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Caster flutter on a Permobil M5-DME supplier cannot seem to fix

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    Caster flutter on a Permobil M5-DME supplier cannot seem to fix

    I have a Permobil M5 and I'm having trouble with caster flutter on both front casters. I don't quite understand it. I can roll over good-sized bumps in the sidewalk etc. and nothing happens, then I roll over a shadow or a pebble and one or the other starts fluttering badly enough that I have to come to a complete stop. I rolled all over a parking lot, which is quite bumpy and it didn't trigger it. But, I roll around the streets in my neighborhood or a paved bike path and they trip fairly often. It's often enough to be more than just an annoyance.

    This is my 1st Permobil chair. If anyone is familiar with this and has suggestions on how to prevent, please let me know
    thank you

    #2
    More than likely a speed wobble. On flat clean pavement you go faster and it starts, though it shouldn't. Are the casters angle adjustable, pneumatic? Bearings in fronts good? Caster stems and wheel axles tight? Did you get new rear tires that would have changed the angle of the fronts? If all else fails I put a rubber washer (the one that goes in a garden hose) between the top nut and the bearing. That helped.

    Comment


      #3
      My F5 definitely gets speed wobble when I ride at reasonable speeds on flat terrain. Quite annoying.
      C5/6 complete (maybe) circa June 2018

      Comment


        #4
        Is there a way to tighten the casters in front? Looking at a photo, it looks like a person just has to pop the top of the front caster housing off and tighten the bolt a bit. I/d start with 1/4 turn. Probably a 3/4 or 11/16" socket should do it.
        If possible, lift the front wheels off the front and see how easy they swivel. If swivel really easy it's an indication they are too loose.
        Last edited by Patrick Madsen; 11 Jun 2020, 1:02 AM.

        Comment


          #5
          If one caster is higher than the other, then the lower caster will have more weight on it than the higher caster. Flutter happens as the weight on the casters modulate at just the right frequency. A highly irregular surface will tend to create random modulation which isn't going to create flutter or at least not a lot of it. It's the surfaces that are level with some degree of irregularity that tend to create fixed frequency modulation and hence create flutter. Asphalt is the perfect storm for flutter.

          Either limit your speed or align your casters.

          Comment


          • wchair
            wchair commented
            Editing a comment
            I see, that pretty much explains my problem.

          #6
          It's a simple feedback situation. With a caster'd wheel, there is a self-centering force when the wheel deflects from it's track. The caster effect creates the self centering force to return it to "center" but at higher speeds, the momentum of the moving assembly takes it past center creating an opposite self centering force. The caster can then have enough feedback forces for it to resonate which is what flutter is.

          The first step would be to check and if necessary, adjust the caster fork axis which is the line through the the pair of bearings and the shaft inside.
          It must be vertical in both axis (lateral and fore/aft). If it's off much, see if that suffices.

          If not, you can confirm that the two casters are not at different heights; if you tip the chair back with both casters swung straight forward, the should un-weigh at the same time. If not, you can usually move the high one down with a washer on the stem where it registers on the bottom bearing.

          If these gambits fail, then you need to dampen the forks with friction. (remember those VW Beetles with steering dampeners? Their resonant frequency was at 55mph! Same problem, same fix with a horizontal shock absorber in the steering). I won't suggest how to do this because each setup is different, but basically you want to induce resistance into the rotation of the fork stems in their bearings. The early automotive shock absorbers were friction type. If it was good enough for Bugatti, it's good enough for you!
          69yo male T12 complete since 1995
          NW NJ

          Comment


          • wchair
            wchair commented
            Editing a comment
            Okay, this gives me some other things to explore the technician. It's just a new chair and have really not had this problem before with anything but the Permobil.

          #7
          Watch the shopping carts at the grocery stores. You will see flutter and see the high caster on one side doing it especially outside when speed picks up.
          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.

          Comment


            #8
            Originally posted by baldfatdad View Post
            More than likely a speed wobble. On flat clean pavement you go faster and it starts, though it shouldn't. Are the casters angle adjustable, pneumatic? Bearings in fronts good? Caster stems and wheel axles tight? Did you get new rear tires that would have changed the angle of the fronts? If all else fails I put a rubber washer (the one that goes in a garden hose) between the top nut and the bearing. That helped.
            The chair is roughly 9 months old. The the casters have been checked by the DME technician and the right caster has been replaced. They are solid small tires and I haven't had anything else on the chair replaced. He is insisting that they are tight. I had an Invacare TDX sp prior to this. After 3 or 4 years of use at 6 mph one of the casters would start to flutter occasionally. As I said, this Permobil is only 9 months old and I got the upgraded speed 7.5 mph. I don't understand the point of being able to go 7.5 mph if you have to stop every 8th of a mile to stop your casters from flipping around.

            He did put some silicone spray in the caster mechanism to eliminate a slight rubbing noise, could that be the problem?
            Could this have made things loosen up a little?
            Thanks

            Comment


              #9
              Originally posted by Patrick Madsen View Post
              Is there a way to tighten the casters in front? Looking at a photo, it looks like a person just has to pop the top of the front caster housing off and tighten the bolt a bit. I/d start with 1/4 turn. Probably a 3/4 or 11/16" socket should do it.
              If possible, lift the front wheels off the front and see how easy they swivel. If swivel really easy it's an indication they are too loose.
              Thanks, yep we've been down that road. He initially loosened them too much. But now understands that they have to be very tight and as far as I know they are. I will recheck.

              Comment


                #10
                Originally posted by wchair View Post

                The chair is roughly 9 months old. The the casters have been checked by the DME technician and the right caster has been replaced. They are solid small tires and I haven't had anything else on the chair replaced. He is insisting that they are tight. I had an Invacare TDX sp prior to this. After 3 or 4 years of use at 6 mph one of the casters would start to flutter occasionally. As I said, this Permobil is only 9 months old and I got the upgraded speed 7.5 mph. I don't understand the point of being able to go 7.5 mph if you have to stop every 8th of a mile to stop your casters from flipping around.

                He did put some silicone spray in the caster mechanism to eliminate a slight rubbing noise, could that be the problem?
                Could this have made things loosen up a little?
                Thanks
                Uhh yeah, silicone is the last thing to spray into a caster housing to stop fluttering or noise. All he had to do was loosen up the caster a 1/16th or 1/8th inch turn. What the heck is wrong with todays techs.? No common sense at all. if they flutter with both wheels at 90o and level on ground, tighten up ; if they have noise and no flutter, loosen a degree or two.
                Last edited by Patrick Madsen; 14 Jun 2020, 5:30 PM.

                Comment


                • wchair
                  wchair commented
                  Editing a comment
                  Damn silicone, I had a feeling. I'll get them to clean that out.

                #11
                Originally posted by wchair View Post

                The chair is roughly 9 months old. The the casters have been checked by the DME technician and the right caster has been replaced. They are solid small tires and I haven't had anything else on the chair replaced. He is insisting that they are tight. I had an Invacare TDX sp prior to this. After 3 or 4 years of use at 6 mph one of the casters would start to flutter occasionally. As I said, this Permobil is only 9 months old and I got the upgraded speed 7.5 mph. I don't understand the point of being able to go 7.5 mph if you have to stop every 8th of a mile to stop your casters from flipping around.

                He did put some silicone spray in the caster mechanism to eliminate a slight rubbing noise, could that be the problem?
                Could this have made things loosen up a little?
                Thanks


                If you had/have a rubbing noise, that's probably a bearing. Get each or both front wheels off the ground. Rotate and spin them. If you feel ANY resistance, its probably a bad bearing.

                Comment


                  #12
                  I had no flutter on my chair until I removed the dog hair. The extra resistance from the dog hair was preventing flutter. Newer chairs will have lower caster resistance so they will be more sensitive to flutter.

                  On a separate occasion, I hit a pot hole a week ago that immediately put the casters out of alignment and resulted in flutter. The next day the flutter went away. I looked down and noticed that the caster was even more out of alignment than before. Seems that just a little misalignment may be worse than a lot of it.

                  Unless a new chair is aligned perfectly, it's probably the prime candidate for flutter. Good news is that once it's adjusted and broken in over time it will become less sensitive to flutter.

                  Comment


                    #13
                    Curb hopping or any use that twists, just slightly, a chair’s frame could and most likely will
                    cause an alignment issue resulting in caster flutter.

                    Rob Banks
                    You C.A.N.
                    Conquer Adversity Now

                    Comment


                      #14
                      Thanks for all the suggestions and general information. As I said it's not something I've had to deal with before so this gives me a lot of ideas, things to suggest, if he can't figure it out.
                      So basically:
                      -check for things like bad bearings
                      -check alignment
                      -as tight as possible unless grinding
                      -no lubricants like silicone
                      -let them get a bit "dirty" for lack of a better word and it will help them stabilize.

                      Comment


                        #15
                        Everything except let them get dirty.

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