On Sat, 26 Mar 2005 21:25:41 -0800, "william_b_noble"
wrote:

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
roups.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


How about a cam operated lever driving a loop around two pulleys with
a link to operate the rod.
Gerry :-)}
London, Canada