Controllers

Electronic Controllers

What's different?

If you are used to a resistance controller, here's some thoughts on what's different using an electronic controller

i The transistorized (and Diode) controller will suit motors of widely different current rating on the same setting. People tell me that some Scalextric / Fly / Ninco cars are driven on the same setting as a saloon G12. Look at the graph below (measured on a Streakers controller) shows, an identical setting behaves like a 2 ohm controller with a motor taking 4 amps and a 5 ohm controller with a motor taking 1.3 amps. (however this isn't really that much of an advantage - transistorized controllers are adjustable anyway)

ii With a transistorized (and diode) controller its less noticeable it you've got two cars on your lane.
Looking at the graph, doubling the current changes the transistorized controllers voltage drop by 10-15% for circuits using a Darlington pair (like the "normal British" circuit) and perhaps more with some single transistor circuits).
A second car on your lane isn't likely to be very noticeable switching type transistorized controllers.
Doubling the current changes the resistance controllers voltage drop by 50% so the second car on your lane is much more noticeable.

iii Linear transistorized (and diode) controllers make the car more sensitive to fluctuation in power supply voltage. Single transistor circuits (like the NPN one I've described) tend to be a bit less sensitive to fluctuation in power supply voltage than ones using a Darlington pair (like the "normal British" circuit)
Resistance controllers and switching type transistorized controllers are less sensitive to fluctuations in power supply voltage.
(Hopefully today’s tracks have fairly consistent power supplies so this is not as noticeable as it used to be.)

vi Transistors only work with the current flowing in one direction, resistors will work with it going either way. If you have a resistance controller this doesn't matter. If you have a "dual polarity" transistorized controller this doesn't matter. Most transistorized controllers (including the PNP and NPN circuits described on this site) won't work and will probably by damaged by reversed track polarity. This isn't a problem with tracks wired to BSCRA standards and controllers sold for BSCRA racing - they are all the same polarity. However, some home tracks and many home sets are wired with the opposite polarity.

A diode only passes current one way, but some diode controllers use pairs of diodes (bridge rectifiers) so that they will work either way round. It is much less likely that a diode will be damaged by connecting it the wrong way round. (But follow the manufactures instructions - better safe than get an unexpected big bang!)

v Most linear transistorized (and diode) controllers control the speed of the car where as variable resistance controllers (and a few transistorized designs) control the power (that is speed multiplied by torque). When you lift off from full power the transistor / diode will slow the car more rapidly than with a resistance, this was claimed to be a great advantage by one diode controller supplier, but nobody seems to have noticed their transistorized controller has the same characteristic.

vi The step between the bottom band of a normal transistorized controller and full power is quite large. The ones I've measured using a Darlington pair (like the "normal British" circuit) show about 2 volts. The minimum size of this step is limited by the transistor, it may be possible to choose resistor values to reduce it to about 1.4 volts. Other circuits (like the Paul Bucknell design or the NPN one I've described or circuits using MOSFETs) can halve the size of this bottom step. In some circumstances a large bottom step could be an advantage, but there may be an advantage in being able to adjust this value which is exactly what the "choke" control on some controllers does.
A large bottom step may not be a good idea for almost but not quite flat out corners sometimes found on raceways - you just might want to drive with less than full power but more than the bottom step allows you.
A diode controller will have a bottom step of about 0,7 volts or 1,4 volts depending on if it has I or 2 diodes in the circuit.
Switching type transistorized controllers generally use a completely different type of transistor (called a MOSFET) which allow the bottom step to be very small.

vii Transistorized controllers are more complicated - so there is more to go wrong, and if something does go wrong it is lot difficult to work out what. (Still you might have a better chance if you understand how it works!)

viii When the car is trying to pick up through a film of oxide on the tapes, so there is no current flowing for an instant, what you need is as many volts as possible to break down the oxide. A controller that applies the full power supply voltage in these conditions, even when your thumb (or finger) is part way down, can be a significant advantage. Some of the early attempts at transistorized controllers didn't do this and caused the cars to be more sensitive to bad pick up. As the graph shows, this circuit does not suffer from this problem. Switching type transistorized controllers don't suffer from this problem.
(This is a potential problem with some diode controllers.)

ix There are large differences between the quality of design and build between controllers that employ the same basic circuit – these are often more important than the basic circuit itself.

Back to controller start page

The circuit normally used in British controllers

Good ways to blow up controllers

(and how to avoid them)

The alternative Circuit often used in imported controllers

Switching Controllers

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