Low Tooth Count Ratchet Prototype

Sat, 23 Apr 2011

Further research and development on ratchet driven project. I had made a five tooth and three tooth ratchet which I am trying to drive. Lower tooth count wheels have their own set of difficulties. If you look at the three tooth wheel above you'll see that  a pawl pulling from a fixed point to one side would soon loose grip on the tooth before the wheel has turned the required 120°.

To overcome this I've made the pawl move round with the wheel. Instead of being fixed in one place to the side of the wheel, the pawl is mounted in a housing which moves round the same axle as the wheel.

With the housing complete it works like a treat!

This whole assemble fits inside a box with a secondary pawl stopping the wheel turning backwards. 

Initially in this experimental model, I have attached a long tab to the outside of the pawl housing which threads through a hole in the box top. By pulling the tab up and down I can make the wheel turn in third turns.

As you can see in the picture above, the long tabs has quite a range of travel moving up and down by over 50mm. I could link the long tab to a crank so that by turning a handle on the crank the main drive wheel turns at one third the rate or I could use it as it is it a handle protruding through the box top. 

The same mechanism works just as well with a five toothed wheel with only a few small changes. This mechanism has all sorts of possible uses as a starting point for different character based projects. I'll put the parts together into a download so that members can have a go.