Chain and sprocket Design
Chain and sprocket Design
(OP)
Hi all,
I'm learning to design chain and sprocket mechanisms and i need some help figuring some stuff out.
All of the questions refer to a simple mechanism of single driving and driven sprockets.
I've read that if the mechanism has an alternating running direction (for example pivoting a turret), it is unadvised to use chain tensioners. This sound to me a bit counter intuitive especially if the plain of rotation is horizontal.
And i couldn't find a way to calculate the tension force needed for proper functioning.
I'm learning to design chain and sprocket mechanisms and i need some help figuring some stuff out.
All of the questions refer to a simple mechanism of single driving and driven sprockets.
I've read that if the mechanism has an alternating running direction (for example pivoting a turret), it is unadvised to use chain tensioners. This sound to me a bit counter intuitive especially if the plain of rotation is horizontal.
And i couldn't find a way to calculate the tension force needed for proper functioning.





RE: Chain and sprocket Design
The problem with tensioners isn't so much the direction of rotation, as the torque reversals. If you have a spring-loaded tensioner, and the mechanism applies torque in the direction such that the tension is applied through the section of chain in which the tensioner is installed, the chain pull may overcome the force applied by the tensioner, causing it to back out. If the tensioner is capable of backing out far enough to allow the chain to slip a tooth, bad things happen.
Of course it is possible to apply enough tension to the chain via the tensioner to exceed the foreseeable drive forces, but this is likely to apply unnecessary force on the chain, possibly overloading it and/or shortening its life.
A tensioner that is mechanically locked in position, as opposed to applying a constant spring force, is less likely to back out. And when this type of tensioner is used, or if the chain center distance is locked in position (e.g. motorcycle drive chains), it should be set so as to NOT have any constant tension - it should actually have a wee bit of slack. Motorcycle final drives generally have a specification on the amount that the chain can be moved freely up and down at the midpoint of the slack section - in other words, there is (almost, aside from that applied by gravity) no tension on it but rather a little bit of slack.
Motorcycle timing chain tensioners (between crankshaft and camshaft) are subject to high-RPM torque reversals with every crankshaft revolution. Those chains have full-length guides along the slack sections, the tensioners generally apply a small spring tension but have a mechanism to stop them from backing out.
RE: Chain and sprocket Design
Try this link
http://www.renold.com/upload/renoldswitzerland/con...
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Chain and sprocket Design
https://www.youtube.com/watch?v=u6ZsWwQ072E
RE: Chain and sprocket Design
RE: Chain and sprocket Design
RE: Chain and sprocket Design
The video took me by surprise, wasn't expecting that at all.
But for the sake of the argument, in case i have an horizontally orientated chain and sprocket mechanism with alternating running direction (running at very low RPM), and guide runners are not an option.
What can be done to ensure that the chain stays on the sprockets?
RE: Chain and sprocket Design
RE: Chain and sprocket Design
RE: Chain and sprocket Design
RE: Chain and sprocket Design
I think the firs one (hollow sprocket) will fall out of the chain by rolling closer to the bigger sprocket and the clamp will slide tawards the smaller sprocket.
RE: Chain and sprocket Design
RE: Chain and sprocket Design
RE: Chain and sprocket Design
I guess your lack of posting a diagram of what it is you are doing is complicating what would be a general discussion by hiding the other 99% of the problems you probably have. If you are losing 'most' of the wrap then you don't have a good candidate for a chain drive anyway.
RE: Chain and sprocket Design
catalog
video
RE: Chain and sprocket Design
I'm not constructing anything, just trying to learn some basics in chain-sprocket mechanism design and wondered what to do about the chain tension in a specific case of two sprockets, with odd diameter that can rotate in both ways and the rotation plain is horizontal.
Then dvd suggested the two options (clamp like tensioner and hollow sprocket),I replied that I've seen those but figured that they can only work in an even diameter sprockets mechanism and gave my opinion why.
And i still think that the hollow sprocket will move (for any setup with uneven sprockets) as the tension of the chain on one side or the other is always a bit looser, which results in slightly uneven friction forces on both sides where the chain grips the hollow sprocket, but again this is irreverent for the moment as it doesn't provide a solution for the hypothetical problem that i didn't found an example for, so far.
RE: Chain and sprocket Design
The hollow sprocket cannot move- it has teeth.
There's only two ways for the sprocket to move- either it would have to have slip between its OD and the chain (which could only happen if the sprocket skips teeth) or the two pieces of chain moving across it would have to be moving at different linear velocities. This of course isn't possible with a single length of chain.
RE: Chain and sprocket Design
My idea is that the slack side tension should be enough so that there is no chain sag due to gravity, i.e. chain, cable and chain-to-cable attachment fitting weight. Does this sound reasonable?
Ted
RE: Chain and sprocket Design
RE: Chain and sprocket Design