Drive Link Mystery

[Brian Rupnow]

Okay guys--This is kind of a question that came up when I built my walking beam. I wanted the shaft at one end of the walking beam to rotate in synchronization with the shaft at the other end, and the only way I could think to do it was with two sets of miter gears and a connecting shaft, or a sprocket and chain. Some people offered the solution of a drive link between the two shafts, similar to the drive link between the wheels of old fashioned steam trains. There is a mystery in this. If you only use one drive link, it won't work, unless the driven shaft has a big flywheel on it, or the momentum of a moving train to get it "over the hump". If you use two drive links diametrically opposed to one and other, it still won't work.---It locks up.--If you don't believe me, make two wheels and a connecting link out of cardboard and push pins and try it. By adding a third link, set at 90 degrees to one of the other two links, then it seems that indeed, yes, it does work. Turning one wheel will result in continuous motion in the other wheel, and not lock up. I have modelled it in Solidworks, but you can't always trust software to duplicate reality. who has insight into this? I would like to know more about it. I don't want to go thru the exercise of building it in metal just to see, but I am curious. Look at the video in the attached link to see what I'm talking about.
[ame]https://www.youtube.com/watch?v=ADf7rrYXP4I&feature=youtu.be[/ame]

 

[Jasonb]

Brian, you can do it with two links set a 90degrees to each other this is how trains do it and it is known as "Quatering" eg 1/4 of 360 = 90.

Same porincipal also applies to twin cylinder steam engines, a 90degree crank will make them self starting.

Two toothed pullies and a toothed belt would also drive the shafts in unison as would chain & sprockets

 

[Charles Lamont]

It won't work with the shafts floating in mid-air. You need a rigid 'link' between the bearings.

 

[Brian Rupnow]

Yes, of course you are correct. Two "throws" on the crankshaft offset 90 degrees from each other will get the job done. I only had to look at my horizontal twin steam engine to realize that. I must be getting old!!!