Weight Management

Weight is one of the few constraints in FRC that is both absolute and invisible. A robot that's over the limit at inspection doesn't compete until something comes off, and whatever comes off at that moment is usually something you didn't want to remove. The teams that handle this well don't do it by cutting things at the last minute. They track it continuously from Day 1 and make intentional decisions about where the budget goes.

The Rules (Know These Exactly)

The weight limit changed in 2025, and a lot of older resources still reference the wrong number.

What's being weighed	Limit
Robot only (R103)	115 lbs
Robot + bumpers (R408)	135 lbs
Robot + all swappable mechanisms at inspection (I103)	150 lbs

What's excluded from the 115 lb limit: bumpers, the battery and its Anderson connector half (including up to 12 in. of cable per leg, lugs, bolts, and insulation), and any location detection tags provided at the event.

The battery and bumpers do not count toward your 115 lb limit. You design the robot itself to 115 lbs, and bumpers can add up to 20 lbs on top of that. If returning mentors or old resources reference 125 lbs as the robot limit, that was pre-2025, so update your numbers.

Tracking Weight Through Build Season

Weight creeps up through entirely reasonable individual decisions: a gusset here, a second motor there, thicker polycarbonate because there was a stress fracture last year. None of those decisions are obviously wrong, but they add up fast.

1

Start a weight tracking spreadsheet on Day 1

List every major subsystem with an estimated weight pulled from vendor pages, CAD models, or past robot data. Include drivetrain, superstructure, each mechanism, electronics, and wiring. Update it as designs change. A stale spreadsheet is worse than no spreadsheet because it creates false confidence.

2

Weigh parts as they come off the CNC or out of the printer

CAD estimates are a starting point, not a guarantee. Machined parts, 3D prints, and assembled sub-structures all come out heavier than the model. Weigh them on Mr. Wippler's scale and update the tracker.

3

Weigh the robot at each design review

Mr. Wippler's scale is fine for tracking trends throughout the season. If you need a precise number, especially in the final weeks before competition, take it to the wrestling weight room scale (ask Mr. Wippler who to ask for this).

4

Set a soft cap 2 weeks out

The competition scale isn't always perfectly calibrated with yours, so being close to the limit is a real risk. If you're at 112 lbs two weeks before your first event with work still left to integrate, that's the moment to start cutting, not the night before load-in.

Weight Reduction Techniques

Pocketing and lightening holes

Pocketing removes material from a flat plate in a grid or organic pattern, leaving a structural web while cutting mass significantly. Lightening holes do the same for tube.

When it helps: Plates and brackets that are oversized for their actual load. A 1/4" aluminum plate used as a pivot bracket can often be pocketed down to 30 to 40% of its original weight without real loss of strength.

When it doesn't help: Parts already at minimum thickness, or parts where the shape itself is the structure. Pocketing thin-wall tube just removes the wall you needed.

Practical note: The sponsor CNC can run pocketing operations. Design parts with a dedicated sketch layer for pocket geometry in Onshape so the file is clean to hand off.

Right-sizing fasteners

Fasteners are denser than aluminum. A robot assembled with more or larger hardware than necessary carries real weight penalty that's easy to miss because it accumulates across hundreds of holes.

• 10-32: The default for the vast majority of mechanism and structural joints

• 1/4-20: Primary structural joints (frame gussets, pivot mounts) and high-shear applications only

If a joint has six fasteners and four would hold it, use four. This requires actually looking at the load case rather than filling every available hole in a pre-drilled tube.

Eliminating redundant structure

The hardest cut is removing something that feels like it should be there but doesn't actually carry load. Before adding any structural element, ask: what fails if this piece isn't here? If the answer is "nothing," it probably shouldn't be there.

Common examples:

• A second cross-brace on a frame that already has good triangulation

• A rear plate on a gearbox housing that's there because "the other side has one"

• A polycarbonate cover on a mechanism that no one will open during competition

Design under, not to the limit. Competition scales are not always calibrated identically to yours. A robot that weighs exactly 115 lbs on the weight room scale might read 115.4 lbs at competition. Leave yourself a real buffer. Closer to 112 to 113 lbs is a safer target than 114.9.