University of Maryland

ENES 100

Introduction to Engineering Design [ENES100]
Motor Selection Worksheet
Team name/mission:
Team members contributing to this worksheet: Ben, Yidong
Activity Part 1
See the graph below that represents the relationship between torque and speed of a DC motor at
12 volts. This is called a motor characteristic curve. Each DC motor has a unique characteristic
curve for each voltage. Increasing or decreasing the voltage results in the line moving away from
or towards the origin, respectively.
Take a moment to consider the graph above and discuss with your group what points A and C
represent and how they might change with a different voltage.
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Introduction to Engineering Design [ENES100]
1) Point A represents: RPM’s when there is no torque being applied
2) Point C represents: Torque’s when there is no torque being applied.
3) If the voltage increases to 24 volts, then point A will: stay the same,
and point C will: increase.
4) If the voltage decreases to 6 volts, then point A will: stay the same,
and point C will: decrease.
5) If the voltage is 12 volts and your motor is running at an operating torque of 7.5 N-cm, then
what is the operating angular velocity of the motor?: 45 RPM
If you have a 5 cm radius wheel directly attached to your motor (there is no extra gearing),
then how far will your OTV travel in 5 seconds given this angular velocity?: 1,125 cm
6) If you used gears to double your no-load speed without changing the input power, the
characteristic curve would look like:
1. A (no change)
2. B
3. C