1dof Project from a chair with a stepper servo drive

Concept:

To create an inexpensive project for a deeper immersion into sim racing without cluttering up the space with a large cockpit.

We have a regular office chair with a rocking chair option. Our task is to remove the spring and replace it with a servo drive. We are not changing the rest of the functionality.

Calculations showed that a 2 Nm motor would be sufficient to generate a lifting force of 100 kg. However, we decided to play it safe and go for an 8.5 Nm motor.
Stepper servo drive with encoder (feedback) 86EBP145ALC-TK0 + HBS86H, 8.5 Nm
We will also need a SHV1605 screw and a 10-14 mm D32L45 rigid coupling.

We take apart the chair, remove the spring, drill a hole to put the axle in, cut the axle to size, and screw it on.

Code:

// Pins for connecting to HBS86H driver
#define PUL_PIN 9  // STEP — to PUL+
#define DIR_PIN 8  // DIR+
#define ENA_PIN 7  // ENABLE
#define MICROSTEP_PER_REV 1000     // Microsteps per revolution, set according to driver configuration
#define MAX_REVOLUTIONS    2       // Number of revolutions corresponding to SimTools maximum (adjust for your actuator)
long targetPosition = 0;           // Desired position (in steps)
long currentPosition = 0;          // Current position (in steps)
void setup() {
  Serial.begin(115200);
  pinMode(PUL_PIN, OUTPUT);
  pinMode(DIR_PIN, OUTPUT);
  pinMode(ENA_PIN, OUTPUT);
  digitalWrite(ENA_PIN, LOW); // LOW — enable driver (for HBS86H, usually LOW = ON)
}
void loop() {
  static String inputString = "";
  static bool inputStarted = false;
  // ==== Read command character-by-character for reliability ====
  while (Serial.available()) {
    char inChar = (char)Serial.read();
    if (inChar == '[') {
      inputStarted = true;
      inputString = "";    // start collecting the string
    } else if (inChar == ']') {
      inputStarted = false;
      inputString.trim();
      processCommand(inputString);
      inputString = "";
    } else {
      if (inputStarted) inputString += inChar;
    }
  }
}
// ==== COMMAND PROCESSING ====
void processCommand(String cmd) {
  // Example: "A512"
  if (cmd.length() < 2) return;
  if (cmd.charAt(0) == 'A') {
    int rawValue = cmd.substring(1).toInt();      // numeric value after 'A'
    long mapped = mapPosition(rawValue);
    if (mapped != targetPosition) {
      targetPosition = mapped;
      moveToPosition(targetPosition);
    }
  }
}
// ==== MAPPING SimTools values (0-1023) => step count (e.g., 0 ... 8000) ====
long mapPosition(int val) {
  long minStep = 0;
  long maxStep = long(MAX_REVOLUTIONS) * long(MICROSTEP_PER_REV); // e.g., 2 × 1000 = 2000 steps
  if(val < 0) val = 0;
  if(val > 1023) val = 1023;
  return map(val, 0, 1023, minStep, maxStep);
}
// ==== MOVE to the desired position ====
void moveToPosition(long target) {
  long stepsToGo = target - currentPosition;
  if (stepsToGo == 0) return;     // already in place
  int dir = (stepsToGo >= 0) ? HIGH : LOW;
  digitalWrite(DIR_PIN, dir);
  stepsToGo = abs(stepsToGo);
  for (long i = 0; i < stepsToGo; ++i) {
    digitalWrite(PUL_PIN, HIGH);
    delayMicroseconds(250);      // step speed — adjust for your motor!
    digitalWrite(PUL_PIN, LOW);
    delayMicroseconds(250);
    currentPosition += (dir == HIGH) ? 1 : -1;
  }
}

We received a chair that can be used as a regular chair, but can also be used as a single-axis sim racing chair.