Hi
@blekenbleu
I thought I would reach out to you as I'm designing & building myself a pneumatic G-seat project, and when I started I was using your bellows concept as a starting point as I saw the major limitation of other previous "air wedge" designs being that they have only limited amount of movement, and very restricted airflow rate and hence slow reaction time and response latency.
I got a pair of air pump bellows identical to the ones you've used, however, I was keen to use a much bigger servo, so I am using a pair of
ASME 04a servos
These are great servos and I am succesfully already using them as belt tensioners, heaps of tourque (260 kg/cm), fast (60deg in 0.12 seconds) and easy to interface (standard servo PWM). I am not sure why lots of other DIYers in the sim rig space arent using them more, seems heaps easier and cheaper than stepper motors/controllers/hall sensors etc.... anyway i digress.
I soon realised like you that the standard bellows was not airtight enough, so set about modifying it. I ended up using a aerosol can of s
pray on leak seal that would cover all the internal fabric and hence seal any slow leaks in the stiched areas. I also used a liberal amount of felxible sealant in the join between the fabric and the plastic plates when reasembling. It was all quite messy, but when i applied air pressure on it once dried and assembled, it seemed to hold air OK (I didnt do any prolonged tests, so there may still have been some), but the bulkiness added to the bellows due to the sealant, means it is perhaps not able to move quite as much volume of air.
I then had to come up with a method of operating the bellows, which I manged to do with some tie-rods and careful selection of right length servo horn. As you may have realised yourself the bellows is tricky to mount/hold, as there isnt really any flat or straight faces or edges. I had to try a combo of 3D printed retaining lips to clamp the ends and some custom fabricated mild steel to give something to push/pull on. Ive mounted both into an enclosure type box and then turned my thoughts toward the rest of the system. But in the delay since my early progress on the bellows components, I have changed my mind how I am going to do this component, as I wasnt convinced it would work that well.... more to come on this once I have a protoype to show.
I am planning to use 20mm ID vinyl tubing. This should be a huge improvement on restriced airflow of the smaller diameters, so hopefully giving quick reponse.
For the actuator pillows I have tried
(1) very large party balloons (as a trial), as they would be airtight and flexible. Problem with these is the intial pressure to get hem inflated and the constant resistance to keep them inflated, even when unloaded.
(2) I bought some vinyl fabric hopeing to be able to thermo weld something, but that didnt work out so well (perhaps wrong sort of vinyl).
(3) I have now moved over to a TPU backed fabric material, that is commonly used to make inflatable things like sleeping matress, packraft kayaks and kitesurfing gear. It is easily thermo-welded and very strong. Added bonus is you can thermo weld other TPU things (like 3D printed valves etc.) for air tight seal, I havent yet done this part of the project,
but my research shows it is promising.
Anyways, I hope to make a proper write-up or thread of my project once I have a working prototype
