Re: DC Motors

Jon Slaughter wrote:
Does anyone know what kinda motors that most drills use? I was thinking it was a torque motor but not sure.

Also, for DC motors can I get away with changing the voltage to a lower setting to increase the torque or do I run a huge risk of burning up the motor?(i.e., are they usually designed for a very narrow operating voltage). I have this old broken 18v drill and I want to turn it into opening a gate. I figure that it has enough torque to do it and I can control the speed quite easily. I plan on using some gears so I can open and close it with a change of polarity. I'm a little worried that it might have to much torque or that it might be to fast/slow for the gate(which the gears have a lot to do with of course).

Just wondering how much I can play around with the voltage to get what I want if I need too. Also, I assume that P is pretty much constant for motors? i.e., if the rated power for a drill is P then P = I*V for a large range of I and V? So if I know its a "100w" drill at 20V then I can calculate the current at 15 voltages = 100/20 A = 5A and it should be approximately what the drill will pull? (obviously the load has a lot to do with it but just curious as to some simple approximation)

It's most likely a permanent magnet DC motor. A PM DC motor, by itself, isn't a 'torque' motor or other type of motor. You can _use_ a permanent magnet DC motor to give a controlled torque if you drive it with a set current instead of a set voltage, but you don't change the motor construction to do that.

Lowering the voltage to the motor isn't going to make it deliver more torque. It will lower the stall torque (because the stall torque depends on the stall current, which depends on the terminal voltage). If you need to drive the motor at the most torque you can get without burning it up, then you need a controlled-current supply, and you need to be ready for some interesting accelerations when whatever you're driving breaks loose.

Mostly, if you want more torque you should either get a bigger motor or gear it down.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" gives you just what it says.
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Relevant Pages

  • Re: What passes as Pulse Width Modulation in DC Motor Control?
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    (sci.electronics.basics)
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  • Re: DC Motors
    ... was a torque motor but not sure. ... for DC motors can I get away with changing the voltage to a lower ... I have this old broken 18v drill and I want to turn it into opening a ...
    (sci.electronics.basics)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... loss in torque as speed is lowered as it is when voltage is lowered. ... PWM of the DC supply to a motor has the same effect on available torque ... then discontinuous pulses of current will flow through the motor, ...
    (sci.electronics.basics)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... loss in torque as speed is lowered as it is when voltage is lowered. ... PWM of the DC supply to a motor has the same effect on available torque ...
    (sci.electronics.basics)
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