Momentum - February 2020 - 11

STUDENT
GENERATION

CAD model of M15.

articulation angle, so to determine the magnitude of this
power loss in our application, we built a test bench that
measured input and output power at a representative
torque for a large range of angles, concluding that power
loss doubled at full droop compared to at ride height. 
Given the results from these two tests, we had reason
to reduce our travel: M15 achieves 13.5" and 13.2" of
overall front and rear vertical wheel travel, respectively,
with our all-aluminum independent suspension. Reducing
travel also improved clearances and eliminated the
need for bent suspension linkages to avoid interference,
reducing manufacturing time and cost. 
Another subsystem we focused testing on was the
brakes, a subsystem we had designed and manufactured
entirely in-house for M14. One major change this year
was the switch from custom floating calipers to off-theshelf mountain-bike brake fixed calipers following issues
with binding and manufacturing resource constraints. To
test the feasibility of using stock calipers, we retrofitted
Shimano Zee calipers onto an old car and confirmed we
could lock the wheels reliably before incorporating the
Shimano calipers into M15's design. Eliminating hours
of machining custom calipers freed up time to build a
brake dynamometer to inform brake pad selection by
testing coefficients of friction of available options. We
also measured on-car locking brake pressures to validate
the models our custom brake system components were
designed to, resulting in an extensively tested brake
system that struck a successful balance between custom
and off-the-shelf parts. 
Later in the season, we wrapped up testing for design
and started testing to tune the car for competition. One
of our goals this year was to improve our performance
in the sled pull event, which has been limited by belt
slip in the CVT. M15's primary CVT is actuated by rocker
arms that have an additional bolt hole, allowing the
weights to be moved further radially outwards and
increase the clamping force by 45% without changing

MOMENTUM

Thermal image of steering wheel
highlighting areas of high grip
pressure.

3D body scan of our driver in driving position.

core tuning parameters. To optimize this new adjustable system, we
designed and manufactured a sled-pull so we could tune for a balance
between acceleration and sled-pull performance, subsequently
demonstrating that M15 achieves a 25% increase in torque capacity
compared to M14. 

DESIGN AND INTEGRATION 
Each season we spend about four months designing the competition car
before committing to manufacturing. These months fly by with hours
staring at CAD, dozens of failed meshes in ANSYS, nightly meetings
between sub-teams, and far too many part file names labeled 'REV_
FINAL_FINAL_3'. Even at design finals we struggled to narrow down
which aspects of our designs to present, so here are some highlights I
personally found particularly interesting. 
A car can only perform as well as its driver, so we focused heavily
on how M15 could be designed to optimize the driver's performance.
How could we expect our drivers to succeed in a four-hour endurance
race if they were distracted by the seat constantly bruising them? Our
ergonomics team conducted several surveys to understand the major
contributors of seat discomfort and then used 3D scans of people's
driving positions to design the seat, which follows the contours and
angles the driver's body naturally assumes while driving. So, the driver's
bruised back had been addressed. Now, to help with car handling,
having comfortable hands would probably be helpful. Using a thermal
camera, we took footage of drivers' hands on the steering wheel
to reveal the areas of highest pressures and designed a 3D-printed
removable section of pliable thermoplastic urethane to enhance the
driver's grip and reduce uncomfortable pressure.
Uncomfortable seats and steering wheels are simply awful, but there
are few things worse than a poorly angled pedal. In the past, drivers
reported that the excessively high pedal angles relative to the horizontal
caused muscle fatigue and required more force input to activate the
pedals. This year, M15's pedal-bay is bottom-mounted from the lower
front lateral cross (FLC) member instead of top-mounted from the upper
FLC to reduce the foot angle and increase mechanical advantage and
stroke to the brake pedal, contributing to a 30% decrease in foot force
required to lock the wheels. 

February 2020 11
Momentum - February 2020

Table of Contents for the Digital Edition of Momentum - February 2020
