Sprockets in a Triangular Arrangement

[evolution]

What are your thoughts on using a single piece of chain to connect three sprockets placed at the corners of an equilateral triangular? Is this feasible? I know that there will be less surface area contact between each sprocket and gear, perhaps resulting in greater stress on the sprocket, but do you think this would work?

(I did a quick search on this, but came across nothing - please lead me in the right direction if anything already exists on this. Thanks!)

[Andrew Blair]

Errmm, what exactly are you trying to do with this chain assembly?

[phrontist]

It depends on the ratio between gear radius and triangle side length...

[evolution]

Here is a visual of the sprocket arrangment. The approximate ratio between the smaller and larger gears is 7:32.

The intended purpose is to have two dewalt/CIM setups (the two smaller gears) leading to a sprocket attached to a wheel (this is the larger sprocket). Thus, rather than having two large sprockets and two small sprockets in pairs, I'm trying to see if I can get away with one large sprocket and two small sprockets.

[gburlison]

Originally Posted by evolution

What are your thoughts on using a single piece of chain to connect three sprockets placed at the corners of an equilateral triangular? Is this feasible? I know that there will be less surface area contact between each sprocket and gear, perhaps resulting in greater stress on the sprocket, but do you think this would work?

(I did a quick search on this, but came across nothing - please lead me in the right direction if anything already exists on this. Thanks!)

There are certain rules of thumb like the chain should wrap the sprocket approximately 120 degrees. These all point to the fact that the small sprocket is under the most stress. I think that you can make it work, you might have to use larger sprockets to spread the force across more teeth, or have idler sprockets push in on the sides of the triangle to cause the chain to engage more teeth. You could use stronger, heavier, more expensive sprockets and chains. Each problem has many solutions, but possibly only one will work when you factor in the rest of the issues.

This website might give you some ideas:
http://www.roymech.co.uk/Useful_Tabl...ler_chain.html


Edit: I was posting while you were posting. The small sprockets will endure the most stress. If you add an idle sprocket between them and force the chain down, you might be able to have the small sprockets engage one or two more teeth. This will spread the force across more teeth and reduce the possibility of failure. Unless you analyze the actual forces, it is difficult to know how close you are to failure.

[Andrew Blair]

It's doubtful that you would have any problem with this setup, though with the drivetrain config. I would imagine you ending up with a more obtuse isoceles triangle. However, we used a similar chain route before in our drivetrain, using #25 chain, and never had a failure. With an 10 tooth sprocket, and about 70 degrees of chain contact, we never had a problem. Not saying it can't happen though. However, as was said above, by mounting small idlers in the middle of the sides of your chain triangle, you will increase reliability and accordingly chain wrap. These idlers, if adjustable, also make it very easy to tension your chain. Which is a good thing.

[ahecht]

This is a matter of some debate, but the rule of thumb I usually follow is that there should be almost 180 degrees of wrap around all driven or driving sprockets. While your design would work, adding an idler or two would help (a) decrease the load on each tooth, (b) decrease the likelyhood of the chain skipping, and (c) give you a good place to put in a chain tensioner (since the chain will loosen as it wears).

[Rob]

That is almost identical to the concept we used to drive our arm with 2 F-P gearboxes last year. See the linked images:

http://www.joemenassa.com/Images/ROB.../IMG_5997.html
http://www.joemenassa.com/Images/ROB.../IMG_5812.html

This worked fairly well, although our arm application was low rpm, and a drive application would likely be higher. The idler pulley is key to getting enough chain wrap so that you don't skip teeth under high load. When designing your idler, be sure to make it adjustable so it acts as a tensioner as well.

Good luck with your design, and have fun!

Rob