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Many racers are asking us for advise on high end hand controllers suitable for driving all types of slot cars up to Eurosport and G7. There are indeed many hand controllers on the market, but this, for the practically minded is the “cheap” option to a high end controller which will run anything from a Scalex Car to a Wing Car with all the features you could wish to have in one relatively inexpensive package, using easy to obtain components and even a downloadable, easy to understand schematic wiring diagram. You do not need to be a rocket scientist to build this controller! This is a tried and tested project, I just do not have the time to build them, so here it is complete with double transistors, fan cooling, 8 way, rotary selection choke and blast relay. You should be able to assemble this unit for between £100-£130 and a bit of time with a soldering iron.

The handle is a standard Parma Turbo with the “Heat Sink” bent straight to mount the brake and attack controls. The wiper board in this example is a “Lynx” type but any wiper board will do with a resistor range between 320 & 400 Ohms. The full power contact is kept separate to act as a contact for the blast relay. The cable between the handle and box is a 6 way cable. As very little load goes to the handle (all the hard work electrically goes on in the box) this can be very thin. For the ‘Pros’ - throw away the oilite bearings in the trigger and replace with 1/4” x 1/8” ballraces.
Looking at the box face on (top left), the handle cable enters from the right (this is the fan end where the transistors are located). Output cables exit the the left (this is where the warm air goes out through the vent grille. The Hammond box is ideal for this project as the cover is a slide fit, contained by the plastic end caps and makes for easy assembly and maintenance.
This example has a Mass of LED’s as it was the first one made, all further models have just had 3, for, “chokes on”, “Power” and “Blast relay operation”. The switch switches from full power operation to the first choke and the rotary switch gives the other 7 positions of choke.
The choke is wound on a piece of aluminium angle and uses insulated copper winding wire of 0.022” Diameter. You can determine how long the choke is to be for your application but in the ones I have made the total length of the choke wire is 18 feet, tapped at 2,4,6,9,12,15 feet.

Wiring can be a whole lot tidier, but this was the project base! The Transistors are also mounted on aluminium angle. The copper conductors soldered to common up the transistors makes for easy replacement as there are no “Floppy wires” to contend with. As the fan is right next to the transistors the aluminium angle works fine and is also very cheap. The Aluminium transistor plate is ‘isolated” from the box with nylon spacers and sleeves, so the box is “NOT LIVE”.

Left;- Wire wound choke. The tapping are taken off the choke using lead wire. Remember to number the taps in sequence so you connect them correctly to the rotary switch. Ensure no ‘burrs” on the edges of aluminium which may cause a ‘short’ in the copper wire insulation.

A closer look at the transistor mount plate / heat sink. As the fan is right next to the transistors, the use of aluminium angle is OK + it is very easy to cut and drill as required. Mount the transistors on a ‘slant’ so they are easier to common up. Use solid copper to common the connections, which makes replacing a transistor easier as the are no ‘Floppy wires’ connected to the transistor terminals. Use 3mm bolts to screw mount transistors to the bracket.

You should fuse the controller to protect it. This should be done both on the output live to the track (35 amps) and also the brake line (6 - 10 amps.) That way you do not run the risk of cooking the transistors or blowing the brake wiring in the case of a track short.
The reason we install a 22 ohm resistor in the fan feed is because these fans are designed for 12v operation. If you plug it into a track with 14 or 15 volts (it can happen) the fan will cook and fail to operate. The resistor will keep the incoming voltage to the fan below 12 volts even if the supply voltage is 16V.
WIRING DIAGRAM ;- The diagram is a simple schematic - you do not need to be an electrician to see how it works. Even the transistor connections are ‘offset’ the correct way. The colour coding is mandatory, it just makes understanding the drawing easier. You will also find Maplin and RS Components ref. Numbers on the diagram to help you order the parts.

PROJECT TWEEKS! A real nice guy from Belgium, Willem Kloppenburg, built one of these project controllers and has added yet another tweek! This is a separate pot to alter the Curve of the controller from a linear type, to an adjustable curve. This involves dropping an extra 5K cermet adjustment pot and switch across the wiper board.
For a circuit diagram and also an “adjustable curve plotting diagram” in Excel format CLICK HERE.
Many Thanks to Willem for this development.