When the team at Dynamic Structures designed and built the
large Canada-France-Hawaii Telescope enclosure on Mauna Kea, a dormant volcano,
no one foresaw the company's future expansion to design, fabricate and assemble
amusement rides. "Think of an amusement ride not as a structure but as a large
complete machine and you'll understand the connection," says senior designer
Dynamic Structures designs roller coasters and theme-type rides.
A roller-coaster vehicle rides along a track and nothing else occurs, except
some screaming and white knuckles. The passengers just go along for the ride.
In a theme ride, though, the vehicle travels along a track and interacts with
things along the way. "For a theme ride, we work with a large team from the
buying company," says Breckenridge. "So we regularly review and exchange many
drawings and models. And we must design and fabricate rides with small
tolerances. In a 1.5-mile ride, for example, we have many sections and we must
keep the gap between them to within 30 thousandths of an inch."
"Most of the time we use Autodesk's Inventor for part of a ride
and AutoCAD for the remainder," says Breckenridge. "The programs function
differently and offer different capabilities. Here's an example: Most rides and
roller coasters include mechanical track switches that let operators remove a
vehicle or route a ride onto a different path. We create the switches in
Inventor because they represent compact machines compared with the structure
and mechanics of the rest of the ride."
"Often we create a track in AutoCAD and use Inventor to design a
vehicle," continues Breckenridge. "Then we can put them together in 3D Studio
(3ds) and produce an animation that shows what a ride will look like. We use
Navisworks for visualization and dynamic simulation. Then we can play the video
animation for clients so they can see what the vehicle looks like as seen from
a spot on the ground. Or, we can show them what the ride looks like from the front seat."
"Navisworks also lets us check the reach envelope, or the space a
passenger can reach from a moving vehicle," says Breckenridge. "We must ensure
they can't reach out during the ride and touch something as they go past. We
also run dynamic simulations that tell us the forces a passenger will
experience during a ride. This analysis gives us the maximum g-force
experienced on the center line of the rails. But we also must know the g-force
on the passenger's heart line, or roughly just above the center of a human
torso. When someone sits in a seat, their body can still move, much like a
lever, and experience greater g forces than we would measure along the track's
center line. We want to ensure a ride doesn't put too much strain on the
Breckenridge and his colleagues also use Autodesk tools to help
control the stack-up of tolerances. "We had a ride where we thought we knew how
the tolerances would accumulate, but when we installed the track, it grew
slightly in length. Our method to maintain the proper length of track involved
two fixed survey points, but one had floated a bit. We didn't think about it at
first, but when we got to the site and started to erect the track we realized we had a problem."
"The reference point moved slightly during track fabrication,"
continues Breckenridge. "One point we surveyed to was fine, but the other end
moved by about 1/8th of an inch. That doesn't seem like much, but when the
track comprises 70 pieces, the final assembly can increase by several inches.
When you attach the track to fixed columns, you don't have that leeway." The
Dynamic Structures engineers now include expansion joints between the track and
the column in all rides to let the track move slightly in a prescribed
"We also run thermal analyses for each ride because parts could
have to operate indoors or outdoors," says Breckenridge. "Thus the track
behaves differently based on ambient temperatures. Our designs have used the
Autodesk tools to let the track moved in tightly controlled ways to take out the expansion due to solar heating. That's not a trade secret, but
it might be something engineers haven't thought about."
Some structural-analysis and dynamic-analysis tools used at
Dynamic Structures come from companies that work closely with Autodesk. But the
company still relies on an Excel spreadsheet to "control" those two programs
and provide all the geometrical design information. "Right now it's easier to
communicate that way and have a single source of data," says Breckenridge. "As
the interoperability between software packages gets better - and it happens in
each new release - we'll get to the point where we don't use the spreadsheet.
Now we can take the Inventor model and give it to the dynamic-analysis add-on
package and get the results back out of Inventor. Our last dynamic analysis for
a ride vehicle occurred entirely within Inventor. We didn't export information
to any other software."
Often, Dynamic Structures delivers a complete ride that includes
the electronic controls. "We work with a company that creates all the controls
for us," explains Breckenridge. "They use the AutoCAD Electrical package that
integrates with Inventor, so we take advantage of good interoperability again."
Design software works well and many recent engineering graduates
can create amazing designs. According to Breckenridge, however, many students
lack practical design skills. "On one ride we have a complicated switch that we
assigned to a structural and a mechanical engineer. When their design got to a
peer review, we found the structure was a bit on the light side and the
stiffeners were a bit heavy. When the engineers realized their structure wasn't
quite strong enough, they kept adding heavy stiffeners. So they created a tiny
frame and many big stiffeners. The creation was fine structurally, but
impractical to build. It just didn't look right, either. One of the other
engineers and I say, â€˜If it looks like something you might have designed in
high school it's probably better.' In an amusement ride, aesthetics play a
role, too. We want a nice-looking structure and Inventor helps us create it."
Breckenridge says new
engineering graduates need to learn how to communicate better with their
colleagues. "When they start a design or project, they should talk with fellow
engineers and find people in the company who have a lot of experience. Talk
with engineers who have worked on similar projects and talk with the people in
manufacturing and on the shop floor. Then the new engineers will learn whether
the mechanical shop people can produce that they designed. Can the fabricators
get a weld into the space provided? Can they drill a hole in a given position?
software lets us create a 3-D model to see how it will go together. So we make
sure we can erect what we build. We really like the animation tools."
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