Help with potential energy quandry 3

[fivechop]

Hi everyone, I have a problem to solve, imagine your standing on a platform 7 ft in the air and the only way to get to the ground is a stair stringer that raises and lowers in front of you rotating on an axis on the end of the platform on which you are standing. In the raised position the stair stringer is perpindicular to the platform and lowered it extends to the ground. Now here is the problem; the stairs used to be raised and lowered with a hydraulic pump system, now I am faced with the task of moving it with a non powered system ie. Torsion springs or some other means of stored energy. What I need to know is if there Is a method that I could use to lower the ladder and store enough energy to facilitate its return with little or effort. Any help or guidence would be greatly appreciated. Thanks

 

[rb1957]

a couple of thoughts ...

1) you show a single staircase deploying. maybe it's just a sketch, but i'd suggest using a double folding staircase ... ie one stage deploys, anf then 2nd (folded onto the first) deploys, this'd reduce the stowed height; but maybe you've already thought of this (deploying only 1/2 the staircase ?)

2) instead of unpowered, maybe a simple mechanical system with a lot of advantage ?

3) how are you going to inter-connect this with the truck ? presuably you don't want the truck moving with the stairs down ? presumably a sticker to this affect would be treated with the utmost distain by your operators ? so you need an interlock, presumably with the transmission, yes?

4) it looks as though it would be convenient to hide the counter-weight under the fixed staircase.

 

[MikeHalloran]

Dhengr mentioned a cable rail ladder. I have seen short ones on bucket trucks here. It looks like the cable is plenty stiff, but a person cantilevered from a rung necessarily bends the cable inward, so the ladder rails assume some curvature, which has to make the ladder into a serious knee-knocker. ... not something you'd want to climb regularly.

But suppose you made a cable rail _stair_? I.e., use two or four cables, mounted at a slant, with steps level, or level as could be. ... or one pair of vertical cables per step, cables of stepped lengths in an array.

Or, this might involve payments to the patent holder, a Lapeyre Stair using a single fat slanted cable as its backbone?



Mike Halloran
Pembroke Pines, FL, USA

 

[hendersdc]

I have seen something similar on the back of the Marine Corps 7-ton trucks (MTVR). As rb1957 suggested they fold in half. It is a completely manual design. A quick google search did not come up with any detailed drawings of the ladder but it is worth looking into. This link shows a picture of what I mean, see the truck on the left.

Link

Doug

 

[zekeman]

Maybe RB idea of folding stairs might work if keeping the CM of the folding setup fixed vertically so that the PE remains constant , which solves the problem, but you need a mechanism like a scissor jack to implement it .

The key is keeping the CM fixed vertically, which is less demanding than keeping t fixed ( as in a counterweight setup.

 

[zekeman]

Or simply just rotate the stair with a folding counter "stair " link of equal weight that rotates opposite using a pair of meshed pinion gears at the fixed pivot.
Now you have the PE fixed and all you need is a handcrank to rotate one of the stair pieces, just overcoming friction.