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A Cheap Active Omni-Directional Treadmill

I explain a concept for an active (motorized) omni-directional treadmill that is cheaper and easier to build than most others

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Most active (motorized) omni-directional treadmills are expensive, hard to build, and some suffer from inertia problems. Here I explain my concept for a cheaper, easy to build active omni-directional treadmill.

I Built A Prototype!

Below is a video where I built a small section of the treadmill to test what it would be like.

If I can think of solutions to the issues I described I may make a new version.

A Concept for a Cheaper Active Omni-Directional Treadmill

Many Omni-directional treadmills exist today and I see most if not all of them falling into one of two categories.

  1. Passive - omni-directional treadmills that rely on a smooth, low-friction surface that the user slides his feet on. Also commonly known as slidemills. Examples of these are Omni One by Virtuix and the Kat Walk C.
  2. Active - omni-directional treadmills that use motors to actively move the platform the user is on. Examples of these are the Infinadeck, ACTVR, OmniDeck, and Strider VR.
  3. Each category has its own set of advantages and disadvantages. Slidemills have less moving parts so are cheaper and easier to maintain, but some users may find that sliding instead of actually walking feels uncomfortable. Active treadmills can actually move the floor below you so that it feels very close to actual walking. But active treadmills tend to be more expensive, with the Infinadeck going for $40,000 to $60,000 each for example, have more moving parts so is more likely to break down, and can suffer from inertia problems.

    Here I will explain my own concept for an active omni-directional treadmill. My concept should be cheaper or as cheap to make as other active omni-directional treadmills, not suffer from inertia problems, is scalable to any size, and easy enough to build that anyone with a 3D printer, saw, drill, and basic tools could build one for himself.

    When I first started thinking about my own active omni-directional treadmill concept, my first priority was to try to make it as cheap as possible. You could make an omni-directional treadmill out of omni-wheels using a design similar to the Celluveyor.

    But omni-wheels are not exactly a cheap option when you consider that you would need many of them to make a treadmill out of. I also considered if ball-transfer units could be used, but they are noisy, can't be motorized, and aren't cheap enough either.

    So my first idea was to use simple rollers instead of omni-wheels or ball transfers. A simple roller would be very cheap to make and it wouldn't be too expensive if you needed hundreds of them. The next challenge came with deciding how the rollers should be arranged to achieve have omni-directional capabilities. A the rollers going one way would just produce the motion a regular treadmill produces, so you'd need half of the rollers rotated 90 degrees so you could also have sideways motion. But, each roller has an axle going through it. If you have a set of rollers for forward/back and another set for sideways, won't the axles collide? This stumped me for a while, but then I thought of a solution. Yes, if the rollers are all the same diameter they will, but they don't have to be the same diameter. That led me to make this quick 3D-model.

    This treadmill consists of two sets of rollers. The rollers are of different diameters, so the axles do not intersect as you can see more clearly here.
    Of course, the obvious problem with this idea is that it will produce a lot of friction. If you're walking forward, the sideways rollers will just create sliding friction. This could possibly be reduced by having groves on the rollers or adding a low friction material on the rollers, but then you're going to have to try to balance low-friction with also having enough traction for the rollers to actually move you.

    After this I was again stumped for a while. I decided that the roller had to be a little more complicated, but still be cheap to produce. I recalled the omni-sphere design that I developed for a previous version of my VR shoes.

    These were partially omni-directional, meaning they could produce powered forward, backward, left, and right motion, but nothing in-between. There are other omni-sphere designs, such as this Omni-Crawler....

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sheet - 9.91 kB - 01/31/2021 at 22:18

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  • V2 - An Improved Design

    finallyfunctional7 days ago 0 comments

    I built the first version of my omni-sphere treadmill a while ago and went over my opinion of it in this video.

    Since then I've spent some time thinking about how the design could be improved. The idea I have is mainly around changing the rod that the omni-spheres are mounted on. The changes would make the rod easier to assemble and eliminate the extra space the support columns take up.

    With the design I built, the support columns used to make sure the rods do not flex under the user's weight take up extra space.

    You can see in the image that I had to space the spheres out more to make room for the columns. I want to push the spheres as close together as possible, so this is not ideal.

    What if instead, I could put the support columns at the locations shown in the image below?

    These are all the points where the X and Y rods cross each other (on different Z planes). Support columns in these places may not take up much extra room, and there would be more columns to better support the user's weight.

    I figured I could place support columns in these places if I could imbed a bearing into the rod itself, like shown below.

    To do this, instead of using a 1/4in round rod, I'd use a tube. Specifically a tube with a 1/4in OD and an ID as close to 3mm as possible, 1/8in should be okay. I could try to find tubes that are in metric units with an ID closer to 3mm, but being in the US, and because I will need a lot of tubing if I am going to build this, I'd like to use tubes in imperial units since they're cheaper. Something like this tubing which is cheap, and shipping is free for orders over $100.

    Assembling the rod would look like the image below. The 3mm rods would go through the 3mm bearing and the tubes.

    To make sure the 3mm rods do not spin freely inside of the tubes, I'm thinking I could use epoxy.

    With the 3mm bearings being imbedded, the support columns could look like this. They take up less space than the columns I had previously.

    With this design, the spheres can be spaced closely together while the rods themselves are very well supported, as shown below.

    Additionally, I think a treadmill where the rods are actually metal will decrease the bumpiness. In the build I already made, I made the rods out of plastic because, to be fair, I thought it would be fine to be lazy and let the 3D printer make all the parts. However, it's possible some of the bumpiness was due to the rods being made out of plastic, which means they could have flexed a bit and allowed the spheres to bounce up and down a little.

    The last build was also much bumpier with my shoe than with the piece of wood I tried. Perhaps the user can just wear an overshoe that has a rigid, hard surface on the bottom like the piece of wood to reduce bumpiness and noise.

    So in summary, I believe that if I use this new design to make the rods with embedded 3mm bearings, I can make smaller support columns that will enable me to push the spheres closer together, I can make overshoes that are rigid on the bottom, and using metal rods, will all reduce the bumpiness and noise I saw with my previous build.

    I plan on making a new build that utilizes this design some point in the future, probably within a few months as of the time I am writing this.

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