I built these for my HO track, which has screw post connectors for controllers with alligator clips. There is a 100 ohm rheostat inside of the box, I could have used a potentiometer, but rheostats ar more robust. For 1/32nd cars 25 ohms is the preferred value. The pigtail connects to the track brake connection and the controller brake connection makes up with a screw inside of the box. I wanted to reduce the risk of something getting shorted. Note that potentiometers and rheostats have three connections and the diagram in the reference article does not make it clear which ones to use. The center contact goes to the wiper arm and the other two are at the opposite ends of the resistor. You need to connect to the wiper and one end contact. Take your pick which one. My box has a dial marked 1 to 10 and I have things arranged so that the resistor is out of the circuit when the control is set to 10, which means maximum braking. At 0 the full resistance is in the circuit and braking will be at the lowest level, short of unhooking the brake wire.
Any idea where you can get a 10 or 25 ohm pot from at reasonable money? (UK Based)
I've been searching the net and so far come up with RS that want £20 and Farnell that by the time you add the postage comes in at a wacking £49!
(I'm after 2 by the way)
Instead of a pot, you can use a 12 position rotary switch from (under £2 from Maplin) and suitable 3 watt wire wound resistors (59p from Maplin).
Connect one end straight through for full brakes and the other open circuit for no brakes. Ten 1 ohm resistors give you much the same thing as a 10 ohm pot (although Five 0.47 ohms and Five 2.2 ohms would probably be more useful)
I'll fit in the existing brake pot position on a lot of controllers (The hole size for the switch is the same as most brake pots)
If a controller hasn't already got a brake pot mounting position, one can easily be added.
Alternatively it can be mounted as a separate box like the one in RichD's photo.
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