Mechanical engineers... I need some help

[Mrvile]

Hey all,

For a project I'm working on for school I basically need to come up with a mechanism that can move a somewhat heavy load (up to 50lbs) up and down on a rail rather effortlessly, and stay in place at any point along the rail, without breaking the bank. I looked briefly into balanced tension springs, like on articulating lamps, and their variations (hydraulics, pneumatics). I also noticed that many hardware stores sell pneumatic door openers for pretty cheap, so I figured I could use those.

Can anyone school me on how I would actually go about getting this to work correctly, or why it wouldn't work at all? Are there any alternatives?

Thanks!

 

[Patranus]

Should get you started.
http://www.btinternet.com/~jhpart/stairs1b.htm

 

[PottedMeat]

I'm not a ME but could you use ACME screws on a linear slide?

You can get 3' and 6' lengths of screw threaded rod cheap. Usually they're used for mill/lathe repairs.

When you say 'up and down' do you mean vertically or horizontally or both?

What's the travel distance?

What's the speed required?

 

[Sukhoi]

Yeah need more info on layout, but a power screw would be a pretty good idea.

 

[Mrvile]

Sorry, more details.

The motion is just vertical. Distance travel should be about 3 ft or so. Speed should be pretty rapid, be able to cover the 3 ft within a few seconds.

 

[Mrvile]

Power screw would be too slow, and I prefer not to have any electronics involved. I want the motion to be possible through just lifting the weight with arms/hands.

 

[Mrvile]

One last note. Some examples I was looking at are things like car trunk doors, manual garage doors, balanced arm articulating lamps, etc. That's the type of motion I'm looking for.

Thanks!

 

[PottedMeat]

Power screw would be too slow, and I prefer not to have any electronics involved. I want the motion to be possible through just lifting the weight with arms/hands.

is the load variable - are you being asked to haul a bunch of different stuff? Maybe pulleys + counterweight would be easy.

 

[Mrvile]

is the load variable - are you being asked to haul a bunch of different stuff? Maybe pulleys + counterweight would be easy.

Load should be pretty constant. I said "up to 50lbs" because I'm not sure exactly how heavy it will be yet.

Pulleys + counterweight seems like a good idea, I just figured those pneumatic door things are simpler and more compact as the mechanism is packaged into a relatively small tube.

 

[Bignate603]

Load should be pretty constant. I said "up to 50lbs" because I'm not sure exactly how heavy it will be yet.

Pulleys + counterweight seems like a good idea, I just figured those pneumatic door things are simpler and more compact as the mechanism is packaged into a relatively small tube.

Those gas springs in doors change the force they provide depending on the distance they are extended while a pulley/counterweight system would maintain the same over the complete range of travel. As long as the load would only vary through a small range and the direction remains constant it's a very good way of doing it.

Additionally, it could be difficult to find the gas spring with the amount of force that you need. For a pulley/counterweight you just change the weight until it is the amount of assistance you need. It will be cheap and easy to get it to work perfectly.

As for it stopping right where you want it to, you can use almost anything as long as the load is light. If the load is well balanced against the counter weight you could even introduce a small amount of friction into the system that is enough to make it stick at whatever point you want.

 

[LordMorpheus]

if the load is known and doesn't change, a counterweight system will be good.

Even if the load changes some, if you counterweight it based on the expected load, with enough damping that it won't run away from you if it's underloaded, it should be fine.

 

[Modelworks]

Problem with counterweight is the unknown load . One thing you could try really easily is elastic bands. Get some rubber bands and play around with it. Some type of elastic might work well with varying weights because you could use multiple strengths depending on the need. One above and one below gives a nice counterweight like performance without the weight.

 

[Triumph]

Without any further helpful descriptions of the problem statement, counterweights are the clear answer.

 

[Bignate603]

Problem with counterweight is the unknown load . One thing you could try really easily is elastic bands. Get some rubber bands and play around with it. Some type of elastic might work well with varying weights because you could use multiple strengths depending on the need. One above and one below gives a nice counterweight like performance without the weight.

He said the load wouldn't vary much. Elastic bands may not work well for the same reason that gas springs could be difficult, the force they provide varies greatly depending on the amount of extension. You would get a great deal of force when the band is stretched farther and far less when its more relaxed.

 

[Greenman]

Just get a pony and be done with it.

 

[lxskllr]

You could use some kind of scheme when forward momentum stops, the load rocks back slightly from vertical, and engages a wedge that pinches the rail. A lot of that would depend on the exact setup though.

 

[iGas]

Counter weight pulleys or a fulcrum with counter weight (or sliding counter weight).