The next component on our list was the wheels. We had previously discussed the possibility of including 3D printed tracks as a replacement, but decided against this as wheels would be easier and faster to test and change or alter if necessary, and also gives us the option to experiment with gears. We experimented with two different wheel sizes by laser gutting them quickly out of plywood and calculating the speed for each journey using the formula **speed =distance/t****ime. **

We wrote new code to test the wheels, making sure that the Racer only moved forwards. We marked a two meter track and then timed how long (**time**) it took for the Racer to finish the two meter (**distance) **track.

40mm Wheels completed the 2 meters in 15 seconds.

**60mm Wheels completed the 2 meters in 9 seconds.**

**Calculations for working out the speed for each set of wheels:**

Speed=Distance/Time

**40mm :**

speed = 2 / 15

0.13 meters per second

**60mm :**

speed = 2 / 9

0.22 meters per second

From this we learnt that the larger the diameter of the wheel the faster the rotation, this confirms what we were taught in one our mechanical engineering lecture that the more ground per rotation increased speed.

We chose to carry on using elastic around both wheels for added traction, the same way as we did on the previous sketch model. Due to the increased size in wheels increasing the speed of the Racer, it has been necessary to reduce the delay function in the coding.

After testing the speed of the wheels we chose to calculate **acceleration**, which is change in **velocity/time taken**

60mm Wheels =0.0086 meter / square second {m/s2}

40mm Wheels = 0.0244 meter / square second {m.s2}

Finally we wanted to work out the force depending of the size of the wheels, in order to work this out we needed to weight the Racer, the weight was 250g.

Force = Mass X Acceleration

60mm Wheels :

Force = 0.25(kg) X 0.0086(m/s2)

Force = 0.00215 N

40mm Wheels:

Force = 0.25 X 0.0244

Force = 0.0061 N

Due to a larger acceleration

The larger wheel increases acceleration meaning less force is needed, increasing the efficiency of the Racer. Therefore, we shall use larger wheels in the final model.