Motor Trade-off Study
By Anthony Vo
In order to decide which motor will meet our level 1 and subsystem requirements, it is important to conduct a trade-off study of several motors. The goal of the trade-off study is to compare and contrast the RPM, current draw, torque, and cost of each motor. From the trade-off study, we will be able to determine which motor will best fit out design specifications.
| Type of Motor | |||||
| Cost |
$5.75 |
$5.75 |
$5.75 |
$9.26 |
$5.75 |
| Voltage (vdc) |
6 |
5 |
5 |
5 |
6 |
| Current (mA) free-run |
70 |
57.6 |
73.2 |
24.6 |
29 |
| Power=IV (mW) electrical |
420 |
288 |
366 |
123 |
174 |
| RPM (speed) |
85 |
70 |
66 |
370 |
32.4 |
| Torque (oz-in) |
75 |
43 |
43 |
3.6 |
69 |
| Torque (kg-cm) |
3.096 |
3.096 |
0.26 |
4.97 |
|
| Torque (N-m) |
0.529 |
0.303 |
0.303 |
0.025 |
0.487 |
| Reduction |
120:1 |
143:1 |
143:1 |
81:1 |
228:1 |
| Weight (grams) |
32 |
32 |
5 |
35 |
|
| Weight (oz) |
1.13 |
0.176 |
1.23 |
Above is a chart of 5 different motors with a hyper link to each one. The description and specification for each motor is arranged into a chart for easy comparison. From the data above, we have narrowed down our motor to 2 choices: the GM8 and the plastic gearmotor.
GM8:
The pros for choosing the GM8 over the plastic gear motor include lower current draw at free-run and lower power consumption. The lower power consumption allows us to meet our power requirement defined in the subsystem requirements. However, this motor will not provide the RPM required to achieve our speed requirement at the rated 5 volts.
Plastic Gear Motor:
The pros for choosing the plastic gear motor over the GM8 include higher RPM and higher torque rating. The higher RPM ensures that our level 1 speed requirement is met. This motor also provides more torque which will allow the rover to move over more difficult terrain without stalling.
Conclusion:
After comparing the two motors, we are leaning towards the plastic gear motor. Although the motor is less power efficient, it will still meet the subsystem power requirements. The plastic gear motor will provide the RPM and torque we need to drive the rover at our speed requirement.