tac Foley said:
. . .
The great thing about the more simple AccuCraft locos is that more often than not, only one servo is actually needed - the one that operates the Johnson bar. Setting the throttle beforehand, and selecting the amount of opening or closing of the reversing block allows you to trim the speed to one that you care to handle, up or down-grade. Of course, a model with semi-scale valve gear like the ‘Countess’ or the Garratt, where there is a slight possibility of effecting an element of cut-off on the valve setting whilst in motion, would need the two servos, but they are getting cheaper and cheaper by the weeek, even here in rip-off yUK.
tac
One servo can indeed provide speed control, but you’ll find some debate whether the throttle or the Johnson Bar is the appropriate ‘control’.
Accucraft says don’t try to use the Johnson Bar for control - it’s a forward-off-reverse device. And that’s been my experience with my C-19; the Johnson Bar makes the loco stop or go.
Just controlling the throttle should (in theory) solve the uphill/downhill issues, but (again, my experience with the C-19,) in practice you can’t set the throttle control so that it is hard shut when off, as that can make it difficult to re-open. Consequently, when you close the throtle downhill the loco drifts - very prototypically - but doesn’t slow down much. (It doesn’t tend to go any faster, fortunately.)
My C-19 now has both, and I can usually control it with the throttle and use the Johnson Bar control for any actual stops.
A final comment about the Ruby. There is a ‘kit’ available consisting of a machined block of metal that fits in the cab and has mounts for the two servos and receiver. It seems to be an easy solution to the problem of adding r/c to such a small loco. (One caveat - it is designed for the older locos that had a servo arm type throttle, I believe. Newer ones have a knob so you may have to chase around for an arm.)