About the only thing that probably
comes close to getting paid to design pieces and parts of snowmobiles
and then getting to test and ride those parts on a sled would be
getting college credit for doing the same thing.
That’s what a group of seniors
majoring in mechanical engineering at the University of Utah did last
year.
This group—project leader Sean Wilson
along with Dan Hirst, Julie Painter, Trevor Thomas, Marshall Maughan
and Erik Brockhoff—had the idea of designing and fabricating a
carbon fiber tunnel for a Polaris RMK. The purpose was to—you
guessed it—lighten up the sled.
In the team’s project summary at the
end of the spring semester, they stated, “The purpose of the
project was to reduce the weight of a snowmobile intended for use in
steep terrain with deep snow without sacrificing strength or
stiffness.”
More specifically, the executive
summary stated, “The primary goal of the Carbon Fiber Snowmobile
Senior Design Project was to redesign, fabricate and integrate
portions of a snowmobile chassis made from carbon fiber composite
materials to replace the existing components made from steel and
aluminum in order to reduce weight.”
Polaris donated an 800 RMK 155 to the
engineering students for their senior project and much of the work
was done in a local shop. As stated on the project summary, “The
portions of the chassis chosen to be replaced were the aluminum
tunnel and steel tubular structure. The replacement parts had to be
made just as strong or stronger than the originals, while also being
lighter in order to exceed the stock design’s capabilities.”
Here are some highlights—in the
team’s own words—from its project summary as well as one of
several presentations it had to make during the two semesters of
working on the carbon fiber snowmobile.
Material Selection
In order to select a material
configuration that would satisfy the necessary requirements, samples
were manufactured, tested and the results recorded.
Tunnel
The material chosen for the tunnel was
a sandwich composite comprised of carbon/epoxy face sheets and a Poly
Vinyl Chloride (PVC) foam core. The material produced a strength to
weight ratio nearly five times better than that of 6061 T6 aluminum
alloy.
Tube Structure
The 1-inch OD, .050-inch wall, mild
steel structure was replaced with 6061 T6 aluminum wrapped in
carbon/epoxy composite. Due to the higher yield strength of 6061 T6,
stiffness was focused on rather than strength. About 25 percent of
the stiffness difference created by the lower modules of elasticity
of the aluminum was reduced by the material configuration selected.
The weight of the structure replaced was reduced by about 43 percent.
Cooling System
The carbon/epoxy composite material
does not conduct and dissipate heat in the same manner as aluminum
alloys. This created a problem for keeping the engine cool because
the stock tunnel also doubled as a heat sink/cooling fin with coolant
being plumbed through its structure. A dual fan aluminum radiator
taken from a 1300cc sport bike combined with an electronic thermostat
control was used to solve this cooling problem.
Reassembly/Test Riding
The composite components manufactured
were reassembled with the stock components to produce a fully
functioning, working, running and rideable sled. The sled was ridden
on two occasions by the design team to verify structural integrity
and cooling system function. The newly reassembled sled performed
very well. No damage to the composite components could be seen and
the temperature readout integrated into the stock cluster never
displayed a temperature greater than 215 degrees F (on a very warm
and sunny day ~45 degrees F).
Results/Weight Savings
Factory Composite Replacement
Steel tube structure factory weight: 14
lbs. Hybrid aluminum/carbon/epoxy weight: 8 lbs.
Aluminum tunnel: 30 lbs. Carbon fiber
tunnel w/radiator: 19 lbs.
Total weight reduction: 17 lbs.
Fluid Weight
There is another possibility of weight
reduction due to less coolant being required for the engine cooling
system. The stock cooling system contains roughly 13 lbs. of coolant
with a certain amount of that being held in the tunnel. The amount of
coolant contained in the radiator would appear to be less; however, a
quantifiable amount was not measured and would not be factored into a
dry weight.
Conclusions
The project has been deemed a success.
Based on initial test riding, the goal of reducing weight while
maintaining strength through the utilization of composite materials
has been met. It would also appear that the use of this composite
technology could be expanded into other areas of recreational vehicle
production. The ability to quickly create relatively durable tooling
and prototype parts for complex geometries would lend itself greatly
to developing and testing new designs without the need of expensive
tooling for initial prototypes.
Wilson, the project leader, kept
SnoWest apprised of the progress from the initial tear down of
the new RMK to the test ride last spring. One of the original plans
called for replacing the stock seat with a lighter seat, as mentioned
in an e-mail last March. Wilson wrote, “We have come up with a
creative way of cooling the engine while incorporating a lighter
weight seat that should also increase the strength and stiffness of
the tunnel. We will be using a Hayabusa radiator with carbon fiber
ducting to encapsulate the cooling assembly as well as support the
seat. It should be lightweight and really cool.”
As you read, the radiator was necessary
for cooling due to the removal of the aluminum tunnel and that was
installed but the team wasn’t able to do the seat exchange
Then this e-mail, later in March, where
Wilson said, “The first test ride went really well. The cooling
system worked as intended and the carbon structure matched up to the
stock aluminum. The steel hoop for the seat will be eliminated and
the seat structure will be integrated into a carbon cowling to cover
the radiator we had to install on the tunnel.”
After the second test ride, Wilson
wrote, “On Friday, April 2, we took the sled out for a more
aggressive ride and video shoot. We made a couple of changes and
additions since the first test ride. I managed to bend an A-arm and
rolled the sled three times while riding but see no signs of damage
to the carbon. Everything, including the cooling system, seems to be
working well.”
Popular Display
We attended the Senior Design Day at
the University of Utah, where senior engineering students’ projects
were on display. Gauging by the number of people viewing the
displays, the Carbon Fiber Snowmobile Team’s project was one of the
most popular that day.
And according to the Carbon Fiber
Snowmobile Senior Design Team’s faculty advisor, distinguished
professor K.L. DeVries, it was a “unique” project indeed for
University of Utah students.
DeVries said, “For undergraduate
students, it was rather unique. Not only did they need to design
carbon fiber parts to exactly fit and replace the original metal
parts but they had to design the techniques, etc., to manufacture
parts and attach them to the snowmobile.”
Utah’s DeVries said he was pleased
with how the project turned out. “I was very satisfied,” he said.
“The students demonstrated the use of computer techniques in
design, they manufactured the parts of equal or better strength than
the parts they replaced while maintaining appropriate rigidity at a
50 percent (from 34 to 17 lbs.) savings in weight. They installed the
replacement parts on a functioning snowmobile and operated the
machine, clearly demonstrating that the replacement parts were
completely functional.”
We asked Wilson, the project leader,
looking back over the course of several months of designing, building
and testing what he would do differently on the snowmobile project.
“Given the opportunity to go back and do it again, knowing how much
work it was going to be, I would have started organizing team
meetings and planning for the project during the summer rather than
waiting for the school year to begin,” he said. “We had a lot of
high-stress crunch time right up to the presentation day to get
everything finished up because of some unforeseen delays in the
project.”
In talking with Wilson and other
snowmobile project team members at Senior Design Day, they were
stoked with how things turned out with the sled, despite the delays
and minor setbacks. Wilson would later tell us of one aspect he was
particularly pleased about on the project. “The replacement seat
support and rear cowling were taken from 3D computer model to
finished product in about 10 days and it actually fit. At the
beginning of the project, I never would have thought that our team
could rapid prototype something out of carbon that fast and have it
look exactly how we wanted. I was very proud of our team after those
components were installed the weekend before the due date.”
However, not all was perfect, as Wilson
pointed out. One “setback” he noted was, “When we first did the
finish work on the plug, the male piece that the mold is made from,
the epoxy paint hadn't cured completely and began to peel up. Keep in
mind that we had spent at least 80 hours designing, machining,
sanding and painting this plug, only to have the paint peel up,
rendering it useless. This was a frustrating setback, but the team
had no choice but to spend an entire week reworking it to get it
right.”
But it all worked out in the end and
the team got to see the result of all their hard work when they put
the sled on snow last spring. It really comes as no surprise that the
two test rides were the highlight of the project’s tenure. Wilson
said, “The most fun I had during the project has to be, hands down,
the first test ride with the team. We had just spent eight months
tearing down, redesigning and reassembling an entire sled and not
only did it go back together, but it worked. I have never been so
happy, relieved and excited in my whole life.”
