It’s all about autonomy. When a large global berry producer approached OxDrive co-founder and managing director Chris Horton with a request to provide an extensible, self-driving cart to transport soft fruit, he and co-founder Terence Goad saw a great opportunity for their advanced smart hub technology in the burgeoning electrification of agribusiness.
The client would handle all the robotics, route planning and AI guidance. OxDrive, a UK-based electric drive unit manufacturer, would design and build GoFAR, a self-driving platform outfitted for multiple transport purposes, integrating optical sensors, motors, transmissions and controls.
They just needed to find the right actuator to enable the steering.
The need for speed
“A high-torque actuator is critical for this kind of application because the speed of the steering relates directly to the speed of the vehicle, and that affects the number of vehicles needed and the potential cost savings,” says Horton.
He also noted that the actuator had to be rugged enough to operate 24/7 in challenging off-highway environments, controllable enough to respond quickly to navigation guidance, compact enough to fit within the small platform, capable enough to handle 12-volt input, and cost-appropriate enough to maximize the ROI-based yield improvement.
The berry application involved transporting trays of picked berries through rows of consecutive polytunnels. Automating this operation was increasingly critical because of a growing labour shortage to pick the berries.
The client’s strategy was to increase yield by freeing pickers from the task of hauling the fruit away once they had picked it, so they could spend more time picking.
Picking the right actuator
Horton explained that traditional self-driving platforms often have four wheels that are each capable of 360-degree rotation. Each wheel requires its own actuator and control set, but this degree of flexibility is costly, complex and not needed for berry transport and similar applications.
The new platform would need only to travel down the polytunnel rows, turning the front wheels in the intended direction and the back wheels in the opposite direction.
This capability would enable very tight turning circles, which is a key requirement in agritech and one of the unique features of the platform.
(Figure 1) Or, instead of that U-turn type motion, the platform could steer both sets of wheels diagonally away from a wall or a row of plants, crab style, which often is a challenge for roboticists. Either way, only one actuator would be needed to independently direct the steering on each axle.
After conducting a thorough market sweep, the OxDrive design team settled on the Thomson Max Jac as the actuator of choice for what they have named the OxDrive GoFAR platform.
Their choice was based on considerations of cleanliness of operation, controllability, power flexibility, ruggedness and ease of integration.
Ruling out hydraulic cylinders
Because the platform would be operating among food products, clean operation was mandatory, which ruled out hydraulic cylinders early in the process.
“If hydraulic fluid spills onto agricultural land, you have to skim off a whole layer to safe depths, sacrificing yield and time,” said Horton, adding that they would have also dismissed hydraulics because they require a pumping infrastructure and are not amenable to control or integration.
By taking hydraulics off the table, however, Horton wanted to be certain he was not sacrificing durability.
“The ability to handle peak loads and rapid jaunts was also critical for us, and this can be harder to do with electric actuators. We needed a very rugged actuator that also responds rapidly, traits that can sometimes conflict. But the Max Jac unit has proven itself in that respect. We have been happy with its toughness and high duty cycle,” he said.
Contributing to the Max Jac’s resilience is its IP66/IP69K ingress protection rating. It can withstand 500 hours of salt spray, dirt, dust and water as well as aggressive substances such as fertilizers, acid, oil, grease and cleaning agents.
Its operating temperature stretches from -40 to +85 °C, which is industry leading. It is fully washable and does not need bellows or other protective devices.
Intelligent visibility
Having settled on electromechanical solutions, OxDrive’s initial experience with electric actuators showed that not all smart actuators are created equal.
An initial model had all the intelligence needed to interact with the advanced microelectronics in the GoFAR hubs but offered no visibility of diagnostics or troubleshooting.
Horton says: “The actuator reached its maximum speed fine, but that would drop off rapidly under any load, and if there was even a momentary overshoot, it would just shut off.
“It would also make unexpected moves that didn’t seem to match anything on the data sheet, but all the operating data hid under multiple system layers, so you could never determine what was going on or how to correct it.”
The Thomson Max Jac actuator, on the other hand, not only had the core intelligence and rapid responsiveness needed to interact with the GoFAR robotic operating system, but also has an online logging system that tracks what the system is doing and transmits detailed operating data for troubleshooting and diagnostics.
Configuring the actuator
Working closely with Thomson engineers and their online configuration tools, the OxDrive team configured the Max Jac 12 Vdc voltage option for the berry transport application.
The Max Jac is available off-the-shelf with either a worm screw or ball screw, and even though the 800 N dynamic load capacity of the ball screw force wasn’t necessary to move the wheels, it was specified for the platform due to its high speed, which was critical to operating efficiency.
Also contributing to the speed was a maximum restraining torque of 2 Nm. From a range of 50 to 300 mm in stroke length, they selected 100 mm, which fit comfortably in the limited chassis space.
The Max Jac actuator mounts parallel to each axle with two wires connected to the terminals of an H-bridge, one of which also contains the connection to the 48-volt power supply. (Figure 2)
In motion
The navigation system reads locational information from optical sensors or other route navigation technology, which calculates the travel path and determines the wheel angles necessary to get it there.
The system then signals the actuator via the H-bridge, which modulates current in the actuator motor to turn the wheels left or right at a designated speed. The actuator extends or retracts by changing the polarity of the applied voltage.
Moving ahead
OxDrive’s GoFAR vehicle platform was born out of this soft-fruit transport application and is widely adaptable within agribusiness as well as other industries.
This current model is available as a remote-controlled Robot Operating System (ROS) enabled unit from the factory, and the fact that it connects with standard network protocols simplifies horizontal integration with third-party applications, including enterprise and AI-based systems.
The platform can accommodate robotic arms, automated picking tools and much else.
Horton says: “We are following an ‘internet of things’ model, where we are one more thing delivering both services and data to a wider ecosystem.
“Today, GoFAR is especially appropriate for agribusiness applications because they share a vital role in maintaining both national and global food security and are also under pressure to increase yield amidst shrinking labour supplies.
“But we designed GoFAR to be industry agnostic as a mobile platform that can support best-of-breed technology like Thomson actuators.”
Whether OxDrive’s next application is in agritech, construction, forestry, warehouse logistics or any other untapped use, chances are good that it will need a reliable actuator. And when it does, Horton will likely continue specifying Thomson linear motion solutions.
