ELE 100 Introduction to Engineering
HexA Challenge
Power Supply and Motor Laboratory Guidelines
The objectives of this laboratory are:
1. Become familiar with the instrumentation.
2. Become familiar with the motor and gears provided and determine the gear ratio.
3. Determine the relationship of voltage polarity to motor rotation direction.
4. Determine the speed of the motor rotation.
5. Determine the relationship of motor voltage and motor speed.
Put your team name on the sticker on the motor board. This is your motor gear set
that you will be using for the rest of the semester.
Gear Ratio
By counting the number of teeth on a large gear and on a small gear, determine the gear
ratio of one set of gears. Compare the gear ratio calculated as the ratio of number of teeth
to that calculated as the ratio of the gear diameters. What is the gear ratio of the entire
assembly – from the motor to the final pulley constructed out of two large gears?
Instrumentation
Use the power supply provided on the bench. Connect to the plus and minus terminals,
not the ground terminal.
Motor and Gear Rotation Directions
Connect the circuit as shown in the diagram and photograph. Everyone on the team
should verify that the circuit is correct before turning on the switch.
Make sure the power supply is not current limited. Set the voltage to 0 volts.
Use the data sheet provided.
Part 1 Motor and gear rotation
Leave the tape on the pulley so the string doesn’t unwind when the pulley rotates.
Turn on the switch. Increase the voltage to 0.5 volts.
Observe and record the direction of rotation of each gear and the motor (clockwise or
counterclockwise as you face them). Reverse the polarity of the voltage applied to the motor by
reversing the connections of the leads to the motor terminals. Observe and record gear and motor
rotation directions. Make a sketch showing the gear and motor configuration, so that you can
refer to it when describing gear and motor rotation direction and gear ratios. Show gear and motor
rotation directions for each voltage polarity.
Part 2 Gear and motor speeds for different voltages
Set the voltage to 0.5 volts. Using the stopwatch, measure the time it takes gear 3 (the slowest
gear) to make 10 rotations. Calculate and record the speed of gear 3 in rotations per second and
radians per second. Calculate the speed of gears 2 and 1 and the motor in radians per second.
What is the overall speed ratio from motor to slowest gear?
Repeat the preceding measurements and calculations with the voltage set to 1.0 and then 1.5
volts. Disconnect the motor from the power supply.
Including zero volts, plot voltage on the horizontal axis and angular velocity of gear 3 in radians
per second on the vertical axis. Find the best fit straight line with equation.
Now you will measure the speed of gear 3 by measuring how fast the motor and gears lift a mass
a certain distance.
Attach the motor board to the bench as described by your instructor. Remove the tape from the
pulley and tie a paper clip to the end of the string.
Set the voltage to 1.0 volts.
Lower the clip on the string nearly to the floor. Attach the meter stick to the bench so the string is
near and parallel to the meter stick. Use lower end of the clip as a reference point. Raise the clip
by manually turning the gears until the reference point is just opposite 20 centimeters on the
meter stick. The motor will be raising the clip until it is at 80 centimeters on the meter stick, so
the distance will be 60 centimeters. The diameter of the pulley is 0.75 inches or 1.91 centimeters.
Since C=3.14d, the circumference of the pulley is 3.14 x 1.91=6 centimeters. Therefore, lifting
the clip 60 centimeters means that the pulley has made 10 rotations.
Using a stopwatch, measure the time it takes to raise the clip 60 centimeters. Turn off the switch
on the board before the clip reaches the pulley. Repeat two more times. How do the times
compare to one another? How do they compare to the time you previously measured it took for
10 rotations at 1.0 volt?
Calculate gear 3 speed in rotations per second and radians per second.
Homework
Using the Laboratory Report Guidelines, each team member write an entire laboratory report.