Battery and Motor Lab - University of Southern Maine



Battery and Motor Lab

Craig Baron, Drew Somers, and Rebecca White

ELE 100, Introduction to Engineering

HexA Challenge

Lab done 11/17/04

Report due 11/22/04

Abstract

This lab was similar to the previous lab (the Power Supply and Motor Lab), but was more directly related to the HexA Challenge. We measured the voltage and current of the circuit as our motor lifted several different weights at two different gear ratios; this let us calculate our motor’s power and efficiency when it is powered by 2 AAA batteries. Analysis of this lab is limited by the fact that we did not reach peak power and/or efficiency during our trials; however, we did find that at a 64:1 gear ratio, our motor operates at maximum efficiency when lifting 400 grams. We calculated the approximate maximum power to be 0.58 watts lifting 640 grams with a 64:1 gear ratio, and 1.52 watts lifting 470 grams with a 16:1 gear ratio.

Introduction

The purpose of this lab was to find some characteristics of our motor when it is powered by two AAA batteries. We related the linear velocity to the load and the angular velocity to the torque. We also found the input (electrical power) and the output (mechanical power), and calculated the efficiency of the motor. We were able to identify the torque and angular velocity when the power was maximized.

Experimental Setup

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The lab requires:

1. a battery holder

2. 2 AAA batteries

3. a DC motor

4. 3 gears (1:4 ratio) (the third gear has a string wound around it, for lifting things)

5. several bags of weights

6. meter stick

7. stopwatch

8. voltmeter

9. ammeter

Procedure

1. Set the wiring of the voltmeter, ammeter, batteries, and motor up according to the diagram, so you will be able to measure the voltage and amperage at different points in the experiment.

2. Use a clamp to keep the engine steady and firm.

3. Measure out 60 centimeters, this is the distance the engine will lift the masses.

4. Time how long it takes for the engine to lift the masses 60 cm with a stop watch.

5. Connect the gears together for a 64:1 gear ratio, then lift masses of 200, 300, 400 and 500 grams. For each mass, record the voltage and current readings as well as the time the motor takes to lift it.

6. Repeat with a 16:1 gear ratio, lifting masses of 50,100 150, and 200 grams.

Each trial should be run a few times to make sure results are accurate.

|mass, kg |current, |voltage, volts |power input, |time, s |force, N |

| |amps | |watts | | |

|64:1 |0.1192 |0.06 |9.75 |0.58 |0.64 |

|16:1 |0.0881 |0.04 |34.43 |1.52 |0.47 |

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Discussion of Results

In our trials, the trend of our measurements indicated that the motor didn’t reach maximum power. We calculated the maximum power of the motor to be 0.58 watts lifting 640 grams at a gear ratio of 64:1, and 1.52 watts lifting 470 grams at a gear ratio of 16:1. The interesting thing about the second calculation is that we did lift 500 grams with the 16:1 gear ratio, and found the power to be 1.59 watts. The last data point at the 16:1 gear ratio seems out of line with the other three, but we did 5 trials and did not record any specific sources of error.

Only the 64:1 gear ratio yielded a maximum efficiency: 32%, with a corresponding mechanical power of .50 watts (the load was 400 grams). We can’t predict the maximum efficiency for the system with a 16:1 gear ratio, because we don’t have a measurement of the current and voltage when the motor is operating with 1.52 watts of power.

Our results would have been more complete had we tested the motor under higher loads. This procedure also does not take into account is how much the batteries run down over the course of the lab.

I was curious about how much the class’s different motors’ maximum power and efficiency vary.

Appendix

To complete this lab, we used our class notes on:

- torque and angular velocity

- current, voltage, and power

- maximum power and efficiency

We also used an email from Professor Hodgkin which explained how to calculate the maximum power of our motor if we had not found a maximum in our trials.

Original Data:

|64:1 gear ratio | | |

|.2 kg |a |v |t |

|  |0.46 |2.438 |3.86 |

|  |0.47 |2.434 |3.68 |

|(average) |0.465 |2.436 |3.77 |

|.4 kg |a |v |t |

|  |0.700 |2.245 |4.680 |

|  |0.700 |2.230 |4.710 |

|  |0.700 |2.238 |4.695 |

|.3 kg |a |v |t |

|  |0.580 |2.336 |4.250 |

|  |0.580 |2.332 |4.390 |

|  |0.580 |2.334 |4.320 |

|.5 kg |a |v |t |

|  |0.870 |2.154 |5.430 |

|  |0.840 |2.149 |5.060 |

|  |0.840 |2.148 |5.280 |

|  |0.850 |2.150 |5.257 |

|16:1 gear ratio | | |

|.05 kg |a |v |t |

|  |0.470 |2.370 |0.800 |

|  |0.440 | |0.750 |

|  | | |1.000 |

|  |0.440 |2.390 |0.890 |

| (average) |0.450 |2.380 |0.860 |

|.1 kg |a |v |t |

|  |0.710 |2.480 |1.000 |

|  |0.770 |2.240 |1.050 |

|  |0.770 |2.240 |1.210 |

|  |0.800 |2.240 |1.080 |

|  |0.763 |2.300 |1.085 |

|.15 kg |a |v |t |

|  |0.870 |2.100 |1.360 |

|  |0.940 |2.100 |1.150 |

|  |0.900 |2.100 |1.120 |

|  |0.903 |2.100 |1.210 |

|.2 kg |a |v |t |

|  |1.100 |1.900 | |

|  |1.100 |1.920 |1.920 |

|  |1.100 |1.900 |1.870 |

|  |1.090 |1.930 |1.770 |

|  |1.098 |1.913 |1.853 |

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Motor

Voltmeter

Ammeter

2AAA

~2.5v

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