2.1 Equipment List
- A piece of wooden plank, with a minimum area of 900 cm2
- 2 pieces of 1m wooden ruler
- 100:1 HP micro DC Gearmotor
- 75:1 HP micro DC Gearmotor
- 50:1 HP micro DC Gearmotor
- 4 AA size Battery Holder
- 4 1.5V AA battery
- 3 Motor Hubs
- 1 Mounting bracket(with its specific screws in its packaging)
- Screws suited for motor hubs
- A Pen or marker
- 1 Knife-blade Switch
- A roll of duct tape
- A roll of double sided tape
Items (to be borrowed from the laboratory):
- 1 Kitchen Scale
- 1 Saw
- 1 Drill
- 1 Glue gun
- 4 Alligator clips
2.2 Diagrams of experimental setup
Note: wooden structure is the structure made from the ruler pieces(explained later in the procedure)
1. First, wear safety goggles. Then, take the piece of wooden plank and cut out a 4.0 cm x 3.0 cm plank using the electric saw. Keep the leftover wood for the wooden wedge and platform.
2. Then, saw the wooden ruler into three pieces and drill the holes on the ruler pieces as shown in the diagram below, keep the remaining piece of the ruler:
Each hole should be 3.0 mm in diameter
Note: We are comparing the distance between the centre of the motor shaft to the wooden wedge in multiples of 2, starting from 12.0 cm, 14.0 cm, 16.0 cm, 18.0 cm, 20.0 cm, and finally 24.0 cm. We have 1.0 cm at the end is because we can position the motor shaft nicely. Otherwise, the motor shaft would be positioned away from the ruler piece. Also, we left some space at the other end, because if it is exactly 12.0 cm, the ruler piece may slide off from the wedge so it may be an unfair test. To obtain the first and last holes on the ruler pieces, put the motor hub on the ruler piece, then use a pen or marker and then mark the location of the hole.
3. For the 4.0 cm x 3.0 cm plank, put the mounting bracket on top of the plank. Then, use a marker or pen to mark the holes of the mounting bracket, where the screws are supposed to go in. Then, drill two holes into the points marked by the marker. The holes should be big enough for the screws to go in.
4. Use the remaining plank and cut two corners of the plank, which would form two triangles. It should be 0.5 x 3.0 cm x 1.8 cm each. Then, glue them using a glue gun such that the total dimensions become 0.5 x 3.5 cm x 2.0 cm x 1.0 cm.
5. Then, cut out 25.0 cm, 11.0 cm, 9.0 cm, 7.5 cm, 6.5 cm and 5.0 cm pieces from the ruler, before arranging them from longest to smallest, stacking on top of each other. Put double sided tape and glue between each layer. This would be our wooden structure. Then, place the wooden structure onto the remaining part of the huge piece of wooden plank and attach it with double sided tape and glue.
6. Then, stick the 4.0 cm x 3.0 cm plank onto the top of the structure made in step 5 and attach it with glue and double sided tape. Afterwards, wrap the structure with duct tape, but make sure it does not cover the top face of the 4.0 cm x 3.0 cm plank. We wrap it with duct tape because the structure may be a bit unstable and can shake slightly, which will affect our readings.
7. Afterwards, put the motor on the 4.0 cm x 3.0 cm plank. Then put the mounting bracket on top of the motor and fasten it by screwing the screws through the holes. The purpose of the mounting bracket is to hold the motor in place.
8.Attach the shortest ruler piece onto the motor shaft. Do it by attaching the motor hub onto the shaft. Then use screws to screw into the first and last holes of the ruler piece to attach the motor hub with the ruler piece.
9.Place the weighing scale onto the wood and switch it on. Next, stick the wooden wedge onto the middle of the weighing scale with a blue-tack. This would serve as the middle point where the red line on the ruler piece must land onto.
10. With the motor not powered, move the ruler piece such that it rests on the wooden wedge. Do not apply force on top of the ruler piece. Tare the reading of the wooden wedge and ruler piece. This is because if we do not tare it, their mass will affect the readings of the force. We tare the ruler piece to exclude its mass as its mass would affect the force, which in turn affect the moment.
11. Then, connect the alligator clips to the switch, motor and batteries in the battery holder, before powering the motor by closing the switch. The motor should be moving the ruler piece towards the scale. Get a friend to film the readings.
12. Let the motor exert force until the readings reach its highest(readings should start to drop once it does so). Once it reaches this stage, open the switch.
13. Watch the readings from the video and find out the highest possible reading attained.This is to ensure accuracy as we may miss out. Convert the reading shown on the kitchen scale to kilograms(reading is shown in grams), before multiplying it with the gravitational acceleration of 9.8 m/s2 to get the force exerted on the scale to stall the motor. To find the torque of the motor, simply multiply the force with the distance of the ruler piece from the centre of the motor shaft to the wooden wedge in metres(Convert from centimetres to metres because our measurements are in centimetres).
14.Repeat step 13 again 2 more times. Afterwards, take the average of the three readings.
15. Repeat 8-13 with the two longer ruler pieces, using the different lengths from the centre of the motor shaft to the wooden wedge (14.0 cm, 16.0 cm, 18.0 cm, 20.0 cm, 24.0 cm) to test.
16. Repeat steps 7-15 with the two other motors.(Skip steps 2, 3, 4, 5 and 6 because you have already done it and the plank, ruler pieces, wooden wedge and wooden structure can be reused.)
2.4 Risk Assessment and Management
We are dealing with electricity so someone may get an electric shock or in severe cases, they may get electrocuted.
Be aware of surroundings, do not close the switch when building the setup. Make sure hands are dry before dealing with wires and power source. When power is switched on, do not touch the bare ends of the wire.
Someone may carelessly put his hands near the ruler piece while the motor spins it, so the ruler piece may hit the person’s hand and injure him.
Do not put hand close to the motor when it is turned on.
If you need to be close for measurement, make sure body parts do not face the edges of the wooden ruler piece.
We will be sawing and drilling the wooden ruler and may injure ourselves and other people if we are not careful.
Be alert and also look around and assess if there is danger, before sawing or drilling.
Be focused, do not swing the saw or drill around for fun, especially when people is near you. Wear safety goggles.
We may accidentally short the battery by accident by accidentally connecting the wires of the battery together. This would boil the chemicals in the battery and set the battery holder on fire.
Be alert, when not using the battery holder, do not load it with batteries. If using the battery holder, make sure wires are not connected directly together, before closing the switch.
Unlikely and not severe harm
Likely but not severe OR Unlikely but severe
Likely and Severe harm
Table 3: Risk Assessment and Management table
2.5 Data Analysis
1. Tabulate the data and calculate the amount of force and pair them together with the fixed distances used accordingly for each motor.
2. Plot a graph that shows how distance and force changes according and the results for the different types of motor.
3. From the graph, we can tell which motor has the highest torque and how force changes with distance due to the fixed torque of the motor.