2DOF harness tensionner with Fly PTmover

RacingMat · Dec 9, 2020

Hi!

My cockpit is static, I've build a pressure gSeat with bladders and RC servo.
I wanted to increase immersion by a harness tensionner.

I'd already tested a static harness tensionner on a 2 DOF plateform, and the feeling was great.
As my rig is static, I'll have to actuate the harness but the advantage is that I can make a 2 DOF tensionner.

principle:
2 DOF harness -> the strength on the right shoulder and left shoulder will be different

both will react along Surge (longitudinal acceleration)
and Sway (lateral acceleration) will tight one shoulder or the other (depending on left turn or right turn)
(maybe later add some heave information?)

harness : 5 points
the 5th will prevent the harness to move up, this will give actual tension (vs movement)!

prefer larger harness 3" (vs only 2")

actuators:
RC servos 35kg.cm (5V to 8,3V)
PSU @7,3V

arduino:
code for 4 servos as I want to combine the harness and the gSeat pressure bladders also RC servo driven.

software:
FlyPT mover https://www.xsimulator.net/community/faq/flypt-mover.29/category

Here is a video showing step by step how I drive the 2 DOF belt with Fly PTmover:

The strength from 35kg.cm servo is enough.
Power up the servo, sit down, thight the belt as you wish, and start the sim. If you tight the belt before powering up the servos, they are loose and they could be pushed out of their range...

The only drawback, in my opinion is the noise of the servos: they are whinning...

here some infos gathered in this FAQ https://www.xsimulator.net/community/faq/harness-tensioner-simulation.361/

► shopping list
"HV high torque servo motor Robot servo 35kg RDS3235 Metal gear Coreless motor digital servo arduino servo for Robotic DIY"

1X HV hohe drehmoment servo motor Roboter servo 35kg RDS3235 Metall getriebe Kernlosen motor digital servo arduino servo für robotic DIY - AliExpress 26

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www.aliexpress.com

17€
I chose 270° range
You'll need a dedicated power supply (5V slower to 7,4V fastest)

Speed: 0.13sec/60 degree at(5v)
0.12sec/60 degree at(6v)
0.11sec/60 degree at(7.4v)

Torque: 29kg.cm.at(5v) -1.9A
32kg.cm.at(6v) -2.1A
35kg.cm.at(7.4v) -2.3A

or stronger but unecessary in my opinion
60kgcm 24€
https://www.aliexpress.com/item/4000055027119.html

speed is voltage related
torque is current related!

1/ choose speed AKA voltage
2/ check the spec which gives you the current at chosen voltage
3/ buy your PSU ;-)

if you choose 7,4V PSU, verify it'll be able to deliver up to 2.3A in order to give full torque (add a BIG margin ;-) )
https://fr.aliexpress.com/item/32823922664.html
11€ 7V 10A

here is my ball bearing support (12€ for 2 supports)
they are made of:
P000 https://www.aliexpress.com/item/32833812473.html
Zinc Alloy Diameter Bore Ball Bearing Pillow Block Mounted Support
they allow a big static disalignment as the bearing is mounted like a joint articulation

and 200mm Ø10 linear shaft Cylinder Chrome Plated Liner Rods
https://www.aliexpress.com/item/4001294745058.html

► budget:
2x 17€ for 35 kg.cm servo
11€ for 7V 10A PSU
(maybe consider a 12V 10A PSU + an Adjustable Power Module Constant Current 5A)
12€ for bearing rollers
15€ any arduino with a USB port (an original to support the community or a clone)

50€ for a used 3" width 5 points harness
total = 120€ all included

arduino code (for up to 4 servos)

C++:

// Multi Direct
// -> 4 servos
// <255><LeftBelt><127><127><RightBelt>
// Rig : Bit output -> 8 bits
// avec inversion
// PT Mover envoie de 0 à 255 par axe

/*Mover = output "Binary" et "10bits"
Arduino = Byte Data[2]
Data[0] = Serial.read();
Data[1] = Serial.read();
result = (Data[0] * 256 + Data[1]);

OU

Mover = output "Binary" et "8bits"
Arduino = Byte Data
Data = Serial.read(); on obtient directement le résultat*/

#include <Servo.h>  // local library "Servo.h" vs library partagée <Servo.h>

const byte nbServos = 4;

// create servo objects to control any servo
Servo myServo[nbServos];
const byte servoPin[nbServos] = {2, 3, 4, 5};  // pins digitales (pas forcément ~pwm)
const byte inversion[nbServos] = {1, 1, 0, 0 }; // paramètre à changer si un servo part le mauvais sens
int OldSerialValue[nbServos] = {0, 0, 0, 0};
int NewSerialValue[nbServos] = {0, 0, 0, 0};

// servo span:
int servoHomeDegres[nbServos] = { 0, 0, 0, 0}; //sera mis à jour avec la mesure de pression initiale
int servoMaxDegres[nbServos] = { 90, 90, 90, 90}; // cuisseG, cuisseD, côtéG, côtéD
int servoPositionTarget[nbServos] = {0, 0, 0, 0};

const byte deadZone = 0;

// =======================================
// Variables for info received from serial
// =======================================
int bufferPrevious = 0;      // To hold previous read fom serial command
int bufferCurrent = 0;       // To hold current read fom serial command
int bufferCount = 0;         // To hold current position in bufferCommand array
// byte bufferCommand[2*nbServos] = {0};  // (*2 if 10 bits) To hold received info from serial
int bufferCommand[4] = {0};  // To hold received info from serial

void setup()
{
  Serial.begin(115200); // opens serial port at specified baud rate

  // attach the Servos to the pins
  for (byte i = 0; i < nbServos; i++) {
    // pinMode(servoPin[i], OUTPUT); // done within the library
    myServo[i].attach(servoPin[i]);  // attaches the servo on servoPin pin
    }
  // move the servos to signal startup
  MoveAllServos255toDegres(125); // mi-course
  delay(1000);
  // send all servos to home
  MoveAllServos255toDegres(0);
}

void loop()
{
  // SerialValues contain the last order received (if there is no newer received, the last is kept)

  if (Serial.available())
  {
    bufferPrevious = bufferCurrent; // Store previous byte
    bufferCurrent = Serial.read(); // Get the new byte
    bufferCommand[bufferCount] = bufferCurrent; // Put the new byte in the array
    bufferCount++; // Change to next position in the array
    if (bufferCurrent == 255) bufferCount = 0; // one 255 is the start of the position info
    if (bufferCount == nbServos) //si 8 bits, nbServos // si 10 bits nbServos*2
      //Having reach buffer count, means we have the new positions and that we can update the aimed position
    {
      for (byte i = 0; i < nbServos; i++) {
        NewSerialValue[i] = bufferCommand[i];
        //NewSerialValue[i]= (bufferCommand[i*2] * 256) + bufferCommand[i*2+1]; // si 10 bits
      }
      bufferCount = 0;
    }
  }
  // Update orders sent to motor driver
  for (byte i = 0; i < nbServos; i++) {
    if (abs(OldSerialValue[i] - NewSerialValue[i]) > deadZone) {
      if (inversion[i] == 1)
      {
        envoiServoConsigne255toDegres(i, (255 - NewSerialValue[i]));
      }
      else
      {
        envoiServoConsigne255toDegres(i, NewSerialValue[i]);
      }
      OldSerialValue[i] = NewSerialValue[i];
    }
  }
}

void envoiServoConsigne255toDegres(byte servoID, int val )
{
  byte targetDegres;
  val = constrain(val, 0, 255); // constrain coupe au dessus et en dessous : écrêtage et pas mise à l'échelle (comme map)
  // sécurité pour éviter les cas où Simtools enverrait du négatif ou au-delà de 255
  targetDegres = map(val, 0, 255, servoHomeDegres[servoID], servoMaxDegres[servoID]);
  //  map(value, fromLow, fromHigh, toLow, toHigh)
  myServo[servoID].write(targetDegres);              // tell servo to go to position in variable : in steps of 1 degree
  // servo.write(angle)  -> angle: the value to write to the servo, from 0 to 180
}

void MoveAllServos255toDegres( int target)
{
  // send all servos to home
  for (byte i = 0; i < nbServos; i++) {
    envoiServoConsigne255toDegres(i, target);
  }
}

here is the setup:

and the file itself: replace .txt extension by .Mover extension

blekenbleu · Mar 21, 2021

I still do not see a ground connection in the image between UNO and servo.
I suppose that the UNO is being powered via USB;
at least, that is how my STM32 "blue pill" is powered.

deandsfsdfewsad · Mar 21, 2021

blekenbleu said:
I still do not see a ground connection in the image between UNO and servo.
I suppose that the UNO is being powered via USB;
at least, that is how my STM32 "blue pill" is powered.

I think the issue may be the Arduino because when I open the Arduino software it's unrecognised so I have returned and ordered a legit R3 from the website direct

Arduino Uno Rev3

Arduino Uno is a microcontroller board based on the ATmega328P (datasheet). It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator (CSTCE16M0V53-R0), a USB connection, a power jack, an ICSP header and a reset button. It contains...

store.arduino.cc

I'm not that sure what I'm doing here but I don't want to give up yet!

blekenbleu · Mar 21, 2021

deandsfsdfewsad said:
when I open the Arduino software it's unrecognised

Before returning, be sure to try Arduino software with the UNO connected ONLY by USB;
electrical interference can confuse these microcontrollers so that their firmware gets lost.

I'm not that sure what I'm doing here

I am also not sure what you have connected in that image;
is that red wire connected to ground at the UNO end?
If so, bad color choice.
The other end appears to be connected to green wire ground (for AC power)
which is NOT the same as black/ground to the servo, which is wanted.

deandsfsdfewsad · Mar 21, 2021

blekenbleu said:
Before returning, be sure to try Arduino software with the UNO connected ONLY by USB;
electrical interference can confuse these microcontrollers so that their firmware gets lost.

I am also not sure what you have connected in that image;
is that red wire connected to ground at the UNO end?
If so, bad color choice.
The other end appears to be connected to green wire ground (for AC power)
which is NOT the same as black/ground to the servo, which is wanted.

I tried with just the USB like this:

sadly no dice nothing happened. I followed the exact same pinouts as above using a generated Arduino code but when I tried sending it to the Arduino all it gave was this error:

And yeah sorry forgot to mention, I only have red wire currently I placed the ground to the AC input ground to see if that would work and also tried the V- line (first) but that did not work.

As a result, I decided to return that Arduino for the genuine R3 model, I hope I haven't burnt out the servos that's one slight concern I have in my head still

blekenbleu · Mar 21, 2021

deandsfsdfewsad said:
I hope I haven't burnt out the servos

One of these US$4 servo testers is handy:

blekenbleu · Mar 21, 2021

deandsfsdfewsad said:
all it gave was this error:

I am no Arduino expert, but I guess that message means that lacked a fully qualified board configuration for which to compile your sketch and send to your UNO.

deandsfsdfewsad · Mar 22, 2021

blekenbleu said:
I am no Arduino expert, but I guess that message means that lacked a fully qualified board configuration for which to compile your sketch and send to your UNO.

Yep that is my hope that replacing it with a genuine one will fix my problem

RacingMat · Mar 25, 2021

what sketch did you upload into the arduino?

deandsfsdfewsad · Mar 25, 2021

RacingMat said:
what sketch did you upload into the arduino?

For initial system testing I tried to use this

Arduino/servo/servo.ino at master · primerobotics/Arduino

Get latest tutorial code for Arduino. Contribute to primerobotics/Arduino development by creating an account on GitHub.

github.com

For sim use I used the instructions from your video on FlyPT Mover:

But once connected when manually changing the slider no servo movement happened.

RacingMat · Mar 25, 2021

okay...
I guess you're new to arduino

you have to setup accordingly
- the serial communication in FlyPTMover parameters
- the arduino serial communication parameters in the code
- the RC servo wiring on the arduino board according to pin declared in the arduino code
It's mandatory.

The arduino code you used, is standalone: no serial communication is setup. It automatically moves the servos from position to position.
So, if your test didn't succeed:
- your servo is not wired on the right arduino pins
- your servo is not connected to the power supply? (edit: I skipped your previous message, you don't use a power supply unit (I hope you're not using a 35kg.cm servo, it cannot be powered from Arduino board))
- the code is actually not loaded into the arduino (edit: your previous message confirmed my supposition)
Try some basic arduino tutorial first. You'll succeed eventually!

I'll add the code that goes with the Fly PT mover video I made, in the first post with some wiring scheme.

blekenbleu · Mar 25, 2021

RacingMat said:
the code is actually not loaded into the arduino (edit: your previous message confirmed my supposition)

Based on the error message,
perhaps the target board selection step was not completed successfully.
That would be Part 3 in these instructions..
Beyond that are workarounds for less than ideal UNO clones:
5 Most Common Arduino Nano Clone Problems and Their Solutions

RacingMat · Mar 26, 2021

yes, clones may be faulty and buying genuine Arduino help the community

deandsfsdfewsad · Mar 26, 2021

RacingMat said:
okay...
I guess you're new to arduino

you have to setup accordingly
- the serial communication in FlyPTMover parameters
- the arduino serial communication parameters in the code
- the RC servo wiring on the arduino board according to pin declared in the arduino code
It's mandatory.

The arduino code you used, is standalone: no serial communication is setup. It automatically moves the servos from position to position.
So, if your test didn't succeed:
- your servo is not wired on the right arduino pins
- your servo is not connected to the power supply? (edit: I skipped your previous message, you don't use a power supply unit (I hope you're not using a 35kg.cm servo, it cannot be powered from Arduino board))
- the code is actually not loaded into the arduino (edit: your previous message confirmed my supposition)
Try some basic arduino tutorial first. You'll succeed eventually!

I'll add the code that goes with the Fly PT mover video I made, in the first post with some wiring scheme.

Oh I did not realise there was additional code required for the Arduino I assumed the mover software would handle all the code in the background, I am new to Arduino

Unfortunately, I am not a coder so maybe looking at some servo tutorials will be beneficial, I will try your code when the new board arrives but then I would like to learn a little

deandsfsdfewsad · Mar 29, 2021

I managed to replace the Arduino but sadly it did not fix the problem, I think I will have to continue looking into this error, I tried the Code @RacingMat but this is the recieved error.

RacingMat · Mar 30, 2021

deandsfsdfewsad said:
View attachment 459420

I managed to replace the Arduino but sadly it did not fix the problem

I think you should start slowly and try the very first tutorials
these videos have more than 10k of likes, maybe one would suit you?!

Once mastered, Arduino will help you for many simracing peripherals!

deandsfsdfewsad · Mar 30, 2021

I finally had success the issue was I needed the correct library Servo.h for the Arduino, I managed to successfully get one motor working, tomorrow I will continue my basic test and if proof of concept works I will then move to the structural design

I can see why people say they are noisy just one alone sounded like a squealing bunch of ferrits

blekenbleu · Mar 30, 2021

deandsfsdfewsad said:
one alone sounded like a squealing bunch of ferrits

Powering servos near rated voltage (e.g. 8 vs 5) makes them respond more quickly,
but seemingly also quieter (higher pitch sound is more directional).
Suspending servos, e.g. between sections of strap, instead of attaching to rigid structures
reduces coupling of vibrations to air.

blekenbleu · Apr 10, 2021

Niels endorses harness tensioning:

RacingMat · Apr 14, 2021

oh yeah, sustained G forces rule!

and parasitic, inverted pushes are evil!

deandsfsdfewsad · Apr 17, 2021

I got everything set up and working well but one of the motors get extremely hot after two laps and I think it burnt out as it no longer works, since I need to get another motor I am taking the opportunity to move to the 60kg ones as I was wanting a bit more strength

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Technically the current power supply should work for this still but may require changing as well