Chain and Sprockets

How it works#

Chain transmits power between two sprockets the way a bicycle does. It tolerates misalignment, handles shock loads well, and is easy to repair. In FRC two sizes dominate, named by the ANSI standard:

• #25 chain — pitch (link spacing) 0.250". Lighter and smaller; the standard for most drivetrains and mechanisms.
• #35 chain — pitch 0.375". Fatter and harder to derail, but significantly heavier. Used where loads are high.

Ratios with sprockets#

A sprocket ratio works exactly like gears: driven teeth ÷ driving teeth. A 12T driving a 24T sprocket is a 2:1 reduction.

Chain wrap and idlers#

The chain must wrap far enough around the smaller sprocket to engage enough teeth. The common rule is at least ~120 degrees of wrap on the small sprocket; a sprocket ratio of about 3:1 or less guarantees this regardless of center distance, while higher ratios in a single run risk dropping below 120 degrees and skipping teeth. For larger reductions, add an idler sprocket to increase wrap, or split the reduction across two stages.

Tensioning#

Chain stretches slightly with use and must be tensioned. Common methods:

• Sliding bearing blocks / tensioner cams (e.g., WCP cams) that move one shaft to take up slack.
• Idler sprockets/tensioners pressing on the slack span.
• Designing the center-to-center distance so a whole number of links fits snugly (using a chain-length calculator).

Master links#

You join a chain into a loop with a master link (a removable connecting link). Carry spares: a thrown chain mid-match is a classic failure, and a master link lets you re-join quickly in the pit. Many teams instead use riveted or factory-pressed loops for runs they never plan to open.

Chain vs. belt vs. gears (quick guide)#

• Chain: rugged, forgiving of alignment and distance, but heavier and can throw if loose.
• Belt (GT2/HTD): quiet, light, no lubrication, very efficient, but requires precise center distance and is less tolerant of debris.
• Gears: most compact and efficient for short distances, but require tight tolerances and the correct center distance.