How to unbrick STS3215 servo motor?

Other Hardware Motors, Mechanics, Power and CNC
1

Hi!

I am using ESP32 and STS3215 servos in my robotic arm project. If during movement my servo meets an obstacle my code switches it into holding mode. With a brand new servo it works pretty well but after a while servo just stops moving at all, it's built in LED blinks, servo responds to Ping/ReadPos/ReadLoad commands from WaveShares Library but does not move at all. The only suspicious thing I see is that ReadVoltage shows 0mV but multiple different testers show clearly that there are 6V on servo's input pins.

Here is the code that I use to move the servo. If anyone knows what happened to my servos and knows how to restore or prevent this from happening please help!

namespace Defaults {
     constexpr int MOTORS_STANDBY_TORQUE = 200;
     constexpr int MOTORS_OVERLOAD_PERIOD = 100;
     constexpr int MOTORS_STANDBY_CURRENT = 850;
     constexpr int MOTORS_GRIP_ACCELERATION = 25;
}

void MotorDriver::close_grip_with_hold_current(uint16_t protection_current) {

    int MOTOR_ID = 1;
    const int release_offset = 5;
    const int max_wait_ms = 4000; // Maximum wait time for closing (adjust as needed)
    const int position_tolerance = 5; // Acceptable error in position
    const int unchanged_cycles_required = 3; // Require position unchanged for 3 cycles
    const int position_stall_threshold = 2; // Threshold for considering position unchanged
    // unlock eeprom to allow writing protection settings
    sms_sts.unLockEprom(MOTOR_ID);
    sms_sts.SetProtectionCurrent(MOTOR_ID, protection_current);
    sms_sts.SetOvercurrentProtectionTime(MOTOR_ID,    Defaults::MOTORS_OVERLOAD_PERIOD/10); // sms_sts expects time in 10ms units
    // lock eeprom to prevent accidental writes
    sms_sts.LockEprom(MOTOR_ID); 
    sms_sts.WritePosEx(MOTOR_ID, pGlobalConfig->close_position, pGlobalConfig->speed, Defaults::MOTORS_GRIP_ACCELERATION); 
    vTaskDelay(50 / portTICK_PERIOD_MS);
    int elapsed = 0;
    int last_pos = -1;
    int unchanged_cycles = 0;
    while (elapsed < max_wait_ms) {
      vTaskDelay(30 / portTICK_PERIOD_MS);
      elapsed += 30;
      int moving = sms_sts.ReadMove(MOTOR_ID);
      int pos = sms_sts.ReadPos(MOTOR_ID);
      int load = sms_sts.ReadLoad(MOTOR_ID);
      if (!moving) break;

      if (abs(pos - last_pos) <= position_stall_threshold) {
        unchanged_cycles++;
        if (unchanged_cycles >= unchanged_cycles_required) break;
      } else {
        unchanged_cycles = 0;
      }
      last_pos = pos;
    }
    vTaskDelay(100 / portTICK_PERIOD_MS);
    int final_pos = sms_sts.ReadPos(MOTOR_ID);
    int final_load = sms_sts.ReadLoad(MOTOR_ID);
    if (abs(pGlobalConfig->close_position - final_pos) > position_tolerance) { // Not reached, obstacle detected
      sms_sts.WritePosEx(MOTOR_ID, final_pos-release_offset, pGlobalConfig->speed, Defaults::MOTORS_GRIP_ACCELERATION); // loose grip a bit and hold
    }
    sms_sts.unLockEprom(MOTOR_ID);
    sms_sts.SetProtectionCurrent(MOTOR_ID, Defaults::MOTORS_STANDBY_CURRENT); // Reduce current to standby value
    sms_sts.LockEprom(MOTOR_ID);
    sms_sts.WritePosEx(MOTOR_ID, final_pos-release_offset, pGlobalConfig->speed, Defaults::MOTORS_GRIP_ACCELERATION);
    elapsed = 0;
}

void MotorsDriver::open_grip() {
  sms_sts.SetOverloadTorque(MOTOR_ID, Defaults::MOTORS_STANDBY_TORQUE);
  sms_sts.WritePosEx(MOTOR_ID, m_conf->open_position, m_conf->speed, Defaults::MOTORS_GRIP_ACCELERATION);

}
2

Hi, @tornado67
Welcome to the forum.

Can you post link to data/specs, manual of the servo?
There should be a way of reading any error code from the LED or the comms link.

I assume it is a servo and controller in one housing.

Tom.... :smiley: :+1: :coffee: :australia:

1 Like
3

Hi Tom! Thanks for your reply.

Here is the only manuals I was able to find

https://www.waveshare.com/w/upload/f/f4/ST3215_Servo_User_Manual.pdf#page18

The thing is that all the functions in their library return an error code or 0 on success and in my code they all keep returning 0 and pretending that everything is okay. The library does not provide anything to read alerts or errors and their manual didn’t seem helpful to me… I used some ChatGPT to generate diagnostics/alert reading and “unbricking” code but that was unhelpful as well.

4

Those extra blank lines between code lines is NOT helpful. Will look at code only after you remove and do an Auto Format.

5

Sorry, this is how it pasted, cleaned it up. Any help would be appreciated.

6

A simple google of STS3215 returns the following

ST3215 Servo User Manual

7

It appears that some of the code at least is missing. Nobody can help if the code is incomplete.

8

I saw the manual you sent me and it was not helpful and if you would pay a little more attention you would have seen that I have attached the same manual to my second message. Here is the initialization code. The rest is already provided.

void MotorDriver::begin(){
    pinMode(2, OUTPUT); 
    digitalWrite(2, HIGH); // board's specific, enables servo's power.
    m_log = Logger::getInstance();
    pGlobalConfig= GlobalConfig::getInstance();
    Serial1.begin(1000000, SERIAL_8N1, S_RXD, S_TXD);
    sms_sts.pSerial = &Serial1;
    delay(1000);
    int ID = sms_sts.Ping(MOTOR_ID);
    if (ID == -1){
        return;
    }
    pos = sms_sts.ReadPos(MOTOR_ID);
}
9

My apologies, I did indeed miss your link to the manual.

I see you are a first-time poster and that @TomGeorge in post 2 advised you what to read as a first timer. Once we see ALL the code and a wiring diagram someone may be able to help.