Guys...somewhere in the dim dark past I have read about "spring loaded steam throttle cushioning" ..mounted between the servo & the throttle
So even with proportionate RC control trimming of the servo arc of travel [stroke].....the "spring loaded steam throttle cushioning" ensures full desired stroke can be achieved....also with positive steam shut off.....but prevents any additional movement from what ever force or applied torque that could cause damage to the throttle internal mechanical stops or weakest part being the linkage arrangement
Am sure it was two captive springs that work in a push pull arrangement ......from memory the original concept came from Sandy Campbell....but cannot find any reference to it via Google
Any thoughts appreciated

... Derek