I am trying to use a high torque dc motor with gears to drive a low torque dc motor but with higher rpm.

Is there a relationship between the current draw of a DC motor with the torque? I have seen a lot of dc motors with currents around 80mA.. I am wondering if a higher torque dc motor will draw more current.

Do you think the dc generator(High RPM fixed with gears around the armature of the dc motor) will stop the high torque dc motor (High torque low RPM) from turning?



1 Answer 1


When you have one motor drive another, the second is no longer a motor, but a generator

There is a relationship between the current draw and torque, generally it looks like this:

DC current vs torque graph from Pololu

(image from Pololu)

Gearing can increase torque at the cost of speed and efficiency - I also have yet to see a fixed RPM DC motor - they may have an unloaded RPM for a specific voltage, but RPM will vary greatly depending on the load

  • \$\begingroup\$ Exactly I'm trying to use the second motor as a generator..But what i wanted to check if i use the High torque motor will it lag to drive the low torque generator? Will it draw more current to drive the generator or it won't affect the turns since the generator is of low torque> \$\endgroup\$
    – Ziad
    Apr 22, 2016 at 14:49
  • \$\begingroup\$ @Ziad these are getting into mechanical issues - yes, there will be a lag caused by the gearing, this is called backlash - it will take more current to drive the generator - you can't get power for free - how much depends on your gearing and the motor characteristics - I would suggest looking at the total power going in and the total power going out - in electrical world that's voltage times current, in the mechanical world for this case its torque times speed - you won't be able to create more power, it's always a conversion (and a loss due to imperfections). \$\endgroup\$ Apr 22, 2016 at 14:53

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