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This instructable shows how I made a switch operated scalextric controller to allow young people with a disability who cannot operate a traditional scalextric controller to use a scalextric set. This method uses a variable resistor to allow pre-set precision control of the speed of the car and stop and go to be operated via any jack plug connected switch. This project was originally for use by the William Merritt Disabled Living Centre (www.wmdlc.org)

The main problem with a standard scalextric controller is that it requires precision operation of a spring loaded trigger to allow the cars to run and then to stay on the track. This rules out its use for many young people who lack fine finger control. The purpose of this controller is to replace the speed control trigger with a separate speed control adjuster and switch. It was important that any type of single pole switch could be used with the controller to allow its use by as many people with disabilities as possible (e.g. cerebral palsy, muscular dystrophy, spinal injury and any other conditions that may affect hand control).

The controller replaces the standard scalextric plug-in controller and should work with any standard scalextric set. It will not however work with the scalextric digital sets.

The standard scalextric controller consists of a high wattage variable resistor connected in series with the power supply to one side of the track. It adds in a "brake" facility by shorting a third wire across the brushes of the car to allow instant braking. The controller I have built does not use this third wire as the car stops almost instantly in any case.

The circuit used is shown in the figure below.

The tools needed to complete this are:

A terminal screw driver
A small posidrive/Phillips screwdriver
Pliers
Soldering Iron and fluxed core electrical solder
Electric drill
Drill bits to suit the mounting holes for the potentiometer used and jack socket
Wire crimping tool

Components needed are:

1 * small plastic box with lid
1 * 3W minimum, 100-200ohm rotary potentiometer (the higher wattage you can afford, the better. I used one similar to this from Farnell components http://uk.farnell.com/bourns/3540s-1-101l/potentiometer-100r/dp/1700931 but I would recommend going to a higher wattage if your budget will stretch)
1 * 20mmm fuse holder (chassis mounting type)
1 * 20mm 1A (max)  slow blow fuse (its important its slow blow as sometimes the instantaneous motor start up current is far greater fro a very brief time instant). I have used a 1A but in reality 500mA would probably do.
3.5mm chassis mounting jack socket
3.5mm stereo jack plug (it is vital that it is a stereo jack and not a 2 pole mono due to the connections in the scalextric power supply)
2 core cable to connect between the jack plug and the box (I used 3 core 3A cable as it was all I had and cut off one of the cores)
3A single core insulated cable
2 * pass through cable crimp connectors
1 * cable tie
1 * 2mm flat head screw and nut

This project requires basic soldering skills but nothing too difficult.

Some much older scalextric sets may use a higher resistance in their hand-controllers and in these cases a higher resistance potentiometer (such as a 100Kohm may need to be used.

All of the components are available from Farnell or Maplins

The essential part is knowing how the scalextric controller connects into the power supply module. Most controllers using a jack plug will connect as per the connector diagram shown. The contact nearest the cable end is connected to the power and this is used to feed the fuse. The centre contact is connected to the potentiometer wiper (the middle contact on the potentiometer that gives a variable resistance to the two other terminals). The end contact is connected to the controller brake band and we don't need it in this circuit. It is for this reason that a stereo jack plug is essential for the connection to the scalextric. If a mono jack plug is used then the brake and wiper connections will be shorted and the car will not move. If you have a different type of controller connector (such as the old type banana or xlr connector type) then this page here might help you http://www.slotcar.org.uk/control/index.htm

Some experimentation with the potentiometer setting will be required to get the best balance of speed and staying on the track. The attached video shows the effect that turning the potentiometer has.

When it all works, drill some holes in the box to keep it all cool!

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