Ahh, the feeling of acomplishment. Until the sharper radii curves hit. First a coat of 5 minute epoxy on the suspect surfaces. Then test run. That's not why I bought the two Overland A and B units.
Photo below shows the power chassis apart from the shell.
The dual motors are loose and turned over so the epoxy can be applied. Make your own tethered throttle We have used this design on our local throttles at the club for industry switching and yards. The mainline cabs run on a similar design, but are fixed in panels in our elevated cab control room, and use a larger regulator with higher current capacity. The TIP-120 has a low current rating, around 1.5 amps, so the use of either a fuse or a lamp ballast is needed to hold back any short circuits that do occur on the layout. The lamp ballast is a neat idea.