A Concept Sprint is a structured session where your team generates multiple mechanism ideas, models the top candidates quickly in CAD, and picks the best one with evidence — not gut feel.
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Sprint
2
Concepts
3
Tradeoffs
4
Packaging
5
Select
// Section 01
The Concept Sprint Method
Top teams never build the first mechanism they think of. They generate at least three different approaches, model them quickly in CAD, compare them against criteria, and pick the best one. This is the EDP Brainstorm → Select cycle done properly.
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Sprint timeline: 45-minute session. 10 min: define what the mechanism must do. 15 min: sketch 3 concepts on paper. 15 min: rough CAD of top 2. 5 min: fill in the tradeoff matrix. Output: one selected concept with documented reasoning.
What the Mechanism Must Do — Define This First
Before you brainstorm, write down the requirements. Vague requirements lead to vague designs. Specific requirements let you evaluate whether a concept actually works.
📝 Mechanism Requirements — Fill Before Brainstorming
✅ Saved
Why CAD Before Build?
A physical prototype of a mechanism takes 2–4 hours. A CAD concept takes 20–40 minutes. You can evaluate 3 CAD concepts in the time it takes to build 1 physical prototype. When you pick the wrong concept with a physical prototype, you have wasted 2–4 hours plus materials. When you pick the wrong concept in CAD, you press delete.
Professional engineering teams use design reviews at the concept phase before committing any resources to building. Boeing, NASA, and SpaceX all hold Preliminary Design Reviews (PDR) and Critical Design Reviews (CDR) before physical fabrication begins. The goal is identical to a Concept Sprint: generate multiple approaches, model them analytically, review as a team, and select based on evidence. Skipping the concept phase is what leads to expensive redesigns late in a program — the same way it leads to rebuilds at VRC competitions.
🎤 Interview line: “Before we built our intake, we ran a Concept Sprint — we modeled three different designs in Onshape, evaluated each against our requirements, and selected the best one using a tradeoff matrix. That decision is documented in the notebook. The mechanism we built on the first try was competition-ready because we evaluated it in CAD first.”
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// Section 02
Generating Concepts
The rule for brainstorming: generate first, evaluate second. Do not kill an idea during the brainstorm phase. Quantity first, quality second — the best ideas often come after the obvious ones.
Paper Sketch Rules
Minimum 3 distinct concepts. If concepts 1 and 2 are the same mechanism with small differences, they don’t count as separate ideas.
Each sketch should show the mechanism in two states: stowed (within robot perimeter) and deployed (actively engaging game elements).
Label key dimensions on the sketch even if rough: overall width, height, reach, and approximate motor positions.
Include the game element (block, ring, etc.) in the sketch — it must show how the mechanism interfaces with the game piece.
🔬
Look at reference designs, then close the tab. It is fine to research what other teams have built. It is not fine to open Onshape with a reference photo and copy-model it without understanding why it was designed that way. Look at references for inspiration, understand the principle, then design your own version from scratch.
Common Mechanism Types for VRC
🏅 Roller Intake
Motorized rollers that pull game elements in on contact. Fast cycle time. Works well with round or tumbling game elements. Can be single-roller or counter-rotating pair. Simple to build and repair.
🔗 Claw / Gripper
Mechanical gripper that closes around game elements. More precise pickup, slower cycle. Best for irregularly shaped objects or when you need to hold during movement. More complex mechanically.
✅ Belt / Conveyor
Continuous belt or chain with paddles. Moves elements through the robot continuously. Used when elements need to travel a longer path (from pickup to scoring height). Good throughput, more parts.
📦 Scoop / Bucket
Passive scoop that collects elements by driving into them. Zero motors used. Works only when elements are stationary. Fastest possible pickup but very limited in where/how you can score.
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// Section 03
Tradeoff Analysis
Once you have 3 concepts, evaluate them against the same criteria. The one with the best score across your team’s specific priorities wins. This is your decision matrix — and it goes in the notebook.
Interactive Decision Matrix
Score each of your three concepts on each criterion (1–5). The one with the highest total wins. Adjust criterion weights to reflect your team’s priorities.
🎯 Design Decision Matrix
Weighted Totals
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Take a screenshot of this matrix and paste it into your notebook. This is exactly what the RECF rubric means by “multiple detailed diagrams with pros/cons and research backing.” A decision matrix with three concepts, weighted criteria, and a documented winner is Expert-level evidence for the “Select Best Solution” EDP step.
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// Section 04
Mechanism Packaging in CAD
“Packaging” means fitting your mechanism into the available space on the robot without conflicting with the drivetrain, electronics, or other mechanisms. This is where most student designs fail.
Packaging Checklist — Check Every One
Starting configuration within size limit: With the mechanism stowed, the full robot must fit within the legal starting size. Measure this in Onshape with all mechanisms in their stowed positions.
Electronics space reserved: V5 Brain (8.7” × 5.5”), battery (6” × 3.2” × 2”), and all 8 motor cables need to route somewhere. Model placeholder volumes for electronics before finishing the mechanism package.
No interference with drivetrain: Run Onshape’s interference check between the mechanism assembly and the drivetrain assembly. Any red highlight = crash at competition.
Mechanism motion clearance: If the mechanism moves (arm, elevator, rotating intake), trace its full range of motion in CAD. Does any point in that range hit the drive, the frame, or the field perimeter?
Service access: If a motor or shaft on this mechanism fails, can you access it in under 5 minutes in the pit? If not, redesign the mounting so the fasteners are reachable.
Cable routing: Sketch where each motor cable runs from the mechanism back to the brain. No cable should cross a moving joint, wrap around a shaft, or pull taut during mechanism movement.
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Weight distribution: Mechanisms mounted high or far forward move the center of gravity forward and up. A robot that tips during fast movements loses points. In Onshape you can estimate CG by using the “Mass properties” tool — it will show you the CG location for the full assembly. Keep it as low and centered as possible.
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// Section 05
Select & Document
The sprint ends with a decision and a notebook entry. Both are required. A decision without documentation is not engineering — it is just building.
What Goes in the Notebook
Paper sketches of all 3 concepts — labeled with dimensions, annotated with pros/cons
CAD screenshots of top 2 concepts — both stowed and deployed views
Written rationale — one paragraph explaining why you chose the winning concept over the others. Reference specific criteria.
What you learned from the rejected concepts — this is what judges look for as “research backing.” Why didn’t the claw work? What specifically would have made the belt conveyor worse in this application?
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Expert-level notebook evidence for “Select Best Solution” is exactly this: multiple detailed designs with a scored decision matrix and a written rationale that references specific data from your testing or analysis. If your notebook shows you always built the first thing you thought of, judges know you skipped this step.