COTS vs Custom Parts

COTS stands for Commercial Off-The-Shelf. In FRC, this refers to any part you buy from a vendor and use as-is (or close to it). A custom part is anything your team designs and fabricates. Knowing when to buy and when to make is one of the most important practical decisions during build season.

When to buy (COTS)

Situation	Example
A commercial part does exactly what you need	Swerve modules, MAXPlanetary gearboxes, bearings, wheels
You're short on fabrication time	Buying a gearbox is faster and more reliable than designing a custom gear reduction
The part is a commodity item	Bolts, nuts, bearings, sensors, raw aluminum stock
Reliability matters more than optimization	COTS parts are tested by thousands of teams. Your custom version is tested by one.

When to make (custom)

Situation	Example
No commercial part fits your geometry	A mounting plate that needs specific hole patterns for your frame layout
The COTS option is too heavy or bulky	A custom bracket that combines two functions into one lighter part
Integration is cleaner with a single custom part	A plate that serves as both a gearbox face and a structural mount, reducing part count
You have the tools and skills to do it well	CNC'd plates, laser-cut parts, well-designed 3D prints

To help put this in context, here is a rough breakdown of what's typically COTS and what's typically custom on most competitive robots:

Almost always COTS

• Motors (Kraken X60, X44)

• Gearboxes (MAXPlanetary)

• Swerve modules

• Bearings, shafts, shaft collars

• Wheels

• Hardware (bolts, nuts, rivets)

• Sensors and electronics

• Raw material stock (aluminum tube, sheet, hex bar)

Almost always custom

Could go either way

Good to know

• If you modify a COTS part (for example, drilling extra holes in a bracket you bought), it becomes a custom part in the eyes of FRC rules. This usually doesn't matter, but be aware of it.

• Having parts fabricated by an outside service like SendCutSend is allowed, but the design has to be your team's work.

• Keep a Bill of Materials (BOM) that tracks what you bought and what it cost. Some awards and events ask for this.