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• # CVT Design

Discussion in 'Calculations' started by Staedtler787, Feb 12, 2012.

1. ### Staedtler787New Member

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I'm working on a CVT transmission for a bicycle. Does anyone know how to calculate the forces involved in a CVT? Obviously it will be much different than one you would find in a car, so I don't think it would hurt to run some calculations before I get too far into it.

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3. ### akshayMember

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Well it depends on the design you wanna use. I think you gotta know what your torque requirement is, then see if the CVT can transmit that much torque without slipping. Next comes how you want the gear ratio to change with speed, how to actuate depends on the design. The concept used in cars is to match the ideal traction curve(tractive force reqd. at particular speed or acceleration) with the CVT. But I think in case of bicycles, comfort of rider has to be taken into account. So better see what torque range is fit and comfortable for the rider, actuate the CVT ratio changing in that range. Never did any such thing with bicycle. Correct me if I'm wrong.

4. ### VirguleActive Member

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Is your transmission belt driven?

If so, I could give you basic belt drive theory.

5. ### Staedtler787New Member

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yes its belt drive, I would appreciate it very much.

6. ### VirguleActive Member

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Ok here it is.

(direct link : http://i1189.photobucket.com/albums/z434/Virgule99/Belt drives/Pulley_belt.png)

This is just the basic theory. You'll have to adjust it to your system. Also, the design process will have to take a few things into account, so these formulas aren't exactly a step by step guide. There are also tons of other factors you want to check ; slip, number of pulleys required, strength of belt, number of teeths if any, efficiency of torque transmission, ...

If you have a CVT, I guess the radius of one of the pulleys will change so you'll have to take that into account. Also, keep in mind the length of the belt will stay the same, so a change in radius will affect other parameters.

If you think of doing a direct contact CVT, some of this applies but it would be more useful to look into basic gear transmission theory. Let me know if I can help further.

Last edited: Feb 14, 2012
7. ### VirguleActive Member

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Correction :

V is the belt velocity, not V^2
sin-1 is really asin ; sin-1 does not equal sin^-1

Last edited: Feb 15, 2012