Bearings
In any FTC robot, bearings are an essential part of a well-functioning power transmission system. They allow rotating shafts to spin smoothly, reduce friction, and maintain mechanical alignment between components. Without bearings, your robot's drivetrain, gearbox, or intake system would suffer from excessive wear, efficiency loss, and mechanical instability.
When power is transferred from a motor to a mechanism—whether through gears, chains, belts, or shafts—bearings serve a critical role in supporting that motion. This page explores how bearings are used in power transmission systems, why they matter, and how to design with them effectively in your FTC robot.
The Purpose of Bearings
Bearings are designed to support loads and minimize friction between moving parts. In the context of power transmission, they are usually used to support rotating shafts or axles that transmit torque. When a shaft rotates under power, it naturally wants to shift, flex, or push against its mounting points—especially when side loads are applied by belts or chains. Bearings counteract these forces and allow the shaft to rotate freely while staying aligned with other components.
Without bearings, the shaft would directly rub against plastic or metal plates, leading to high friction, poor efficiency, and eventual deformation of the mounting holes. Bearings eliminate this problem and drastically improve both the performance and lifespan of rotating systems.
Bearings in Drivetrains and Gearboxes
In drivetrains, bearings are most commonly used to support wheel shafts. Even if your motors are mounted directly to the drive wheels, any shaft that passes through the robot's frame should have bearings on both sides. This prevents the shaft from flexing under load and helps ensure consistent alignment between the motor, gears or sprockets, and wheels.
In custom gearboxes, bearings are used to support each shaft that holds gears. At least two bearings should be used per shaft—typically one on either side of the gear cluster. This setup ensures the shaft remains parallel to others and prevents gear mesh misalignment. It also helps to isolate the motor from external loads, improving motor health and transmission reliability.
Bearings in Chain and Belt Systems
When chains or timing belts are used to transfer power, they introduce side loads on the shafts they connect to. Bearings are crucial in these cases to support the radial force caused by tension. For example, if a sprocket is mounted on a shaft driven by a motor, the tension in the chain can push or pull the shaft sideways. A pair of well-placed flanged bearings will support that shaft and allow it to spin freely under tension.
If a system lacks proper bearing support, belts can cause the shaft to sag or misalign. This leads to power losses due to friction and can cause components like pulleys or sprockets to wear out quickly or even fall out of place.
Types of Bearings Used in FTC
The most common type of bearing in FTC is the flanged ball bearing. These typically have a ½” outer diameter and a 5mm or ⅛” inner diameter, depending on your shaft type. They’re designed to press-fit into metal or plastic mounting plates and are used for supporting through-shafts. The flange helps keep the bearing from sliding out of the hole.
Pillow block bearings are another useful option when you need to support a shaft away from a structural plate. These are standalone bearing housings that mount to flat surfaces. They’re great for supporting long shafts, such as those used in drivetrains or lifting arms, but take up more space than flanged bearings.
Thrust bearings are used when a shaft is under axial load—meaning the force is pushing along the length of the shaft instead of perpendicular to it. These are most often found in screw-driven elevators or rotating arms where a motor or gearbox is applying force along the shaft’s axis.
Lastly, plastic bushings or sleeve bearings can be used in lower-load, lower-precision applications. These rely on low-friction materials like nylon or acetal and don’t contain rolling elements. While they’re simple and compact, they are much less efficient than ball bearings and are not recommended for high-load or high-speed power transmission.
Best Practices for Using Bearings
Whenever you are designing a power transmission system, make sure that each rotating shaft is properly supported by bearings. Ideally, a shaft should be supported by two bearings spaced apart to prevent wobble and reduce strain on the shaft and any connected gears or sprockets. For high-speed or high-load applications, this is absolutely essential.
Bearings should be carefully aligned in CAD before manufacturing. Even small misalignments can cause friction and make the system bind. If you are using 3D printed or laser-cut parts, test your tolerances to make sure the bearing fits snugly without being too tight, which could deform the bearing or shaft.
Use shaft collars or spacers to prevent axial movement of the shaft between bearings. A loose shaft can slide and cause inconsistent performance or component failure. For belt or chain-driven shafts, position the bearing directly under the pulley or sprocket to minimize bending loads.
Finally, don’t rely on the motor alone to support a shaft. Doing so places side loads directly on the motor shaft, which can lead to internal damage or reduced efficiency. Bearings should always be used to support power transmission loads, especially when the output shaft connects to anything larger than a simple roller or gear.
Designing for Bearings in Onshape
Linear Motion Systems
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