Belts, Pulleys, and Gear-on-Gear

Timing belts#

A synchronous (timing) belt has teeth that mesh with toothed pulleys, so it transmits motion without slipping (unlike a flat or V-belt). Two profiles are common in FRC:

• GT2 / GT3 — a fine, modern tooth profile; 9 mm and 15 mm widths are typical.
• HTD 5 mm — a slightly older curvilinear profile still widely used.

Belts are measured by pitch (tooth spacing, e.g., 3 mm or 5 mm), width, and number of teeth/length. You size them with a belt calculator to land on a standard length for your center distance.

Why belts#

• Light and quiet, no lubrication, very efficient.
• Clean — no chain oil flinging onto the field or mechanisms.
• Inside swerve modules and many mechanisms, belts are common. Some modern modules (e.g., WCP Swerve X2) advertise no belts by using gears instead, but belts remain extremely common in FRC mechanisms.

Belt trade-offs#

• Precise center distance required. Too loose and the belt skips teeth (ratcheting); too tight and you overload bearings. Many designs use a tensioning idler or adjustable mount.
• Less debris tolerance than chain; a jammed game piece can skip a belt.

Direct gear meshes#

When two shafts are close together, you can mesh gears directly. This is the most compact and efficient option and is how the stages inside a gearbox work. The critical parameter is center distance, which is set by the gears' diametral pitch (DP) (or metric module) and tooth counts. Common FRC gears are 20 DP for general drivetrain/mechanism use and 32 DP for compact, lighter assemblies. Gears must share the same pitch to mesh — 20 DP and 32 DP gears are not interchangeable — and the center distance must be correct or they bind or skip.

Choosing among the three#

• Short distance, need compactness/efficiency → gears.
• Medium distance, want light and clean → belt.
• Long distance, dirty/abusive environment, or shock loads → chain.