🔌 Integration · Onshape + EZ Template · Intermediate

CAD to Code: The Engineering Thread

CAD decisions have direct consequences in EZ Template. Every number in your chassis constructor came from somewhere — and that somewhere is your Onshape assembly. This guide maps every connection explicitly.

Why this matters: Most students treat CAD and programming as separate workstreams. They're not. If your Onshape model has motor port 3 on the left front, your robot-config.cpp must have that. If your wheel diameter in CAD is 4.125", your chassis constructor must say 4.125". Every mismatch between CAD and code is a bug before you even write any auton.

🔌 The Connection Map — CAD → EZ Template

📐 Onshape Assembly → ⚡ EZ Template Constructor

📐 Onshape: Motor Position

Motor labeled "L-Front" at Brain port 1 in assembly annotations

→

⚡ robot-config.cpp: Left motors array

{-1, -2} // negative = reversed
Check motor direction in CAD

📐 Onshape: Wheel Part Properties

Right-click wheel → Properties → "Diameter: 4.125 in" (from VEX parts library)

→

⚡ main.cpp: wheel_diameter

4.125 // NOT 4.0
Always read from CAD, not memory

📐 Onshape: Drivetrain Width

Measure tool: center of left wheel to center of right wheel = 12.5 in

→

⚡ chassis.drive_width_set()

chassis.drive_width_set(12.5);
Used for odometry calculations

📐 Onshape: Tracking Wheel Offset

Mate connector position: tracking wheel center is 4.0 in right of robot centerline

→

⚡ tracking_wheel constructor

ez::tracking_wheel left_tracker
(port, 2.75, 4.0); // 4.0 = offset

📐 Onshape: Motor Cartridge Color

V5 Motor part → configuration: Blue (600 RPM) selected in configurator

→

⚡ main.cpp: MOTOR_GEAR

pros::E_MOTOR_GEAR_BLUE
// Blue=600, Green=200, Red=100

🔧 Robot Config Generator

Enter your measurements from Onshape. Get a complete robot-config.cpp snippet ready to paste.

Left motor ports (comma-sep, - = reversed)

Right motor ports

IMU port

Wheel diameter (from Onshape)

Track width inches (Onshape measure)

Tracking wheel offset (if using odom)

📏 How to Read Measurements from Onshape

Wheel diameter: Right-click the wheel part in the Feature Tree → Properties. Check the diameter from the VEX parts library — 4" omni wheels are 4.125".
Track width: Tools menu → Measure. Click center of left wheel, then center of right wheel. Read the distance. Use this exact number.
Tracking wheel offset: In the Assembly, right-click the tracking wheel's mate connector → Edit. The X or Y offset from the robot's origin mate is your distance to center.
Motor ports: Add a text annotation to your assembly labeling each motor with its Brain port number. Update it whenever wiring changes.

The port map habit: Create a simple table in your engineering notebook: Motor → Location → Port → Direction. Update it every time wiring changes. When a motor fails and needs replacing at a tournament, you don't want to guess which port it was on.

📖

DOCUMENTATION: BOTH TOOLS

Onshape measurement tools and EZ Template drive constructor reference

⚡ EZ Installation → 📦 VEX Parts Library → 📏 Tracking Wheel Offset →

⚙ STEM Highlight Engineering: Systems Integration — CAD as a Design Specification

The translation from CAD model to working code is a systems integration problem. In professional engineering, a CAD model specifies exact constraints — gear ratios, pivot radii, link lengths — and the software team uses those measurements as inputs. When a robot’s drivetrain CAD specifies a 4:1 gear ratio, the code’s RPM calculations must use that exact ratio. Discrepancies between the mechanical design and software parameters are one of the most common causes of auton drift.

🎤 Interview line: “Our CAD model drives our code configuration. When we update gear ratios in Onshape, we update our EZ Template wheel settings to match. This systems integration approach eliminates a category of bugs where mechanical and software assumptions diverge. Our drivetrain documentation shows the CAD specs side-by-side with the code constants.”

Your Onshape model shows a 3.25-inch wheel diameter, but your EZ Template chassis is configured with 4.0 inches. What is the most likely symptom?

⬛ The robot drives faster than expected because the code thinks wheels are larger

⬛ Autonomous movements will consistently overshoot — the robot drives farther than commanded because the code calculates travel based on the wrong wheel size

⬛ The robot steers to the left because one side is configured differently

📝

Notebook entry tip: Build & Program — Orange slide — Write a CAD-to-code handoff entry: include your Onshape wheel diameter measurement, gear ratio from the CAD assembly, and the corresponding EZ Template config values. Side-by-side documentation of CAD specs and code constants shows judges that your software was derived from your design — not invented separately.