Clever Guys -- Here's one

Andrew wrote:

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Quoted message said:

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

Cannibalise a lawnmower? /Robert

"Andrew" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

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

I thought you said it had to be sinusoidal and variable stroke. A
crankshaft is neither, although it approaches sinusoidal for infinite
connecting rod length.
How much money do you have?

A big solenoid and a 2.2 kw driver?

del cecchi

"Andrew" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

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

Andrew, Balance will certainly be a problem at 30hz to deal with but here is
an idea.

Use a scrap yard two-stroke motorcycle engine with manual clutch and
transmission. Turn the crankshaft through the countershaft
(transmission)output sprocket. Using the dirtbike motor's flywheel as you
output; mount a disk with a radial slot (or series of holes) milled to allow
adjustment of your stroke.

Del Cecchi said:

"Andrew" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

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

I thought you said it had to be sinusoidal and variable stroke. A
crankshaft is neither, although it approaches sinusoidal for infinite
connecting rod length.

If you don't have room for an infinite length connecting rod, an
alternative is to use a connecting rod which changes its length once per
revolution to counteract the distortion a regular connecting rod
introduces. This is a trivial mechanism to implement if you can drive
your connecting rod from the end, rather than the middle, of your shaft.
At least some spinning type fishing reels, such as those made by
shimano: http://tinyurl.com/5bxww use this sort of mechanism, which sort of
brings me back on topic.

(Andrew) said:

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.

30Hz? That's 1800 rpm. An 8" stroke at 1800 rpm is a *lot* of
motion. No lawnmower engine has a stroke over about 3.5", for
comparison; some lawn tractors might hit close to 5", but no higher.
Even a big Harley-Davidson doesn't come close to that much stroke. No
current automotive engine comes close. Some really old one-lung
marine and oil well pump engines might have a stroke that long, but
good luck finding one in one piece that's not still in use...and then
you still won't get a real sinusoidal motion, as others have pointed
out.

I'd rig a scotch yoke, but the forces involved for that amount of
oscillation are going to take nontrivial (but relatively crude and
potentially achievable) levels of engineering.

Your task is not impossible, but I'm glad I'm not the one trying to do
it.
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