sacharlie wrote:foghornleghorn wrote: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.
Burgerman wrote: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 wrote:Dunno. I am paralyzed. If I wasn't then I wouldn't need one?
Burgerman wrote: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 wrote: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.
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