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Motor Characteristics/Stall Torque Setup

The motor used in the Mechatronics project has some specifications posted at Pololu Part No. 2282. However, these on-line specs. are not complete, and some are suspect. Accordingly, we will measure the characteristics ourselves. Below is a setup and measurements that can help.

To find the stall torque of your motor, you will use the setup shown below. The setup can be found in EBU2 rm 311 (across from the design studio. you should all have the code for this room).

The motor is hooked up to 5V on the power supply. The yellow multimeter is set to read current, while the green multimeter is set to read the voltage across the motor (see circuit below).

Check the wiring before proceeding. Turn on both digital multimeters. Hold the arm attached to the motor while turning on the power supply (otherwise it will jump). To get an accurate reading of the stall torque, hold motor arm in the position shown below.

From the multimeter readings (voltage across the motor and current), you can obtain a value for the internal motor resistance.

Slowly pull back on the motor arm with the spring gauge, and take your reading when the motor arm begins to move. Make sure when you take your reading that the motor arm is perpendicular to the spring gauge. (remember that torque=radiusxForce).  The length of the motor arm is 14cm.

Motor Characteristics

The characteristics of the gears in the motor can be seen on the page below:

Mass of encoder wheel: ~3.1 grams

Characteristics of the motor rotor:
Mass: ~24.8 grams
Diameter of rotor: 0.705 inches. Note; the rotor is not solid so you will need to estimate a radius of gyration. Indicate the value that you choose. See: 

Additional pictures of disassembled motor: