ELE 100 Introduction to Engineering
HexA Challenge
Battery and Motor Laboratory 1
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.
Setup
Use the motor-gear set and voltmeter provided. Connect the circuit as shown in the photograph and circuit diagram. Do not insert a battery or turn on the switch until instructed to do so. Everyone on the team should verify that the circuit is correct before turning on the switch. Trace the actual circuit, using the circuit schematic diagram as a guide. The yellow jumper wire, not shown in the circuit diagram, is for when a single AAA battery is used. The red jumper wire, shown at the top of the circuit diagram, will be replaced later with an ammeter.
Use the data sheet provided.
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?
Part 1 Motor and gear rotation
Leave the tape on the pulley so the string doesn’t unwind when the pulley rotates. Secure the paper clip to the shaft.
Insert a single battery. Turn on the switch. The motor and gears should turn.
Observe and record the direction of rotation of each gear and the motor (clockwise or counterclockwise as you face them). Turn off the switch, reverse the polarity of the voltage applied to the motor by reversing the connections of the clip leads to the motor terminals, and turn on the switch. 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.
Part 2 Gear and motor speeds for different voltages
With the switch off, record the speed of the motor and gears. Turn on the switch, with one battery in the holder. Using the stopwatch, measure the time it takes gear 3 (the slowest gear) to make 10 rotations. Turn off the switch. 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?
Remove the battery jumper wire. Insert the second battery into the holder. Turn on the switch and repeat the preceding measurements and calculations.
Homework
Next time we will continue this laboratory. There will be a single lab report for both sessions. Study and absorb the results of this session.
Plot motor speed in radians per second versus voltage and find the best fit straight line that fits the data.
What is the effect of changing the polarity of the voltage applied to the motor terminals?
What is the effect of increasing the voltage on the speed of the motor?