"So I guess I'll need 3 sets of controllers to cover each class/manufacturer I run on my track."
This would probably be cost prohibitive. Electronic controllers allow you to adapt the controller to the various track, motor, power, traction, gearing, wiring setup, etc., conditions that affect how easily and efficiently you can drive the car. Most electronic controllers can be adjusted to replace the need for several resistor based controllers. Electronic controllers start around $60 and go well beyond $300.
Resistor based controllers (set controllers, classic Parma controllers, etc.) are inexpensive but are always a compromise. However, a lot of people can adapt their driving style to be able to run quite well with standard resistor controllers, especially if they pick a good compromise resistor value. The resistance ratings you see here are well known good compromise values for common types of cars and track conditions.
All unmodified resistor controllers are basically the same. At minimum throttle you have the maximum resistance of the controller and at full throttle you have near zero resistance (a short). The resistor rating tells you the range of control you have between these extremes at the wiper arm of the controller. So a 45 ohm resistor gives you 45 ohms of variability and a 90 ohm gives you 90 ohms of variability. The amount of current that gets to the track rails is inversely proportional to the amount of resistance at the wiper arm. So assuming the resistors both have evenly spaced windings (and a power supply that's not current limited), the 45 controller will deliver approximately twice as much current to the track as will the 90 ohm controller set at the same wiper arm position.
Different cars have different current requirements. That's why you'd like to match the controller to the needs of the car and the other factors. The JL TJets don't need a lot of current to run fast due to the armature windings and numerically higher gearing, so a JL with a lower ohm controller will make the thing take off with little movement of the controller wiper arm. That tends to make the car more difficult to control, unless of course you have long straights and wide sweeping turns that allow you to maintain a fairly high speed and your don't mind the lack of variability in controlling the car.
As far as winding your own control resistor with copper wire goes... plan to get a lot of copper wire. The resistance of copper is pretty low so you'll need a lot of windings to achieve the resistance ratings you'll need. Assuming 30 gauge copper wire, you'll need about 7.5 feet of wire per ohm. Do the math. ;-) The wire used on wire wound resistors has a much higher resistance than copper. I think it's nichrome or a similar alloy.
rr
