Momentum - October 2019 - 12

STUDENT
GENERATION

A small-scale version of the car was built for wind-tunnel testing.
The car was designed to greatly reduce aerodynamic drag.

Working on the car in preparation of the Endurance Event at Baja SAE Rochester,
where the team finished second in that event and second overall.

70% of the original EVT, and the planetary gearbox only
added a few hundred grams of mass. Once our concept
was proven, we moved on to the controller tuning to get
the best performance for the competitions. The EVT 2.0
was fully used at the California and Rochester Baja SAE
competitions, where it proved itself capable of competing
with what the top teams had to offer.

AERODYNAMICS

ÉTS finished fourth overall at Baja SAE California, which concluded with a muddy
Endurance Event.
Once we had the BLDC motor in hand, we started testing our control
software, which became a lot more complex because of the way a BLDC
motor works compared to brushed DC motor. Instead of sending out the
PWM, set by the PID controllers, the three phases of the motor must be
controlled individually and in turn to allow full rotation. This adds a lot
of time to the development of the software. In the long run, since there
are no brushes causing friction, the BLDC motor is a lot more energyefficient and lightweight.
Once the motor was fully functional, we set it up with our control
algorithm and did some table testing. When these tests were successful,
it was time to try out the CVT shifting on the car. This was the first
time there was a bigger load applied to our BLDC motor. During these
validations, the current draw was seen to become very high during the
peaks. The goal was to reduce the power consumption and weight. The
weight of this motor was a lot lighter, 25% of the weight of the original DC
motor, but for the power consumption goal something had to be done.
By looking back at the calculations, we decided that adding a planetary
gearbox to the motor would reduce the top speed and increase the
output torque. In-car testing of the planetary gearbox was conclusive,
and we had now achieved both our goals since the max current draw was
12 October 2019

In the past, no real analysis or design was made with
aerodynamics because we did not think we could gain
much. But for 2019, we put in a lot of work. To start, we
built a small-scale version of the car for wind tunnel
testing. With this data, multiple CFD validations were
made to validate how the aerodynamic drag affected the
car. This information allowed us to build a Simulink model
where we could modify some inputs and see the effect
of these changes. This tool was essential in the complete
redesign of our chassis and firewall because it allowed us
to aim for the most impactful changes we could do with
the resources we have available.
Once they were modelized, some CFD analysis was
done to confirm the positive effect of the new design.
After this validation, we built a small-scale model of
this new version for more wind tunnel testing. All the
design changes we did on the chassis, as well as reducing
the firewall size, allowed us to achieve a 20% decrease
in aerodynamic drag, which is a substantial change
for the speed and acceleration of the car. Based on
the experience acquired, multiple additional changes
are currently in the works to further optimize vehicle
aerodynamics for the coming competitions. We've noticed
much interest in the aerodynamics design from other
teams as well as the Baja SAE judges. Aerodynamics and
electronic CVT are both new concepts that are gaining a
lot of popularity in the Baja SAE competitions because
the cars are getting better and better.
Gabriel Gagnon, captain of the ETS Baja SAE
team for the 2018 and 2019 seasons, wrote this
article for MOMENTUM. He expects to graduate in
December 2019 with a bachelor's degree in electrical
engineering (specializing in firmware) and is already
employed as a firmware developer at Novo.

MOMENTUM

Momentum - October 2019

Table of Contents for the Digital Edition of Momentum - October 2019