Suggestions for low friction surface materials for a "beltless static treadmill"

I'm currently developing a treadmill for clinic gait research. If I were to build a flat treadmill with no moving surfaces what materials or coatings would be worth exploring as walking surface. Ideally, the surface would be durable, safe to touch with bare skin, capable of supporting a healthy adult, and low cost. The user would most likely use the treadmill wearing socks, made of either cotton, wool, spandex, or nylon. Delrin has been explored but is not adequate and produces a residual friction load on the user, producing artifacts in gait.

If you don't necessarily have a suggestion for a material, please suggest a way of calculating the equivalent friction coefficient between a surface and a fabric. This method could be experimental or based on theoretical methods using a materials database.

• I think the problem will be in allowing motion in the direction of the stride while restraining it laterally. Oct 29, 2015 at 12:04
• The user will be in a load bearing harness which may help. Oct 29, 2015 at 15:20

While it is an interesting idea, I don't think a "static treadmill" is going to give you results similar to walking. A PFTE(teflon) surface would be really low friction, but I think there are some bigger issues you may need to address first.

Walking is essentially a repeated process of balancing, tipping, and re-balancing. The algorithms your brain uses to do this process will not be the same as the algorithms it will develop to slide your feet as if you were walking. The physics is different and your brain will accommodate the new physics. So while I'm sure one could become quite proficient at doing it, I don't think that it will model actual walking/running very well. Let me give you some examples:

1. When your body is in the re-balancing stage it is providing a net amount of force to move the mass of your body forward. The movement of your body relative to the surface provides a somewhat constant velocity for your legs to rely on and manage. On your static treadmill you legs will be permitted to travel at any velocity they choose and may even change that velocity during a stride without consequence.

2. Putting the person in a harness artificially changes their weight; so now the person's stride will change because the legs do not have to support as much weight during the walking process.

3. The low friction surface will not provide the stability needed for a normal stride. You can walk on ice, but your stride is much different and purposeful than when you walk normally.

• I agree with with everything you said here. The idea is just to develop a device that works almost like walking. There could be interesting things in analyzing modified walking like this. Oct 30, 2015 at 19:58

If you have to select a material for this application, I would use ultra high molecular weight polyethylene (UHMW). It has a very low coefficient of friction, very high wear resistance, and is a lot cheaper than Teflon.