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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.
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.
