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

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

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



Peter

Is there any way you could make use of the concept where a line, like a
string, could be attached to a 9 foot long shaft?? If the string is
attached to one end and at the middle, then looped around a perpendicular
shaft so when that perpendicular shaft is twisted it pulls the 9 foot shaft
along its axis. 4 1/2 feet is used for the "thrust mechanism and the other
4 1/2 feet it your extending shaft. I suppose this isnt clear unless you
already know what I'm referring to. I have seen this "string around a
shaft" used to tune old radios where a dial is moved left to right as the
tuning knob is turned..

Jerry

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


2 sets of same sized bicycle sprockets and chains on opposite sides of the
rod with a tab on the chains to hook a tab on the rod.
Timing is everything!

Two timed semicircles would to the same thing but at the speed and length
you want, they get kind big : )

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

Thanks for the replies! I like Geralds idea quite a bit because it
seems simple. Itis like the piston business but solves the problems I
was having. However, how do you attach the link to the loop? Maybe the
loop is a chain?

wrote:

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




Could you use a shaper type of linkage? Check the diagram about half
way down this page:

http://www.manufacturingcenter.com/t...01/0701bk7.asp

On 26 Mar 2005 21:05:42 -0800, wrote:

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

Pneumatics with a long stroke cylinder with adjustable restrictor
valves in both air lines.

I think Ive a brand new Festo......

Something like this
http://catalog.festo.com/enu/asp/Def...D=532447&L=001


Gunner

Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats.
H. L. Mencken

wrote in message
ups.com...
Thanks for the replies! I like Geralds idea quite a bit because it
seems simple. Itis like the piston business but solves the problems I
was having. However, how do you attach the link to the loop? Maybe the
loop is a chain?

I've seen these in McMaster carr for timing belts. Bet they have one for
chain also.

Karl

Thanks Karl. I found Roller Chain Attachments on page 922 online. I
cannot find the equivalent for timing belts. Maybe I'm not searching
for the correct words. I did browse about 100 pages around the timing
belts. Any idea where it is in the catalog?

Peter

In article . com,
says...
Thanks Karl. I found Roller Chain Attachments on page 922 online. I
cannot find the equivalent for timing belts. Maybe I'm not searching
for the correct words. I did browse about 100 pages around the timing
belts. Any idea where it is in the catalog?



This is a good source...
http://www.misumiamerica.com/

for example...
http://www.misumiamerica.com/Categor..._pdf/p1077.pdf

Breco or Brecoflex is another manufacturer.

Ned Simmons

On 27 Mar 2005 00:49:35 -0800, wrote:

Thanks for the replies! I like Geralds idea quite a bit because it
seems simple. Itis like the piston business but solves the problems I
was having. However, how do you attach the link to the loop? Maybe the
loop is a chain?
The loop can be any flexible material with the pulleys farther apart
than the desired range of motion. the oscillating rod can be firmly
attached to the loop on one side while the lever is attached to the
other side by passing the end through a ring to eliminate any
circumferential motion from a point on the lever. The shape of the cam
determines the characteristics of the motion imparted to the rod.
Gerry :-)}
London, Canada