re: "The resistance of a track is made up of the resistance at the joints plus the resistance of the rails."
See, the thing is, you have to start by imagining the copper tape on top of the rails all the around to get my point. If so...at any small section along the rail...the effective resistance in that section is the least of the following actually: the copper itself, the rail (and/or joint) itself or the combination of copper and rail and/or joint. That's one. The second point comes from extending this idea. Suppose you have amazingly good conductivity (low resistance) along the rail for 40% of the way and then suddenly have a bad joint...and of course the copper tape is on top of the rail all along...at the very point where the rail voltage would drop dramatically, the copper tape "kicks in" and delivers higher voltage, effectively becoming a power tap. And because it is right there, all along the rail, just waiting until it becomes the path of least resistance at any point...is effectively a semi-infinite power tap. That's the point I was trying to make.
One other point...I'm not sure what copper tape you guys are using, or how amazing your rail steel is, amazing joints, huge cross-section etc...but in my experience (and i prefer thick and wide copper tape personally), the copper tape alone is superior to the steel and/or joints anywhere and everywhere. I used to run it on my Carrera track (which admittedly has more nickel and chromium content and less conductivity than Scalex steel) and now run it on a wood track with no parallel run of steel at all (and no power taps)...and I get no noticeable voltage drop, and actually run at significantly lower voltages than I used to (partly because of so much less mechanical resistance from eliminating the joints, and less hysteresis at the tire/track interface).
I know some people have very strong feelings about this...steel vs copper etc. For me it's just a practical problem/practical solution situation...no strong feelings either way. But I do have the sense that it's worth reminding people once in a while that copper is actually a superior conductor to steel (like 10:1 better). Your rails aren't steel because it's a superior conductor, but rather because it's less likely to deform with use, more resistant to abrasion over time, and cheaper to obtain. To my mind, the ideal combination...the more robust design...is to let the steel do it's "rigid" thing and then clad it with copper for superior conductivity and even for the decreased mechanical resistance (negative impulse) at each joint.
Anyway, those are my thoughts sitting here with my afternoon smoothie *grin* No big deal...
with best regards,
PS I'm tempted to pose another question...why do you think your power taps help? Is it (more) because they are shorter runs, or because you are using continuous, copper wire? *grin*