Dynamic chain loading in multi-pilot drivetrains

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Joined: 27 Dec 2011, 12:01 pm

Dynamic chain loading in multi-pilot drivetrains

Post by DrDiabolical »

Good news:
My new 4-seat tricycle survived its first public trial - a 1-1/2 mile parade last Saturday. That may not sound remarkable, but the parade route is a 3-6% uphill grade for its entire length! Our loaded weight with pilots was over 1,500 lbs and average speed was around 2 mph. That's the equivalent of pushing a 60's Volkswagen uphill for 45 minutes.

During the ride, we experienced something that I hadn't anticipated. Oscillating dynamic loading of the chains. My machine has two independent drivetrains. One per side, each turning its own wheel. In each, two pilots are seated in tandem. Each pilot powers a standard bicycle style setup. Each of those is connected via fixed sprockets and chains to a jackshaft. The jackshaft then connects to the axle 1/2-shaft with fixed sprockets and a #40 chain.

While riding, the power impulses from the pedaling pilots were not synchronized. That caused the jackshaft sprockets to load and unload several times per rotation as each power impulse tried to speed up the jackshaft. The problem occurred as each power impulse caused the input chains to tension and slacken. When one pilot applied power, the other's input chain would momentarily go slack.

This problem was absorbed by a good chain tensioner in the left drivetrain. But the right side wasn't applying enough pressure to soak up the impulses and let the long forward chain whip a little too much. The result was a chain that jumped off the sprocket. No big deal in this ride. But definitely something to pay attention to and keep in mind when building.

Dr. scott Diabolical
evil genius
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Joined: 17 Apr 2013, 9:45 am

Re: Dynamic chain loading in multi-pilot drivetrains

Post by Rayray »

A very simple and inexpensive way to reduce long chain whip is to use narrow, think 3/8, pvc pipe to put chain inside. Experiment with length and positioning. A tension spring or two will keep it in line.
Got this idea from Kinetic Bill.
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Joined: 11 Jan 2011, 6:23 am

Re: Dynamic chain loading in multi-pilot drivetrains

Post by crazydave757 »

Another method of chain management is to place a chain guide as close to the input and output sprockets as possible at the point where the chain comes onto the sprocket. The guides should have slots cut in them only as wide as the chain and no wider. The guides should be made from a thick nylon cutting board and/or piece of hardwood. By placing guides as close to the sprockets as you can you will essentially eliminate all possibility of the chain having enough play to come off the sprocket as it has no opportunity to become misaligned. Care must be used in positioning the guide so its guide slot is centered on the sprocket. If the slot is a little tight it will wear in as you pedal. You can also mount a large turnbuckle between the two sprockets so flex in your frame and pedaling apparatus will not cause variation in the distance between your two sprockets. By eliminating flex and derailments you can pretty much eliminate chain problems. See attached image of my human powered watertcraft illustrating these concepts in action.
Chain Guides & Turnbuckle
Chain Guides & Turnbuckle
Chain Guides.JPG (76 Bytes) Viewed 50630 times
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