Momentum - October 2019 - 11

STUDENT
GENERATION

The team poses with its car after
the close of Baja SAE California
2019, where it placed first in
both the Cost Event and Sales
Event en route to a fourth-place
finish overall.
Even so, we still got all three of our overall results in the top ten.
Having all this new data, we pulled up our sleeves and started early to
work countless hours on the new designs for the Baja SAE 2019. We
completely redesigned the chassis, our suspension geometry, our body
panels, our steering wheel, and our multiple electronics systems such
as the dash screen, power management unit, and CVT. Other parts, we
optimized to reduce the weight, which was our main goal this year. In
fact, the only parts that we did not change this year were negligible,
such as the gas tank mounts and our throttle system. All these
changes have allowed us to reduce car weight from 341 lb to 311 lb. The
engineering cycle, which consists of going through research followed by
prototyping, testing, and improving before going back to researching
where the cycle restarts, is followed during our whole design process.
Exploded view of the complete EVT system on the ÉTS car.

ECVT
The electronic CVT-or what we call EVT-was first seen in our car at the
2017 competitions, where it proved to be very efficient. Ever since that
season, we have been using the same concept to control our CVT. This
consists of an almost identical system as a conventional CVT, but instead
of having weights and a spring on the primary pulley, they are replaced
by a cam. This allows transferring the rotation from an electric motor to
a linear movement that closes the primary pulley; if no pressure is set on
the pulley, it will open based off the force applied by the strap. In other
words, the system does not pull on the primary.
Our control algorithm requires many inputs for optimal drive
performance: engine RPM; throttle position monitor; the current position
of the primary sheave; and a push-button, which is used only to set
the target position at open even if the gas pedal is pressed (this is also
called the launch control). With these inputs, we have two cascading PID
controllers. The first one determines the target RPM for optimal engine
performance, which commands the second controller. The second one
determines the required position to achieve this target RPM.
The baseline of this software has been kept, but in 2019 multiple
software changes were made to increase the control cycle speed by a
factor of 10. The first iteration of the EVT was done with a traditional
brushed DC motor that was controlled by a custom drive we've designed
MOMENTUM

CFD analysis of the vehicle, made to improve aerodynamic drag.
and coded in-house. During the summer, as well as at the
2018 Midnight Mayhem (a non-SAE-sanctioned baja event),
we've done data acquisition on the current draw from the
electric motor to know the maximum load, in worst-case
conditions, required to actuate the primary pulley. This was
done by correlating the collected data with the electric
motor current constant, given by the manufacturer. With
this information in hand, we knew the required torque
to make our system function, which allowed us to find a
brushless DC motor that meets our requirements.
October 2019 11
Momentum - October 2019

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