How should the throttle cable be routed, and why do sharp bends cause problems?
The cable should be routed as straight as possible, with wide radii and proper support. On a Bowden type cable every sharp bend increases friction; increased friction leads to hysteresis and produces a different speed at the same potentiometer position. The GS740's cable has a special anti-friction plastic inner liner and needs no lubrication, but this does not compensate for a bad route.
A Bowden cable consists of a low-friction liner inside an outer sheath and an inner wire inside that. What determines the accuracy of the system is how freely the wire slides inside the sheath.
Routing rules:
- Take bends with a wide radius; do not leave a break point pressed against a corner.
- Avoid diagonal and unnecessarily long runs; the shorter the run, the lower the friction and the delay.
- Fix both ends of the sheath. If the sheath moves, stroke is lost by the same distance the inner wire pulls.
- Do not let the cable touch moving parts, steering/lift joints or hot surfaces.
- Fix the route using the cable guides and hook-and-loop ties supplied in the set.
Symptom: if the route is bad, when you increase and then decrease the potentiometer the speed comes out different at the same point; this is the classic sign of hysteresis. In addition, the servo draws more current to pull a binding cable. On the GS740-3P this shows up as hitting the current limit, whose factory setting is approximately 7A, or as the mechanical strain protection kicking in. The solution is not in the electronics but in the route: shorten the run and soften the bends.
Full topic: Electronic speed and throttle control on a diesel engine