Slow Regeneration in Big Drivebase Assemblies

A full robot in Onshape can grind to a crawl. Sluggish regen kills iteration speed, so treat it as a real bug with a real workflow.

Symptom: every sketch edit lags for seconds. Root cause is usually a giant single sketch — large numbers of entities force Onshape to solve all constraints and dimensions simultaneously. Fix: split monster sketches into smaller ones, and prefer feature patterns over sketch patterns for repeated holes. Big repeated geometry as sketch arrays is especially hard on the solver.

Symptom: regen takes many seconds after any change. Profile it with the Regeneration panel in the feature list to find the slow feature, then replace feature patterns with face patterns where possible. Face patterns regenerate noticeably faster because they copy finished geometry instead of re-running the feature recipe at each instance — Onshape's own tech tips document real multi-times speedups this way — one official example shows an 80x improvement switching a circular pattern from feature to face. Lightening grids and hole arrays are prime candidates.

Symptom: the whole document is slow, not one part. Check tab count and document size — large amounts of geometry and an oversized tab list both drag performance. Fix: split the robot into linked documents or version-locked derives so each document stays lean.

Symptom: the assembly is unbearable with hundreds of COTS parts. Every fully-detailed COTS module from a parts library — the current community standard is FRCDesignLib (inserted via the FRCDesignApp Onshape plugin; it replaces the older, now-deprecated MKCad library) — multiplies the geometry, and excess mates compound it. Fixes: (1) Use simplified/representation versions of COTS where detail does not matter. (2) Keep mates minimal — roughly one well-chosen mate per key part rather than many. (3) Derive key driving sketches into subsystem studios and assemble subsystems, rather than one flat mega-assembly. (4) Use versioned derives so the source is not recomputed live.

Profiling workflow: (1) Note which action is slow — sketch, feature regen, or assembly solve. (2) For sketches, count entities and split. (3) For features, swap pattern types (sketch → feature → face) and measure. (4) For documents, reduce geometry/tabs. (5) For assemblies, reduce part and mate count or use derives. Always change one thing and re-measure so you know what actually helped.

The theme: Onshape is fast until you make it solve too much at once. Smaller sketches, smarter patterns, leaner documents, and versioned derives keep a full FRC robot responsive through build season.