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Mechanism idea needed for varying throw on a crankshaft

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picclock:
Hi Richard

Using a helix to change the relative positions is a neat and simple idea i hadn't thought of  :scratch:.

I would like to be able to adjust the throw with as little force as possible, hence the initial differential gearing type approach.

Still havn't really made a decision. I may make some models and see which turns out best.

Sadly work seems to have stolen my time at the moment, but if I come up with anything better or weirder that may be of interest I'll post it.

Best Regards

picclock

 

ken572:
picclock,

Goto your local auto-truck junk yard and find some old swash plate,
AC cylindrical compressers, they made them in 3,5,7,9, piston units.
They shorten and or lengthen the stroke to change the cubic inch's
on the fly depending on the load needed. Vicker's also made hydraulic
swash plate pumps with a hand crank on the front to vary the speed
using the same as above. :thumbup:

Ken.

BillTodd:

--- Quote ---Using a cam within a cam such that when both lobes are opposite the eccentric isnt :-), and when the lobes are aligned maximum throw is achieved. As this works on the relative position of the cams to each other I would have to figure out a way of rotating them when they are turning. Not impossible but quite complex. Best I can come up with is a gear on either side each connecting to the cams. One connects directly to a central gear the other to an idler then to the central gear. That way the central gear won't turn but if turned the relative position of the cams will change.
--- End quote ---

Like this?...

 I have the same problem as you in that I also need a variable stroke mechanism that can be easily varied while running. This is the crank part of a provisional slotting head design I've been working on; The position of the crank pin can be moved from the centre of the crank (i.e. zero stroke) to the outside (max stroke) by a worm screw. The worm is suppose to be turned by pawls catching on the star head as the crank rotates past. I'm not yet convinced it will be up to the job, so I'm open to new ideas.

(the screw is supposed to be rotating smoothly but I haven't had time to remove the aliasing)

Bill

picclock:
Hi Bill

I'm finding it hard to understand how your idea works. I did post some sketches that were lost when the site went down which I've attached using rod ends. They both rely on an axial movememt of a sleeve on the shaft. For me that works out quite well as it can be linked to an engine speed governor or similar device.

Best regards

picclock

crabsign69:
  very clever there bill  i like it. :beer:  :headbang:  bet it would be hard to make but i like it.

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