Introduction to Engineering HexA Challenge

Power Supply and Motor Lab ELE100

Drew Somers, Rebecca White, Craig Baron

Done 11/3/04

Due 11/8/04

Abstract

In this lab we familiarized ourselves with our DC motor. First we explored the direction of rotation of the motor and the gears. We found that each gear turned in the opposite direction from the previous gear, and that switching the polarity of the power supplied changed the direction the motor turned. Second, we investigated the speed of the motor and the gears attached to it, and found that higher voltages made it rotate faster, proportional to the voltage increase. Our motor turns at 217 radians/sec at .5 volts, 441 rads/sec at 1.0 volts, and 693 rads/sec at 1.5 volts. We found the gear ratio to be 4 to 1, which meant that each gear turned ¼ as fast as the gear before it. Last, we looked into the motor’s ability to lift different weights. Higher loads slowed it down, higher voltages sped it up. Our motor would not lift 300 grams when we used only 1.0 volts. We noticed that at 2.0 volts, the time to lift 150 grams and to lift 300 grams were very similar.
Experimental Setup

Below is a DC motor attached to a piece of wood. The wood was held in place on the table by a vice, and the meter stick was taped to the edge of the table. The motor was powered by a DC power source (located in top left of picture).

Items Used:

  • 1 DC motor with gears attached
  • 1 Stopwatch
  • 1 Meter stick
  • 1 Plastic bag containing 300 grams
  • 1 Plastic bag containing 150 grams
  • 2 Wires with alligator clips on each end

We have presented the purpose, procedure, results, and discussion separately for each part of the lab.

Part 1

The purpose of Part 1 was to gain an understanding of the relation between the voltage polarity and the direction of the motor’s rotation. It also familiarized us with the direction that each gear spins.

Procedure

We first connected the clip on the end of the rope to the pulley allowing the pulley to rotate freely without the string being unwound. After making the final connection to the motor, we then observed and recorded the rotation of each gear and the motor. We then reversed the connections of the power supply on the motor terminals and observed and recorded the direction of rotation of the gears and motor.

Results/Discussion

When observing the direction of each gear we used two different connections. We simply reversed the connection to the motor terminals to see what effect this might have on the direction of rotation of the gears and the motor. We will call the first connection polarity 1. While observing the effects of the direction of rotation during polarity 1, we found that the direction of rotation of the motor was clockwise, gear 1 rotated counterclockwise, gear 2 rotated clockwise, and gear 3 rotated counterclockwise. When we reversed the connections (polarity 2), we found that the motor rotated counterclockwise, gear 1 rotated clockwise, gear 2 rotated counterclockwise, and gear 3 rotated clockwise. We concluded that when the polarity of the motor is reversed the direction of each gear and the motor is reversed as well.

Gear and Motor Rotation
Direction of rotation, clockwise (cw) or counterclockwise (ccw)
Gear 1 / Gear 2 / Gear 3 / Motor
Polarity 1 / ccw / cw / ccw / cw
Polarity 2 / cw / ccw / cw / ccw

Part 2

The purpose of Part 2 was to determine the speed of the motor and the gears. To do this, we first determined the gear ratio, and then measured how many seconds it took for the slowest gear to make 10 rotations. We timed the gear and motor with the voltage at three different levels so that we could relate the speed to voltage.

Procedure

We first set the power supply to 0.5 volts and hooked up battery and motor. When everything was ready, we connected the last alligator clip and started the timer. The last gear, gear 3, had the pulley and paperclip on it. We counted ten times that the paperclip passed the top of its' circle and then stopped the timer. We repeated this at 1.0 and 1.5 volts.

Results

large gear / small gear / gear ratio
48 / 12 / 4

The gear ratio is the number of teeth on one gear divided by the number of teeth on the other. The gear ratio of these two gears is 4 (or ¼), so the smaller gear (12 teeth) will have 4 times the angular velocity of the larger gear.

gear 3 / gear 3 / gear 3 / gear 2 / gear 1 / motor
volts / 10 rot, s / rot/s / rad/s / rad/s / rad/s / rad/s
0 / 0 / 0 / 0 / 0 / 0 / 0
0.5 / 18.5 / 0.54 / 3.40 / 13.59 / 54.34 / 217.36
1 / 9.1 / 1.10 / 6.90 / 27.62 / 110.47 / 441.89
1.5 / 5.8 / 1.72 / 10.83 / 43.33 / 173.33 / 693.32

We timed how long it took for gear 3 to make 10 rotations, which gave us seconds per 10 rotations. To get rotations per second from this, divide rotations by seconds.

There are 2*pi radians per rotation, so to get radians from rotations, multiply by 2*pi.

The gears get progressively faster as they are closer in the chain to the motor. Because the gear ratio of each gear to the next is 4, each gears’ angular velocity is 4 times greater than the previous one. This means that the motor has 64 () times the velocity of gear 3.


The graph shows the relationship between voltage and angular velocity, namely that angular velocity increases depending on the voltage. Its increase can be predicted by the line of best fit:

y = 454.44x or

angular velocity = 454 * voltage.

Discussion of Results

The time it takes for gear 3 to make 10 rotations at 1.5 volts is about 1/3 the time it takes at 0.5 volts. Similarly, the angular velocity of gear 3 at 1.5 volts is approximately 3 times its angular velocity at 0.5 volts. This shows a linear relationship between the angular velocity of the motor and the voltage. We can also see this result in the line of best fit on our graph of angular velocity vs. voltage, where the angular velocity equals 454 times the voltage.

At one volt, our measurements indicate that our motor rotates with an angular velocity of about 440 radians per second, and our line of best fit indicates that it rotates at about 450 radians per second. We most likely had some error in the timing, specifically in coordinating the start of the motor with the start of the stopwatch.

Part 3

In Part 3 we timed how long it took the motor to raise three different loads at three different voltages, so that we could see the relationship betweenload, voltage, and the speed of the motor.

Procedure

  • From the floor, measure twenty centimeters vertically.
  • Then from the floor, measure eighty centimeters vertically so there is a sixty centimeter gap between the two measurements.
  • The purpose behind measuring sixty centimeters is:

Circumference= 3.14 x diameter, d=1.91cm so the circumference=6cm. Over the span of 60 cm the gear rotated ten times.

  • Make sure the paper clip and string reaches the twenty centimeter mark so you can use this to hook the two masses onto it for later on in the procedure.
  • Measure the time it takes the motor to raise the paper clip 60cm at 1.0 volts, 1.5 volts, and 2.0 volts.
  • Next clip 150 grams of mass on the paper clip and use the stop watch to see how long it takes it to raise 60cm with 1.0volts, 1.5volts, 2.0volts.
  • Then clip 300 grams of mass on the paper clip and see how long it takes to raise 60cm with 1.0volts, 1.5volts, 2.0volts.

Results:

Part 3 / Gear 3 speeds for different loads
Volts=1.0
Gear Ratio / 64 to 1 / gear 3 / gear 3
Load, g / Time,s / rot/s / rad/s
0 / 7.77 / 1.287 / 8.086
150 / 37.65 / 0.266 / 1.671
300 / NA / NA / NA
Volts=1.5
gear 3 / gear 3
Time,s / rot/s / rad/s
0 / 4.95 / 2.02 / 12.69
150 / 12.34 / 0.81 / 5.092
300 / 16.34 / 0.611 / 3.845
Volts=2.0
gear3 / gear 3
Time,s / rot/s / rad/s
0 / 4.2 / 2.38 / 14.96
150 / 5.09 / 1.965 / 12.344
300 / 5.5 / 1.818 / 11.424

Summed up (values in center are angular velocity, in radians/second):

voltage
mass, g / 0 / 1 / 1.5 / 2
0 / 0 / 8.086 / 12.69 / 14.96
150 / 0 / 1.671 / 5.092 / 12.344
300 / 0 / 0 / 3.845 / 11.424

Angular velocity
, the speed of the gear, increases as the voltage increases. When the load is increased, the gear speed decreases. The angular velocity depends on both the load and the voltage.

On the next graph, each line slopes downward, showing that for each voltage, angular velocity decreases as the load increases.


The results of this lab show that the more we increased the voltage the more rotations per second we had with the different weights.

Discussion of Results

For every run, we used the outermost gear, gear three. As you can see, the more voltage we put into the DC motor the faster it would rotate and the more it would work. The 2.0 volt runs went well without any difficulties. The motor seemed to carry the weights up easily. But when you look back at the runs we did with the 1.0 volt testing it was fine with just the paper clip, sluggish carrying the 150g, and couldn’t move the 300g bag.

By measuring how many seconds it took for the DC motor to raise the bag 60 centimeters, we were able to calculatethe rotations per second andradians per second of gear 3.

Extra Points

The data from part 3 (inside cells are in radians/sec):

volts
load / 0 / 1 / 1.5 / 2
0 / 0 / 8.086 / 12.69 / 14.96
150 / 0 / 1.671 / 5.092 / 12.344
300 / 0 / 0 / 3.845 / 11.424

As a 3d plot:


This graph represents the angular velocity of the largest gear based on the load on the system and the voltage applied to the motor. It shows that the gear has the highest angular velocity when the load is 0 and the voltage is 2, and the lowest (in fact, 0) when the load is high and the voltage low.