On Fri, 1 Oct 2004 18:27:18 -0400 (EDT), Peter L. Peres <obf> wrote:
> 
> Why can't you use a mechanical latch that is armed by the load put on it ?
> Someone mentioned mousetraps. There are other ways to do it. F.ex. if the
> container is balanced on a horizontal axle (above it), then the necessary
> retaining force will be near zero regardless of its weight. Good
> mechanical design principles (I read up once upon a time) demand that you
> do not use levers with a ratio larger than 1:10 (1:20 for ball raced I
> think). So your force will have to be about 1/10th of the weight of the
> hopper unless you use an arming mechanism. F.ex. if the hopper must be
> pushed against a spring to latch it then the spring would have to push
> with 1/10th of the (reduced by lever, up to 10 times, see above) weight of
> the hopper, and your latch would have to handle 2/10ths of the spring
> force (lever again). That would give a mechanical gain of 500. Just how
> heavy is that hopper ? Finding a magnet that holds 2kg on contact and a
> solenoid that cancels it when energised is not so hard. That would allow a
> total hopper weight of 1 ton. Big enough ? Then there is fail safe, fail
> unsafe, whose standing under the hopper when someone is tinkering with the
> wiring or lightning strikes nearby etc. I like the servo motor idea better
> than a solenoid I think.
> 
> Peter

Obviously you are much more mechanically adept than I.  ;-)  I tend to think of
things in a largely electrical sense, but this is also quite mechanical.

I will look also at spring balance methods, too.  I have decided to try a servo,
to rotate a second magnet away from the first.  That should work, because
pushing magnets apart laterally is much easier than pulling them.

Thanks!

Mike H.

PS- The hopper in question will be loaded with less than 5 kg of food, so
fail safe is not so important.  It will be battery operated, so power
interruption
isn't an issue either (except when the user lets the battery die, but that's
their problem.  All I can do is make sure they're aware when the batteries
run low, and make the batteries last as long as possible!)
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