If you’ve ever studied speed reducers or robot actuators, you’ve probably come across the concept of the cycloid curve. Originally discovered by mathematicians searching for the fastest path of descent, the cycloid curve is now a core principle behind the tooth profile design of robotic speed reducers. Applying this smooth trajectory to gear teeth enables a rolling contact motion much like a ball rolling along a surface.
Today, we’ll take a closer look at the cycloidal tooth profile built on this smooth curve, and explore why cycloidal reducers have been drawing so much attention in the robotics industry lately.
Table of Contents
The Smoothest Curve: The Cycloid
Key Summary — A cycloid is the smooth curve traced by a point on the edge of a circle as it rolls along a flat line. Applied to gear teeth, this trajectory allows meshing gears to rotate through rolling contact rather than friction.
To understand the cycloidal tooth profile, it helps to first understand the cycloid curve itself. A cycloid is the path traced by a point on the edge of a circle as it rolls along a flat, straight line.
Picture standing a coin on its edge on a desk, marking a point on its rim, and rolling it sideways. The gentle, arching curve that point traces through the air is the cycloid.
The defining feature of this curve is that it is extremely smooth and continuous. When applied to gear teeth, meshing gears no longer push against each other through friction, but instead rotate naturally, sliding along the curved surface. This structure reduces the gear wear that can occur during meshing and allows rotation to flow more smoothly.
The reason cycloidal tooth profiles stand out in robotic reducers comes down to this structural characteristic. A cycloidal tooth profile distributes force across a broad contact surface rather than concentrating it at a single point. This allows for stable performance even under sudden shocks or load changes.
Thanks to these properties, cycloidal reduction technology has found its way into a wide range of industrial robots. That raises another question worth exploring: how is this actually implemented inside real reducers and actuators?
The Pin-less Cycloidal Structure
Key Summary — The Pin-less structure implements the cycloidal principle without separate pin components. An external gear and internal gear are carefully engineered to mesh directly with each other, simplifying assembly and supporting long-term reliability.
The Pin-less structure is a design direction that implements the cycloidal reduction principle without separate pin components. An external gear and internal gear are carefully engineered to mesh directly with each other, forming a single unified structure.
By reducing the number of internal components, this structure can help simplify the assembly process. When the component composition becomes concise, it can also help reduce the burden of assembly and maintenance and support consistent quality during long-term operation.
This makes Pin-less designs a strong fit for collaborative robots working alongside people, or for AGVs with limited internal space, where drive units must be arranged within a confined structure.
The single-piece structure of the Pin-less type also helps minimize structural deformation and supports strong rigidity, allowing it to maintain stable driving performance even in environments like walking robot joints, where repetitive loads and shocks are a constant factor.
Purpose-Built for Compact Robots: Bonsystems Cycloidal Reduction Technology
Key Summary — As drivetrain miniaturization becomes a defining factor in robot competitiveness, Bonsystems Pin-less cycloidal reduction technology develops drivetrain components for compact robot environments. Its thin profile, hollow structure, and wide range of reduction ratios support flexible robot design.
As drivetrain miniaturization increasingly becomes a defining factor in robot competitiveness, our cycloidal reduction technology has become a core element in building accurate, lightweight drivetrains.
Through Pin-less cycloidal tooth profile design, we develop drivetrain components suited to compact robot environments. Our designs deliver strong torque output even at a thin profile, helping to make better use of a robot’s limited internal space.
We’ve also incorporated a hollow structure to address the wiring issues that come up during robot assembly and operation. By routing power and communication cables through the empty space at the center of the reducer, we reduce the risk of wiring interference or damage from external exposure as joints rotate.
We also offer a wide range of reduction ratio options, allowing flexible adaptation to the different requirements of each joint. Since a single series can support an entire robot system even when individual joints have very different requirements, this gives development teams the flexibility to apply the same series across multiple parts of a robot.
As robots increasingly take on repetitive tasks once performed by people, the hardware behind them is being held to a higher standard of accuracy. Within that shift, the cycloidal tooth profile stands out as one of the most fitting choices for robot drivetrain design.
Selecting a drivetrain component requires carefully weighing factors like intended use, required torque, and reduction ratio. For that reason, we recommend closely reviewing technical specifications from the earliest stages of design, and working with experienced specialists to determine the right approach.
If you’d like more detailed technical materials on Bonsystems reducers and actuators, or would like to discuss the drivetrain for a robot or piece of equipment you’re currently designing, please reach out through our website. We’ll work with you to find the solution that best fits your requirements.
F.A.Q
Q: Why exactly is the cycloidal tooth profile considered resistant to shock?
A: Because a cycloidal profile distributes force across a broad contact surface rather than concentrating it in one place, it stays stable even under sudden loads or impacts. This structural rigidity helps prevent damage or deformation to the reducer’s internal teeth in environments with frequent load changes, ultimately extending the robot system’s lifespan and supporting driving reliability.
Q: Why does a hollow structure matter in a reducer?
A: In environments where a robot joint rotates repeatedly, externally exposed wiring can suffer from repeated twisting or friction. A hollow structure lets cables pass through the empty space at the center of the reducer, reducing wiring interference during joint operation. This goes beyond simple cable management. It’s an important design factor that affects the robot’s stable operation and ease of maintenance.
Q: What’s the advantage of offering multiple reduction ratios within a single series?
A: Multi-joint robots have different torque and speed requirements at each joint. With limited reduction ratio options, different product lines have to be combined across joints, making it harder to maintain a consistent mounting structure or design standard. With a wide range of reduction ratios available within a single series, however, the entire robot can be built with a more consistent structure, improving both design efficiency and system scalability.
