Scalextric Subaru Challenge

The Subaru Impreza is a World Champion car with the following specifications:

• Engine: 2.5L Horizontally opposed SOHC, 16 Valve four
• Configuration: 4 Wheel drive
• 0 to 60 mph: 8.3 seconds
• Top speed: 125 mph
• Power: 165 hp @ 5,600 rpm
• Length: 172.2 inches
• Width: 67.1 inches
• Height : 55.5 inches
• Fuel economy: 22/29 mpg (city rating)

The aim of the experiment is to measure and record the speed of the car with an ADC-11. Due to budget limitations purchasing the above Subaru Impreza RS was out of the question. The only alternative was to go for the next best thing:

The Subaru challenge box set was purchased, set up and tested. After a few days of testing it was decided that the technical staff should stop playing with it and actually perform a datalogging experiment. The following equipment was used:

• PC with PicoScope installed
• ADC-11 multi channel data logger
• ADC-11 Terminal block
• Scalextric Subaru Challenge
• EL031 Light sensor
• High intensity LED
• Magnifying glass
• 100 k resistor
• 1 k resistor

The equipment was set up so that the cars will break the light being received by the EL031 light sensor, thus affecting the resistance and causing a larger voltage drop across it.

Circuit diagram

Equipment

Note that the digital output (DO) from the ADC-11 is used to power the LED and provide the voltage across the EL031. The light sensor was setup so that it was directly in the line of the LED. It was found that better results were achieved when the light emitted from the LED was focused with the aid of a magnifying glass.The track itself was setup as an oval, with the following parts following:

The equipment

The track

It would not be fair to race cars using the above sections as no cross over sections are employed so the distances that the cars have to travel to complete a lap has a difference of over half a metre. The table below shows the track used:

The general idea was to track the time taken for the car to complete a circuit. See the PicoScope display below for an example of how it works:

Notice the two different peaks. The lower peaks represent the car on the inside track, the larger peaks represent the car on the outside track. It can be seen that the car on the inside was overtaken by the car on the outside. The reason for the difference in signals is that the nearer the car is to the light sensor the less light reaches it, thus the resistance is greater which makes for a bigger voltage drop.

The above display shows that the car on the outside overtakes the car on the inside.

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

Velocity = Distance / Time

The car on the inside can be seen to take 2997 ms to travel 3.7 metres. The first stage is to identify the units, to compare the car to the real thing we should use mph and hours.

Distance (km) = (3.7/1000) = 0.0037
Time (Hours) = (2997/(1000*60*60)) = 0.0008325

The average velocity can now be calculated:

Velocity = 0.0037 / 0.0008325 = 4.44 km/h

There are 1609 metres to the mile so:

Velocity = 4.44/1.609 = 2.759 mph

If the same calculations are performed for the car in the outside lane then its average velocity is seen to be 3.698 mph.

The above speeds do not seem very fast, however this is just a demonstration of how to log the average speed of the devices. In practice the staff here at Pico managed to get a top average speed of around 8 mph with the car on the inside lane.

Following on from this experiment there are a number of other parameters that can be recorded:

• Maximum speed
• Power consumption of each car
• Automation of all of the readings

View a version of this experiment using the DrDAQ data logger and DrDAQ reed switch sensors