Ratchets

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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.