Setup & Calibration

Initial Setup

  1. Compile the firmware using the Arduino IDE or arduino-cli and upload it to your Arduino board.

  2. Open a serial connection to the board with a baud rate of 115200.

  3. Check that the board connects successfully by looking for the READY message in the serial monitor.

Checking Motor Directions

Before running any automated movements, make sure the physical rotation of each motor matches the software’s expectations.

  1. Disconnect motor power and manually move the arm into the mechanical home position:

    Mechanical Home Orientation

  2. Send the M17 command to turn on the motors. The joints should lock in place.

  3. In this position, the software assumes the internal joint angles are: Theta 1 = 0°, Theta 2 = 90°, and Theta 3 = 0°.

  4. Reference the coordinate diagram below to understand the defined positive rotation vectors:

    Kinematic Sign Convention Top View Sign Convention

  5. Move each joint a little bit using absolute positioning commands (e.g., send G1 T145 to move Theta 1 to 45°). Note that relative positioning (G91) does not work for direct joint commands (T-parameters).

  6. If a motor turns in the wrong direction:

    • Software Fix: Change the direction in code by toggling the MOTORx_INVERT setting in Config_Robot.h and upload the code again.

    • Hardware Fix: Turn off the power and swap the coil wires for that stepper motor.

Testing Limit Switches

Caution: Homing the arm with broken limit switches will cause the arm to crash and potentially break hardware.

  1. Send the M119 command to check the limit switch status.

  2. Make sure all switches show as open (0 for default setups).

  3. Manually press each limit switch one by one while sending M119 again to confirm they change to triggered (1).

Auto Homing

  1. Send the G28 command to start homing.

  2. The controller will move all joints toward their limit switches.

  3. When a switch is hit, the system moves back by a set number of steps and sets the internal angles to the home position.

Emergency Stop

If something goes wrong or the arm is about to crash:

  • Send the M112 command (or just !) to trigger an immediate software stop. This immediately cuts the ENABLE line to the motors.

  • After a software stop, you must run a full G28 homing cycle before moving the arm again.

  • Hardware Override: Physically unplugging the main DC power supply is always the safest way to stop the robot.

Calibration

Steps Per Degree The STEPS_PER_DEGREE setting tells the software how many motor steps equal one degree of movement. It needs to be calculated based on your motor, microstepping, and gear ratio.

\[\text{Steps}/\text{Degree} = \frac{\text{Motor Steps Per Revolution} \times \text{Microstepping Factor} \times \text{Gear Ratio}}{360}\]

Home Offset Calibration The HOME_OFFSET_STEPS_THETA* settings control how many steps the arm moves away from the limit switch after hitting it.

To calibrate the home position:

  1. Run a full homing cycle (G28).

  2. Check the current software position with M114.

  3. Measure the actual physical angles of the robot.

  4. Calculate the difference between the software angles and physical angles, convert this difference into steps, and update the offset numbers in the code.