(1b)
I Get it but why ?

(2)
by “crack” i mean it make noise (like when you go out of the limits) and it don’t go to the right position.
Command would be SM,502,-12531,413
or a less extreme case SM,361,-7215,-1175
I infer than the problem is doing that from a still position,
This is why I would like to know what the rules to accellerate decellerate gently as you say.

Thanks
Mâa