Bill wrote:
The old man wants to put a 'dumbwaiter' into the barn so he can get
'stuff' up to the second story easier, he's getting old (79) and walking up
stairs is getting harder so I've been kicking plans around and want to see
if anyone could help with a detail I haven't worked out yet. I'd like to
make it that the 'dumbwaiter' gets locked in place when on the second
floor, was thinking of something like pawls on the guide tracks that the
carriage would click by so if the 'dumbwaiters' hydraulics would fail then
there would be no way for it to fall. This way if you are loading a couple
of hundred pounds on it it can't suddenly drop taking your arms, legs or
feet with it, although since I'm planning on hydraulics it would take a
really big failure of the cylinder to get that fast a drop. What I'd like
to do is make it that the 'dumbwaiter' would have to be raised a few inches
before going down to disengage the pawls but I'm not sure how to go about
designing it to do this. I could do it with a solenoid but I think that
adds another failure point and would rather have it be all mechanical in
nature. I'm not worried about a failure while ascending or decending since
the failure mode would be a slow descent as the fluids bleed out, so I
don't need pawls all the way up the guide rails just at the 2nd floor.
Anyone ever seen something like this and could point me in the right
direction??

Put the moving part on the track, the dumbwaiter carriage lifts them as
it passes, If the dumbwaiter side is c-channel, when they pass the top
flange a limit switch fires a lamp and you stop and lower to lock. To
lower the dumbwaiter, go up until they fall free, then roll down right
over them.

I saw a very interesting dumbwaiter design once that used a hose sitting
on the top of the lifting rail, a wheel pair around the track squeezed
the hose flat, as water or air was added to the bottom of the hose, it
inflated it, forcing the wheel to roll up the rail.

Stuart