CurtisRider Posted March 4, 2012 Report Share Posted March 4, 2012 Hi guys, i have a project in which i will be building some crutches for a young lady who has no cartilage in her knees. She has said that she wants some form of give in the crutches and that a suspension system would be ideal. There is already a suspension crutch available but it is not user adjustable, and is way overpriced. An on the fly adjustable system like how MTBs have would be an interesting concept and make the crutches more universal (she wants them for walking but others use them for football, etc). I am looking at suitable systems to apply to the suspension idea. I have a basic idea on how oil damping works, but i am hazy as to how air shocks work? How do they actually adjust? I can't find any detailed info as to how lock out works and things like that. I am also interested in the old style elastomer systems, but i cant find any images of thier construction (fairly sure its just a long tube of elastomers instead of a spring?) Any diagrams of how stuff works is appreciated! Also if anybody has any old or broken suspension forks/suspension seatposts/rear shocks that they have to donate, i would happily pay postage and a few quid for your troubles Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted March 4, 2012 Report Share Posted March 4, 2012 Air shocks use oil damping. Quote Link to comment Share on other sites More sharing options...
CurtisRider Posted March 4, 2012 Author Report Share Posted March 4, 2012 I'm aware of that but they also use air to adjust them? My Rebas have an air chamber on top and at the bottom or is this just for the stiffness? Do they not use air at all for the dampening system? Quote Link to comment Share on other sites More sharing options...
dezmtber Posted March 4, 2012 Report Share Posted March 4, 2012 an air for genraly has one sidehop full of air as the spring or elastomer. and the other side with two damping pistons on lowere piston for rebound damping (the return rate) and one higher for compresion damping (the speed which it uses travel) lockout is very basicly a hole which is plugged by a rod to stop oil flow. forks with a blowoff valve lockout system basicly the valve which the lockout rod locks is mounted onto a very hard spring which once this spring is compressed it hits a point which another rod hits a blow off valve to reopen the closed lockout valve. rear shocks use the same damper system, with the air chameber on the outside or the damper. if you have a rear shock you can let out all the air and unscrew the air chamber from the outside to reveal the damper sytem on the inside. a stytem that would be very good for stilts would be simmilar to a air pogo stick. with a damper rod inside, simmilar to car boot struts. Quote Link to comment Share on other sites More sharing options...
CurtisRider Posted March 4, 2012 Author Report Share Posted March 4, 2012 Ok i think i get the air chamber arrangement now and lockout, thank you! I have been looking at air pogo sticks but they go for too much money! Quote Link to comment Share on other sites More sharing options...
Revolver Posted March 4, 2012 Report Share Posted March 4, 2012 You could buy some diiiiiiiiiiiirt cheap suspension forks from CRC and modify them? Spring system, mind. Quote Link to comment Share on other sites More sharing options...
CurtisRider Posted March 4, 2012 Author Report Share Posted March 4, 2012 They don't seem to have any dirt cheap ones right now I will just have to look secondhand or hope somebody has some snapped ones kicking about! Quote Link to comment Share on other sites More sharing options...
Tomm Posted March 5, 2012 Report Share Posted March 5, 2012 The problem is that on any modern fork, one leg will be only damping (I.e. won't return by itself) and the other side will be undamped. I would investigate elastomers - essentially they're both sprung and naturally damped. Would certainly be the simplest option, and I doubt the damping on crutches needs to be that sophisticated. Quote Link to comment Share on other sites More sharing options...
bike_dummie Posted March 5, 2012 Report Share Posted March 5, 2012 Surley a lefty ( spelling ) would be ok because its only one leg anyway so its an all in one kinda thing. Quote Link to comment Share on other sites More sharing options...
CurtisRider Posted March 5, 2012 Author Report Share Posted March 5, 2012 Regarding sophistication on crutches, there is a reason to get more technical than a dodgy spring with no adjustability! For example crutch football, the crutches will take pretty heavy abuse and be set stiffer, but then afterwards, when doing normal walking, they would require something a bit more forgiving as they won't be pushed at hard. A form of damping would be necessary as otherwise they will react horribly when taken off the floor, which could cause problem with balance. Elastomers certainly seem the easiest plan and do tick most of the boxes (not sure how to make them stiffer on the fly?). I had been looking at leftys on ebay but they go for too much i can't find the internal workings of them either. I'm sure theres a way to combine the internal workings of a fork to 1 leg, it will just be a case of pulling some apart to find out! Quote Link to comment Share on other sites More sharing options...
Tomm Posted March 5, 2012 Report Share Posted March 5, 2012 Elastomers won't be adjustable, I'd probably have some different thickness of elastomers and then make it easy to swap them. Mashing a set of forks into each leg sounds like it'll be quite heavy? Quote Link to comment Share on other sites More sharing options...
Revolver Posted March 5, 2012 Report Share Posted March 5, 2012 If you have a metal lathe, you could make your own coilover type suspension unit Take apart an RC car one, reverse engineer that. Quote Link to comment Share on other sites More sharing options...
CurtisRider Posted March 5, 2012 Author Report Share Posted March 5, 2012 The rc ones are crap though! I am going to put this idea on the back burner now, realisitically its not worth the hassle, and i have some far better plans up my sleeve for something else Thanks everybody for your help! Quote Link to comment Share on other sites More sharing options...
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