Friday, February 25, 2005

How to get state uphill

"But," I hear you thinking, "Gravity-driven balls are all very well and good for calculation, but at some point you're going to have to bring the results back uphill for storage." Yes, that's true, but I've got it all figured out. I'm going to do it with mirrors pulleys.

In fact, I may even use several kinds of pulleys.

In the traditional pulley, two wheels are forced to move in lock-step by a loop of cord that goes completely around both of them.

We can make a similar pulley system that has pretty much the same behavior by using two rods, and connecting the ends of each to the corresponding ends of the other with 2 separate strings. It doesn't have quite the range of motion of the traditional pulley, but I expect that it'll be enough for my gates, which require only 60° of rotation.

However, if we remove one of the strings, we get more interesting behavior. For example, in the below diagram, the lower pulley can tip the upper one to the right by tipping to the right itself [thus pulling on the cord], but can't force it to tip to the left.

Likewise, the upper can tip the lower to the left, but not to the right.

In bcd, I allow pulley connections that represent either double-corded pulleys or one of the two single-corded possibilities. However, rather than think of them as left-connected or right-connected pulleys, I describe them in terms of their actions in relationship to the gates to which they are connected. That is, when do they send a signal [tug on a cord], and what do they do when they receive a tug?

The three types of pulleys are therefore:
  1. S or SOSROR [Send On Set, Reset On Receive]

  2. R or SORSOR [Send On Reset, Set On Receive]

  3. D or DOUBLE [Send On Toggle, Toggle On Receive]

Obviously one can't connect a D pulley to an S or R pulley, but an S can connect to either an S or R, and vice-versa.



Blogger WisTex said...

You could use smoke and mirrors in addition to pulleys. ;)

7:10 AM  
Blogger WisTex said...

You could use smoke and mirrors in addition to pulleys. ;)

7:10 AM  

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