Focus This Week

This week is focused on Mechanical Design and Machine Design. The goals were to work as a team to design and build a machine (incorporating mechanism, actuation, and automation), construct the mechanical components, and write control software. I designed the Go-Kart Steering Linkage Mechanism and developed an automated Steering Durability Test Rig Machine to physically cycle the steering assembly and evaluate mechanical wear.

Group Assignment — Durability Testing Machine

Our group project was to build a machine that automates mechanical reliability tests on fabricated kart parts. The full machine layout, assembly schematics, and group contribution files are documented on the Fablab Dilijan Group Machine Page.

Machine Mechanism & Actuation

• Mechanical Structure: Constructed from 20x20mm T-slot aluminum profiles, linear guide rails, and 3D printed carriages.
• Actuation System: A NEMA 17 stepper motor coupled to an 8mm lead screw. This translates rotational force into linear motion.
• Automation Logic: An Arduino Uno with a CNC Shield V3 driving an A4988 stepper driver. The controller runs a cycling code that pushes the tie-rod back and forth, simulating 10,000 steering cycles.

Individual Assignment — Linkage Design and Integration

My primary contribution to the group machine was the mechanical design and assembly of the Go-Kart steering linkages. I designed a system using dual tie-rods connected to a central steering column arm (Pitman arm) and outer steering knuckles.

Ackermann Steering Geometry

To ensure the wheels roll smoothly during turns without slipping sideways, I calculated the geometry based on **Ackermann steering principles**:
* The inside wheel must turn at a sharper angle than the outside wheel because it follows a smaller turning radius.
* I angled the steering arms inwards so that lines drawn through the steering knuckle pivot pins and tie-rod ends intersect at the center of the kart's rear axle.

Automation Control Code

I wrote the stepper cycling software that runs on the test machine, using the AccelStepper library to ensure smooth acceleration profiles:

// Machine Stepper Controller - AccelStepper Durability Test
#include <AccelStepper.h>

// Define pin connections for CNC Shield (X-Axis)
const int STEP_PIN = 2;
const int DIR_PIN = 5;
const int ENABLE_PIN = 8;

// Define stepper parameters
AccelStepper stepper(AccelStepper::DRIVER, STEP_PIN, DIR_PIN);

const long TARGET_POSITION = 4000; // Total steps per sweep (approx 50mm travel)
int cyclesCount = 0;

void setup() {
  Serial.begin(115200);
  pinMode(ENABLE_PIN, OUTPUT);
  digitalWrite(ENABLE_PIN, LOW); // Enable stepper drivers
  
  stepper.setMaxSpeed(1000.0);
  stepper.setAcceleration(500.0);
  stepper.moveTo(TARGET_POSITION);
}

void loop() {
  // Cycle back and forth
  if (stepper.distanceToGo() == 0) {
    long nextPos = (stepper.currentPosition() == 0) ? TARGET_POSITION : 0;
    stepper.moveTo(nextPos);
    cyclesCount++;
    
    Serial.print("Cycle Completed. Total: ");
    Serial.println(cyclesCount / 2);
  }
  
  stepper.run();
}

Original Design Files

Download the 3D assembly CAD and code files for the steering mechanism:

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Week 12 — Summary

This week focused on mechanisms, kinematic assembly, and automated testing. Here is a summary of the accomplishments: