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Steering

Active steering controller running on Rigby. Reads a target angle over serial, reads current wheel angle from a potentiometer, and drives the steering motor with proportional control.

Source: FT-Hardware/Code/Rigby/SteeringCode/SteeringWithPotCode/SteeringWithPotCode.ino

How It Works

  1. Receives a target angle (degrees) over serial as a newline-terminated float via FTSerial
  2. Reads current angle from a potentiometer on the steering column
  3. Proportional controller drives the motor until the error is within the dead band
  4. Prints telemetry (angle, target, error) at ~20 Hz

Hardware Setup

Pin Constant Function
A3 POT_PIN Potentiometer (steering feedback)
5 RPWM_PIN Right PWM to motor driver
6 LPWM_PIN Left PWM to motor driver
7 REN_PIN Right enable on motor driver
8 LEN_PIN Left enable on motor driver

Motor driver is a BTS7960 dual H-bridge. If steering turns the wrong way, swap RPWM_PIN and LPWM_PIN.

Configuration Constants

Calibration — must be set before deploying:

Constant Default Description
POT_ADC_LEFT 150 ADC reading at left mechanical extreme
POT_ADC_RIGHT 870 ADC reading at right mechanical extreme

POT_ADC_LEFT must always be less than POT_ADC_RIGHT. Move steering to each extreme and record the ADC values.

Control:

Constant Default Description
ANGLE_LIMIT_DEG 80.0 Max steering angle in either direction (degrees)
STOP_BAND_DEG 1.0 Dead band — how close to target before motor stops
GAIN 3.0 Proportional gain
PWM_MIN 35 Minimum PWM (avoids stalling)
PWM_MAX 200 Maximum PWM
ANGLE_SMOOTHING 0.20 Smoothing filter coefficient. Must not be 0 or motor won't move
SERIAL_TIMEOUT_MS 1500 Miliseconds without serial before timeout
HOLD_LAST_VALUE true On timeout: hold last angle (true) or return to 0 (false)

Serial Protocol

Input: newline-terminated floats 

25.5

Output: telemetry at ~20 Hz 

angle= 12.34 target= 25.50 error= 13.16

Functions

float directionCheck(float x, float a, float b)
Clamps x to [a, b]. Used to enforce angle limits.

float mapPotToDeg(int adc)
Maps a raw ADC reading to degrees. Linear from [POT_ADC_LEFT, POT_ADC_RIGHT] → [-ANGLE_LIMIT_DEG, +ANGLE_LIMIT_DEG].

void drive(int pwmSigned)
Drives the motor. Positive = right, negative = left, 0 = stop.

void coastStop()
Stops the motor.

void driverEnable(bool en)
Enables or disables the motor driver.