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Showroom 3 DOF racing sim

Discussion in 'DIY Motion Simulator Projects' started by NickD, Jun 11, 2022.

  1. NickD

    NickD Member

    Joined:
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    My Motion Simulator:
    3DOF
    I appreciate your reply and would like to say I haven't been random choosing values and saying "this is what will work". I have read those those posts in the links you provided many times and have a good understanding of PID loops (even before starting this project). I got to those values after trail and error over that past 6 months or so and have admittedly changed things on the fly so as to see how a specific parameter may affect how things perform. If you see something that is totally out of whack, I definitely appreciate you or anyone questioning why that was chosen or even making recommendations.

    As for the Fpwm, it was my understanding that the lower the frequency, the higher the effective torque delivery and subsequently the cooler the drivers are by reducing switching transitions. I hadn't seen in those initial guides that 25 kHz was the recommended "set it and forget" figure.

    In any case, I took your advice and started from scratch again. Below is the bare bones start having added just enough PWMmax to get the motor to move:
    upload_2026-3-29_22-20-10.png

    As you can see I am back to the question I've asked before; why isn't the the target received (dark blue) not reaching the target sent (light blue)? Since I am at square one basically, is this something to do with the SMC3 code in the arduino? The reason I am hung up on this, is because I don't get much movement at all from motors 1 and 2 whereas motor 3 (the one that the received value reaches the sent) moves a noticeable amount.

    Attached Files:

  2. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

    Joined:
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    Occupation:
    Innovative tech specialist for NGOs
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    Tasmania, Australia
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    154,460Coins
    Ratings:
    +11,182 / 57 / -2
    My Motion Simulator:
    3DOF, DC motor, JRK
    I fear I may have triggered offense when that was not the intent, and if so I apologize.

    If Hall sensors are being used are they being direct driven 1:1, if not that is likely the cause of the target line issues.
    Last edited: Mar 30, 2026 at 09:25
  3. Gadget999

    Gadget999 Well-Known Member

    Joined:
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    My Motion Simulator:
    2DOF, DC motor, Arduino, 6DOF
    If you are using 3 motors on one arduino, the 3rd pwm has less resolution so it may be making bigger steps compared to tbe other two
  4. NickD

    NickD Member

    Joined:
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    My Motion Simulator:
    3DOF
    We're all good. :cheers Like I said before, I appreciate you trying to help and understand the difficulty of doing so remotely and not in real time. Every setup is different whether it be the geometry or equipment or configuration.

    They are hall effect sensors and they are being driven at a ratio of 1:2.5. I feel like this is something to do with the code though because the moment I click and command for movement, the sent and received signals don't match/diverge like seen in the screenshot. I have ordered another arduino though and will load SMC3 on it and swap out to see if maybe it's something to do with the .ino file or the arduino itself.
  5. NickD

    NickD Member

    Joined:
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    My Motion Simulator:
    3DOF
    I have tried lowering and raising the pwm of motors 1 & 2 but that doesn't affect any change in this issue.
  6. NickD

    NickD Member

    Joined:
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    My Motion Simulator:
    3DOF
    Well I figured out what was causing the problem and I admit it was totally my fault.:oops: When I started this a few years ago and was bench testing the motor driver and the motor, I enabled the "pot_scaling" in the SMC3 code:
    upload_2026-3-30_22-32-35.png
    I don't remember why I enabled that but I do vaguely remember back then doing so. Commenting that back out gives me the full received target that is sent (matching light and dark blue lines) for both motors 1 and 2 now. It is laid out what it does here AND in full caps says don't do it unless a POT is attached:
    upload_2026-3-30_22-35-20.png
    Since nothing was terminated to A5, my guess is it must default to 50% which is what I was experiencing. Turns out this setting doesn't get applied to motor 3. I am so embarrassed and feel quite stupid. I am sorry for asking for help on what turned out to be a problem I caused.

    Attached Files:

    • Informative Informative x 1
  7. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

    Joined:
    Jul 13, 2014
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    Occupation:
    Innovative tech specialist for NGOs
    Location:
    Tasmania, Australia
    Balance:
    154,460Coins
    Ratings:
    +11,182 / 57 / -2
    My Motion Simulator:
    3DOF, DC motor, JRK
    Nothing to be embarrassed about, your learnt something and kindly passed that on for anyone who also did the same, hopefully saving them hours of head scratching :thumbs