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Thread: COG for new TiLIte

  1. #21
    Oddity and August - thanks for all the help and advice you have given me. I have been in the new wheelchair for four days now and it is still stiff. One other question I have is that it seems more difficult to turn the chair left and right, but it is not a showstopper. Do you think once I move the COG up a half inch that it will help resolve the turning issue ? In other words if the front caster axle is closer to the rear wheel axle should that make the chair easier to turn ?

    -Ronnie

  2. #22
    Senior Member Oddity's Avatar
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    Yes. Wheelbase is probably the most significant variable in the turning agility equation, assuming everything else is in good working order (bearings, etc.)
    "I have great faith in fools; self-confidence my friends call it." - Edgar Allen Poe

    "If you only know your side of an issue, you know nothing." -John Stuart Mill, On Liberty

    "Even what those with the greatest reputation for knowing it all claim to understand and defend are but opinions..." -Heraclitus, Fragments

  3. #23
    Quote Originally Posted by reaton View Post
    Oddity and August - thanks for all the help and advice you have given me. I have been in the new wheelchair for four days now and it is still stiff. One other question I have is that it seems more difficult to turn the chair left and right, but it is not a showstopper. Do you think once I move the COG up a half inch that it will help resolve the turning issue ? In other words if the front caster axle is closer to the rear wheel axle should that make the chair easier to turn ?

    -Ronnie
    While wheelbase will affect turning, there could be other factors. If turning becomes more difficult as you increase the angle of your turn, then one caster may be higher than the other. Two reasons for this are: 1) caster fork angle is not square (see my previous post), and 2) footplate is not square. Casters not being square will also create safety issues like fluttering casters at increased speed (typically going downhill), which could lock up your chair and throw you out.

    Otherwise, if turning is difficult regardless of the angle of turn, then it's probably just the longer wheelbase.

  4. #24
    Senior Member Oddity's Avatar
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    One thing to note about caster angle and flutter...

    A fork angle that isn't perpendicular to the floor can actually increase the stability at the cost of agility. A caster angle that is off a bit toward the rear when in the trailing position has increased "trail" which is one way to actually decrease fluttering at high speeds. This is one reason the Freewheel has a fork angle parallel to the floor instead of perpendicular. It's much more stable at high speeds. Flutter based on fork angle is more about one being higher than the other than the angle itself. More trail (a larger difference between the axis of the fork and the caster contact patch) is actually better for less flutter if both forks are off to the same degree.

    edit: all forks have trail built into them for this reason. Adding more isn't needed but doesn't in and of itself cause flutter unless the forks are imbalanced.
    Last edited by Oddity; 01-15-2020 at 08:21 PM.
    "I have great faith in fools; self-confidence my friends call it." - Edgar Allen Poe

    "If you only know your side of an issue, you know nothing." -John Stuart Mill, On Liberty

    "Even what those with the greatest reputation for knowing it all claim to understand and defend are but opinions..." -Heraclitus, Fragments

  5. #25
    Quote Originally Posted by August West View Post
    I have increased dump by 1/2" without adjusting caster angle. It's not the ideal 90 angle but I didn't find a difference in turning. But I like to keep it 90 degrees just because. Not sure why you call it a pain. On my TRA, it's just loosening a bolt, adjusting the caster angle, and tightening the bolt.
    Last TRA I had was when they came out; it was a pain getting the two to line up properly. I hope the last series of TRA's use a different design for adjusting the barrel housing.

  6. #26
    Quote Originally Posted by Patrick Madsen View Post
    ...it was a pain getting the two to line up properly.
    Still could be a pain or it could be easy depending on how you measure a successful result - quantitatively or qualitatively. A quantitative measure would be setting each caster angle at 90 degrees with a square. That will require multiple resources, time, and effort. A qualitative measure would be setting each caster angle at 90 degrees by eye and checking for smooth turns. That will require an allen wrench, a flat floor, and a few minutes.

    I prefer the qualitative approach. Good enough is good enough beyond which point you're just polishing cannon balls - a needless level of refinement.
    Last edited by August West; 01-16-2020 at 02:56 AM.

  7. #27
    lol, yep cannon balls don't need to be shiny.

  8. #28
    And your caster angle doesn't need to be exact. After all, it will get thrown away from 90 degrees the first time you hit a pothole.

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