Bolts, Screws & Fastening Hardware
1. Bolts & Screws (Fasteners)
Bolts and screws are the most common way to attach parts together. In FTC Vietnam, 4mm (M4) fasteners are the most popular.
2. Types of Bolts
3. Nuts
Nuts are threaded components screwed onto bolts to clamp parts together. They provide an alternative to threading holes directly into the material.
4. Bolt Retention
Bolt retention is a critical factor for robots in FTC competitions. To avoid the nightmare of a robot falling apart mid-match, it is best to apply an anti-loosening method to all bolts on the robot. The two most common methods in FTC are threadlocker and nylon lock nuts. Additionally, a few other methods can be useful in certain situations.
- Threadlocker (Loctite): A liquid adhesive applied to threads to prevent bolts from vibrating loose. Blue threadlocker is suitable for size #8 screws and smaller, while red threadlocker is suitable for size #10 screws and larger and can typically be removed without heat. Red threadlocker can still be used on smaller screws with extreme caution to avoid stripping threads or breaking bolts. High-strength threadlockers can be broken free using a heat gun. Retaining compounds are also available, used to secure bearings in bores or components onto shafts.
- Material Warning: Polycarbonate plastic can crack if exposed to standard blue or red threadlockers. Note that wheel hubs in standard FTC kit drivetrains are often made of polycarbonate. Threadlocker will also degrade the nylon inside nylon lock nuts, so these two methods must never be combined. If threadlocker is required near plastics, use a plastic-safe threadlocker compatible with polycarbonate.
- Material Warning: Polycarbonate plastic can crack if exposed to standard blue or red threadlockers. Note that wheel hubs in standard FTC kit drivetrains are often made of polycarbonate. Threadlocker will also degrade the nylon inside nylon lock nuts, so these two methods must never be combined. If threadlocker is required near plastics, use a plastic-safe threadlocker compatible with polycarbonate.
- Nylon Lock Nuts: Nuts featuring a nylon ring inside that creates friction against the bolt threads to prevent loosening from vibration. While opinions vary on reusing them, reuse is generally accepted in FTC. Never use nylon lock nuts alongside threadlocker.
- Locking Heli-coils / Screw Thread Inserts: Used to secure bolts or repair stripped threads. The hole is tapped with a special tap, and the insert is installed using an installation tool. Due to their unique thread profile, most of these inserts are self-locking, making them great for creating strong threads in softer materials like aluminum or plastic.
- Distorted Thread Nuts: Function similarly to nylon lock nuts but are made entirely of metal, allowing them to be used in high-temperature environments. However, they are usually unnecessary in FTC and are mostly single-use.
- Interfering Thread Nut and Tapered Thread Nut: Have a minor thread diameter smaller than standard, causing the bolt threads to undergo plastic deformation upon installation. Typically used for permanent, fixed joints and virtually unnecessary in FTC.
- Safety Wire / Lock Wire: An active mechanical locking method commonly used in aerospace. Metal wire threads through multiple bolts to physically prevent them from vibrating loose. This method is complex and unnecessary for FTC.
- Pins and Castle Nuts: Uses a slotted nut tightened like a regular nut, with a pin passed through a cross-hole in the bolt and sitting inside the nut slots to prevent rotation. Common pins include cotter pins, hairpins, split rings, or safety wire. Like many of the methods above, this is generally unnecessary in FTC.
5. Welding
Welding is a lightweight, high-rigidity joining method between metal parts. Because it is a permanent joint, welding is typically reserved for the drivetrain frame and primary structural components of the robot. When designing assemblies for welding, jigs should be built to hold parts in accurate alignment during the process.
Because welding assemblies easily causes warping (especially with thin materials), designs should account for minor post-weld distortion. When welding closed sections like square tubing, small vent holes are usually drilled near the joints to let trapped gas escape, preventing explosions or poor weld quality. In competition, if a weld cracks or fails, teams often temporarily reinforce it using patch plates; keeping an emergency patch kit of thin sheet aluminum, shears, and rivets is very useful.
- Complexity of Welding in FTC: In FTC, welding is resource-intensive not because of financial cost, but due to technical complexity. Welding thin aluminum requires exceptional craftsmanship, and weld quality depends heavily on the operator's skill rather than just the equipment. Most teams with welded frames rely on sponsors, outside weld shops, or experienced mentors. If a team plans to weld themselves, investing significant practice time into thin aluminum is strongly advised, as burn-through happens easily and minimizing frame warping is difficult.
- MIG Welding (Gas Metal Arc Welding): Uses a continuously fed wire electrode that acts as both filler material and arc creator. The arc spreads over a wider area, and MIG welding tends to produce minor spatter and microscopic porosity in the weld.
- TIG Welding (Gas Tungsten Arc Welding): Can be performed with or without filler metal; if used, the filler wire is fed manually by hand, making the process significantly harder. The arc is tightly focused, heating the material quickly and intensely. It is slower and more expensive but yields the highest quality welds.
Aluminum can be welded using either method, though DC-only welders cannot weld aluminum. MIG is generally easier and common for steel, while TIG is much harder and typically preferred for aluminum and stainless steel. If your team wants a welded robot frame, finding a skilled welder or a sponsor proficient in TIG welding is ideal.