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

 

[Compositepro]

A counterbalace using a weight and pulley is common.

 

[desertfox]

Hi mlong4765

Can you provde a sketch of the situation and some physical sizes/ masses of the stringer etc

 

[fivechop]

Sure I can whip up a basic sceth for you, as for the exact masses of the stairs I would have to track down the exact weights and sizes, but a ball park figure would be, stairs are about 350 lbs and dimensions would be 8.5ft long 3 ft wide and side of the stringers are about 1 ft tall.

 

[fivechop]

P.S I forgot to mention the platform is mounted on the front of a piece of mobile mining equipment

 

[fivechop]

Here is a link to a quick sketch, let me know if it doesn't work

http://picture.vzw.com:80/mi/773703...345,345&outquality=56&ext=.jpg&border=2,0,0,0

 

[desertfox]

The link doesn't work for me

 

[hydtools]

Make the stair a ladder that moves in a vertical plane like the bottom portion of a building fire escape. Like compositepro says, counter-balance it.

Ted

 

[fivechop]

Ok ill copy and paste it from my computer

 

[fivechop]

So far theese are good suggestions guys, thanks

 

[fivechop]

Try this link for the sketch @Desertfox

 

[fivechop]

I like the idea of a counterbalance system but I was hoping to find something a little more rigid, I'm not sure how that would work on a piece of equipment that travels up to 30 mph through rough conditions.

 

[dhengr]

Don’t most of these have a fixed stairway to within about 3 or 4' of the ground, then a flexible hanging ladder which can bend out of the way if it hits anything near the ground? My guess is that these are made up of treads which are attached to two very heavy pieces of cable, as stiles, so they are not too flexible as a person climbs them, but will bend out of the way if they hit something. Then fixed hand grabs (grab irons) can be reached from the ground for climbing these first 3 or 4 steps, and transition to the fixed stairway.

 

[MikeHalloran]

I can't see a cable/counterweight system surviving long on what appears to be a mining truck.

I'm thinking a torsion bar on or near the hinge line to balance most of the weight of the deployable stair, with a gas cylinder or two to fine tune the force required to lift it manually, and a sturdy latch to hold it in the stowed position.

I'm guessing the torsion bar will need to extend behind the plane of the paper for a fair distance, i.e. along the frame horn for a couple of feet.





Mike Halloran
Pembroke Pines, FL, USA

 

[fivechop]

@dhengr. What your referring to is a typical step used on heavy equip/ haul trucks, this ladder system was designed to eliminate that step and make an easier mounting process, the ladder system works great, but for reasons I can't mention the mine manager wants to replace the powered system with a manual/ un-powered system and that is my dillema

 

[fivechop]

@Mike Halloran. That sounds like a viable solution, and is similar to what I had in mind except I left out the torsion bar and instead had just a torsion spring system, I just wasn't sure how much force would be applied to the stairs on the return cycle. Is there a way I can latch the stairs in the down position and initiate the return cycle by simply unlatching the stairs or am I going to need some manual assistance with raising the stairs

 

[MikeHalloran]

I suggest some caution about implementing anything that moves when you unlatch it, because someone will find a way to get hurt when it moves. ... and they will have no trouble finding a product liability lawyer.

Regardless, you are ahead of the game if you have a suitable stair already designed. Given its weight, CG, and geometry, it's a relatively pleasant engineering exercise to work out the forces and torques required to move it over its range of rotation, either graphically or with Excel or whatever numerical hammer you have.

Actually, since you probably already have a physical stair available to mess around with, it might be quicker to mock up the truck's landing platform, and alternate design sessions with physical hacking sessions, measuring what happens and raiding the local junkyards for parts. Work fast, but be careful.






Mike Halloran
Pembroke Pines, FL, USA

 

[fivechop]

Thanks again for the advice Mike, I think I will move forward with this design and see where it takes me, i'll post the end results later.

 

[zekeman]

I vote for the counterweight idea.

The problem with the torsion spring or bar is that you reduce your input energy by only 1/2 . Ideally the counterweight is theoretically much superior; you fight friction only.

Perhaps a little more thought should go into this before you discard it.

 

[TheTick]

Start with a graph of force (if linear motion) or torque (rotational motion) vs. position that must be counterbalanced. Superimpose a graph of the input provided by the counterbalancing system.

Springs work well for linear systems. A garage door is a great example of this, where the weight diminishes linearly as the door opens.

Counterweights work best for rotating systems, as they match the non-linear (sinusoidal) function of force as the system goes through its range of motion.