The image below is not a concept render or a lab prototype. It's a working end effector built by one of our customers, a robotic cutting head designed to autonomously harvest crops by gripping and severing plant stems. At the center of this mechanism is the Actuonix P16 linear actuator, which drives the scissor blade responsible for cutting the plant stems.
P16 is used in various other creative applications, but agricultural robotics has become one of the most active areas. This article explores a real customer built end effector, showing how the P16 performs in a stem cutting application, why it is well suited to the task, and how to configure one for your own harvesting robot.
Why Stem Cutting is a Hard Task to Automate in Harvesting
Detecting ripe fruit in a cluttered, leafy environment is often considered the most difficult challenge in robotic harvesting. While camera guided remote operation is certainly complex, studies in agricultural robotics show that end-effector failure is a more common cause of unsuccessful picks than detection errors. The robot can often identify the fruit correctly. The real challenge is designing a reliable mechanism that can grip and cut the stem without damaging the crop.
The cutting step is harder than it looks. Stems aren't uniform; a strawberry petiole might be under 3 mm in diameter while a pepper peduncle can be 10 mm. They grow at unpredictable angles. They deflect away from the blade under pressure. Cut too slowly and you crush rather than shear, misalign the blade and you miss entirely. And all of this has to happen multiple times a day in a humid greenhouse environment.
The actuator driving that blade needs to deliver the right force, at a repeatable speed, reliably across multiple cycles.
Why a Mini Linear Actuator Beats Pneumatic and Hydraulic Options
Engineers have a number of options when designing a stem cutting mechanism, including a servo motor, a pneumatic cylinder, or a linear actuator. Each approach has trade-offs worth understanding.
Servo Motors
Servos are a natural first choice, compact, widely available, and already built into most robotics platforms. Servos produce rotational output, and closing a blade requires linear push/pull motion.
Bridging that gap means adding a crank, cam, or multi-bar linkage. Each extra pin joint and pivot introduces mechanical play that stacks up across the assembly, so the blade responds with a lag. The force delivered at the blade tip also shifts continuously as the linkage geometry changes through the cut, making stem cutting difficult.
A direct-drive linear actuator eliminates both issues. The motion is already linear, there is no conversion mechanism, and the force along the stroke stays consistent and as expected.
Related Article: Servo Actuators vs Linear Actuators – What's the Difference?
Pneumatic Cylinders
Pneumatic cylinders give you fast, clean linear motion and can handle high cutting forces. But they mostly come with a significant infrastructure requirement like a compressor, pressure regulator, solenoid valves, and air lines. On a mobile field robot or a greenhouse harvester, routing compressed air to a moving arm is difficult.
Small Linear Actuators
A small linear actuator gives you direct linear push/pull motion with no conversion mechanism needed. It runs on 12V DC from the same supply powering the rest of the robot. The motor, gearbox, and lead screw are all packed into one compact unit, so there is no external wiring, mounting, or maintenance required. With the right model that has built-in position feedback, the controller knows exactly where the blade is at every point during the cut.
For agricultural end effectors where weight, space, and simplicity all matter, it is genuinely one of the cleanest solutions available.
Inside the Customer Build: How the P16 Powers this End Effector
The Frame
The housing appears to be 3D-printed in grey polymer. The flat base plate at the bottom serves as the mounting interface to the robot arm flange.
The P16 Actuator
The P16 small linear actuator is the black rectangular unit mounted centrally on top of the frame. The side-by-side placement of the motor and gearbox is what makes the P16 shorter than the Actuonix L-series actuator, which uses an inline configuration for the same stroke length, while delivering more speed and force. The rod extends forward and connects directly to the scissor blade arm via a stainless mounting bracket and pivot screws, keeping the mechanical connection clean and direct.
For this application, the customer selected the (P16-50-256-12-P), the 256:1 gearing variant with a 50 mm stroke running on 12V. The P series provides position feedback signal used with the (Actuonix LAC board), which allows the controller to monitor blade position throughout the cut cycle. The 256:1 gearing was chosen to handle stem diameter variation across plants and growth stages without needing to make any changes in the built structure. The 50 mm stroke suited the compact scissor linkage geometry visible in the images without adding unnecessary length to the assembly.
The Scissor Blade
Two stainless steel blades sit at the front of the assembly. When the P16 rod extends, the movable blade arm rotates around its pivot and the blades close. Reversing the polarity retracts the rod and opens the blades ready for the next cut. Given the short lever arm between the pivot and the blade tip, the linkage geometry concentrates force at the cutting point, which is particularly useful when dealing with thicker or tougher stems.
Choosing the Right P16 Gear Ratio
This is the most important decision. The P16 is available in three gear ratios, each suited to different cutting demands. The 256:1 gearing delivers up to 300 N of force, making it well suited for crops with thicker or tougher stems such as tomato, cucumber, and pepper. This is the variant used in the customer build shown in this article.
The 64:1 sits in the middle of the range and works well for lighter cutting tasks on crops like strawberry, herbs, leafy greens, and cut flowers where stem diameter is less.
The 22:1 may suit very fine stemmed applications depending on the specific crop and cutting requirements.
When selecting the right P16 variant, stroke length and control input compatibility are worth thinking through carefully. The P16 is available in 50 mm, 100 mm, 150 mm and 200 mm strokes depending on the linkage geometry of the end effector. Control input compatibility with the existing system, whether that is a simple relay, a LAC board, or an RC receiver, should also factor into the decision.
Use the Actuator Selector Tool to find the exact P16 configuration that matches the application requirements.
Related Article: Actuator Comparison Chart: Complete Specifications for All Models
Ready to Build Your Agricultural End Effector?
The build in these images shows what's possible when you pair a well-chosen actuator with a thoughtful end effector design. The Actuonix P16 linear actuator handles the cutting step reliably, stays compact enough to fit inside a multi-function end effector, and gives you the control options to integrate with whatever structure you're building.
Start with the P16 product page to compare stroke lengths and gear ratios, or use the actuator selector tool to narrow down based on your force, speed, and control requirements. If you have a specific crop or end effector design you would like to discuss, get in touch with our team. We are always happy to help you find the right fit.
Robotic Stem Cutting Demonstration
FAQ
What actuator force is required to cut plant stems in robotic harvesting?
The force required depends on the crop type and stem diameter. Soft stems such as strawberries or herbs require relatively low cutting force, while crops like tomatoes, cucumbers, or peppers may require significantly more force due to thicker peduncles. Actuators used in harvesting tools must therefore deliver repeatable force and controlled motion to cut stems cleanly without damaging the crop.
How do you select the right linear actuator for a robotic harvesting tool?
Selecting the right actuator depends on the force required to cut the stem, the stroke length needed for the cutting mechanism, and the the speed required for the harvesting cycle. It is also important to ensure compatibility with the robot’s control system and the operating environment. Compact solutions like the P16 series integrate the motor, gearbox, and lead screw in one unit, making them easier to integrate into robotic end-effectors.
What crops can robotic stem-cutting end effectors harvest effectively?
Robotic stem-cutting end effectors are commonly used for crops where fruit or flowers grow on a distinct stem, such as tomatoes, cucumbers, peppers, strawberries, and cut flowers like roses. The cutting mechanism must handle variations in stem thickness, angle, and stiffness to make clean cuts. These end effectors are not limited to these crops and can be adapted for many other stem based harvesting applications.
Explore P16 Actuators for Agricultural Robotics
The Actuonix P16 actuator provides compact size, high force capability, and multiple control options for robotic harvesting systems. Visit the P16 product page or contact our team to discuss your application.
