i have read a spec. about gear motor and it shows that Stall: 9-13 Nm torque 25A max

Per my understanding Stall torque is the maximum torque that can be applied to the shaft and cause the motor to stop rotating. So i wonder why it appears a range from 9-13Nm. As defination that i found, i think we only need the maximum value 13Nm and the current 25A is for this torque value. Could you please give me an advice about this range meaning. Thabk you very much.

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    $\begingroup$ It would be easier if you could post the motor spec. directly and not just your description of the spec. $\endgroup$ – 50k4 Feb 18 '19 at 12:35
  • $\begingroup$ Hi, the Spec. belong to company so that I cannot post it on. $\endgroup$ – zickk2894 Feb 19 '19 at 6:49

Why is there a range? Manufactures often list a range for their torque because their torque is highly dependent on the Voltage applied to a motor. A motor has an operational voltage and you'll reach the upper values of the stall torque by powering your motor with the upper values of the voltage range.

Stall Torque is the amount of weight the motor can hold without moving. Let's say your motor 0 degrees is facing the ground and 180 degrees is facing the sky. If your motor is at 90 degrees (parallel to the ground), then your 9-13Nm stall torque means that your motor can hold ~90-130kg at 1cm from the shaft of your motor (the gear that rotates out of the motor). If you put a weight more than 130kg at 1cm from the motor, the motor will not be able to hold its current position. As a result, the motor will be forced from the 90 degrees position to the 0 degrees position.

The 25A of your motor means that your motor can drain up to 25 amps of current under maximum load.

Remember that stall torque value is often higher than your continuous torque value. Continuous torque is the amount your servo can reliable lift and rotate. It's easier to keep a heavy object in place vs being able to push it against the force of gravity. Sometimes the manual will specify the continuous torque, other times, you'll just have to test it yourself.

So what does Nm means for torque. You'll often see oz/in, kg/cm, or Nm when looking at servo motors. 5 Nm just means your motor can generate 5 newtons of force at 1 meter away from the shaft of the motor. 10 newtons is about 1 kg of force (1 kg * force of gravity = newtons).

Remember that torque of your motor is inversely related to the distance at which it's carrying the weight:

T = F * D where F is force and D is distance. Thus going from 1 cm to 1 m will reduce the carrying capacity of your load by a factor of 100.

If you have more questions, I recommend watching youtube videos that explains the concept of torque.

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    $\begingroup$ This doesn't answer the question at all. The OP seems to understand what torque is but not why its been given as a range rather than a single value. $\endgroup$ – Chris Charles Feb 18 '19 at 18:16
  • $\begingroup$ Opps, I misinterpreted the asker's question. Updated. $\endgroup$ – aztrorisk Feb 18 '19 at 20:40
  • $\begingroup$ Thank @aztrorisk but the Spec shows that motor only apply for 24V only, it is not a voltage range. I understand your answer but as my question, if we put 13Nm the motor can hold without moving so why vendor shows 9Nm? $\endgroup$ – zickk2894 Feb 19 '19 at 6:47
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    $\begingroup$ @aztrorisk Thanks for the update, have a +1 $\endgroup$ – Chris Charles Feb 19 '19 at 9:18
  • $\begingroup$ @zickk2894 Can you give me the name of the motor exactly? There's also variability between how different companies present information. Since I'm working with incomplete information, my best assumption would be that the manufacture motor yields may vary in performance. As a result, they can only guarantee that their motor will perform somewhere in the 9Nm to 13Nm range. I mentioned 13Nm as the upper limit, your motor may only be able to hold 9Nm. I usually test my motors manually. In addition, even if a motor is listed at 24V, most of them accept slightly lower and higher voltage. $\endgroup$ – aztrorisk Feb 19 '19 at 9:28

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