Robot Building for Beginners by David Cook

Author:David Cook
Language: eng
Format: epub, pdf
Publisher: Apress, Berkeley, CA

mN·m

/ 10.2

= gf-cm

dyn-cm

/ 0.001

= gf-cm

Sliding Torque

A full can of soda is about 380 grams. A motor with 380 gf-cm of torque can rotate a 380-gram mass connected 1-centimeter away (380 gf × 1 cm = 380 gf-cm).

Torque isn’t restricted to a 1-centimeter distance. A 9 V battery is a little over 38 grams. That same motor could rotate 38 grams connected 10 centimeters away (38 gf × 10 cm = 380 gf-cm). Torque allows for less mass farther out or more mass farther in, as long as the numbers multiplied together are less than or equal to the motor’s torque.

This has practical implications. If you build a robot arm that the motor can’t move, you can either get a motor with higher-rated torque, you can shorten the arm (the length), or you can reduce the mass (the weight).

The example of a soda can connected one centimeter away isn’t totally accurate because the can itself is longer than one centimeter. In reality, you need to be careful to determine exactly the force from a large or odd-shaped object. At the very least, measure from the center of the mass to help determine the distance the mass is “connected” as far as the torque is concerned.

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