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Question 2DOF RC servos harness tensioner with PT Mover

Discussion in 'DIY Motion Simulator Projects' started by RacingMat, Nov 20, 2020.

  1. RacingMat

    RacingMat Well-Known Member Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, Arduino
    Hi!

    Here is my harness tensioner :)

    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
    Mandatory, the 5th will prevent the harness to move up hence we'll have actually some tension (vs movement)!


    prefer 3" width harness (vs only 2") it's more comfortable

    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 pressure bladders also RC servo driven.

    software:
    PT mover from @pmvcda :thumbs

    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"

    US $17.29 5% OFF|1X HV high torque servo motor Robot servo 35kg RDS3235 Metal gear Coreless motor digital servo arduino servo for Robotic DIY|high torque servo|digital servorobot servo - AliExpress


    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
    Last edited: Feb 8, 2021
  2. Ads Master

    Ads Master

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  3. RacingMat

    RacingMat Well-Known Member Gold Contributor

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    +2,056 / 20 / -2
    My Motion Simulator:
    2DOF, DC motor, Arduino
    here is the prototype board
    components are glued with hot glue. A good way to prevent short-circuits...
    racingMat harness (2).jpg

    1/ before all, move the servo without anything mounted on it:
    mark the way the servo goes from 0 to full
    and mark the middle position.
    Useful to prevent any damage, and to mount it the right way at the first try ;)
    racingMat harness (3).jpg racingMat harness (4).jpg

    2/ in place, use T-raps to link the harness and the servos
    Quickly done! and nice mechanical fuse by the way
    racingMat harness (1).jpg
    • Like Like x 2
    Last edited: Nov 20, 2020
  4. RacingMat

    RacingMat Well-Known Member Gold Contributor

    Joined:
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    My Motion Simulator:
    2DOF, DC motor, Arduino
    Serial Setup:
    PTMover send 1 byte in binary (value from 0 to 255) for each Rig Key
    @8 bits, 115200 bauds
    I followed the example Output String: <255><255><LeftBelt><RightBelt>

    To find the beginning of the serial output string, it's advised to look for 2 following 255.
    After some trials, it appears that some times (when clipping) 2 axis are @255 and the serial is badly read.

    I'm ready to loose a little range by constraining the output value between 0 and 254
    in order to free the 255 value and be sure it'll be unique.
    But in the RIG windows, CROP(Value, 0,254) or REMAP(Value, 0,255,0,254) doesn't work... I still have 255 value outputed in serial. :confused:

    Can you advice me @pmvcda, please? I post the screen shots in the following message :)
    Last edited: Nov 20, 2020
  5. RacingMat

    RacingMat Well-Known Member Gold Contributor

    Joined:
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    My Motion Simulator:
    2DOF, DC motor, Arduino
    PT Mover:

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

    Attached Files:

    • Informative Informative x 1
    Last edited: Nov 26, 2020
  6. RacingMat

    RacingMat Well-Known Member Gold Contributor

    Joined:
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    My Motion Simulator:
    2DOF, DC motor, Arduino
    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

    [​IMG]

    upload_2021-2-8_14-13-9.png

    upload_2021-2-8_14-13-29.png

    conclusion:
    Pros:

    After some time spent using the harness tensionner, I really like how it help to break correctly (hardest first then decreasing.
    It's really immersive.

    Cons:
    The drawback is the noise: i'll try a muffle box.
    Last edited: Feb 8, 2021
  7. pmvcda

    pmvcda aka FlyPT

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    My Motion Simulator:
    6DOF

    Why use the pose?
    For seat belts, directs are enough.
    upload_2020-11-21_7-16-34.png
    Create one for each seat belt
    Put 8 bits (0 to 255)
    Value range to bit range is what values you want to map to the 256 bit values.
    I used -10 m/s^2 acceleration is bit 255
    4 m/s^2 is bit 0
    Default value is zero.
    I use negative values here, so on acceleration you would feel the belt loosing, but not so much as we have in braking.

    Now crop the value to ensure you don't get 255.
    Since 255 is achieved at value -4, I used 3.99 in the crop.
    So the resulting bit never reaches 255.

    I have bee making changes in the code. And made some small ones in the directs. I think what I say is working. But I remember that 10 to -4 might not work. You might have to use -4 to 10.
    The image is the build I'm working on. That is now corrected.

    Also, use the multi direct. The simple direct might disappear soon, there's no reason to exist.

    EDIT:
    Note acceleration is positive values
    Braking negative
    So I might have swapped the values. Should be between -10 and +4.
    It all depends on what is bit 255 and bit 0 mechanically
    • Informative Informative x 1
    • Useful Useful x 1
  8. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
    3DOF, DC motor, JRK
  9. RacingMat

    RacingMat Well-Known Member Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, Arduino
    Bingo! It works like a charm:thumbs
    Here is a video showing step by step how I drive the 2 DOF belt with Fly PTmover:



    thanks @pmvcda
    • Like Like x 1
    Last edited: Nov 25, 2020