Our first Scalextric Subaru challenge showed the use of light gates for timing. This version repeats the experiment using DrDAQ reed switch sensors. (It also gives us another excuse to play with our Scalextric set!)

The following equipment was used:

• PC with PicoScope installed
• DrDAQ data logger
• Scalextric Subaru Challenge
• 2 x DrDAQ reed switch sensor
• 1 magnet

The idea was to record the speed of a scalextrix car as it passed between two points. To do this two reed switches were mounted beside the track with a distance of 1 metre between them.

So the reed switches could detect the car as it passed, the car was fitted with a magnet taped to the side of the car. Whenever the car passed the reed switches a waveform was recorded on PicoScope.

Figure 1: experiment set up

The PicoScope display below shows the results obtained. PicoScope rulers were used to measure the time interval between the two peaks.

The first peak (Blue) represents the car going past the first reed switch at the start of the 1 metre straight, the second peak (Red) represents the car passing the second reed switch.

From the above screen capture in PicoScope it is possible to calculate the speed of the Scalextric car using the following equation:

Velocity = Distance / Time

The car took 0.633 seconds to travel 1.0 metres so its velocity is 1.58 meters per second. Although this is fairly slow for a car (approx 6 km/h or 3.5 mph) it should be remebered that this is a scale model. Had the car been full size, the speed would have been around 100 mph / 160 km/h.