Design for Serviceability
Between qualification matches you have roughly 20 to 25 minutes from the time you leave the field to the time you queue for the next one. After transport and getting the robot on the pit table, that's closer to 15 minutes of actual work time. A robot that takes 40 minutes to repair gets sent back out broken or sits out a match entirely.
Serviceability is a design decision made in CAD, not something you can add after the fact.
What Actually Breaks
Structural members almost never fail mid-competition. The things that do are small, wear-prone, and usually buried somewhere inconvenient.
Belts
Snap or jump a pulley
Need to pass a new belt through the mechanism
Shaft retention bolts
Back out or strip
Need a straight hex key path to the bolt face
Small fasteners
Strip, loosen, or disappear
Need clear access without removing other assemblies
3D printed brackets
Crack on impact
Need to unbolt and swap without disassembling the mechanism
Physical Access
The most common pit problem isn't a complicated failure. It's a simple failure that takes forever because you can't reach it.
Belts run on fixed center-to-center distances so there's nothing to adjust, but a snapped belt still needs to be swapped. Design belt runs so the path is reachable from the outside without pulling a side plate.
An access cutout sized to pass a belt loop through, or an open-profile design on one face of the mechanism, is usually enough. If the only way to reach the belt is to remove a structural plate, fix that in CAD before it happens in the pit.
Shaft retention is the most commonly overlooked access issue. If the retention bolt on a shaft is behind a motor, a gearbox, or a tube wall, it will be invisible exactly when you need it.
Put retention bolts on the face of the mechanism that's easiest to reach from outside, and make sure nothing blocks a hex key from getting there straight. Check this on every shaft before the mechanism leaves CAD.
Fasteners that are recessed behind other parts, inside tube, or facing inward toward the robot tend to get forgotten during pit checks and stripped during rushed repairs.
Orient bolt heads outward wherever possible. On joints that need to be accessed frequently, avoid designs where you have to hold a nut on one side while driving from the other. Where two-sided access isn't possible, use Loctite instead of a lock nut, as covered on the Fasteners and Hardware page.
Before finalizing any mechanism, trace the steps to replace a belt and to tighten shaft retention on every shaft. If either path requires removing more than one other assembly, redesign for access.
Hardware Consistency
Every unique tool requirement on the robot is another thing someone has to find in a rushed pit. The standard on this team is 10-32 and 1/4-20 socket head cap screws throughout. One hex key set covers every fastener on the robot.
Don't introduce button heads or other drive types because a COTS part came with them. Where you control the fastener choice, socket heads only.
A single mechanism that requires a Phillips screwdriver and two different hex key sizes has already failed the serviceability test.
Designing for Replaceability
Some things won't be repairable in 15 minutes. The right answer for those is to replace the whole subassembly and fix the broken one after the event. This only works if the mechanism was designed to come off cleanly in the first place.
A replaceable mechanism has:
4 to 6 bolts at a defined mounting interface
Geometry consistent enough that a spare drops in without adjustment
No fasteners buried behind other assemblies at the attachment points
Most important mechanisms to design this way:
Intake (extends past the frame, takes the most contact)
End effector (highest chance of game piece jams or impacts)
Any mechanism that can't be repaired with the robot assembled
Modular mounting in Onshape
When designing a mechanism's attachment to the frame, think about whether a spare built from the same Onshape assembly would bolt on identically. If your intake mounts at four 1/4-20 bolts on a defined hole pattern in the frame tube, you can prebuild a spare before competition and swap the whole thing in minutes.
Design each major mechanism as its own sub-assembly in Onshape rather than modeling everything in a single top-level assembly. This forces you to define clean interfaces at the attachment points, makes it easier to share files with whoever is building the spare, and keeps the top-level assembly organized.
Spare Parts
Build a spare of anything you designed to be replaceable. Beyond subassemblies, the pit should have on hand at minimum:
Every belt size used on the robot (at least 2 spares of each)
One fully assembled spare MK5i swerve module per event
Full assortment of 10-32 and 1/4-20 socket heads in all lengths used on the robot
Spare shaft retention hardware for every shaft size on the robot
Any 3D printed parts likely to crack on impact (brackets, housings, guides)
At your first competition, keep a running list of everything that breaks and how long it took to fix. Use that list to build the spare parts kit for the next event and to flag which mechanisms need a serviceability redesign in the future.
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