Why ODT’s Do Not Support Natural Locomotion
A linear treadmill provides an excellent simulation of running or walking at a constant velocity, i.e., when no acceleration is taking place. The problem comes when a person tries to accelerate (/decelerate).
To accelerate along a straight line in the real world, one must apply force to overcome the body’s physical inertia (Newton’s laws of motion). All of your reflexes are tuned to apply just the right amount of force to attain the desired change in velocity. Your inner ear senses accelerations, and your proprioceptive system senses the applied and reactive forces your body experiences.
On a treadmill, however, you’re not really going anywhere (or at least not very far). That means you do not have to apply horizontal forces to overcome your body’s inertia to accelerate (with respect to the treadmill’s surface). An ODT simulates what it would be like to remain under the influence of gravity, and retain angular inertia, but eliminate linear inertia. This unusual condition is at odds with a person’s natural reflexes for directing their body’s motion, rendering their natural responses ineffective, i.e., making it difficult to stop, accelerate, or redirect one’s motion quickly on a treadmill.
ODTs are challenging to build because of the demands of their mechanical and control systems. I suspect that a lot of people believe that it is just a matter of perfecting ODTs to keep the user nearly centered of the treadmill in order to provide a realistic simulator for natural human locomotion. That is not the case.
There is a way to simulate linear inertia: Strap the user to an active mechanical tether that pulls and pushes on them to apply the forces necessary to substitute for the (simulated) absence of inertia. The Sarcos Treadport system did just that, albeit it is a linear treadmill:
http://www.cs.utah.edu/research/areas/ve/LocomotionDisplay.html
I have yet to see such a harness built to apply omnidirectional (horizontal) forces for simulating inertia on an ODT.
There may be another alternative. People can learn a wide variety of motion skills. They can learn to skate and ride a surfboard. With enough practice people may be able to master virtually accelerating and decelerating on a well-designed ODT. But they will not be performing natural locomotion and there is no reason to believe that their performance (speed & accuracy) at varied motion tasks will match their real world performance.
-JimT
To accelerate along a straight line in the real world, one must apply force to overcome the body’s physical inertia (Newton’s laws of motion). All of your reflexes are tuned to apply just the right amount of force to attain the desired change in velocity. Your inner ear senses accelerations, and your proprioceptive system senses the applied and reactive forces your body experiences.
On a treadmill, however, you’re not really going anywhere (or at least not very far). That means you do not have to apply horizontal forces to overcome your body’s inertia to accelerate (with respect to the treadmill’s surface). An ODT simulates what it would be like to remain under the influence of gravity, and retain angular inertia, but eliminate linear inertia. This unusual condition is at odds with a person’s natural reflexes for directing their body’s motion, rendering their natural responses ineffective, i.e., making it difficult to stop, accelerate, or redirect one’s motion quickly on a treadmill.
ODTs are challenging to build because of the demands of their mechanical and control systems. I suspect that a lot of people believe that it is just a matter of perfecting ODTs to keep the user nearly centered of the treadmill in order to provide a realistic simulator for natural human locomotion. That is not the case.
There is a way to simulate linear inertia: Strap the user to an active mechanical tether that pulls and pushes on them to apply the forces necessary to substitute for the (simulated) absence of inertia. The Sarcos Treadport system did just that, albeit it is a linear treadmill:
http://www.cs.utah.edu/research/areas/ve/LocomotionDisplay.html
I have yet to see such a harness built to apply omnidirectional (horizontal) forces for simulating inertia on an ODT.
There may be another alternative. People can learn a wide variety of motion skills. They can learn to skate and ride a surfboard. With enough practice people may be able to master virtually accelerating and decelerating on a well-designed ODT. But they will not be performing natural locomotion and there is no reason to believe that their performance (speed & accuracy) at varied motion tasks will match their real world performance.
-JimT