Springs, Bungees, Counterweights

[Rick TYler]

I've been watching this board for a couple of weeks and haven't seen a proposed design for an arm that uses either a counterweight or a spring system on the arm itself.

The problem with a counterweight, of course, is that if it is mounted on the arm it raises the CG and does not contribute to the other functions of the 'bot. I suppose the counterweight could have been mounted on a 1/2-height tower using a 2-1 pulley-and-cable system, but that would be clumsy, still add weight up high, and only apply half the downward force as a weight connected through a 1-1 purchase. Of course, if there were a backwards-extending arm just as long as the main arm, you could hang a fairly small weight on the back (see construction cranes). You would still have the high CG problem.

If you committed to a backwards counterbalance arm as long (or almost as long) as the main arm, you could use bungee cord material or a spring to store energy when the arm is descending that could be used to help lift the arm-and-tetra. There are some issues to be solved regarding the effective length of a spring and whether it could be used over the effective length of the arm's motion, but there are ways to work around this. A spring-over-shaft design, sort of like a roll-up garage door spring, might work pretty well.

If you think about it for a few minutes, it would be trivial to design a counterbalance that could be extended automatically after measurement.

Anyway, our team rejected the concept of counterbalancing forces (grumble, grumble), and went with a straight lifting arm system. I am curious if anyone is planning to use this sort of stored energy (smart teams), or considered it and rejected it. Talk amongst yourselves.