make a dc motor giving high torque as well as high speed

Buy a new motor.

A bigger one.

Cheers, James Arthur

Measure the unloaded RPM and the stall current. The motor is designed to run at about half that speed and half that current. Compute the watts. You can run the motor from twice as high a voltage if you restrict the duty cycle to about 25% and keep same average thermal wattage flowing from the case.

The motor is going to deliver torque that's more or less proportional to the input current, and speed that's more or less proportional to the input voltage.

Giving the motor more than its rated continuous current will burn out the coils or the armature. Running the motor at higher than its rated speed will lead to accelerated wear on its bearings, or in extreme cases will blow the armature apart from centripetal effects. Running the _gearbox_ at higher that _its_ rated input speed will cause problems, and gearboxes usually aren't rated as high as motors.

If you're not getting the power you need out of the motor its either because you're not using the motor right or you need a bigger motor. If your desired speed out of the gearbox comes when you're running the motor quite a bit slower than maximum, then you need a different gearbox. If your desired speed is close to the motor's maximum, and you're running flat out with your current input, you need a different motor.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

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Say wha???

(Maybe you should qualify that with the type of DC motor you're thinking about. It's most certainly not true in general.)

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