Sojourner F17: Motor Characteristics

Generic Motor Calculations and Testing- GM6 Motors & Micro-Metal

By Zach Oyog | Sojourner Team | Fall 2017

Figure 1 (circuit to measure current)

Motor	max Current (mA)	min Current (mA)	Time (sec)	Voltage (V)
GM6 w/ cap	102	99.1	5	5
GM6 w/o cap	100.9	98.5	5	5
GM6 w/ cap	92.1	88.3	5	3.3
GM6 w/o cap	89	87.2	5	3.3
Micro Gear (Soj) w/cap	13.3	13.2	5	5
Micro Gear (Soj) w/cap	13.7	13.6	5	5
Micro Gear (Soj) w/cap	11.8	11.7	5	3.3
Micro Gear (Soj) w/cap	11.8	11.7	5	3.3
Micro Gear (Gol) w/cap	27.6	27.3	5	5
Micro Gear (Gol) w/o cap	27.4	27.1	5	5
Micro Gear (Gol) w/cap	23.2	23	5	3.3
Micro Gear (Gol) w/o cap	24.1	23.9	5	3.3

Discussion:

When measuring the current there was a fluctuation in values, which is why the table has a “max” and “min” current, and the current value would decrease by a low amount as time progressed. The “Time” column represents the amount of time passed before the readings were recorded. Decoupling capacitors were added to filter any high-frequency noise coming from the power supply but when removed the values were marginally different. However, since the Arduino Leonardo output is a direct current voltage, high frequencies would not affect the operation of these DC motors.

For gearmotors, there exists a user-created MATLAB file that uses the manufacturers motor parameters to create characteristic motor curves. From parameters needed, voltage rating, stall current, stall torque, no-load current, and no-load speed (rpm), the file generates five different curves: Torque vs. Speed, Torque vs. Current, Torque vs. Output Power, Torque vs. Input Power, and Power Efficiency vs. Torque.