Traditional tractors use PTO (power take-off) mechanisms as a way to transmit energy from the tractor’s engine to tools pulled behind the tractor. This allows the farmer to purchase and maintain a single engine that can power a wide variety of tools, which makes the tools much cheaper and simpler.
The PTO interface has industry-defined standards. For example, a Type 4 PTO has a shaft with 22 splines and a major diameter of 57.5 mm, which rotates at 1300 RPM, providing up to 450 kW of mechanical energy. Tractors also provide standardized connections for hydraulics and other control and support mechanisms.
We are interested in starting to explore and discuss standards for electric field implements. The standards would include transmitting power and data, along with specifications of mechanical attachments. These standards could include configurations for different scales (similar to the PTO types 1 through 4), though for now we are mainly interested in light-weight (<200 kg) low-power (<2 kW) tools.
A key feature of the electrical and mechanical specification could be automated tool swapping. We would like electric tractors to be able to attach and detach tools without manual labor. This will allow a small electric tractor to be an efficient utility vehicle, quickly switching between different tasks with minimal overhead and minimal risk of injury.
Our current designs incorporate a vertical tool lifting mechanism (a Z axis) into the tractor itself and lets the tractor to support the entire weight of the tool on that lifting mechanism, so the tool does not need it’s own wheels. This assists with automated tool swapping and provides an easy way to switch between transport mode (tool lifted) and work mode (tool contacting the ground/crops). It also allows the tractor to use onboard soil height sensors to dynamically raise/lower the tool to match undulations in the field surface. With this automated tool lifting capability, the tools themselves can often be fairly simple.
For transferring power from the tractor to the tool, we believe it is better to provide electrical energy than mechanical energy. Electric motors and motor controllers are getting sufficiently cheap and efficient that it makes more sense to fit the motors to the task, rather than use a PTO-style mechanical connection that requires heavy, expensive, and dangerous transfer of all power through a single rotating shaft. Electricity allows energy to be easily distributed to multiple smaller motors onboard the tool.
An important goal of creating this kind of standard would be allowing farmers and farm equipment companies to create their own tools. We want to support a thriving ecosystem of electric farm implements, supporting many crops, many field conditions, and many types of farms. These standards should be free and open, including at a software/control level, so that anyone can build and repair electric farm tools.