Scalextric Subaru challenge

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

Subaru Impreza RS Engine : 2.5L Horizontally opposed SOHC, 16 Valve four
Configuration : 4 Wheel drive
0 to 60mph : 8.3 seconds
Top speed : 125mph
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)
Price : $15,895 to $20,000

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:-

scalextric logo

The Subaru challenge box set was purchased, setup 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: The equipment was setup 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.

The setup
Circuit diagram:
Circuit diagram

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 track:
The track
The equipment:
The equipment

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:

LanesStraightStraight QTYCurveCurve QTYTotal distance
Inside0.3560.2083.7 Metres
Outside0.3560.26584.22 Metres

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:

PicoScope screen shot

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 2997ms 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 = 4.44km/h There are 1609 metres to the mile so:

Velocity = 4.44/1.609 = 2.759mph

If the same calculations are performed for the car in the outside lane then its average velocity is seen to be :- 3.698mph.
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 mannaged to get a top average speed of around 8mph with the car on the inside lane.
Following on from this experiment there are a number of other parameters that can be recorded:
These topics are covered in the next technical note on the subject :Scalextric analysis

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