EV conversion question: disabling the CVT?

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Mike asks: I was looking at your bike and realized: Your CVT might not be working properly. Actually, I don't know if it is or not. Here's what's on my mind:My concern is that the CVT on your bike (which is different from the Motobecane) requires TWO movable pulleys to function. As the engine pulley closes, increasing the effective diameter, the tension on the belt pulls the cheeks of the driven pulley (on the wheel) apart, reducing the effective diameter at that end.With only a single pulley able to change ratio under load, would the electric motor not be subjected to varying belt tension as the bike accelerates and decelerates? I could be totally wrong about this - but as far as I've wrapped my brain around it, I thought I ought to ask.

My response:

Continuously Variable Transmissions (CVTs) on scooters have two movable pulleys -- the rear one is a simple spring and the front one is connected to a centrifugal arm. The faster the front pulley goes, the centrifugal arm forces it to become smaller. This forces the rear pulley to expand.

When the bike is at standstill, the front pulley to rear pulley ratio might be 2:1 but when it is at full speed it might be 1:2. This allows for low-speed torque and high-speed acceleration.

What I did with my EV conversion was to replace the front centrifugal pulley with a fixed pulley. This is because the old centrifugal pulley wouldn't fit on my electric motor. The end result is that I have a fixed gear ratio on my scooter (disabling the CVT) but one side benefit is that the belt is always tension properly since the rear pulley is always trying to become as large as possible.

A fixed gear on a little scooter isn't a problem as my ideal max speed is 30mph and electric motors have a lot of low-end torque. If I wanted the scooter to go 60 mph, I might try to machine the original back on, but at this point it's not worth it.

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This page contains a single entry by Karen Nakamura published on December 20, 2008 12:31 PM.

12mm flanged bearing was the previous entry in this blog.

EV questions: Metric pulley? is the next entry in this blog.

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