Pneumatic lift system

[bahndo]

I am getting to the point of my camper design to start nailing down specific components. I have moved in the direction of a hard sided pop up, very similar to Sonke's ************ Land Cruiser. For the lift mechanism I am leaning towards a pneumatic system for the reasons below:

1) I will have an OBA system (I also need to spec it out so if it is going to lift the roof I need to know that first)

2) Length of travel is in the 32"-35" range

3) Speed of operation

I originally thought of going with an electric actuator but they are way too slow for the amount of force and travel required- the ones I have seen are in the ~.5"/sec range, a snow load on the roof could be as heavy as 700#'s, the section of roof will be around ~250# so they need to be able to supply at least 250 lbs of force each, I'll probably shoot for more like 500 lbs each in case I put anything else up top and in case there is any friction encountered. A hydraulic system sure seems like a good call but if I already have air why not go pneumatic? Does anyone have one? For those with hydraulic why did you go that route? The pneumatic system I have been piecing together with cost somewhere around $1500 with everything including a remote system. I think this is comparable to a hydraulic system cost wise but I don't have a system just for the roof lift. I am shooting lift time of 5-7 sec. that way if I want to get in to grab something I can just "pop" it up and be done with it. Thoughts?

-Bahndo

 

[JRhetts]

You might want to take a look at the lift system described by westyss in this thread:
http://www.expeditionportal.com/forum/threads/48351-out-with-the-old-in-with-the-new

He seems to have sorted out how to do a great job with an electric system.

 

[bahndo]

I looked at Yves system and yes it looks great but those actuators are s-l-o-w. I find it hard to belive that no one has actually tried a pneumatic system. I guess this can be my opportunity to try to add to the wonderful information on this site...
-Bahndo

 

[ThomD]

Pneumatics have been done. Behold my favorite custom camper.

http://www1.ttcn.ne.jp/~gyo/English/index.htm

 

[JRhetts]

ThomD

Thanks so much for that link. I remember seeing the vehicle in still photos a number of years ago. What fun to see the animation!!

John

 

[cwsqbm]

I've worked with pneumatic cylinders in other applications, and one thing is that they can be difficult to get to move smoothly. With less pressure than is required to lift the roof, nothing will happen. With more pressure than necessary, the roof accelerates quickly until the cylinder has increased in volume enough so that the pressure isn't enough to lift anymore. You end up having to play with flow restricters, but its difficult to get it right as pressure on the input side of the restricter won't be constant without some additional components too. By the time you get it smooth, you might not be any faster than with linear actuators. The other problem is if you have more than one cylinder - synchronizing them requires some mechanical device such as what sarconcepts did with his build.

Hydraulic doesn't have the same problem because fluids aren't compressible like air - pressure flucuations in hydraulic fluid won't cause an uncontrolled acceleration as long as the volume of fluid remains constant.

 

[JRhetts]

you might also contact mike hiscox, a member of this forum, about how he implemented his air/pneumatic lift on his former EarthRoamer JP. his great re-built thread [ http://www.expeditionportal.com/forum/threads/51254-EarthRoamer-XV-JP-quot-Northwest-Edition-quot ]does not go into very much detail on this aspect of his project.

 

[redneck44]

Dual action cylinders. Manifold the supply, 1 in 4 out, to each cylinder (assuming 4 cylinders) likewise the return. Flow restrictors on the exhaust (not the supply) of your 3 way valves, one valve on each of your manifold supplies, this way you don't have to "balance" all 4 actuators separately. Suggest you fit a mechanical lock when in the up position in case of an air leak.

 

[herm]

hydraulics would be much easier to control. you could even do air over hydraulic. an air operated ram that has enough volume to push fluid to your 4 lift cylinders would be very neat. I have designed a few pneumatic and hydraulic systems, the hydraulic systems usually turn out much easier to control and tune.

 

[mhiscox]

you might also contact mike hiscox, a member of this forum, about how he implemented his air/pneumatic lift on his former EarthRoamer JP. his great re-built thread [ http://www.expeditionportal.com/forum/threads/51254-EarthRoamer-XV-JP-quot-Northwest-Edition-quot ]does not go into very much detail on this aspect of his project.

Not too much information because it was pretty straightforward: The two cylinders used are from Peninsular Cylinders in Roseville, Michigan. They have a two inch bore and a 45 inch stroke and are manifolded together. There's much additional specification at http://www.peninsularcylinders.com/. We thought that straight pneumatic was the preferred system, especially given that we already had a capable onboard air system. Plus we were concerned about the potential for leaks of hydraulic fluid in inaccessible areas.

I've worked with pneumatic cylinders in other applications, and one thing is that they can be difficult to get to move smoothly. With less pressure than is required to lift the roof, nothing will happen. With more pressure than necessary, the roof accelerates quickly until the cylinder has increased in volume enough so that the pressure isn't enough to lift anymore.

This is an important point, but it has not proven to be a big problem in actual use. When the air-to-roof switch is first pressed, nothing happens for a second or two, and then the roof rapidly goes up. Assuming you're paying attention, letting loose of the switch stops the roof raising at something between 30-60 percent of full travel. From that point on, it's easy to move the roof up to the optimal point by a series of quick touches on the switch. It's not idiot-proof, but thirty seconds of training is enough to develop sufficient proficiency.

As i said before the interior was installed, the "struts are proving to be great . . . smooth and lightning quick." That's still the case, and they are one of the best things about our redo of the XV-JP.

 

[redneck44]

This is an important point, but it has not proven to be a big problem in actual use. When the air-to-roof switch is first pressed, nothing happens for a second or two, and then the roof rapidly goes up. Assuming you're paying attention, letting loose of the switch stops the roof raising at something between 30-60 percent of full travel. From that point on, it's easy to move the roof up to the optimal point by a series of quick touches on the switch. It's not idiot-proof, but thirty seconds of training is enough to develop sufficient proficiency.

As i said before the interior was installed, the "struts are proving to be great . . . smooth and lightning quick." That's still the case, and they are one of the best things about our redo of the XV-JP.[/COLOR]

Are you using dual action cylinders, if so then manifold the exhaust ports and fit a flow restrictor this will smooth things out and slow things down, adjustable to your taste
A UK based supplier http://uk.rs-online.com/web/c/pneum...-flow-regulator-restrictor-function-fittings/ but I'm sure you can find the same in the U.S.

Fit them to the lift side as well for a nice smooth lowering of your roof.

They give full flow to pressurise the cylinder and restrict on the exhaust.

I've built and maintained high speed packaging machinery and they are used all over the place for timing and to stop the equipment shaking it self to bits.

 

[mhiscox]

Are you using dual action cylinders, if so then manifold the exhaust ports and fit a flow restrictor this will smooth things out and slow things down, adjustable to your taste
A UK based supplier http://uk.rs-online.com/web/c/pneum...-flow-regulator-restrictor-function-fittings/ but I'm sure you can find the same in the U.S. Fit them to the lift side as well for a nice smooth lowering of your roof.

Thanks for this advice. At the moment, the current system works well enough that there's no motivation to take the camper interior apart enough to get at the cylinder connections, but if and when that happens, we'll make the modifications you suggest. I appreciate your expertise.

 

[bahndo]

Thanks for all the input, there is tons to learn about this stuff. I have been talking with a co-worker about it and he is pretty keen on working on a feedback loop (turn our own PCB with an MSP running the show) to really tune the speed. It certainly would be the "trick" way to do it, but I'm not sure how complicated I want to make the system. A thought I had was to use a plain old ball valve and control the speed manually, ie: crack the valve and open further/faster as needed. Sure would be simple...

 

[bahndo]

Are you using dual action cylinders, if so then manifold the exhaust ports and fit a flow restrictor this will smooth things out and slow things down, adjustable to your taste
A UK based supplier http://uk.rs-online.com/web/c/pneum...-flow-regulator-restrictor-function-fittings/ but I'm sure you can find the same in the U.S.

Fit them to the lift side as well for a nice smooth lowering of your roof.

They give full flow to pressurise the cylinder and restrict on the exhaust.


I've built and maintained high speed packaging machinery and they are used all over the place for timing and to stop the equipment shaking it self to bits.

I order a pair of these regulator valves (not sure if that what they're called, but seems to be what they do) and 4 cylinders, double acting. Should be a couple weeks before it all shows up but I'm psyched to ge the stuff on the bench and play with it. The actually shell design is about 90% there and the build method layed out. I will be doing some tests on layup to finalize it but I hope to actually start building by the end of Oct.!!!! I'll start an actual build thread for that to try an leave this one dedicated to the pneumatic system.