When is a parabolic joystick characteristic better than a linear one?
With a linear characteristic, every millimeter of lever travel produces the same amount of speed change. With a parabolic characteristic the slope is low near the center and steepens toward the ends, so the same lever travel allows both millimetric approach and full-speed transfer. It gives a clear advantage on work requiring precise positioning.
The problem with a linear curve is that it offers a single resolution. For precision work you have to use the lever at small angles; but small angles are where the human hand is least stable. If you enlarge the travel to gain sensitivity, you then have to push the lever excessively to reach full speed.
The parabolic (square-law) curve makes the travel serve two functions:
- Center region: low slope, millimetric movement. Setting a load down, aligning a hook and approaching in tight spaces happen here.
- End region: high slope, fast transfer. Empty return and long-distance movements happen here.
The joystick characteristic on AXI's HCT402 set is designed with exactly this logic: millimetric precision in the middle region, high speed at the ends.
The linear curve, on the other hand, is more predictable on constant-speed, repetitive and rhythmic work; the operator maps lever angle to speed one to one in their head. In short, work dominated by precise positioning benefits from the parabolic characteristic, while repetitive work at a constant pace benefits from the linear one.
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