A more flexible drive rod?

This is my most recent push stick for inline skating. It works OK but it is still being improved.

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In the bottom right, there is a yellow gearbox.

Between that gearbox and the crankshaft inside of the orange body, there is a 1/4 inch aluminum rod connecting the two.

Being a two cycle engine, there is some sputtering. The wheel bounces back and forth as it turns and the gears get banged around a lot. I'm afraid that's going to eventually break stuff.

The 1/4 inch aluminum drive rod is about 8 inches long. I would like to replace it with something flexible, or put a clutch in there. Anything that would absorb some shock. I suppose a clutch would have to be at the gearbox output, since the motor spins the rod at thousands of RPMs.

Any easy possibilities?

How about a smaller diameter 8 inch rod of spring steel? I don't know if spring steel works that way, just asking.

Or perhaps the amount of stress when it's banging around at idle is no greater than the more uniform stress when it's pushing me up a hill. I could just wait and repair it as needed. I'm definitely going to continue testing it as is.

Thanks.

Reply to
John Doe
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How much room do you have for whatever would replace the 8" x 1/4" rod?

A freewheel (a ratchet mechanism as used with a bicycle's rear gearset) might handle the problem better than a clutch.

Reply to
James Waldby

Google flexplate. Some vehicles used one made of rubberized fabric between the steering wheel and the steering gear box. My big CNC mill uses one between the X axis motor and the X axis drive screw made of stacked thin pieces of stainless spring steel sheet.

Depending on your shop capabilities you could make your own.

Reply to
Bob La Londe

My 1983 Mercedes 300 SD uses at least one flex plate in the drive line. Handles lots of torque for lots of years! It's metal, I am sure.

I have seen small flex plates used in electronic equipment to allow for slight misalignment of control shafts. 1/4 inch shaft, etc.

Paul

Reply to
Paul Drahn

On a motorcycle you'd be looking for a 'cush drive'.

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Doesn't need to be anywhere near as fancy as that.

Easiest to incorporate in the wheel drive somehow.

Problem with a metal torsion spring driveshaft is if you hit a resonant frequency, things get worse instead of better.

BTW the 'sputtering' is typical 2-stroke 3-stroking, 4-stroking, 5-stroking, etc, at partial throttle settings the engine may only fire once every 3, 4, 5 etc strokes.

Reply to
spamTHISbrp

Perhaps he needs a larger flywheel to reduce torque and speed variations. jsw

Reply to
Jim Wilkins

frequency, things get worse instead of better.

etc, at partial throttle settings the engine may only fire once every 3, 4, 5 etc strokes. How about replacing the aluminium ros with one of these (minus the screwdriver bits, of course)?

Reply to
geraldrmiller

Really? That's weird, but that's how it appears to be.

That goes for a four-stroke engine too? I never noticed that from a four-stroke engine motorcycle.

Reply to
John Doe

frequency, things get worse instead of better.

etc, at partial throttle settings the engine may only fire once every 3, 4, 5 etc strokes. I agree with the sputtering cause, but it should not be that way. Something is wrong with the carburetor or it's adjustment. I have had several 2-cycle chain saws and if they are properly adjusted, there is no difference in running from idle to full throttle. Could the wrong gasoline/oil mixture be causing this?

Paul

Reply to
Paul Drahn

...

I just bought another Echo grass trimmer. Just like the same grass trimmer that I've had since October 2012 (the one in the picture), it starts every time on ½ pull. But when observing closely while it is idling, there is an obvious inconsistency in the way the sparkplug fires.

Funny though, I'm having a difficult time finding mention of this on the Internet. Must be a well kept secret. Maybe most people can't hear or feel it.

Reply to
John Doe

Looks like a lot of fun. Got a video in action?

Best advice I can offer is to keep prototyping your new design ideas. With each iteration you will learn something new. You'll get there.

BTW, "sputtering" or un-fired cycles in a 2-stroke, can aid in lubrication as the fuel carries the oil, and the sputter is an extra shot of oil, so may not be all bad.

Safe skating,

Reply to
PCS

I assume you do not have a way to watch the output of the magneto to see if it is the problem. Pull the spark plug and check/set the gap to the recommended value.

If you have access to an oscilloscope, wind a few turns of insulated wire around the spark plug wire and attach the scope probe to the wire. should be able to see a pretty good trace of each plug firing.

Paul

Reply to
Paul Drahn

No, only happens on 2-strokes, it happens because at some load/speed/thrott le triple-points the cylinder fires, traps a lot of exhaust that keeps the next cycle from firing, maybe the cycle after that it's too rich... all kin ds of really cool almost organic behaviors.

Reply to
spamTHISbrp

frequency, things get worse instead of better.

etc, at partial throttle settings the engine may only fire once every 3, 4, 5 etc strokes.

missed the link -

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Reply to
geraldrmiller

There is no problem. Just like the duplicate grass trimmer (Echo GT-

225) I've had since October 2012, it starts on ½ pull, it has lots of power, and it runs smoothly when it's revved. It almost starts when I look at the cord :) It's like they designed the thing around easy starting. But I suspect it just points to overall quality.

I'm pretty sure they can be tuned to run properly at certain speeds. So if it runs perfectly at idle, it might sputter at some other speed. I'll post more if I find other discussion on the Internet.

Reply to
John Doe

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There's one thread. No doubt there are many more. Anyways, it's just amusing to me.

Reply to
John Doe

Yesterday, another failure occurred. This time, it wasn't one of my sloppy connections, the right angle gear taken from a Dewalt 18 volt cordless drill broke. Feels like sort of a triumph :)

The great thing about gas is that it goes a very long way compared to battery power. Unfortunately, the motor is heavy. This 21.2 CC engine has just enough power.

Inline skating will be ready for this when battery technology is much improved. For now, I might use my new engine to make a gas powered scooter, instead. And this time, I won't remove the gas trimmer's built-in clutch.

Maybe another electric version is in order, for short & fun trips. When I can do it.

Reply to
John Doe

Actually, the right angle gear breaking is not a surprise, since there was no support on the other side of the wheel opposite of the right angle gear.

Reply to
John Doe

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