Two toothed ratchet prototype

Mon, 2 May 2011

Further experiments with ratchets. With only two teeth on the ratchet gear I can make a model with a character in two states. Up, down. Stand, sit. Eyes open, eyes closed. There are other ways to achieve the same effect, this is prototyping for the sake of the interesting mechanism. 

A two tooth ratchet turns 180º for each cycle. I need two pawls, one that drives the gear round, the other one that holds the gear still on the return stroke. Space was short on the original prototype, there was room for only one pawl. To get round this I added a second ratchet gear to the same drive shaft and added the second pawl this gear.  

I've used a pull tab to move the drive pawl back and forth. This has worked well with the five tooth and three tooth prototypes I had made earlier. With the two tooth model it didn't work so well. The problem being that as the tab wrapped around the pawl housing is reached a  point where it left the surface of the housing and stopped moving it round. To overcome this problem I added a curved support to hold the tab into position against the body of the pawl housing. It seems to work. I now have a working prototype in need of some tidying up. Next step is to re lay all the parts and try out an updated model. I also need to add some way of limiting the movement of the pull tab.