM, the high speed setting goes to 1800. The manual lists low speed torque as 600 in.lbs. and the high speed at 300 in.lbs.

I am trying to get an idea of how much power this drill can actually put out. Might it put out 1 hp? Say 35 in.lbs. of torque at 1800 RPM or 300 in.lbs at 210 RPM?

I have never worked with such a beefy drill but would love to hear from someone who has and the manufacturer (and other drill makers) has not been very helpful.

Thanks,
Mike

 

[MintJulep]

A pulley, a string and some weights.

 

[byrdj]

I was thinking a drum, a strip of crocus and a fish scale

 

[Kallog]

Usually a DC motor at constant voltage has maximum torque at stall and zero torque at maximum speed, with a linear relationship between them. So if you assume the torque and speed ratings are the maximums, you can find that the low-speed torque is 600in-lb - N * in-lb/RPM.

 

[zekeman]

Get a pencil and some graph paper and plot the two sets of data speed-torque where the y coordinate is speed and the x coordinate is torque. Now draw a straight line thru the points and that is the curve for a DC motor. The x and y intercepts reprresent the stall torque and no load speed respectively.

 

[mechengineer18]

So you are saying that at the midpoint the drill puts out 300 in.lbs of torque while the shaft is turning at 900 RPM? That seems high to me.

 

[geekEE]

mechengineer18, I think you've mixed up the numbers between the two curves. The high speed curve would give results of 150 in.lbs at 900rpm at the midpoint.

 

[mechengineer18]

Thanks geekEE. My head wasn't in the game.

 

[sreid]

While it is true that DC motors will develop maximum torque THEORETICALLY at zero speed, in reality this is not done. To design an efficient motor, the motor resistance needs to be low. If one allowed full stall current to flow the result would probably be

Demagnetized motor magnets

Blown Power Transistors

A Battery taken to it's knees

Brushless motor controllers sense the motor current and limit the current to a maximum value.