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Thread: Reducing Overall Length of Invacare TDX Powerchairs w/ Formula CG Tilt Systems

  1. #1

    Reducing Overall Length of Invacare TDX Powerchairs w/ Formula CG Tilt Systems

    One of the pre-fitting configuration tasks we perform on nearly every TDX SP or TDX SR that comes from Invacare is to relocate the power seating system as far back on the powerbase as possible. Most of Invacare's Formula CG power seating system is actually manufactured by Motion Concepts. In fact, it uses many of the same components found on Motion's UltraLow power seating systems. We started doing this routinely a couple of years ago after noticing that TDX's ordered with UltraLow systems came in with the seating system mounted further back than was the case on TDX's with comparable Formula CG systems.

    These three chairs all use the 16-19" seat depth package and were at least 47" long when they arrived from the factory.

    The first chair shows a 18x19 TDX SR Formula CG tilt only system with 70 degree swingaway legrests...

    Attachment 42903

    It is for an end user who has marginal active range of motion to drive with a joystick. In order to do so successfully, he needs the joystick to be located precisely where it's at. People have no idea how hard it was to get the joystick positioned exactly where it is while ensuring it cleared the top of the armrest pad using the Stealth Gatlin mount. The grey rod is very hard steel and extremely difficult to bend--even with a vice (If I didn't achieve that objective, he would probably still be trapped in the chair!). Also, note the build up on the Power/Drive/Select Toggle.

    The headrest also has an Egg switch mounted to the left half of the shell beneath the cover. The switch plugs into an extension cable on the backrest is routed to an input jack on the tilt actuator. This allows him to recover from a fully tilted position with his head because he can not reach the joystick with his upper extremity against gravity.

    Next up is a 17x18 TDX SR Formula CG tilt for a C6 quad with limited knee flexion which necessitated he use 60 degree swingway legrests.

    Attachment 42904

    In order to get the footrest so they were a just in front of the casters when they are in the trailing position, we used a second set of holes tapped into the seat frame to gain an additional inch.

    The heel loops on both of those chairs are 2" longer than the size Invacare typically installs. This locates the foot more squarely on the footrest and allows the overall length of the occupied chair to also be as short as possible.

    As the seating system goes further back, Invacare's longish push handles become more prominent. The reduce protrusion and hopefully avoid future drywall repairs, we trimmed about 2-3 inches off their length on all three of these chairs.

    This last chair is a 19x20 TDX SR with a Formula CG Tilt/Elevate system. In this case we had to move the seating system further back on the power elevating seat actuator pedestal

    Attachment 42905

    If all three chairs use Invacare's 16-19 seat depth package, how can this chair be 20" deep? This is accomplished by telescoping the legrest hangers out of the seat rail and sliding the seat pan forward 1". Finding that extra inch while staying with the 16-19 depth package saves a couple of inches.

    How much work is it to move a tilt system back? Not much at all, maybe 10 minutes if the tech is experienced doing it. All it takes to move the seating systems back is a 1/2" wrench. Tilt/Elevate systems take about 20 minutes more and require a 1/2" wrench and 3/16" Allen wrench.

    Tilt/elevate systems are a little more difficult to do because it is harder to access the four bolts mounting the seating system to the pedestal. More seating functions also means more cables and connectors. Currently, a big clump of cables are currently zip tied to the back posts and back pan of CG Tilt/Elevate systems. To put them in a more-protected area and improve the aesthetics, we mount a little "L" bracket on the side of the seat frame using an existing bolt, and route the bundle underneath the seat frame beside the pedestal as shown.

    Why go through the additional work to trim just 3 or 4" off the overall length of a powerchair? I'm firmly convinced that any added costs are a worthwhile investment because:

    • Any reduction in the overall length of a midwheel drive chair reduces the turning radius by the same amount.
    • Better maneuverability in tight areas means less possibility of damage to the front riggings, walls, or toes.
    • Shifting some weight off of the front casters onto the drive wheels results in better weight distribution. This can be especially noticeable--especially climbing over obstacles and minimizes the possibility of the chair dipping forward under hard deceleration.

    Generally-speaking, the result will be improved usability, better maneuverability, less wear & tear, and fewer minor annoyances over time.

    There are some instances where it may be preferable to keep the seating system where it's at (e.g. if carrying oxygen and/or a vent on the back). I should also note that extreme caution must be exercised on rear wheel drive platforms as the center of gravity is very different and the occupied chair may tip backward when the seat is tilted if it has been moved too far back. For this reason, I recommend anyone contemplating having this done consult a qualified provider who is familiar with your specific model for any center of gravity adjustments.

    I decided to post this because most end users, clinicians, and DME's don't even realize it is possible to do this. Therefore, the vast majority of TDX's with Formula CG seating systems out there are probably a few inches longer than they need to be. In any event, it certainly couldn't hurt to bring up the topic in seating clinic if you decide on a TDX with a Formula CG tilt or tilt/elevate system.
    Last edited by SCI_OTR; 11-30-2011 at 11:12 PM.


  2. #2
    1/8" ABS plastic shim used to reduce slop on conventional flip back armrests found on most Invacare powerchairs...
    Last edited by SCI_OTR; 11-30-2011 at 11:21 PM.


  3. #3
    SCI-OTR, you are right on!! I've been making the same changes to most of my customers too. Need to move the CG back on most SP's.

    Another TDXsp trivia/suggestion. The distance between the armrests is 2" wider then the seat pan. When a person needs a 18 wide chair, I order a 17 wide chair and a 18 wide cushion. It helps to bring the over all width of the chair down. This really helps when a 19wide or bigger is needed.

    Really looking forward to 2nd generation TDXsp. Supposed to be launched in January. (I'll be looking for it in February...)

  4. #4
    Quote Originally Posted by jakeyboy1 View Post
    SCI-OTR, you are right on!! I've been making the same changes to most of my customers too. Need to move the CG back on most SP's.

    Another TDXsp trivia/suggestion. The distance between the armrests is 2" wider then the seat pan. When a person needs a 18 wide chair, I order a 17 wide chair and a 18 wide cushion. It helps to bring the over all width of the chair down. This really helps when a 19wide or bigger is needed.

    Really looking forward to 2nd generation TDXsp. Supposed to be launched in January. (I'll be looking for it in February...)
    I just heard "sometime during the first quarter" yesterday.

    I've seen the new arm design and that infamous Invacare slop will be gone (currently another reason to go 1" less than spec with the seat width so the cushion puts slight pressure on the current conventional armrests. For now, we'll continue to stick a 1/8" thick ABS shim on the side of the back post near the rear receiver to reduce the gap that causes the wiggle. BTW, Invacare has that .pdf for routing the tilt/elevate harness. They are currently looking at where they routing harnesses and modules.

    Doesn't the location of the multipl actuator interface box make total sense? Then again, you've probably never had those 4-40 screws come loose on you, right?


  5. #5
    Quote Originally Posted by jakeyboy1 View Post
    Really looking forward to 2nd generation TDXsp. Supposed to be launched in January. (I'll be looking for it in February...)
    I'm about to put the order in for a new SP and I was going to add the GB motors to it. Should I wait for the 2nd generation to come out? I'm not in a huge rush...

    This is very good info. Thanks SCI_OTR!

  6. #6
    My$.02
    GB motors are totally worth it!
    If you can wait two to three more months (could be 4) I would wait for second generation.

    I would go through with the approval process and just ask your dealer to hold off ordering chair until it launches.

  7. #7
    Quote Originally Posted by jakeyboy1 View Post
    My$.02
    GB motors are totally worth it!
    If you can wait two to three more months (could be 4) I would wait for second generation.

    I would go through with the approval process and just ask your dealer to hold off ordering chair until it launches.
    I'll hold off then. I'm already approved, I have 6 months. Hopefully it comes out in time! I forwarded this thread to my OT, too. Thanks for the help

  8. #8

    One More Time...

    Here's a before and after pic of a TDX SR with Formula CG Tilt/Recline/Elevate power seating (16-19 seat depth package reconfigured for an effective seat depth of ~20").

    Attachment 43205
    r is the turning radius of the powerchair before and after reconfiguration.

    It is more difficult to get an effective seat depth of 19-20" with the 16-19 seat depth package on recline systems because the reclining hardware eats up some seat depth and the back posts are bolted through seat rail (i.e. they can't be slid back in the channel). On this chair, the legrest receivers were telescoped out all the way and the seat pan was moved forward to get the necessary seat depth.

    In this instance, if the seating system is not mounted as far back as possible on the power elevation actuator, it would be a very front heavy chair.


  9. #9
    Attachment 43439
    Another pic of the black TDX tilt/elevate after re-routing the harnesses beneath the seat
    frame and relocating the multiple actuator interface box to the left back post where
    it is less-vulnerable. Whenever a 4 way toggle or quad push button is used, this location
    will reduce strain on the DB9 connector because it is no longer near the tilt actuator.


  10. #10
    This TDX SP Tilt-Elevate arrived this morning. Note the stock routing of the harnesses and the push handle length.

    Attachment 43482

    Note also the limited gap between the tilt actuator and the multiple actuator interface box when the seat is tilted...

    Attachment 43483

    The black TDX shown in the previous post started out the same way.
    Last edited by SCI_OTR; 01-23-2012 at 01:23 AM.


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