Active alternating air cushions???

[MichaelB]

Alternating works on my mattress and should on a cushion. I'd prefer to have a high cell and as many as possible with short change times but not easy to find. I have lost weight and that is part of the problem, use my FES bike almost every day to try and keep some muscle but can't do that with a sore which is when I need it. Got no choice on hoist C3 tetra vented as well.

[stevelawiw]

Are you building your pump from scratch or buying one of the shelf? Any idea of where I can buy a replacement pump from?

[Burgerman]

China...
Or at silly cost the same place my cushion came from. Mine is not the pump in the picture. They have a newer quieter more expensive one...

Yes if I have any trouble I will build a pump. Was going to anyway, but this one is already diaphram and quiet. And probably not cheap. *Takes so little current that a simple voltage reg chip at 12V would feed it from your chair. You need between 70 and 100 mm mercury (2psi) and anything from 2 litres a minute upwards. With 5 minute cycles. On some pumps thats labled 10 as they count a cycle as starting again so... If this senses a low battery it inflates all cells and turns off. But it beeps first to warn before that. Has alarm on low battery and low pressure. 5 settings for pressure, static or cyling, and 10, 15, 25 mins. Which actually means 5, 7 and 12.5 mins... Its labeled as ALERTA MOBILE and most places have the older one that makes more noise. 50mm x 90mm x 190mm approx by eye. Comes with a case, straps, etc. And a charger brick. The brick puts out 12.6V and 0,9A according to the label. Sounds as if it might keep working!

*2Ah battery? garanteed 20 or 48 hours? So will take so little from a wheelchair its not worth having a seperate battery. Bit I will charge it at 12V dead, 24/7 from the chair so the cells are not stressed, and leave them in.

[stevelawiw]

Ok thanks.
Good luck with the cushion design/build. I'll be very interested to see what you come up with, much better than anything available of the shelf no doubt

[Burgerman]

It will be super simple. A slab of hard foam thats the correct width and length for me, and a 6 bar air thingy sunk into the rear. Made from a couple of sheets of foam.

This it the 2 inch thick top part.

Sat on a 1 inch thick hard foam base, the same overall size. No cutout.
On top of the whole thing a 10 or 12mm soft foam layer - not the air part.

So the non critical legs etc are on hard, foam and dont give much, so that at least some weight is taken by the foam. And stable. And easy to transfer. With a Jay2 cover of course.

[foghornleghorn]

What sort of seat base are you using, board or sling? I can't sit for long with a solid board under the cushion and had to special order a sling seat for my current wheelchair. With the sling seat any pressure is constantly shifting even with a fairly hard standard gel cushion.

How taut is your sling seat? As loose as on a folding manual chair or tight as on a manual rigid chair.

Seat side rails are fixed position H frame not folding. Visually seat is tight and level when nobody is sat on it. If you press down in the centre can poke about 10mm but the whole thing definitely isn't saggy like a hammock.

[Burgerman]

The advantage uf a sling seat is that it puts more pressure on the outer edges, and reduces pressure in the centre where your IT bones are. So even if its only half an inch, when seated, its quite significant. The same as an extra inch of foam at the seat cushion outer edges. That works too of course.

A really loose sling puts much less pressure on the important bits compared to a flat seat/cushion base. Tapered wedges can do the same thing on a flat base.

[snaker]

BM, does this kind of pumps have a technical name so I can search it? My alternate air cushion does not work due to its wrong pump. I just need to replace it by a proper one.

You need between 70 and 100 mm mercury (2psi) and anything from 2 litres a minute upwards. With 5 minute cycles. On some pumps thats labled 10 as they count a cycle as starting again so...

[Burgerman]

The actual pumps are these, or similar, hundreds of such things available, they are diaphram pumps. 2 needed. http://xmajk.en.alibaba.com/product/605 ... _Pump.html

High quality brushless versions designed to last a decade are available at silly money. Or a bucket full of these for the price of a .

But, Theres also some complex circuitry, programming etc. To do it their way, along with pressure sensors, etc.

But basically all you really need is a 555 chip. Or two. Timed by one. So that...
Each pump runs one at a time, until pressure reaches about 1.9 psi (about 100mm/hg) and then a pressure switch cuts it off, and allows it to restart if it loses pressure. Which it will. After 4 mins, do the same with the opposite pump/bank. ONLY when the 2nd lot of cells are full to 1.9PSI remove power from pump 1. And rinse and repeat. Theres mechanical, and SSR and 555 chip ways to do this. As I would. Or theres the fancy computerised way that they use which requires mass production and a level of electronics and programming thats way beyond me. Both work!

[Burgerman]

Unless you mean to buy ready to go one? In which case ebay or chinese auction sites.

[flagman1776]

What does it feel like to be sat on one of these alternating cushions? I'm just not up to programing chips level... I'd like something i could drop onto existing furniture type chairs... maybe even move it around or if cheap enough (from china) have a couple in my seats. I know my butt is at risk now. Getting up every hour is not enough to prevent injury.

[Burgerman]

Dunno. I am paralised. If I wasnt then I wouldnt need one?

[flagman1776]

Dunno. I am paralyzed. If I wasn't then I wouldn't need one?

Sorry. I didn't mean for it to come out like that. Some areas I have sensation, even if I don't have function. The only sensations I have are unpleasant in some way.

Even though I can stand enough to self transfer... doesn't remove my risk of tissue damage. I'm currently dealing with fluid ulcers in my legs... again.

[Burgerman]

Dont know if it would help those. My carer says he can feel it working under him but not uncomfortable.

I used it today, cant tell what its doing! But the box of tricks is a pain, as theres nowhere to put it that I can then reach to control it. The foam of the cushion is so soft that it may as well not exist. Would work for a child. So as expected I will need to make a basic heavy foam base for the air bladder works to fit into. Which is easy enough.

[sacharlie]

Any noticeable noise?

[Burgerman]

I can just hear it. But dont notice it. Every few mins it sort of hums. No tune, just hums... Sounds like an aquirium pump. You feel it with your hand on the pump rather than hear it...

[sacharlie]

It hums and vibrates and don't talk back. What more could ask for!

[Burgerman]

My foam is ordered.

3 parts.


1 hard reconstituted foam base, (made from lots of bits glued together) 500L x 480W x 50mm deep with a large rectangular hole for the air parts. see download/file.php?id=8797&mode=view
1 hard reconstituted foam, 500L x 480W x 50mm deep with a large rectangular hole for the air parts at the rear as per drawing.
1 soft foam part 1/2 inch (12mm) that goes on the top, covers the air cells, and wraps over the front. It is 480W X 585L.

All will be glued together with simple spray carpet glue. And a 20 x 18 Jay2 cover.

https://www.foamcushion.co.uk/

[sacharlie]

Good for airflow under your butt.

http://www.supracor.com/custom/breathable-sheets

[Burgerman]

So are those alternating things. Every cycle, as one inflates and another deflates it shift and allows air to move about. Provided the lower 1 inch of foam has perforation holes about 15mm diameter in it that connect the rear and sides to the outside world. I intend adding about 18 holes by heating a copper tube and pushing it through the foam. Or by cutting the end to look like a saw and twisting it and pushing it. Then theres only the cushion cover itself between you and fresh air. As long as you use a cover that allows air transfer. Such as that spacer fabric.

If really serious you could fit a third motor, same type as used in those cheap blood pressure monitors, to push air into that square cutout down a tube. And have forced cooling and drying and airflow out through the cushion skin. Just needs a 12 or 24V supply. And we have that on board.

[sacharlie]

Since it's active & alternatiing just a sheepskin top layer might work to help keep your bum cool aND dry.

[ex-Gooserider]

Arguably easier than a 555 setup or other discrete components would be an Arduino based approach.... The Arduino or similar microcontrollers have a bunch of outputs that can be used to turn a relay or FET on and off, and internal timers that would make this a very straightforward thing to program. The big advantage is that it allows trivially easy changes to the timing (down to the microsecond if you feel so inclined)

To change the timing on a 555 requires recalculating the R-C values and swapping parts or playing with pots and so on... But to change timing on an Arduino would be a question of changing a few variables in the controlling program, and uploading the new code...

This is generally the big difference and advantage of microcontrollers over traditional electronics approaches - it becomes trivial to change the software instead of re-engineering the hardware... (even something as hairy as the Roboteq script is still WAY less complex than trying to make the same changes in hardware....)

ex-Gooserider

The actual pumps are these, or similar, hundreds of such things available, they are diaphram pumps. 2 needed. http://xmajk.en.alibaba.com/product/605 ... _Pump.html

High quality brushless versions designed to last a decade are available at silly money. Or a bucket full of these for the price of a .

But, Theres also some complex circuitry, programming etc. To do it their way, along with pressure sensors, etc.

But basically all you really need is a 555 chip. Or two. Timed by one. So that...
Each pump runs one at a time, until pressure reaches about 1.9 psi (about 100mm/hg) and then a pressure switch cuts it off, and allows it to restart if it loses pressure. Which it will. After 4 mins, do the same with the opposite pump/bank. ONLY when the 2nd lot of cells are full to 1.9PSI remove power from pump 1. And rinse and repeat. Theres mechanical, and SSR and 555 chip ways to do this. As I would. Or theres the fancy computerised way that they use which requires mass production and a level of electronics and programming thats way beyond me. Both work!

[Burgerman]

I heard arduino, programming and my head exploded. I cannot do that. Be easier to learn klingon.

[Burgerman]

OK.

To make a custom air cushion that is your own size, with firm sides and edges, and firm front, you just need some carpet glue spray. And order 3 bits of foam cut to your size. No skill required.

3 parts.

Two here, these are 1 inch thich bottom, and 2 inch thick with the hole already cut in the top. You just glue these together to foirm a 3 inch thick hard cushion, and then drop the 6 air cell part from the cushion I bought into the hole! The hole is the exact right size.

And a soft foam top. This sits above the cushion, and is glued on. But its wrapped into the edges of the hole to give a smooth rounded edge on the sides and the front and back. Total cushion is 3.5 deep. With a hard supportinve foam base and a thin soft foam top. No cutting required.

Top, to be glued on, and glued into the hole. Then put into your favorite cover. I will use my Jay2 cover.

One small thing. Its important to add a layer of fabric. Between the two heavy foam layers. Because otherwise the susion "spreads" and hains about half an inch in use ofer a few months. Cut two bits from an old sheet, the same size as your cushion. One on the bottom. One between the two heavy layers. This can be glued with any contact adhesive or PVA diluted etc..

[Burgerman]

Scrap the white top.

This black foam on the right is softer, and allows better airflow, and its self adhesive saving me a job! Its a bit like memory foam. It will form a little shape, where I double it up. And the top layer.

The orange foam is hard. The yellow bottom layer is very hard as foam goes.

Assembled here with PVA and I am using a professional jig/rig to hold it together firmly while glue dries. The white bits are white scrim, as it does not stretch. So the cusion cant spread with a lot of use. Keeps it 19 wide, 20 deep.

Frankly any idiot can make a wheelchair cushion. You can build one that suits you. or is shaped to suit you. With the firmness where you need it, or with a place for a gel, or air, or in my case the cyclic air cells.
All the foams are available cut to your dimensions cheap on eBay.

[arpetterborg]

Been a couple years since my self-centered ass posted, but this in particular is helpful as I pore over WCD pages that talk about tires and emphasizing their use in shock absorption in lieu of a suspension setup with not enough travel that adds weight to the frame with all the extra hardware. From previous posts it looks like I'll need to build a seat (likely shamelessly modifying Burgerman's designs with permission) with what I need for musculoskeletal support, then play around with various tubeless tire pressures.

Google is telling me breathable foams with varying rigidities are easy to find; this quoted post gives me some hints about keeping the seat from turning into a sink hole for my bony bum.

Scrap the white top.

This black foam on the right is softer, and allows better airflow, and its self adhesive saving me a job! Its a bit like memory foam. It will form a little shape, where I double it up. And the top layer.

The orange foam is hard. The yellow bottom layer is very hard as foam goes.

Assembled here with PVA and I am using a professional jig/rig to hold it together firmly while glue dries. The white bits are white scrim, as it does not stretch. So the cusion cant spread with a lot of use. Keeps it 19 wide, 20 deep.

Frankly any idiot can make a wheelchair cushion. You can build one that suits you. or is shaped to suit you. With the firmness where you need it, or with a place for a gel, or air, or in my case the cyclic air cells.
All the foams are available cut to your dimensions cheap on eBay.

[MichaelB]

Are there any cheap/affordable pressure mapping systems to help check how effective the cushion is? I usually get mine checked at local wheelchair services when I get any new equipment.

[Burgerman]

Not sure. But I would like one. Be interesting to be able to fine tune a cushion shape and depth in various areas to better support you than a flat slab.

[Burgerman]

Not sure how useful those are.

Because like everything its a useful tool. But expperience and a little thought may be at least as useful. For eg I actually suspect that my problem may be the transfer board more the cushion. So and doing something about both things at once. Others may spend an age with mapping etc only to find that its temperature or moisture thats the real cause. Or that chemicals or lack of adequate cleaning (hygene) is the issue. I started using azo alcohol wipes or may carer does 2x a day. And so on. Also from experience, you get a different result on the map, by day. Or by doing a pressure lift and re settling... Or by adjusting tilt or recline to a bery slightly different position. Even leaning on one arm or the other makes the map change. Or different trousers. Sheer forces for eg, cause by crappy suspension or pavements or a rigid foam or gel type cushion may be a bigger issue than pressure while sitting still. Every case is different. My coccx issue turned out to be a candida infection issue hence the alcohol wipes.

But used as a help along with many other factors and a little thought rather than some sort of diffinitive answer they can be useful.

[MichaelB]

A very useful tool, I usually try different amounts of tilt, get my support workers to push on cushion and see what changes. For the Roho I have a pressure gauge which we check pressure when we get the best mapping. I am hoisted so no sliding. Would definitely use a mapping system if I had one.