Clever Guys -- Here's one

[Andrew]

Ok, so here's what I've been tasked to do

Build a system to produce smooth sinusoidal oscillations with a
variable stroke of up to 8" and variable frequency up to 30hz. The
driver required will be around 3 hp.

since this is supposed to be running by the end of august, and there
isn't time to machine all the necessary parts, my basic idea was to
cannibalize an existing single cylinder engine and connect the drive
shaft to a D/C or variable speed A/C . The arrangement will require a
connecting rod as the thing that I am driving cannot sustain the side
force. The stroke will be varied by allowing for different
crank arm lengths.

My question is. Where in tarnation do I find a single speed engine
that might be a candidate? Any other ideas for doing this? Any help
you can provide would be greatly appreciated.

Thanks in advance,
Andrew

[William]

"Andrew" <awiggins@mit.edu> wrote in message
news:cc7e7bdb.0408030927.6191280@posting.google.co m...
> Ok, so here's what I've been tasked to do
>
> Build a system to produce smooth sinusoidal oscillations with a
> variable stroke of up to 8" and variable frequency up to 30hz. The
> driver required will be around 3 hp.
>
> since this is supposed to be running by the end of august, and there
> isn't time to machine all the necessary parts, my basic idea was to
> cannibalize an existing single cylinder engine and connect the drive
> shaft to a D/C or variable speed A/C . The arrangement will require a
> connecting rod as the thing that I am driving cannot sustain the side
> force. The stroke will be varied by allowing for different
> crank arm lengths.

Kind of off topic, but, why not?

I don't think you'll find an engine with a variable stroke (and 8" is
pretty serious for a single cylinder engine in first place). I'd go with
a machined solution, but keep the machining simple.

Hardest part: Get someplace to cut you a 10" circle out of some
suitable metal. Needs tob e pretty thick to support a connecting
rod on a bolt.

Drill a center hole, and holes spiraliing outward at whatever interval
gives you enough adjustment in the stroke. The linkages could be
made from bar stock (thick aluminum would probably do) and use
either sintered bronze or ball bearings depending on how durable
you need it to be. Adjust the stroke by moving a bolt from one
hole to another. Other than the 10" disk, and the cut bar stock,
all the hardware can be had from various places like Stock Drive
Products. (Secure the disk to the drive shaft a modified pulley or
gear bolted to the disk; I'd probably use a pin through the shaft
for simplicity.)

I don't think the machining would take very long. (There are
on-line shops that could probably cut the disk using a water
knife, laser, plasma cutter, etc. Everything else is hacksaw
and drill press work.)

At the speed you're talking about, balancing it probably isn't a
problem, but you could put a pulley or gear on the shaft behind
the disk with an offset weight that can be rotated to balance
the crank. -Wm