[concrete_joe]

hi all,
this project ties to my Spa project (see http://www.diychatroom.com/f49/spa-208358/)
but this one deserves its own thread. gonna be building a rolling credenza for my backyard and will have TV, stereo, cd/dvd, wifi, all 100% wireless. yep, designed to run at 200watt for 6hrs on lithium batteries !! sounds crazy, but thats the type of projects i do. the TV will also be on a lift, so it hides inside the credenza when not in use. i recently got a 43" visio from B&H on sale, so got a good deal on that item. TV lifts are way to much $$$ to buy, so i am making my own. to buy a lift is around $500, but as of now my working pneumatic has only cost me $35! granted, i need some peripheral items to make the lift function, but probably less than another $100 for that. i could not find any cots pneumatics of the size and price i need, so i made my own pneumatic cylinder out of 3/4" pvc. this is literally the 1st step in seeing if my idea can move forward. i made the piston in CAD and had my machine guy carve it up for me in 6061 AL. its a dual o-ring design, the upper is more of a wipe than it is a seal, but this 1st test proved promising. i need about ~25lbs of lift to get TV up (TV weighs just 22lbs). my 1st test was to see if i could generate some force using compressed air, and yikes, this thing can certainly create some force. i wedged it between my shipping scale on table and a fixed shelf, and with not much air at all the thing was into 60lb area w/o blowing the seal(s). i need to now take it into phase-2 of testing to see 1) how much psi do i need to lift ~25lbs (ez to calc, but there's some drag due to o-rings, etc), and 2) once pressurized i need to see if i can hold it at that psi w/o leak-down, and 3) can pneumatic work 100% in a operating temp of 25-110F. not that ez, but a challenge i am up to.

 

[concrete_joe]

why is this site so slow, and full of bloat ads, really a drag trying to view stuff here....!

anyways, test #2, to see if my piston can hold psi. so far so good, holding at 75psi for last 30min, will check it again every 30min.

 

[concrete_joe]

cool thing about DIY, if you need a tool just make it. i needed a very thin wall socket to screw this air fitting into the inside of a pvc fitting, so i made it. basically heated the end of thin wall copper pipe and tapped the fitting in with a hammer to form the socket, and voila, i have a socket that fits.

the small sintered bronze muffler serves two purposes, one to keep crap out of the cylinder, and two to help slow the airflow some, it actually may be too restrictive but i made two full size 24" stroke cylinders for testing, one with and one without the air muffler.

another gotcha when using std PVC stuff is that PVC dimensions are not that straight or concentric. i found that the 1" fnpt caps i am using the threaded section is not exactly coaxial with the center of the cap.

i have all of the pneumatic components. 6port manifold, solenoid valve, digital pressure switch, safety cutoff switch, one way valve, and the air pump. i still need to build the electronics that run it all, but its literally looking like 9 discrete items. i found the inverter i need to run 200watt continuous, but i need to find batt and batt charger.

 

[r0ckstarr]

Very interesting. I'm curious to see the final assembly. What will supply air to your lift? Are you going to have an air tank hidden inside that you can refill with an air compressor?

 

[concrete_joe]

i have a mini/micro sized 12vdc air compressor. i did think about a holding tank by that would be pumped up only when the unit is plugged in to 120ac for recharging, but thats another component that can fail and it makes the overall system more complex.

the full size air cylinder is built, and i have all the the pneumatic items needed to run the show, just need to build the electronics (~9 parts).

i am however stuck on a telescoping rig that this cylinder will lift. i am think 3 pieces of something, each 18" in length, the 1st stationary while the other two telescope up off the 1st, this gives me a full 36" of lift, but to remain stable there needs to be some overlap, so lifting just 24" high keeps some overlap. any ideas for telescoping rig??