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Thread: Modified All-Terrain Third Wheel

  1. #1
    Senior Member elarson's Avatar
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    Modified All-Terrain Third Wheel

    I would be interested in hearing any and all input on making a modified all-terrain third wheel. I am sure there was a thread specifically about this, but I can not seem to find it. My apologies if it is duplicating past information.

    We are doing this project because there are no viable options on the market that will work. The primary use is for the when my husband uses his ZX-1 power add-on, which is mounted on the camber tube, with a TiLite ZRA wheelchair with individual flip-up footrests. Products mounted on the camber tube or on the on the footplate will not work. See All-Terrain Third Wheel Options on our website for an overview of products we have looked into.

    We decided to use the Rio Mobility attachment because we also have a full Firefly that he will be using at other times, and we want to use the same mounting brackets and pawns. There is not enough room on the front frame for any other attachments.

    I have some rather rough information about this project on our website if you want to know more details: Modified All-Terrain Third Wheel.

    After the initial testing, I think it all comes down to getting the wheel to trail properly. I'm thinking that I could get some welder friends to extend the Wing Plates to the length we need. Probably it would be better to have the steerer more vertical (thanks @nonoise) so it can turn, and then cold bend a fork to make a negative rake.

    Here are some photo's showing where we are now. It is with a 12" wheel, which I think is the maximum size it could be without tipping the chair too far back and getting in the way of the adaptor (and his feet). The red lines in the 2nd photo show what I mean about extending the Wing Plates. I'm going to give it a try to extend the Wing Plates with some wood, and see how it works.

    Last edited by elarson; 04-26-2014 at 09:58 PM.
    Partner of an incredible stroke survivor. Limitations: hemiparesis and neglect (functional paralysis and complete lack of awareness on one side). Equipment: TiLite ZRA 2 and 2GX, Spinergy ZX-1, RioMobility Firefly. Knowledge: relative newbie for high-level equipment (2012), but willing to try to help others who are new with similar limitations (definitely not a guru, but inquisitive).

  2. #2
    Nice project
    Chas
    TiLite TR3
    Dual-Axle TR3 with RioMobility DragonFly
    I am a person with mild/moderate hexaparesis (impaired movement in 4 limbs, head, & torso) caused by RRMS w/TM C7&T7 incomplete.

    "I know you think you understand what you thought I said, but what I don't think you realize is that what you heard is not what I meant."
    <
    UNKNOWN AUTHOR>

  3. #3
    Ohhhh, I just saw something in your second pic. The negative steerer angle might work since the wheel or rather carriage could tend to fall forward instead of backwards. My upstairs indoor chair GPV, that I use more than any other has slightly backwards steering casters and it works fine. I've never bothered to "right" them vertical. Yours is more extreme and may be too dominate for smooth turning. What happens is the wheelchair lifts up and down a little so you fight that.

    As for wheel size, I wanted a larger one than 8 inches, but that is what I had and it fit the available fork. So I tried it first. Now I see no reason for a larger one as it combined with the long wheelbase goes anywhere.except I have not tried flying off a curb.
    I have had periodic paralysis all my life. I lost my ability to walk in 2011 beginning with a spinal block, which was used for a hip fracture caused by periodic paralysis.

  4. #4
    Senior Member elarson's Avatar
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    I have been playing around a bit more today (it's raining).

    Here are some photo’s showing a 12″ wheel and the original 16″ fork shipped with the Rio Mobility attachment. I’ve copied an extension that is already on one side of the fork, but lowered it (Photoshop) and used it to connect to the axel. I think it will be strong enough, because the Firefly also uses a similar fork extension to connect to one side of the axel.

    The photo’s show the wheel touching the fork under the crown, but the fork would be raised to give some space. The fork blades will also need to be cut and we will not need the dropouts. Now I just need to figure out how to prototype this to get all of the positioning correct, including with the front casters off the ground. Any idea’s?

    [Note: we will also be taking the little coloured balls off the wheel ]

    Partner of an incredible stroke survivor. Limitations: hemiparesis and neglect (functional paralysis and complete lack of awareness on one side). Equipment: TiLite ZRA 2 and 2GX, Spinergy ZX-1, RioMobility Firefly. Knowledge: relative newbie for high-level equipment (2012), but willing to try to help others who are new with similar limitations (definitely not a guru, but inquisitive).

  5. #5
    Senior Member elarson's Avatar
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    @nonoise, Thanks for the input. I could use all the help I can get on this. Interesting what you say about the negative steerer angle. It is my concern also that it will not turn well enough if it is too far off the vertical.

    The 12" wheel is about the smallest wheel that fits standard forks. Just in case it is not obvious, it comes from the smallest kids bike I could find. Otherwise I would need to figure out how to get a caster fork to connect to a steering tube, and I think that would be more difficult. Also, I think it will help with bumps more, because we can put some big fat knobbies on it.
    Partner of an incredible stroke survivor. Limitations: hemiparesis and neglect (functional paralysis and complete lack of awareness on one side). Equipment: TiLite ZRA 2 and 2GX, Spinergy ZX-1, RioMobility Firefly. Knowledge: relative newbie for high-level equipment (2012), but willing to try to help others who are new with similar limitations (definitely not a guru, but inquisitive).

  6. #6
    Senior Member elarson's Avatar
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    Interesting.... I just went to look more at other third-wheels again. I looked closer at the Rollick Tracks, which has an optional steering column. What I realise is that they are also using the RioMobility attachment (they are a distributor). I can only surmise, but I think that without the steering column, the wheel would trail, and it seems to be using a similar fork extension to my photoshopped photo to connect to the axel. I had talked to this company about a year ago, but they did not seem really keen on making more. I'm not sure if that is because there are problems with the design, or just their lack of interest.
    Partner of an incredible stroke survivor. Limitations: hemiparesis and neglect (functional paralysis and complete lack of awareness on one side). Equipment: TiLite ZRA 2 and 2GX, Spinergy ZX-1, RioMobility Firefly. Knowledge: relative newbie for high-level equipment (2012), but willing to try to help others who are new with similar limitations (definitely not a guru, but inquisitive).

  7. #7
    Wow, your photoshopped pic looks like you're done.
    Try the kids tire before investing in a knobby. I think you will be pleasantly surprised how well it handles bumps.
    Rollick Tracks needs the handlebar for steering because their wheel is preceding instead of following the fork.
    I have had periodic paralysis all my life. I lost my ability to walk in 2011 beginning with a spinal block, which was used for a hip fracture caused by periodic paralysis.

  8. #8
    Senior Member elarson's Avatar
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    I did the photoshopped pic's because I want to explain it to a welder easily in another language. I definitely won't be making any more investments in this just yet for wheels, but I like the idea that it should be possible.

    Apparently the Rollick Tracks can also be had without the handlebars, that's why I had not noticed it earlier. I'm assuming that without the handlebars the wheel would be following the fork. There are just no pictures of it that way.

    Quote Originally Posted by nonoise View Post
    Wow, your photoshopped pic looks like you're done.
    Try the kids tire before investing in a knobby. I think you will be pleasantly surprised how well it handles bumps.
    Rollick Tracks needs the handlebar for steering because their wheel is preceding instead of following the fork.
    Partner of an incredible stroke survivor. Limitations: hemiparesis and neglect (functional paralysis and complete lack of awareness on one side). Equipment: TiLite ZRA 2 and 2GX, Spinergy ZX-1, RioMobility Firefly. Knowledge: relative newbie for high-level equipment (2012), but willing to try to help others who are new with similar limitations (definitely not a guru, but inquisitive).

  9. #9
    Senior Member elarson's Avatar
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    I'm feeling pretty confident about this now, and have a welder friend that is willing to help. I have made yet more photo’s. I hope nobody minds, but if you see anything really off, please let me know.

    In these photo’s it is showing the fork plate extension used for the Firefly. It is looking like the same dimensions will work for this (I have reversed it). I think going for a complete vertical on the fork is the best way to go for handling. I’ve read that a good starting point for fork offset (rake) is about 30 mm behind the contact patch, which is exactly where the Firefly axel is now in reverse. If you are interested, see this link about Caster angle, e.g., fork offset (rake), trail, steer angle, etc.

    Partner of an incredible stroke survivor. Limitations: hemiparesis and neglect (functional paralysis and complete lack of awareness on one side). Equipment: TiLite ZRA 2 and 2GX, Spinergy ZX-1, RioMobility Firefly. Knowledge: relative newbie for high-level equipment (2012), but willing to try to help others who are new with similar limitations (definitely not a guru, but inquisitive).

  10. #10
    I started with a 40 mm offset, which did not work. The chair wandered all over the place. When I added the extensions to increase the offset to 140, it worked perfectly. You are lucky to have a welder helping in that should you need to you can experiment using adjustable clampable plates to be welded later.
    I have had periodic paralysis all my life. I lost my ability to walk in 2011 beginning with a spinal block, which was used for a hip fracture caused by periodic paralysis.

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