MechBase Starter Kit — Project 1: Rolling Chassis
Age: 7+ | Concept: Basic circuit, motor control, cause & effect
Before you build: Download
BrickLink Studio (free, Windows/Mac). Build the chassis virtually, then print professional step-by-step instructions with photos. Studio uses the LDraw part database — every LEGO-compatible part is available.
BrickLink Studio — Quick Start
- Download: bricklink.com/v3/studio/download.page (free)
- Platform: Windows 10+ or macOS 12+
- Part library: 100% of LEGO parts + compatible alternatives
- Instructions: Build → File → Create Instructions → Auto-generates step-by-step with photos
- Export: PDF, PNG, or interactive HTML
Workflow: Build the chassis in Studio using the parts list below → Generate instructions → Print for the kid. The software handles part positioning, collision detection, and photo rendering. Way better than hand-coding SVGs.
📋 Verified Parts List
Part numbers verified on BrickLink. Search these exact numbers.
| Part # | Qty | Name | Use |
|---|
| 3811 | 1 | Baseplate 32 × 32 | Chassis foundation |
| 3701 | 4 | Technic Brick 1 × 4 with Holes | Axle mounts, beam structure |
| 3894 | 4 | Technic Brick 1 × 6 with Holes | Longer structural beams |
| 3895 | 4 | Technic Brick 1 × 8 with Holes | Frame rails |
| 3896 | 4 | Technic Brick 1 × 10 with Holes | Main frame rails |
| 3704 | 4 | Technic Axle 2L | Short connectors |
| 3705 | 6 | Technic Axle 4L | Wheel axles |
| 44294 | 2 | Technic Axle 7L | Long spans |
| 3737 | 2 | Technic Axle 10L | Drive axles |
| 44260 | 10 | Technic Bushing ½" | Wheel mounts, friction rings |
| 4256 | 2 | Technic Gear 12 Tooth | Motor reduction |
| 4257 | 2 | Technic Gear 20 Tooth | Speed reduction |
| 4258 | 2 | Technic Gear 40 Tooth | Output gearing |
| 32202 | 2 | Technic Bevel Gear 12 Tooth | Direction changes |
| 6259 | 4 | Technic Wheel 1.25" | Drive wheels |
| 6258 | 4 | Technic Rim 1.25" | Wheel hubs |
| 99233 | 8 | Technic Pin 1L with Friction | Beam connectors |
| 32062 | 6 | Technic Axle 2L Notched | Secured axle connections |
🔌 Electronics (Same as Before)
| Item | Qty | Notes |
|---|
| Raspberry Pi 4 8GB | 1 | Already owned |
| Adafruit Dual Motor Driver HAT | 1 | I2C, powers 2 DC motors + servos |
| TT Gear Motor (90 RPM, 6V) | 2 | High torque |
| SG90 Micro Servo | 1 | Future projects |
| HC-SR04 Ultrasonic | 1 | Distance sensing |
| TCRT5000 IR Sensor | 2 | Line tracking |
| Limit Switch (Micro) | 2 | Position sensing |
| LiPo 7.4V 2200mAh (2S) | 1 | Motor power |
| 2S LiPo Charger (1A) | 1 | Safe charging |
| Breadboard + Jumper Kit | 1 | Prototyping |
🛠️ Step-by-Step Build Instructions
Step 1 — Frame Rails
Attach four
Technic Brick 1×10 with Holes (3896) to the baseplate in a rectangular frame:
- Two along the long edges (rows 4 and 29)
- Two along the short edges (columns 6 and 27)
This creates your chassis perimeter. The holes in the beams accept axles and pins.
Step 2 — Axle Supports
Attach Technic Brick 1×4 with Holes (3701) perpendicular to the frame at each corner (rows 8 and 25, columns 10 and 23).
These create the axle mount points. The beams slot into the frame holes using Technic Pins with Friction (99233).
Step 3 — Install Axles
Slide
Technic Axle 10L (3737) through each pair of axle support beams (left side and right side).
- Axle goes through: Beam hole → Axle 10L → Beam hole
- Secure with Axle 2L Notched (32062) on each end to prevent wobble
Step 4 — Wheels
On each axle end: Bushing ½" (44260) → Rim 1.25" (6258) → Wheel 1.25" (6259)
The bushing provides friction so the wheel stays on the axle during operation.
Step 5 — Motor Mounts
Mount each
TT Gear Motor to the rear axle area using:
- Beam 1×6 with Holes (3894) as motor bracket
- Motor shaft aligns with Gear 12 Tooth (4256)
- 12T gear meshes with Gear 40 Tooth (4258) on the drive axle
This gives ~3:1 speed reduction — slower but more torque for the chassis.
Step 6 — Electronics
- Mount Pi 4 on top of the chassis (use rubber feet or Technic brackets)
- Plug Adafruit HAT directly onto Pi GPIO pins
- Connect Motor 1 → HAT M1, Motor 2 → HAT M2
- Connect LiPo to HAT VIN/GND terminals
💻 Code (Copy to Pi)
See the separate software document for the full Python code. This is the basic drive logic:
# Forward
motor_left.throttle = 0.5
motor_right.throttle = 0.5
# Reverse
motor_left.throttle = -0.5
motor_right.throttle = -0.5
# Turn left
motor_left.throttle = -0.3
motor_right.throttle = 0.5
🎮 Project 1 Challenges
| # | Challenge | Concept |
|---|
| 1 | Drive forward 1 meter, then stop | Motor control, timing |
| 2 | Drive forward, reverse, turn — make a square | Sequencing logic |
| 3 | Use limit switch to stop at a wall | Sensor feedback |
| 4 | Obstacle avoidance (ultrasonic) | IF/THEN logic |