I'm working on a project trying to make some electric roller curtains. I can use 2 motors on this curtain, on each side to lift and pull down the curtain. Pulling down the curtain requires not as much power to pull it back up since pulling it up is bringing the weight of the curtain back up against gravity.

So if this curtain weighs in total, lets say 2 kgs. Once the curtain is all the way down, it's on a stall and I have to get it out of stall and roll it back up.

If I have for example a motor with the following data:


  1. Rated Voltage: DC 12V
  2. Reduction Ratio: 1: 31.6
  3. No-Load Speed: 100RPM
  4. Rated Torque: 4.5Kg.cm
  5. Rated Current: 1.1Amp
  6. Gearbox Size: 37 x 24.5mm (1.46" x 0.96") (D*L)
  7. Motor Size: 36.2 x 33.3mm (1.43" x 1.31") (D*L)

There's the rated torque of 4.5 kg.cm which means I can move 4.5kg with an "arm" of 1 cm. Here's my first doubt, what exactly does it mean 4.5kg with an arm of 1 cm. Does it mean that if I attach a 1 cm arm, perpendicular to the motor shaft, and then at the other end of that arm I have a weight of < 4.5 kg, it will move?

Will this motor have the power to lift the 2 kg curtain based on the data? What other variables should I analyze?

  • $\begingroup$ To really solve this I think you will also need to specify how fast you want to pull up the curtain. The actuator torque requirement depends on angular velocity and acceleration as well as angular displacement. $\endgroup$
    – guero64
    Commented Mar 10, 2020 at 19:57

1 Answer 1


The unit of torque is force times a distance. Your understanding of kg*cm is correct, basically if you had a chain on a gear with a radius of 1 cm (and a diameter of 2 cm) the chain would be pulled with 4.5kg. I think you should be fine to lift your curtain. If you do have problems anyway, you can also always use different sized gear wheels to increase your pulling power at the cost of lower speed, like on a bicycle.


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