"Randy MacKenna" wrote in message
oups.com...
Thanks!

For a 75Kg object on Earth, it is exerting a downward force of 735.5N,
so if I have a coefficient of friction of 0.004, then F_f is (roughly)
3N, so I don't think I need to even worry about it (for my application,
anyway).

So, if I'm dealing with a motor that can produce 2000N of force
(through a screw drive), I think I'm well within my design limits if I
want this object to reverse direction in under 5 milliseconds.

Split the problem into two parts. 1) the time to stop 2) the time to get
going again. Then it's a matter of making two sets of equations using:

a = (v-u)/t
and
f=ma
and
T=t1+t2

(u or v = zero depending on which phase)

If friction was significant you would just add it to the force available to
slow down the object (because it helps) then for the second part subtract it
from that available to accelerate it (because it hinders).

The rest is maths.