Page 1 of 3 123 LastLast
Results 1 to 10 of 28

Thread: TiLite Single Swivel Caster Anti-Tipper - fine tuning

  1. #1

    TiLite Single Swivel Caster Anti-Tipper - fine tuning

    Well, my Single Swivel Caster Anti-Tipper (SSCA) is finally installed (the saga began in January - over four months ago), and I have now discovered it was not quite fabricated correctly to meet my needs . . . so the saga continues.

    Name:  IMG_20130502_180239.jpg
Views: 1200
Size:  275.4 KB

    I asked for it because I like to dance, but I cannot safely hold a wheelie because of dysmetria in my arms. When I would lean back on the two-armed anti-tippers and twirl, their brackets would bend, which I considered very unsafe.

    Today, after I installed the SSCA, I immediately realized the SSCA would not allow me to even reach a wheelie position, so I set about designing a solution (following this methodology with CAD). I determined how much the SSCA tubes should have been bent to allow a wheelie ("SSCA w/wheelie bend").

    (Note: I placed my CoM according to pages 3 & 13 of the attached paper: about 12" above my ischium and about 8" in front of my backrest. I ignored chair mass as a small safety factor.)

    Attachment 49687

    This next sketch shows that the SSCA (as fabricated) barely allows me to climb a small curb (I can lift the front casters only 3" with the SSCA caster adjusted all the way up).

    Attachment 49688

    But if the SSCA arms were bent 38 Degrees about 3" from their ends, I could hold a wheelie!! And my CoM would remain comfortably in front of (to the left of) the SSCA tipping point. (My balanced wheelie position (CoM directly above the axle) leaves the front casters about 8.5" off the ground, but I drew 9.5" so I could rest back on the SSCA.)

    Attachment 49689

    So now I will search for a local metal shop who will bend the tubing for me.
    Last edited by chasmengr; 05-03-2013 at 03:08 AM.
    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>

  2. #2
    With the bent SSCA, I can safely ascend up to about a 15 degree incline, too. The steepest ramp allowed by the ADA is 12.5% (1:8 for a 3" max rise in tight existing buildings).

    Attachment 49691

    Reminder: error exists in all these calcs/drawings, so I'll be skeptical that these results are right until after they've been cautiously field tested.
    Last edited by chasmengr; 05-03-2013 at 01:28 AM.
    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
    Senior Member
    Join Date
    Aug 2012
    Location
    United States
    Posts
    382
    This worries me. Have you investigated yield strengths? What about creases (leading to fractures) at the bend point? I know you have thought of this.
    E
    There is no such thing as a stupid question but there sure are a lot of inquisitive idiots. -modified from despair.com

  4. #4
    Quote Originally Posted by Essie View Post
    This worries me. Have you investigated yield strengths? What about creases (leading to fractures) at the bend point? I know you have thought of this.
    E
    I'm not intimately familiar with metallurgy, no. But my college classes (structural steel design, strengths-of-materials, statics) and internet videos of tube bending (done cold) tell me that bending titanium properly (with rollers) will not adversely affect its properties. Think of the TiLite titanium Z chairs: ZR and ZRA. Their titanium frames are bent and hold up just fine.

    BTW I found no shop in my city with equipment to bend titanium tubing that is willing to perform such a small order. I was told I'd have to go out of town to have it bent - titanium is strong stuff!

    And apparently my request is unique - I stopped at the VA, and the wheelchair clinic said "Oh, that's what you meant. You want anti-tippers that allow wheelies? No one has ever asked for that before." (paraphrased)

    Until today I never realized they had misunderstood my original request - I didn't know it was unusual. I had shared the details of my chair mods (field adjustments) when they ordered this custom-made-for-every-chair component along with this written language: "I need the anti-tipper to allow me to rock back and forth to maintain a wheelie while still inhibiting me from falling backward."

    For a custom fabricated component (a TiLite Designs-Unlimited offering), I had AssUMe'd that was a straight forward request, and my drawings prove to me it can be easily designed.

    Apparently "anti-tipper" has always meant anti-wheelie to the wheelchair clinic. Just because dysmetria in my arms won't allow me to reliably hold a wheelie for very long, does that mean I am relegated to a flat world? Lots of wheelers don't even use anti-tippers. With anti-wheelies, how do I ascend small curbs or lean back against a wall to rest. Sometimes I even stand and push my chair up taller curbs; the anti-wheelies now prevent my doing that because the front casters lift only 3" off the ground.

    The VA wheelchair clinic was eager to accommodate my (unique) request, and eagerly agreed to follow up on it. They just had not understood it.

    -- I didn't know that they didn't know that they didn't know. -- communications 101!
    Last edited by chasmengr; 05-03-2013 at 11:58 PM.
    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>

  5. #5
    Senior Member
    Join Date
    Jun 2011
    Location
    Mesa, Arizona
    Posts
    1,078
    Chase I like the single caster idea. maybe Icon can come up with something like this as well? He he he. Just ideas or maybe I can fine one off a tilite with the brackets and mod it! Lol!

  6. #6
    Senior Member
    Join Date
    Aug 2012
    Location
    United States
    Posts
    382
    Quote Originally Posted by chasmengr View Post
    I'm not intimately familiar with metallurgy, no. But my college classes (structural steel design, strengths-of-materials, statics) and internet videos of tube bending (done cold) tell me that bending titanium properly (with rollers) will not adversely affect its properties. Think of the TiLite titanium Z chairs: ZR and ZRA. Their titanium frames are bent and hold up just fine.

    BTW I found no shop in my city with equipment to bend titanium tubing that is willing to perform such a small order. I was told I'd have to go out of town to have it bent - titanium is strong stuff!

    And apparently my request is unique - I stopped at the VA, and the wheelchair clinic said "Oh, that's what you meant. You want anti-tippers that allow wheelies? No one has ever asked for that before." (paraphrased)

    Until today I never realized they had misunderstood my original request - I didn't know it was unusual. I had shared the details of my chair mods (field adjustments) when they ordered this custom-made-for-every-chair component along with this written language: "I need the anti-tipper to allow me to rock back and forth to maintain a wheelie while still inhibiting me from falling backward."

    For a custom fabricated component (a TiLite Designs-Unlimited offering), I had AssUMe'd that was a straight forward request, and my drawings prove to me it can be easily designed.

    Apparently "anti-tipper" has always meant anti-wheelie to the wheelchair clinic. Just because dysmetria in my arms won't allow me to reliably hold a wheelie for very long, does that mean I am relegated to a flat world? Lots of wheelers don't even use anti-tippers. With anti-wheelies, how do I ascend small curbs or lean back against a wall to rest. Sometimes I even stand and push my chair up taller curbs; the anti-wheelies now prevent my doing that because the front casters lift only 3" off the ground.

    The VA wheelchair clinic was eager to accommodate my (unique) request, and eagerly agreed to follow up on it. They just had not understood it.

    -- I didn't know that they didn't know that they didn't know. -- communications 101!
    I made the assumption that it was Al. It's hard to tell from the pic but is there any way to adjust the receivers so the top bars of the anti-tipper are perpendicular with the camber bar?
    E
    There is no such thing as a stupid question but there sure are a lot of inquisitive idiots. -modified from despair.com

  7. #7
    Quote Originally Posted by randomryan007 View Post
    Chase and you move them above the camber tube? <copied from here>
    Quote Originally Posted by Essie View Post
    . . . is there any way to adjust the receivers so the top bars of the anti-tipper are perpendicular with the camber bar?
    E
    Great ideas, guys! During install, neither of those ideas were obviously possible to me, but I wasn't looking for them. I'll check them out in detail before pursuing the bending idea; if possible, either idea would sure be easier than bending.
    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>

  8. #8
    Senior Member
    Join Date
    Aug 2012
    Location
    United States
    Posts
    382
    Chas-

    I am also concerned that if you bend the anti-tip bar (ATB) it will bring the ATB wheel further into the rear wheels (obviously and as your drawings indicate). If you are rotating as you go back onto the ATB wheel, I worry you will end up solely on the ATB wheel. This would be analogous to a child's top and, much like the top, you would tumble.

    I tried not to get all techie and keep this post short; let me know if this does not make sense.

    E
    Last edited by Essie; 05-04-2013 at 12:48 PM.
    There is no such thing as a stupid question but there sure are a lot of inquisitive idiots. -modified from despair.com

  9. #9
    Senior Member ~Lin's Avatar
    Join Date
    Nov 2011
    Location
    Indianapolis, IN
    Posts
    3,070
    Essie, what you said seems contradictory to me... If bending made the ATB wheel further into the rear wheels, wouldn't that end up with the chair just on the rear wheels without the anti tipper reaching far enough back to be functional?

    I don't see a way that would make the anti tipper further out of the rear wheels, without adding material somehow... And even then I don't see a way that would be possible to end up just on that wheel and not on the rear wheels as well.

    Chas, do you know what they thought you meant at first? Thats baffling me, if they didn't understand your request (which seemed clear and obvious to me) what DID they think you meant?
    Board Member of Assistance Dog Advocacy Project working in Education. Feel free to ask me any service dog questions!

    I am not paralyzed. I have a genetic connective tissue disorder with neuro complications and a movement disorder.

  10. #10
    Senior Member
    Join Date
    Aug 2012
    Location
    United States
    Posts
    382
    Quote Originally Posted by ~Lin View Post
    Essie, what you said seems contradictory to me... If bending made the ATB wheel further into the rear wheels, wouldn't that end up with the chair just on the rear wheels without the anti tipper reaching far enough back to be functional?
    It is not THAT far back into the rear wheels.

    E
    There is no such thing as a stupid question but there sure are a lot of inquisitive idiots. -modified from despair.com

Similar Threads

  1. TiLite TR3 Single Swivel Anti-Tip
    By SCI_OTR in forum Equipment
    Replies: 65
    Last Post: 03-04-2014, 10:11 PM
  2. For Sale: Mag wheels and TiLite single swivel rear anti-tip
    By Jeff B in forum Equipment & Services
    Replies: 12
    Last Post: 05-24-2012, 03:55 PM
  3. Replies: 3
    Last Post: 07-29-2011, 04:02 PM
  4. TiLite User-Friendly Anti-Tipper
    By JMS in forum Equipment
    Replies: 9
    Last Post: 11-23-2010, 08:10 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •