Intro to Computer Motion
Motion Chairs bring with them new capabilities and a bit of a new vocabulary. Some of the new words have to do with the mechanical aspects as to how the motion is created, while others have to do with the types of motions themselves.
"The idea of motion is not to simulate, the idea of motion is to stimulate." Brad Engstrand, Chief Kinaestetician (AKA Motion Guru), 2015
This is a concept that is often lost when discussing motion chairs. It is very easy to judge these devices by what an observer sees from the outside. In the case of a flight simulator, this would literally be if the plane is banking 20 degrees, the platform should bank 20 degrees. Observationally, this would appear to be an accurate simulation. Practically, the feel to the pilot will not be as good as it looks. Why? A real plane doesn't just bank 20 degrees. While banking at that angle, your butt is being pushed fairly hard into the seat. The plane is also vibrating and shaking constantly. Not necessarily with big enough motions to see much, but you sure do feel it. This all adds up to a set of "feels" that is not nearly as simple as "We're banking at 20, the chair is at 20, job done."
Other real world issues go into this as well. If the motion chair can only go to a bank of 20 degrees and you are literally trying to match the motion to the numbers, what happens when the pilot calls for 45 degrees? We can probably agree that it is more important to get the feel of an additional bank rather than worry about how the bank looks to an observer. To accomplish this, there are tricks. Remember that we are only trying to trick the human vestibular system, which evolved over time to keep people standing upright and help prevent them from falling out of trees. It's not that difficult a system to trick using newfangled, modern equipment, like our motion chairs. So how do we deal with getting more of a bank? While the turn is held at 30 degrees, we might slowly back the motion chair down to 10 degrees. Slow small moves are very hard for a person to detect, especially when combined with background rumble and minor turbulence. So when the call comes in for more bank, the motion chair can quickly respond with a large motion. None of this will look exactly correct to an observer, but it feels more correct to the pilot.
Generally, when someone uses the word stimulate, it is another way of saying "making you feel." And that is what motion chairs can do. When used well, they not only have an effect on your sense of position and balance, but they can also affect your emotions. What? You scoffed emotionally? Why yes, it is true. Motion chairs can elicit an emotional response. (Since we've moved into the world of psychology, I have to use bigger words for a while.) Imagine, if you will, that you are watching a horror movie. The good guy is casually walking down the hall of the abandoned steel mill. While he's walking, you are gently being tilted to one side. You probably won't even notice that the tilt is happening, but you will get an extra sense of unease. On the screen, the good guy is still just walking.
What you are experiencing in this situation is an emotional response to the motion. (Notice that motion is at the heart of the word emotional.) You may not have been consciously aware of the tilt, but a lot of warning signals were being sent to your brain about the situation. As far as you sensory system knows, a little more of a tilt and you'll fall out of that tree.
On the opposite side of the emotional spectrum, motion can make funny things extra funny. (While we take equal opportunity in motion experiences very seriously, I'd like to talk to the males for a moment.) Some people lament the death of physical comedy in movies and TV, but there are still great examples out there. It’s hard to watch a Ben Stiller or Will Ferrell movie without laughing at the pratfalls. Imagine watching “Blades of Glory” with motion added, so you can feel the difference between the grace of skater Jimmy MacElroy (Jon Heder) and the rough raw power of skater Chazz Michael Michaels (Will Ferrell). Will you survive the Iron Lotus? Always funny. More funnier with motion.
OK males, you may skip this paragraph if you wish. In almost any Jennifer Anistan movie, there will be a scene in a bar where a random guy is encroaching her personal space. As she moves back, you'll move back. It's a simple motion, but it helps you quickly connect to the story.
Now let’s start with the mechanics.
The new iMovify motion chair is a pneumatic system.
That is, it uses air pressure to create the motion. Other options that have
been tried over the years include electric and hydraulic. An electric system
would use motors to create the motion, while a hydraulic system would use
fluids. The different systems each bring something different to the table in
terms of capabilities.
Pneumatic was chosen for a number of reasons, but one
of the most attractive features of using pneumatics is the extremely fast
response time associated with it. Small valves open and close to set the
position of the pneumatic actuator. The effect of opening a valve is felt
very quickly. A quiet air compressor is used to provide the air pressure.
An electric motor, on the other hand, tends to have a
longer response time. Motors powerful enough to move a person don’t
really like changing directions very quickly. This limits the types of feels
that can be generated affordably.
A hydraulic system uses fluid, as opposed to the air used in a pneumatic system. The fluid is pressurized and pumped using electric motors. Hydraulic systems can be made to be quite responsive, but they are not as cost effective. If there is a break in an air line, things will hiss and you might feel a breeze. The worst that would happen is that a little bit of water condensation might form. A break in a hydraulic line will result in a leak of fluids that you probably don’t want around your feet, and certainly not on the living room carpet.
Degrees of Freedom
The term
Degree of Freedom, or DOF, is used to describe the types of motion that
a motion base can make. A typical kid’s ride at the mall can be thought of
as a 1 DOF machine, in that it can move up and down. (I’m not sure if it
would be a half DOF if it only went up, but it wouldn’t be much of a ride.)
A 2 DOF machine can give a wide variety of moves. The iMovify chair is a
2DOF machine. Generally a 2DOF can be thought of as providing Pitch and
Roll. That is, it can tilt front to back for pitch and tilt side to side for
roll.
These motions can be combined so as to give the feel
of other types of motions as well. With tilt and roll the iMovify chair can
essentially have your head do a roll under the programmer’s control. This
allows for a great deal of control over how your inner ear responds to the
motions that are programmed in. What someone sees the iMovify chair do is
not quite the same as what you will feel riding it. For our Arcade units, we sometimes had to put in big movements so that the spectators
could see interesting looking motion while the player was getting the full
feel from motions that could barely be seen.
The iMovify chair can create many types of motions
that aren’t particularly visible. The rumble of a car doesn’t look like a
lot, but it dramatically enhances the feel of driving. Rumble for a road feel is accomplished by providing short pulses of
motion in various directions. It might look like the iMovify chair is
twitching a little. What you feel is real road rumble and occasional rocks
under the tires.
Moving up from the 2DOF system is a 6DOF.
Occasionally someone will try and build something between 2 and 6, but 6 is
more common. A 6DOF motion chair has pitch and roll, like the 2 DOF, but
also has Yaw, slide X, slide Y, and Heave.
Yaw – Rotates right or left while keeping level
Slide X – Slides right or left while keeping level
Slide Y – Slide forward or back while keeping level
Heave – Moves up or down