Download Lab Instructions

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. Correctly connect the motor and power supply.
4. Determine the relationship of voltage polarity to motor rotation direction.
5. Determine the speed of the motor rotation.
6. Determine the relationship of motor voltage and motor speed.
7. Determine the relationship of motor load and motor speed.
Put your team name 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 that you used for the resistor experiments. Connect to the plus and
minus terminals, not the ground terminal.
Motor and Gear Rotation Directions
Connect the circuit as shown in the diagram but don’t connect the wire to the motor.
Everyone on the team should verify that the circuit is correct.
Power
Supply
Motor
The current knobs fix the maximum possible current that the supply will deliver. Set the
coarse current knob so that the mark is vertical and up. This setting limits the current to
more than that needed for this experiment. Set the voltage to 0.5 volts.
Be aware. If the red light on the current side of the power supply is on, it means that the
current is limited to that set by the current knobs, and you will be unable to adjust the
voltage to a higher value than the one displayed on the voltmeter. For this experiment, if
the current light comes on, it probably means that there is something wrong with the
circuit.
Use the data sheet provided.
Part 1 Motor and gear rotation
Connect the clip to the pulley so that the pulley can freely rotate and the string doesn’t
unwind when the pulley rotates.
Make the final connection to the motor. Observe and record the direction of rotation of
each gear and the motor (clockwise or counterclockwise as you face them). Reverse the
connections of the power supply 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 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.
Part 3 Gear and motor speeds for different loads
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.
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.
Set the voltage to 1.0 volts. Using a stopwatch, measure the time it takes to raise the clip
60 centimeters. Disconnect the voltage before the clip reaches the pulley. How does this
time compare to the time you previously measured it took for 10 rotations at 1.0 volts?
Measure the time it takes to raise the clip 60 cm. with the voltage set to 1.5 volts and 2.0
volts. Repeat any measurements that you doubt; for example because the stopwatch
wasn’t stopped exactly when the clip was at 60 cm.
Calculate gear 3 speed in rotations per second and radians per second.
Clip a 150 gram mass to the string. Measure the time to raise it 60 cm. at voltages of 1.0,
1.5, and 2.0 volts.
Clip a 300 gram mass to the string. Measure the time to raise it 60 cm. at voltages of 1.0,
1.5, and 2.0 volts.
Take one or more digital photographs of your setup to use in your lab report.
Report
Write a laboratory report using the report writing guidelines. Include the following charts.
All plots should be of data plus a best fit straight line. Show the equation but not R2.
For Part 2 of the laboratory
On a single set of axes, plot angular velocity in radians per second on the vertical axis
and voltage on the horizontal axis for each voltage including zero volts.
For Part 3 of the laboratory
On a single set of axes, plot angular velocity on the vertical axis and voltage (including
zero) on the horizontal axis for each load (expressed in grams) including zero load. Title
the chart: Gear 3 Speed Versus Voltage at Different Loads. At a given load how does
angular velocity change as the voltage is increased? What happens if the load is increased
to a new weight and the voltage is increased?
On a single set of axes, plot angular velocity on the vertical axis and load on the
horizontal axis for each voltage, except zero voltage. Title the chart as: Gear 3 Speed
Versus Load at Different Voltages. For a particular voltage, how does angular velocity
change as load increases? What is the slope of each line?
Extra Points: Make and describe a three dimensional plot of angular velocity as the z
variable and voltage and load as the x and y variables. Use the data. No best fit line is
required.