# Thread: Can you Stop Castor Wheel Flutter?

1. ## Can you Stop Castor Wheel Flutter?

I like to play sports in my everyday wheelchair and the castors start to flutter when push faster. Can I help to aleviate the flutter?

2. X 2. Not for sports but for running my dog.

3. Originally Posted by TheAbleChef
I like to play sports in my everyday wheelchair and the castors start to flutter when push faster. Can I help to aleviate the flutter?
That happens to me too, I usually do some miles on my chair when I can and when i get speed they start flutter, i think that the problem is the size of the casters, because i had before a 6" casters in my quickie i and could go faster downhill, but i prefer go a bit solwer and have a little caster.

4. Originally Posted by totoL1
i think that the problem is the size of the casters, because i had before a 6" casters in my quickie i and could go faster downhill, but i prefer go a bit solwer and have a little caster.

I think it has more to do with the frequency of the vibrations based on the geometry of the front end of your chair. Here is a larger scale example based on the same differential equation which as a result (primarily due to vibrations caused by gale winds perpendicular to the span) ended in disaster:

Lucky for us, our front wheels won' fly off.

5. So do you think that i have to change my geometry?
Here is a pic of the geometry of my forks and i have 19.5" in front and 17" rear hight, so with this geometrys i think that they are correct, so where do you think the problem is now?

6. But i`m speaking about flutters with a speed above 10 miles/hour aprox.

For exemple, i can`t go like this guy downhill http://www.youtube.com/watch?v=wslLfJ-yAfQ

7. Caster wheel flutter is not caused by the geometry of your caster wheel setup. flutter is a self exciting oscillation caused by the tread contacting the ground flexing in such a way as to force the wheel to go back towards the centered position with more force than it left. Since the tread takes a certain amount of time to flex back there is a lag in the cessation of the force that re-centers the caster wheel causing the wheel to swing past center in an overcorrection to the other side. And then it repeats itself in the other direction. And back and forth. The solution is to dampen out the oscillation before it diverges with some force(friction) resisting the quick oscillation. Most wheelchairs have a way to tighten down the stem to provide more friction. Often wheelchairs with an inexpensive split ball bearing race used on their caster stems will loose their factory stem preload as their bearings wear out providing more clearance and then the stems and forks then spin freely with almost no friction. You want the fork to turn about a revolution to a revolution and a half when you flip it as fast as you can. if it spins around more freely than that you will not have enough friction to dampen out the flutter as your wheelchair picks up speed. By tightening up your stem assembly you push the speed necessary to overcome the friction present in your stem assembly above the range where you will operate your wheelchair. A loose grocery cart wheel will flutter at a very low speed. As you tighten up the bearings the speed required to cause flutter goes up. If you tighten up your caster stem bearing assembly until you get enough friction the flutter will go away.

But as the manufacturer of the Flight Ultralight wheelchair I have to say buying a wheelchair with better bearings like ours will mean no adjustment due to bearing wear. We offer on a manual ultralight wheelchair what is to our knowledge the only caster bearings rated for what an active user can dish out. The other manufacturers are not giving you a 6000 pound axial load rating and 2000 pound radial load rating bearing. Many offer a bearing rated for 350 pound radial load and not intended for axial loading at all.

I hope this is helpful. Your DME should also know how to adjust your casters to dampen out the flutter. But not all do or care to.

8. To anyone with questions about wheelchair caster shimmy, I'll link you to the best study I have ever read on the topic.
http://www.rehab.research.va.gov/jour/00/37/3/kauzl.htm

I read this before designing the caster assembly for the Flight ultralight wheelchair, and incorporated most of it in our design.
If you read the study you'll know everything I know about caster dynamics.

Check out our highly engineered ultralight wheelchair. http://www.airwheelchair.com

9. I use a news soft roll casters, so i don`t think that the problem could come from the bearings of the casters, because the whelchair do the flutter before with the other caster too.
My chair is a quickie gtx and i don`t think that they put bad bearings in their chairs, my english is not as good for understand all that you tell me, speak to me like you speak to a little baby for can undertand.
I think that your are trying to say me that the problem can come from the bearings of the forks.
If i do that you say to the fork with the caster in, they do about 4-5 revolutions before stop.
I`ll take off the fork and try to see whats happend.