Great link popeye, thanks! This is pretty much exactly what I had in mind, except having one central lever that can steer left and right.
Having separate handles on either side makes me think that I'm going to have to have some pretty quick hand swapping going on to correct oversteer or go from heading left to heading right. But then I realise that I'm an idiot and because moving one lever will affect the other, I'd be able to steer in any direction from either lever, nice.
("either lever" sounds weird)
I'm basically going to get someone to try and copy this basic design, but probably with a roll bar similar, but taller and wider, than peters.
I'm picking up a second hand PL buggy tomorrow to mutilate and experiment with, hopefully I'll find a car repair place or local welders to adopt a project and help me out.
I got in touch with the guys at mobious who made the four wheeled buggy with a steering wheel and talked to them about my plans, just got this back from the guy who built the buggy:
"Steering: We initially tried to have a joystick, as in your design, but the force to turn it when the buggy was stopped or moving slowly was a bit excessive so we bought a second hand 'teleflex' cable steering system (the type used in boats) and fitted a rubber boot from an auto parts store to stop sand getting into the cable. This worked flawlessly, and you could add one of those sweet chrome knobs that bus drivers and truckers love so you can spin the wheel with one hand. I'm sure a joystick as in your drawing coul work if the leverage is enough, but a small round wheel compared to a large metal stick seemed a bit safer on reflection.
Locking the steering sounds a bit scary to me, these things can pick up a hell of a lot of speed, as I'm sure you're aware, and the ability to quickly edge upwind is kindof your only good brake to slow down, same with the straightening spring thing - it was actually quite useful with the wheel, you could turn the wheel so the wheels were pointed one way and then move the kite with both hands to tease the buggy around until it was facing the right direction and then straighten the wheel before you got a huge power dive in.
Kite control: Having used the buggy with the steering wheel, I quite happily flew unhooked with my hand in the middle of the bar and we also used velcro ankle straps to hold wind/kitesurf harness spreader bars onto the frame of the buggy, so you could hook the bar in when you got tired. You can actually carve the kite up and down quite well with it hooked into one of these loops adn you can shift them forward or backward to affect how gusts hit the buggy (ie make it head up or bear away from the wind).
Frame: The three wheeled buggies are pretty stable, but we (the instructors) have flipped them on quite a few occasions, as this would be difficult to recover from, we decided that for this buggy we needed a more stable wheelbase that would be as close to flip-proof as possible. We cut off the front bearing on the three wheel frame and welded a stainless crossbar and supports onto it. Then we added pivots so the wheels could turn parallel (as in a car) and a tie-rod between the wheels. This was easily done using bolts, threaded rod etc. In my opinion, the four wheel buggy with a steering wheel was way more fun than the regular three wheeler (would you drive a reliant?!) although Timo was dissapointed as he couldn't show off to tourists with his 'two wheel' trick as on the three wheelers. Honestly, this thing was crazy, I spun it out at least 720 degrees and it didn't flip. Was like being allowed to have a go-kart on the beach!
As for building from scratch, we were pretty successful in using an existing buggy, in fact we didn't modify the back at all, apart from the harness hooks which were velcroed on. All we needed was an extra wheel and some work done on the front bar, I think we modified it in a day or so."
It sounds like a pretty good way to go, and I've been looking at the teleflex system and even gokart steering systems which I think might both work well if I decide to try four wheels out on the buggy.
Talking about having steering control on the kite bar; I started a thread on a welders forum asking for advice and this type of system came up in the conversation (http://www.mig-welding.co.uk/forum/showthread.php?t=8404), it seemed to get a bit too complicated for me and the thought of so many cables and stuff getting in the way, plus not being about to easily release the control bar scared me off the idea.