Hello,
shift drums using a rotating angle of 60 degrees between every selected gear and for example a six speed shift drum uses a rotation of five times 60deg (300 deg) to shift from first to sixth gear. So the neutral position between first and second has a 30deg rotation, right in the middle.
The grooves, where the selector forks slide through are designed to provide a smooth moving and acceleration of the selector forks on their own shaft. The grooves are radiused on both of the flanks (inner and outer flank), with that you can avoid a locking position by hiting the ramp of the groove. During the rotation of the drum (60 deg) there will be a stroke who moves the selector forks.
At the beginning and at the end of the rotation of the drum (between two gears) there will be a rotation angle where is no stroke. That is needed to compensate tolerances during rotation and to provide a correct selector axial position.
If you need help with the design, feel free to send me your 3D model.
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