Improved speed controller for a Maxitrak Ruston



The 4QD model 1QD single quadrant speed controller supplied with the Maxitrak Ruston is very basic. If the direction switch is thrown on the move the motor and gears could be damaged, and the braking is very harsh.


I decided to replace it with a 4QD model NCC-35-12 four quadrant contoller. This provides very smooth acceleration and regenerative braking, and is pretty much abuse proof.

In place of the recommended 10k potentiometer, I used a 6 way rotary switch with 5 resistors chosen by trial and error soldered between the poles, to get the speeds shown in the diagram, and a keyswitch for the ignition to allow the loco to be fully imobilised.


I also fitted a 3 LED battery condition meter, as I was concerned that I was occasionally running the battery down too far. There is an option on the controller to limit the reverse speed to half that of forward, but I chose to disable this. The total cost of the controller, battery meter and switches was around 85.



The new board and speed selector switch have made a huge difference to the controllability of the loco, and it is now much more child (and adult) friendly and fun to drive. Top speed downhill on my straight has been clocked using a GPS satellite receiver at 7.9 mph with a bogie wagon and driver. Given that the Ruston is to 1:6 scale, this is a equivalent to a full size 47 mph - rather unrealistic but who cares!


There is a very informative instruction manual for the controller and lots of other helpful technical information on the 4QD website at .

My own railway website with many hints and tips  is at .




By Chris Rennie