20 coils are needed for the relays used on the 10 controller switches.

The coils are made of material that is easily obtainable from local stores. (soft iron square tuning and and coper pipe used for plumbing)

The wire is available from any electrical component supplier (e.g.

The dimensions of the coil and the wire diameter can be adjusted to optimise the force of the plunger. (to increase the force, provide more wire tuns in the winding and select a thicker wire)




Cut the 34 mm square tubing in 60mm pieces.

Drill the mounting holes to fit (pop-rivet) the coil onto the controller switch Bakelite base.

Make square end plates to close up the coil sides.

Drill holes in the front end plates to allow for the wire to protrude.

Drill 15 mm holes in the end plates to fit the 15mm coper pipe.


Cut 60 mm length of coper pipe.

Press fit the square end plates to the coper pipe.

Provide isolation to the indicated areas (masking tape) (NB: Isolate wire with tape where it passes through the holes in the end plates).

Add the wire – 500 turns as shown. (Tip – use  an electric hand drill with speed control to turn the winding) (Wire diameter size = 0,95 mm)

There is no heat problem. The processor switches the coils on for only 100 ms at a time.

Insert the coil with end plates into the square tubing and glue as indicated.

Check with a multimeter for proper isolation between the wires and the chassis.

The plunger is made of 12mm soft iron rod, with a non-ferrous metal tip section made of 10mm brass rod.

The tip section is 1/3 of the overall length of 90mm.

The tip section pushes against the switch side arms.

The two sections (brass and iron) are joint together with the aid of a non-ferrous metal (aluminium) tube and glued.

The plunger is shown below.