Mechanically, most standard servos are limited to 270° of travel to stop them damaging the position pot, which in turn is a standard electronic item with 270° of travel. The transmitter has similar pots to create the signal, and normally uses the middle 90° of the available travel to give the pulse length that the receiver, and eventually, the servo or ESC or whatever, expects. This use of just the middle 90° gives lots of leeway for different servos and transmitters, ensuring a good chance that the wanted travel can be got on any mix of makes.
A stretcher like the servomorph takes the received pulse and alters the length of it, so that the standard servo travels further for any given signal (or less, if it has been adjusted that way). Fully extended, there is the possibility that a particular servo might try to go past the end of its mechanical travel, so not going for the full 270° is a sensible safety margin.
A winch is just an ordinary servo fitted with an extra gearbox between the output shaft and the pot, arranged so that the 90° of travel that the pot gets equates to however many degrees of travel that the winch gives. A 2 turn will give 720°, a "single turn" one, 360°, assuming that there is one. The drum is just a different shaped arm, the only problem fitting an arm is finding one with the same number and size of splines. If I remember right, Servo City, in their robotics area, do pulleys that fit certain servos, so there is the possibility of gearing to get the wanted travel.
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Topic: HELP with servo travel (Read 2465 times)