The Bucket Foundry

**Frits Overmars** · 8th January 2016, 22:42

Originally Posted by Flettner

Linear rod crank, no cams, no scotch yoke, just a crank within a crank. Each crank offset is 12.5mm, total stroke is 50mm. Not over hung, fully supported. Clicking sound is the rod touching the case at the bottom.

Maybe it's the rod's way of asking for a bottom guide, so the top guide can be made sorter and the whole engine can become lower.

**Frits Overmars** · 9th January 2016, 19:58

Originally Posted by Frits Overmars

I love Flettner's crank-in-a-crank-setup. It'll be interesting to see which gear ratio he managed to fit in and whether his big end pin velocity is a sinoid.

I must have been high, drunk or sleepy when I asked myself these questions. In order to achieve linear motion, both cranks must have equal strokes and contra-rotate with equal rpm. This will establish the gearing and guarantee pure sinusoidal stroke, velocity and acceleration profiles.

**husaberg** · 9th January 2016, 20:03

Originally Posted by Frits Overmars

I must have been high, drunk or sleepy when I asked myself these questions. In order to achieve linear motion, both cranks must have equal strokes and contra-rotate with equal rpm. This will establish the gearing and guarantee pure sinoidal stroke, velocity and acceleration profiles.

When he gives you a decent drawing Frits, will you be able to put on your maths hat and work out the forces?

**Frits Overmars** · 9th January 2016, 20:37

Originally Posted by husaberg

When he gives you a decent drawing Frits, will you be able to put on your maths hat and work out the forces?

A rough sketch will do for most of the forces. In principle the kinematics for the crank-in-crank are simpler than for a conventional crank with a con rod.
Balancing will be simpler as well, at least in theory, because it may not be so easy to find sufficient room for the balancing masses.
Calculating the stress on the gears will be a horse of a different colour...

**Flettner** · 11th January 2016, 19:07

Originally Posted by Frits Overmars

I must have been high, drunk or sleepy when I asked myself these questions. In order to achieve linear motion, both cranks must have equal strokes and contra-rotate with equal rpm. This will establish the gearing and guarantee pure sinoidal stroke, velocity and acceleration profiles.

Yes Frits, what do you know of this type of crank system? when you are not high or drunk, sure? Yes the ratio has to be 2 to 1 ie 20 teeth to 40 teeth to get the big end to scribe a straight line. Any wear and the rod will not track true, my biggest worry is the gear tooth longevity but we will see, it is soaked in oil. This assembly is pressed up like a normal crank but what a bugger to put together with that ring gear in the way! I have a better system that will be much easier to assemble next time and just as strong, perhaps better?

On the HCCI front I have come up with a drive system that can accelerate and deccelerate the small crank at the right time, not using oval gears or cams and pins. Ironicly I found a set of oval gears on a printing press down the west coast (NZ) at Shanty Town while away on my Holiday, well I think it was a pair as I couldn't see what it was driving. They look like trouble! I spent today mounting up the AG100 to a test bed with a 2.2KW motor mounted, a piece of old channel iron from the scrap yard. Will the head need cooling? so long as initial compression is low enough to not cause detonation, on the upward stroke (big piston), that would be hard to adjust to.

http://prozamet.pl/art_2008_3_08.pdf Gear design paper.

Or just buy some? https://www.google.co.nz/url?sa=t&rc...MMK9yg0IGy0X0A

https://youtu.be/RuDSxrbx_AQ

perhaps an eliptical gear set is worth a look at?

**Frits Overmars** · 11th January 2016, 23:41

Originally Posted by Flettner

Yes Frits, what do you know of this type of crank system? when you are not high or drunk, sure? Yes the ratio has to be 2 to 1 ie 20 teeth to 40 teeth to get the big end to scribe a straight line. Any wear and the rod will not track true, my biggest worry is the gear tooth longevity but we will see, it is soaked in oil. This assembly is pressed up like a normal crank but what a bugger to put together with that ring gear in the way! I have a better system that will be much easier to assemble next time and just as strong, perhaps better?

Like I said, I like the linear crank system. If I'd seen it earlier, I would have tried to convince Ryger to use it instead of what he has now
(don't ask, I can't tell, but I like yours better). I've never seen it applied in a real engine though. Anybody?

On the HCCI front I have come up with a drive system that can accelerate and deccelerate the small crank at the right time, not using oval gears or cams and pins.... Will the head need cooling? so long as initial compression is low enough to not cause detonation, on the upward stroke (big piston), that would be hard to adjust to.... perhaps an eliptical gear set is worth a look at?

I think the head will need cooling; otherwise it will just get hotter and hotter and have a varying influence on the HCCI compression requirement.
But since HCCI does not put a lot of heat into the head, maybe you can get away with oil circulation.

That drive for your little HCCI-crankshaft that we talked about this morning: it will work though I'm not sure whether you can achieve the desired rate of rpm fluctuation with both crankshafts geared 1 to 1. I still think non-circular gears are simpler to implement and they offer a far greater range of fluctuation.
But I would not try to make them myself if I were you; you've got enough on your plate as it is and surely something suitable must be readily available somewhere.

**speedpro** · 12th January 2016, 07:43

What about a toothed belt on pulleys with an offset mounting boss? Could work at lower revs but having the belt whipping back and forth????

**speedpro** · 12th January 2016, 07:45

What about a toothed belt on pulleys with an offset mounting boss? Could work at lower revs but having the belt whipping back and forth???? Could be simple to alter the offset with easily machined inserts

**Flettner** · 12th January 2016, 08:02

I guess I did mean water cooling, some form of cooling will be nessasary, fins for now might do.

**WilDun** · 12th January 2016, 11:18

Neil,
If you did try to cut elliptical gears (on the gear shaper of course) would you also require an elliptical cutter and some method of changing the rotational speed between the cutter and gear blank being cut? also the centre distances between the gears (oh, maybe not!) - but it all sounds like a pretty expensive exercise! - just buy some I reckon!

**speedpro** · 12th January 2016, 11:45

He's probably already made a special tool to do it using old washing machine parts and brush cutter conrods

**Grumph** · 12th January 2016, 12:09

Originally Posted by speedpro

He's probably already made a special tool to do it using old washing machine parts and brush cutter conrods

hey, nothing wrong with brush cutter conrods...

I know you can programme a CNC to cut cams so is it possible to gearcut an elliptical path on a 5 axis ? Just asking...

**ken seeber** · 12th January 2016, 12:17

Elliptical gears, crazy gears, any gears.
Go http://www.gearotic.com/ .... the world is your oyster. Then you could make any of the unusual designs in https://grabcad.com/library/most-lik...2&per_page=100
I would think though one would need to have them cut with a CNC wire cutter as the teeth profile changes along the periphery of the gears, making a regular tooth form cutter unsuitable.

**Flettner** · 12th January 2016, 19:50

Well, more interesting stuff ( I think ) I'm downloading a short film on "HCCI in action"
Got the AG100 running tonight, will run on it's own.
Interesting discoveries
My little piston is just too crude with one cast iron ring with too much blow by. I can see it emitting out the top oil fill hole. So a large squirt of oil is needed to seal things up before the fuel is applied. Will have to make a dual steel ring piston.
Second interesting thing, timing is very critical, too advanced and it will knock badly and hardly run. Small piston needs to arrive at the right place for combustion much more accurately, quicker.
And I think you will agree the fueling is a bit hit and miss

Result My test bed is just too crude, but it does run, watch the video, I'll post it when it's loaded.

https://youtu.be/2L8xH8U7IWQ