Mechanical Design Guide
Learn CAD, design robot mechanisms, and build competition-ready systems
OnShape Setup & CAD Basics
OnShape is a free, cloud-based CAD platform perfect for FRC teams. No installation needed - works in your browser!
Why OnShape?
- Free for students and FRC teams
- Cloud-based - collaborate in real-time
- Access from any device with internet
- Built-in version control
- Extensive FRC parts library
Getting Started:
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Create Free Education Account
Go to OnShape.com and sign up with your school email (.edu). Choose 'Education Plan' for free access.
OnShape Education -
Complete OnShape Learning Center
Take the 'CAD Basics' and 'OnShape Fundamentals' courses. These are essential!
OnShape Learning Center -
Learn FRC-Specific CAD
Follow the FRCDesign.org course - it takes you from zero to modeling a full robot!
FRCDesign.org Course -
Practice with Simple Parts
Start by sketching 2D shapes, then extrude them into 3D. Practice with brackets, spacers, and simple plates.
📚 Essential CAD Skills
- Sketching (rectangles, circles, lines)
- Extrude, Revolve, Sweep
- Constraints (coincident, parallel, perpendicular)
- Assemblies and Mates
- Parametric design
FRC Parts Library
Don't model everything from scratch! Use pre-made CAD models of common FRC parts.
Important Part Libraries:
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MKCad - Essential FRC Library
MKCad is the most comprehensive FRC parts library for OnShape. It includes motors, gearboxes, wheels, and structural components.
MKCad Library -
Vendor CAD Models
Download official CAD models from vendors:
- REV Robotics - Motors, structural components
- AndyMark - Wheels, gearboxes, chassis kits
- VEX Robotics - Various mechanical components
- WCP (West Coast Products) - Drivetrain components
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Link Parts Library to Your Account
Follow MKCad installation instructions to link the library. Then you can insert parts directly into your designs!
💡 Pro Tip
Create a 'Parts Reference' document in OnShape where you collect all commonly used parts. This makes it faster to find and insert parts when designing!
Drivetrain Design
The drivetrain is the foundation of your robot. Without a reliable drivetrain, nothing else matters!
Common Drivetrain Types:
🚗 Tank Drive (West Coast Drive)
Most common for rookie teams. Simple, reliable, and powerful.
- 6-wheel configuration with center wheel dropped
- 2-4 motors per side
- Good traction and pushing power
- Recommended for first-year teams
🎯 Swerve Drive
Advanced - each wheel can rotate and drive independently. Maximum maneuverability!
- 4 independent swerve modules
- Complex programming and mechanical design
- Not recommended for rookie teams
Drivetrain Design Steps:
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Choose Wheel Size
Common sizes: 4", 6", or 8" diameter. Larger wheels = higher speed, smaller wheels = more torque.
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Select Motors and Gearing
CIM motors or NEO brushless are standard. Use JVN Calculator to determine gear ratios for desired speed.
JVN Drivetrain Calculator -
Frame and Wheel Layout
Typical robot size: 28" x 28" starting configuration. Design frame using box tubing (1" x 2" aluminum).
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Add Chain/Belt Drive
Connect motors to wheels via chain (#25 or #35) or timing belts. Ensure proper tension!
⚠️ Common Mistakes
- Drivetrain too slow - check gear ratios!
- Chain too loose or too tight
- Not enough motor power (minimum 4 motors total)
- Wheels rubbing on frame
Intake Mechanisms
The intake collects game pieces. Design philosophy: "Touch It, Own It" - control the piece as soon as you touch it!
Common Intake Types:
🔄 Roller Intake
Most versatile and common. Works for balls, cubes, cones, and more!
- Uses compliant wheels (4" or 6" diameter)
- Powered by 1 BAG motor or 775pro
- Can pivot or extend to reach ground
🤲 Claw/Gripper Intake
Grabs and holds game pieces securely.
- Good for cones and irregular shapes
- Uses pneumatic cylinders or servos
- Simpler design than rollers
Design Considerations:
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Game Piece Analysis
Study the game manual! What shape/size are game pieces? How heavy? Where are they located on the field?
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Mounting and Packaging
Intake should deploy outside robot frame perimeter. Use pneumatic cylinders or motor-driven pivots.
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Power and Control
BAG motors are perfect for intakes. Add limit switches to detect when piece is captured.
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Handoff to Mechanism
Design how intake transfers game piece to shooter/storage. Smooth handoff is critical!
💡 Intake Design Tips
- Make it wide enough to easily capture pieces
- Add compliance (springs, surgical tubing) for better grip
- Test with actual game pieces, not just CAD!
- Keep it simple - complexity = failure points
Shooter Systems
Shooters score game pieces into goals. Three main types: flywheels, catapults, and linear punchers.
Shooter Types:
⚡ Flywheel Shooter
Most accurate and controllable. Wheels spin at high speed to launch game pieces.
- Uses 2-4 NEO/Falcon motors
- Variable speed for different distances
- Best for balls and discs
- Requires PID control for consistency
🎯 Catapult Shooter
Stores energy in springs or pneumatics, releases quickly.
- Simpler than flywheels
- One shot at a time (slower cycle)
- Good for high arc shots
- Uses surgical tubing or pneumatic cylinders
Flywheel Design Steps:
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Calculate Required Exit Velocity
Use physics! Measure max shooting distance and goal height. Calculate required velocity using projectile motion equations.
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Choose Wheel Size and Motor
Typical: 4" compliant wheels with NEO motors at 1:1 or 2:1 gear ratio. Use JVN Calculator!
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Compression and Hood Angle
Game piece should be compressed between flywheels. Adjustable hood angle controls trajectory.
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Add Vision Alignment (Optional)
Use Limelight or PhotonVision to automatically aim at goal. Greatly improves accuracy!
⚠️ Shooter Challenges
- Inconsistent shots - check wheel RPM stability
- Jamming - ensure proper feeding mechanism
- Motor overheating - allow cool-down time
- Not enough power - use multiple motors
Gearbox Design & Motor Selection
Motors provide power, gearboxes convert that power to the speed and torque you need.
Common FRC Motors:
- NEO Brushless (REV) - Modern, powerful, efficient. Great for drivetrains and flywheels.
- Falcon 500 (CTRE) - High power, integrated encoder. Popular for swerve and shooters.
- CIM Motor - Classic workhorse. Reliable for drivetrains.
- 775pro - Smaller, lighter. Good for intakes and auxiliary systems.
- BAG Motor - Lightweight option for mechanisms.
Gear Ratio Basics:
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Understand Speed vs Torque Trade-off
Higher gear ratio = more torque, less speed. Lower ratio = more speed, less torque.
Example: 10:1 ratio means output shaft rotates 1 time for every 10 motor rotations.
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Use Online Calculators
Don't guess! Use these essential tools:
- JVN Design Calculator - Drivetrain speeds and motor loads
- ReCalc - Modern calculator for all mechanisms
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COTS Gearboxes vs Custom
For rookies: Buy COTS (Commercial Off-The-Shelf) gearboxes from:
- VexPro Versaplanetary
- AndyMark Toughbox
- REV MAXPlanetary
Custom gearboxes are advanced - wait until 2nd or 3rd year!
⚙️ Typical Gear Ratios
- Drivetrain: 8:1 to 12:1 (for 12-15 ft/s top speed)
- Intake: 3:1 to 5:1 (moderate speed)
- Flywheel: 1:1 to 2:1 (high speed)
- Elevator/Climber: 15:1 to 50:1 (high torque)
Manufacturing & Assembly
Turning your CAD design into real parts! Understanding manufacturing constraints early prevents problems later.
Common Manufacturing Methods:
🔧 Hand Tools (Drill, Saw, File)
Essential for every team. Can build entire robots with just these!
⚡ Bandsaw & Miter Saw
Cut box tubing and aluminum stock quickly and accurately.
🎯 CNC Mills & Routers (Advanced)
Computer-controlled precision cutting. Great for complex parts but not required!
Design for Manufacturing (DFM):
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Use Standard Hole Sizes
#7 (0.201"), 1/4", and 1/2" holes are most common. Design holes for standard drills you have!
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Minimize Custom Parts
Use COTS parts whenever possible. Every custom part = more time and potential errors.
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Tolerance and Clearance
Add 0.020"-0.030" clearance for slip fits. Parts WILL have manufacturing errors!
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Create Assembly Instructions
Export assembly views from CAD. Number parts and create bill of materials (BOM).
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Test Fit Early
Make prototypes! Use cardboard, wood, or 3D prints to test mechanisms before final parts.
⚠️ Safety First!
- Always wear safety glasses in shop
- Get trained on each tool before using
- Tie back long hair, remove jewelry
- Never work alone - buddy system!
🎉 You're Ready to Build!
You now have the fundamentals of mechanical design! Remember: simple, reliable mechanisms beat complex, fragile ones. Start with basics and iterate!