Electrifying an agricultural robot or a harvesting transport vehicle
Weed-killing robots, harvesting assistants, and small tracked transporters are becoming increasingly common in fields and vineyards. They share a common characteristic: they move slowly, for extended periods, and often in challenging conditions. Their propulsion systems are fundamentally different from those of high-speed vehicles. This guide explains how to choose the right one.
The essentials
- An agricultural vehicle needs high torque at very low speeds, for extended periods, not top speed.
- Machines with two rows of wheels or tracks require two motors that are controlled together.
- Mud, dust, and wash water: the electronics must be protected accordingly.
- The battery capacity is determined based on the actual working day, taking into account inclines and load.
Low-speed torque
A weeding robot moves slowly, but it must start on an incline, fully loaded, in loose soil. Therefore, the motor is sized based on its torque at very low speeds. There are two possible solutions: a hub motor with high torque in each wheel, or a faster motor coupled with a gearbox. The gearbox allows for a smaller and lighter motor, but at the cost of an additional mechanical component that requires maintenance.
Precise control is also crucial for very low-speed operation: without sensors, a motor poorly estimates its position when stopped and during startup. In agricultural vehicles, position sensors are almost always necessary. See our guide on Hall sensors, encoders, and resolvers, and the one on the sensorless observer, which explains its limitations at low speed.
Two motors, one direction
A tracked vehicle or a differential drive robot turns by rotating its two sides at different speeds. Therefore, both motors must be controlled together, in a coordinated manner. A dual controller, which controls both motors, simplifies the wiring and coordination.
Withstand the terrain
An agricultural vehicle operates in mud, dust, and rain, and is regularly cleaned. The controller and battery must be housed in waterproof enclosures, with connectors specifically designed for outdoor use, and the cooling system must be designed without direct air intake. Vibrations and shocks are constant, so the mounting points and cables must be designed to withstand them.
The battery of the day
The season doesn't wait. The battery must provide enough power for a full workday, including hills, loads, and repeated starts. Real-world testing over a typical day is more valuable than any theoretical calculation. The Battery Management System (BMS) must be able to communicate with the rest of the system, often via a CAN bus, so that the control system knows the battery's state of charge.
The dialogue with the steering system
On a robot, it's not a driver who controls the motors, but a guidance computer. The controller must receive its speed or torque commands, send back its measurements and any detected faults, and shut down safely in the event of a communication failure.
What Rage does for the agricultural technology sector
Our engineering department designs the electric powertrains for light agricultural vehicles: motors selected for low-speed torque, dual controllers, batteries sized for a full day of operation, and tracking of each machine through RageLink. See our page agriculture and viticulture.
Workshop tip
From the outset, consider how the machine will stop in the event of a failure: loss of communication, depleted battery in the middle of a ride, motor blockage. In an autonomous vehicle, safety is paramount, even before considering comfort.
For the general method, please refer to our guide on how to electrify a machine: where to start.
Frequently Asked Questions
Hub motor or motor with gearbox?
Hub motors are simple and require no mechanical maintenance. Geared motors, on the other hand, are lighter and more compact while providing the same torque at the wheel. The choice depends on the available space, weight considerations, and ease of access for maintenance.
Do motors require position sensors?
For a vehicle that often starts under load and moves very slowly, yes, in most cases: they provide immediate torque from a standstill.
Can the controller receive commands from a navigation computer?
Yes, provided that it has a digital interface, typically a CAN bus, and a protocol agreed upon with the control system.
Can you produce a small batch?
Yes: We work with prototypes all the way up to small and medium-sized production runs, the typical volumes for robot manufacturers and electric scooter companies.