Need help building fly-by-wire system! Any R/C people here?

Discussion in 'Archived Threads 2001-2004' started by Ryan Wright, Jun 1, 2002.

  1. Ryan Wright

    Ryan Wright Screenwriter

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    So, here's the deal: As many of you know, I'm building a hovercraft. (The web site is outdated, but you get the general idea) In my never ending quest to be unique and make things as cool as I possibly can, I've decided to do away with the control lines.
    That's right: I want a fly-by-wire system. Instead of a run-of-the-mill flight yoke and throttle with push/pull cables, I want an analog joystick connected to beefy servos for throttle and rudder control.
    How the heck do I do it?
    I understand how R/C systems work. The radio sends signals to a receiver over one of many channels, and the receiver then applies the appropriate voltage to the appropriate servo. Easy enough. For obvious reasons, however, a full 20 foot 8 passenger hovercraft is NOT going to be controlled via radio, thank you very much. It's got to be hardwired.
    Where do I buy parts to make something like this? Come to think of it, CAN I buy the parts? Really, I just need a large and cool looking analog joystick (perhaps with some buttons on it for controlling other functions) and some way to interface that bad boy with my servos.
    Servos will need to be reasonably powerful. I was thinking one servo per rudder (four rudders total). I need them to move those rudders back and forth at a fairly good clip if called upon to do so. Figure how long it takes you to turn an outboard boat engine from center to hard right (quarter of a second?), the servos should be that fast. And of course they should be able to handle a reasonable amount of force. If they can push the rudder over with more strength than you could with your hand, they'll be fine. They'll also have to be able to withstand a marine environment. They won't be submerged, but they will get wet. I can build covers around them if necessary but it will be difficult to keep all moisture out.
    So, is there anyone here who can get me started on this monumental task?
     
  2. Ryan Wright

    Ryan Wright Screenwriter

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    *Bump* ... Nobody??? [​IMG] (sigh)...
     
  3. Jay H

    Jay H Producer

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    Hi Ryan, maybe you should watch "Junkyard Wars" [​IMG] They had an episode last season where they had to build a remote control car (full size, not a model). they did use R/C analog controlers and a servo system to do the basics like gas/brake and steering. I think the servo for the steering was more or less a switch to turn on and off a motor. I know one team welded a chainring on a bicycle to the steering wheel and controlled it with a small motor connected with a bike chain that would turn the steering wheel.
    Do you have a local R/C fanatic club near you, look for any model shops who sell R/C planes and helicopters and I'm sure somebody there could point you in the right direction... They're probably the experts on the subject except for maybe whoever owns General Dynamics these days (The maker of the F-16 fighting falcon) and some car manufacturers who are using throttle-by-wire systems...
    Sorry, it's the best I could do... Actually, Junkyard wars had an episode where they made hovercrafts too. I remember seeing it, one team actually had a problem with the skirt and lost lift in the outside edge going around a turn and the craft just dug in and threw the driver out [​IMG]
    Jay
     
  4. Michael*K

    Michael*K Screenwriter

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    Perhaps rather than appealing to the R/C crowd (which use tiny servo motors), you might see if there's bulletin boards and websites for homebuilt aircraft owners. I'm sure the servos they use on their aircraft are more appropriate for what you're looking at.
     
  5. Ryan Wright

    Ryan Wright Screenwriter

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    Actually, there are giant scale RC systems that use large servos which would work great on my craft. [​IMG] I've checked with homebuilt aircraft owners. They don't use fly by wire and just aren't interested in it. For an aircraft, you'd need multiple redundant systems, etc, and aircraft people always tend to confuse "fly by wire" with "sophisticated computer system." Not surprisingly, since aircraft fly by wire systems really ARE sophisticated computer systems. The computer takes input from the pilot and then decides what to do with the plane.
    What I'm wanting is a totally manual system. Move the joystick left, the servo moves left. Move it right, the servo moves right. Just a basic system. It's the same thing R/C people use, except, I need to know how to eliminate the radio link and substitude the little thumb controlled joystick for a larger flight stick (think PC joysticks made for flight sim games). I can't imagine it could be all that difficult to do, for anyone with an electrical engineering background. Unfortunately, while I'm reasonable competant with electrical equipment, I don't know how to do this.
    Jay: The team leaders on the Junkyard Wars episode were Bob Windt (owns Universal Hovercraft and has designed many really cool craft) and Terry Chapman (president of the Hover Club of America). Both great people, I've talked to Bob on the phone and have emailed Terry a couple of times. Also learned a lot about how Junkyard Wars operates. At any rate, that hovercraft episode was cool.
    As for the skirt, actually, it wasn't a problem with the skirt itself. Their engine was giving them fits and not producing enough power, thus they lost some lift. You could see early on that the skirt was not fully inflated. Unfortunately, in a sideslip, you really need power. When operating a hovercraft, you generally increase power in any turn. This actually slows you down faster due to directing thrust opposite your direction of travel. It also causes you to complete your turn more safely. Coming into a turn at low power is a bad idea in a hovercraft. In fact, the sides on the craft I am building are angled precisely to keep it from flipping if you drop it in a sideslip.
     

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