Electrifying a machine: motor, controller, battery – where to begin?
A kart, a lightweight motorcycle, a field robot, a pleasure boat: all these machines can be converted to electric power, using the same basic components. These include a motor, a controller to manage it, a battery and its Battery Management System (BMS), and an interface for the driver. What changes from one machine to another is the way these components are sized. This guide provides the method we follow in our workshop, regardless of the project.
The essentials
- A project begins with the intended use, not with the motor: consider the speed, weight, incline, operating time, and usage conditions.
- The required torque and the desired speed determine the motor and its transmission.
- The motor and battery voltage determine the controller's specifications.
- The amount of energy consumed during a typical day of use determines the battery's capacity, while the current draw dictates the type of cells used.
- Nothing replaces testing: first on a test bench, then on the actual machine, with data recording.
1. Write the specifications document
Before selecting any parts, it's essential to describe the machine and its intended use. The questions are always the same:
- What is the maximum speed? And at what speed does the machine typically operate?
- What is the total weight, including the rider and any cargo?
- What kind of inclines, what kind of starts: with no load, with a load, on an incline, in mud?
- How long does the machine need to run between charges, and how long do we have to recharge it?
- Under what conditions?: Rain, dust, water, heat, vibrations?
- What type of approval is being sought, and for how many units?
It is these considerations that allow for proper sizing. The same motor can be perfect for a rental kart and completely unsuitable for a robot that moves at a slow pace all day long.
2. The motor and its transmission
The motor must provide the necessary torque for starts and inclines, and reach the desired maximum speed. Between the two, the transmission provides the connection: a hub motor (in-wheel motor) has no reduction, while a mid-drive motor drives the wheel via a chain, belt, or gearbox, which allows it to rotate faster and be more compact for the same torque at the wheel.
The choice between motor technologies is detailed in our guides on the difference between PMSM and BLDC motors, and on motors with interior magnets. The relationship between voltage, speed, and torque is explained in our guide on Kv, Kt, and motor poles.
3. The Controller
The controller converts the battery's direct current into alternating current for the motor, and determines at each instant how much current to send to it. It must withstand the battery's full voltage with a safety margin, provide the current necessary for the desired torque, and communicate with the rest of the system: throttle, brake, display, BMS. Our controller guide details these points, and our guide on vector control explains how it drives the motor.
4. The Battery and BMS (Battery Management System)
The battery capacity is calculated based on the energy consumed during a typical day of actual use, not based on a theoretical consumption. The type of cells is then chosen according to the required current: some cells store a lot of energy but deliver it slowly, while others do the opposite. See our guide to read the technical specifications of a cell. The BMS (Battery Management System) protects the battery and, in a well-designed system, communicates with the controller via a CAN bus.
5. The Driver and the Fleet
A display shows the speed, battery charge, and any errors. For a rental or work fleet, it's also necessary to remotely monitor each machine: battery charge, errors, operating hours, and speed limits per user. This is the role of RageLink, our tracking ecosystem.
6. Testing
A motor system is first validated on a test bench, where torque, speed, efficiency, and heating are measured under reproducible conditions, and then on the actual machine, in its real-world use. See our guide on motor bench testing and power measurement.
Workshop tip
The initial version of a specification document is almost always overly optimistic about battery range and too conservative about its ability to handle inclines. Measure the performance of the current machine in real-world conditions before designing the new one.
Our guides, machine by machine
- Electrifying a Go-Kart
- Choosing the right controller for a lightweight electric motorcycle or pit bike.
- Electric retrofit for motorcycles or scooters
- Electrically powering an agricultural robot or utility vehicle
- Electrically powering a boat (no license required)
- Formula Student and school projects
For a professional project, our engineering department designs the entire system, sized specifically for the machine.
Frequently Asked Questions
Which part should I start with?
There's no single answer: it all starts with the specifications. You then choose the motor, and the controller and battery are selected based on those choices.
Can parts from different brands be assembled together?
Yes, provided that the controller is compatible with the chosen motor and that the battery, controller, and display all use the same communication protocol. Often, it's this last point that causes problems with assembling different components.
Isn't a ready-made kit sufficient?
For a standard setup, sometimes. But a generic kit is rarely sized to match your weight, the inclines you ride, and your usage patterns, and it's often poorly supported after the sale.
How long does a project take?
It depends on the specific machine and the number of units being produced. A prototype always goes through the sizing, assembly, and testing phases before any potential production run.