Structure and motion
Subassemblies that mirror the real build, and checking travel before anything is manufactured.
By the end you can
- Organise a robot into subassemblies that match how it is actually built
- Animate a mechanism through its travel and find interferences
- Check that a mechanism stays inside the sizing cube through its full range
On this page · 3 sections
One assembly containing four hundred loose parts is technically a robot and practically unusable.
Mirror the real build
Structure the assembly the way the robot actually goes together:
- Drivetrain subassembly — frame, wheels, motors, bearings.
- Intake subassembly — everything that comes off as one unit at competition.
- Lift subassembly — the same.
- Top level — those three, mated to each other.
The test for a subassembly boundary
If the pit crew removes it as one piece, it is a subassembly. This matches how the robot is maintained, which is what makes the CAD useful on Saturday rather than only in November.
The payoff is real: each subassembly is mated internally once, then placed at the top level with a single mate. Someone can work on the intake without touching the drivetrain.
Checking motion is the whole point
Static clearance is easy and mostly uninteresting. Nearly every real collision happens partway through a motion — at 40 degrees of arm travel, not at either end.
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Drag the mechanism through its full travel. Slowly. Watch the region where parts pass each other rather than the end points.
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Check both directions. A lift that retracts past its own hard stop is a real failure mode.
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Include the game elements. Model the cube, ball, or sample. A gripper that clears everything while empty and collides while full is a common and expensive surprise.
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Check against the sizing cube at every point in travel, not just at start of match. Expansion rules are checked at inspection, and a mechanism that passes at rest can still be illegal mid-cycle.
The mistake that costs a regional
Teams check that the robot fits the sizing cube in its starting configuration, then discover at inspection that the lift sweeps outside the expansion limit at 60 percent extension. The assembly would have shown this in about ninety seconds.
Check yourself
Your arm assembly shows no interference when fully retracted and none when fully extended. What should you conclude?
Next
The model is right. Now get it to the people cutting metal.
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