Are there any gears made that can directly drive a cog?

Specifically, there should be a rounded "flower" gear that could interface directly and reasonably efficiently to a bike cog. However, I cannot find any examples of this.

  • It sounds like you are trying to connect a motor directly to the freewheel. Everything I've seen either has the motor in the hub or connects the motor to the freewheel using a chain. Cogs on a freewheel are specifically designed to work with chains - as RLH said. – David D Apr 17 '19 at 17:49
  • I'm sure it's been done, but, as RLH suggests, they are mechanically impractical for sustained use. – Daniel R Hicks Apr 17 '19 at 18:12
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    I'd like to see a picture. – David D Apr 18 '19 at 1:43
  • Whether this is a good idea or not remains to be discovered, but here's an example of a cog that mates with the shape of teeth on a bike - youtube.com/watch?v=-9gQ1KRhesM – Michael Teter Apr 26 '19 at 21:52

These cogs are very unlikely to exist. A proper gear-to-gear transmission uses an "involute" tooth profile, which is shaped so that the gears maintain a constant relative rate of rotation. A side effect of this design is that the tooth surfaces approximately roll against each other. The flower-cog pairing would have a large amount of slip (and thus friction/wear) between the teeth as they move past each other.

The inner rollers on a bike chain are there to provide a rolling contact between the chain pins and the cog teeth. It might be possible to design a mechanism with a set of rotating round "teeth" attached to a carrier-cog, but this greatly increases your engineering complexity.

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    Actually involute gear teeth do rub against one another. Their critical property is constant ratio of angular velocity - that is of the driving gear has constant angular velocity, so does the driven gear. The 'flower' tooth profile would work but it would introduce a lot of vibration into the motor. See en.wikipedia.org/wiki/Involute_gear – Argenti Apparatus Apr 17 '19 at 17:51
  • Thanks. Edited. – RLH Apr 17 '19 at 22:45

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