depends on required force and velocity - hydraulic ram, air piston, linear
motor, screw motor, parallelogram linkage, the list goes on - how constant a
motion do you require?. an acme screw and a parallelogram is one simple way
to do it
wrote in message
oups.com...
Hi,

I would like to make a long rod move forward 4 1/2 feet along it's axis
and then return to the starting point with constant velocity and a
period of about 3 seconds. This is like the piston in a car engine but
slower and larger distances. Using piston terminology if I turn the
crankshaft then the piston will move up and down. But the piston
doesn't move at constant velocity since the crank shaft is moving in a
circle. If i built a big version of a piston I'd have to have a crank
shaft 4 1/2 feet in diameter which is pretty big. If I go with the
piston type set up it will all be plywood and bolts just so you have an
idea of what I'm working with.

Any clever solutions?

Thanks,
Peter