Formula Student and school projects: choosing your electric powertrain
A Formula Student or Eco-marathon team has one year to design, build, and operate a vehicle, with a team that changes almost entirely each season. The electric powertrain, including the motor, inverter, and battery, is the riskiest part of the project: it's the most expensive, the most closely scrutinized by the officials, and the one that causes the most teams to fail the technical inspections. This guide provides a method for selecting the right components.
The essentials
- The competition rules take precedence above all else: they specify the maximum voltage, required safety features, and mandatory checks.
- The motor and the controller (inverter) must be selected together: the controller must be compatible with and capable of controlling the chosen motor.
- The battery is often the heaviest and most tightly regulated component, and its design requires considerable time and effort.
- Telemetry saves time with each test and transmits knowledge to the next team.
Regulations first
Each competition publishes a set of rules that govern the drive system: maximum voltage, insulation, emergency shut-offs, insulation monitoring, voltage presence indicators, and battery protection. These rules change from season to season. Always read the rules for the specific year before designing anything, and anticipate the documentation that the officials will require.
The motor
The motor is selected based on the torque and speed required by the vehicle at the wheel, taking into account the transmission. Teams often hesitate between a central motor with a differential and multiple motors in or near the wheels, which allow torque to be distributed between the wheels. The second solution is more performant but much more complex to develop. To understand the technologies, see our guides on the difference between PMSM and BLDC motors and on motors with internal magnets.
The inverter
The inverter, often called a controller on a two-wheeled vehicle, drives the motor. It must handle the battery voltage, provide the current required for the desired torque, and read the motor's position sensor. A team would be better off choosing an inverter with documented and accessible settings, rather than a "black box." To understand what it does, see our guides on vector control (FOC), the current regulator, and field weakening.
The battery
The battery is the component that requires the most work: selection of cells, assembly, cooling, BMS (Battery Management System), protections, and quality control. It is also the heaviest component. Its capacity is calculated based on the longest test, often the endurance test, with a safety margin. See our guides to read the technical specifications of a lithium cell and on BMS balancing (active or passive).
Telemetry and the CAN bus
Generally, all components, including the inverter, BMS (Battery Management System), sensors, dashboard, communicate via a CAN bus. Recording these interactions during each test allows us to understand any failures, fine-tune the vehicle, and leave the next team with data instead of just memories.
The workbench in front of the track
Testing the motor and inverter on a test bench before installing them in the car can save weeks: you can adjust the inverter settings, measure torque and heat, without risking damage to the vehicle. See our guide on motor dyno testing.
What Rage offers to schools
We collaborate with engineering schools, student teams, and laboratories: controllers, BMS (Battery Management Systems), telemetry, and testing on benches or on tracks. See our page engineering schools and research. Like the teams, we aim for measurable performance: our RM-X holds the world record for scooter speed, reaching 173 km/h, measured on a track.
Workshop tip
Get the drivetrain running as early as possible, even on a temporary frame or a test stand. Turning on the inverter for the first time just a few weeks before the competition leaves no room for correcting any potential issues.
Frequently Asked Questions
Is it better to design your own motor controller or buy one?
Designing an inverter is a project in itself. For a team that is new to electric vehicles, having an existing, well-documented inverter allows them to focus on developing the rest of the vehicle.
Single motor or multiple motors?
A single motor with a differential is simpler to set up. Multiple motors allow for torque distribution between the wheels, but require significantly more configuration and software adjustments.
How can we pass on knowledge to the next team?
Through data and documentation: records of each test, inverter settings, and up-to-date schematics. A vehicle without data forces the next team to relearn everything.
Can Rage provide support to a team?
Yes: we provide controllers, BMS (Battery Management Systems), and telemetry solutions, and we can conduct testing on a test bench or on a track. Please present your project to us through our "schools" page.