Ratchets

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Copyright 1996, 2000, Denis Cousineau

 

Ratchets

A ratchet is a device where a rotation is transfered if it is turning in a certain direction and not otherwise. A double-acting ratchet will transfer clockwise rotation to the output A and counterclockwise rotation to the output B. There exists three possible state for the RCX, OFF, forward, or backward. The following table summarize the expected behavior of the ratchet:

  Outputs are 
RCX outputs    A      B  
0 0 0
+1 1 0
-1 0 1

The ratchets are limited because they can't control the outputs A and B in any possible combination. More specifically, they can't choose the direction of rotation of the output. On the positive side however, ratchets react fast and are easy to program.

Implementing a ratchet (double-acting ratchet):

 Using electronic circuits: Again, probablity the best option, because there is no friction (and almost no loss of current), and also because the reaction time is instantaneous. This page describe a simple electronic device that implements a ratchet.
 Using mechanical circuit: In terms of mechanics,  ratchets are very easy to built using LEGOs. See for example the following page.