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Question Motors Moving Randomly When Testing Ports

Discussion in 'Forum and Website' started by James Barker, Aug 4, 2025.

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  1. James Barker

    James Barker Up, up and away! Gold Contributor

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    Hi - new build. I have two arduinos each connected to a Sabretooth 2x60. Each Sabretooth runs two motors, 2 on Port 7 and 2 on Port 8. Chatgpt tells me I need to have different addresses for the Sabretooths - 128 and 129 (which means SMC3 doesn't work). I've tried it but it didn't make a difference. I've left them both on 128. When I run SMC3 I can get all 4 motors running (2 at a time for each port). Is it normal for SMC3 to be randomly moving the motors when I click on motion? When I go into Simtools 3 and go to test for that port - it is either port 7 or 8, only one motor on that port starts randomly moving - this is after I click on test. I don't have to move any of the sliders. However, I can normally move the slider for the motor that is moving, and this will effect it in some way - but not stop it moving. This happens with both ports. The motor keeps moving even after I click on stop testing. Any ideas?

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    James Barker, Aug 4, 2025
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  2. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    it looks like SMC3 settings need refining before messing with SimTools, Kp seems low and PWM settings likely need tweaking, plus Clip and Max Limits are set to zero: https://www.xsimulator.net/communit...driver-and-windows-utilities.4957/#post-48121

    Clip Input Used to create a band at either limit of the target range beyond which any values sent to the SMC3 are clipped. In addition to this clipping, if the motor feedback does move beyond this range (typically through inertia), the SMC3 will attempt to brake the motors hard by driving them in reverse until they are back out of this limit zone. The value can be anything from 0-255 (however can’t be less than the current limit setting). Reverse braking is applied in the band between the Clip Input and the Max Limit settings. Reverse braking can be disabled - refer to PWMrev.

    Max Limits Used to create a band at either limit of the feedback range beyond which if the motors move (typically through inertia) the SMC3 will automatically shutdown the drivers and keep them disabled until reset. This is essentially a safety mechanism if something goes wrong. The value can be between 0-255 (however can’t be greater than the current clip setting).

    [​IMG]
    noorbeast, Aug 4, 2025
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  3. James Barker

    James Barker Up, up and away! Gold Contributor

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    Thanks for the quick response! I'd set the SMC3 parameters low to stop the sim moving violently. I'm not sure whether I need limits as the motors can move through the full 360 arc - or am I interpreting that wrong? Is it the lack of limits that is causing the issue? Thanks in advance!
    James Barker, Aug 4, 2025
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  4. James Barker

    James Barker Up, up and away! Gold Contributor

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    Here is a pic of one of the motors and the arms.

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    James Barker, Aug 4, 2025
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  5. James Barker

    James Barker Up, up and away! Gold Contributor

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    I may have found the problem. The SMC3.ino I'm using has the following commented lines:
    // Uncomment the following line to enable the second software serial port.
    // NOTE: This is currently not working - leave commented out until fixed!!!
    // #define SECOND_SERIAL
    Looks like I need to find a more up to date sketch file for the Sabretooths.
    James Barker, Aug 4, 2025
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  6. James Barker

    James Barker Up, up and away! Gold Contributor

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    I've been working on this far too long!!! This is com ports, not motors! Time to go to bed!
    James Barker, Aug 4, 2025
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  7. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    There is a specific variant of SMC3 for Sabertooth: https://www.xsimulator.net/communit...ket-serial-pid-motor-driver-for-arduino.9277/

    Tuning setting for given hardware is part science and part observation, see here for a gentle take, which includes links to more hardcore details: https://www.xsimulator.net/community/faq/a-laymans-analogy-guide-to-pids-pid-tuning.219/

    The purpose of Clip and Max Limits is to set a range of movement. The already posted link also gives details about each of the SMC3 settings. It is about tuning the given hardware, not randomly plugging in numbers.

    The hardware itself can also have its quirks: https://www.xsimulator.net/community/faq/baud-rate-arduino-and-sabertooth.339/

    Then there is the refinement of SimTools motion profiles, review the Quickstart Guide: https://simtools.us/wp-content/uploads/2024/02/QuickStart-Guide-for-SimTools3.pdf

    And Manual: https://simtools.us/wp-content/uploads/2024/02/SimTools-v3.pdf

    In addition here are some handy FAQ tips for refining motion profiles: https://www.xsimulator.net/community/faq/steps-to-create-a-motion-profile.228/
    noorbeast, Aug 4, 2025
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  8. James Barker

    James Barker Up, up and away! Gold Contributor

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    Thank you Noorbeast. I really appreciate your fast and very detailed response. It has helped confirm some of the things I'm doing and also provided help with the others. Cheers!
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    James Barker, Aug 5, 2025
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  9. James Barker

    James Barker Up, up and away! Gold Contributor

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    Only Two Motors Move In SimTools
    Another day of testing, and I'm still stuck! I'm running SMCUtils version 1.01 and can see both motors on Port 7 and 8, and have them moving fine. If I set maxlimit too high, it can end up disabling/turning it off, so I've set it to 30 for now, while testing. I've set KP to 400 as per the documentation, and go up to PWMax to 40, if I go higher the motor can start shuddering. When I go into simtools and test the interface, only the first motor on each port moves. ChatGPT told me to set the Sabretooths' addresses to 128 and 129, but doing that doesn't help, so I've left them both at 128. I've tried testing through the game engine, setting all the axis to roll, at 100% but again, only the first motor for each port moves. Any thoughts?

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    James Barker, Aug 5, 2025
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  10. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Hard to tell if there is an accidental space on 1, it should be like this, so please double check: Interface Output - [A<Axis1a>][B<Axis2a>]

    And fix Output Bit Range - 10

    Can you please post a picture of Comm port 7 SMC3 running the Sine test.
    noorbeast, Aug 5, 2025
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  11. James Barker

    James Barker Up, up and away! Gold Contributor

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    Thanks Noorbeast - it's working! My output parameters were good, and I changed the Output Bit range to 10. Both motors on port 8 started working in Simtools. Using SMC3Utils I checked for what was different between the motor settings in Port 7 to Port 8, and saw that for Port 7 motor 1 I'd set the PWMax to 40 because of the shuddering. This was the motor that wasn't working still. I upped it to 45 (any further and it shudders), went into simtools, and it can now see all 4 motors. Thank you for your timely help!
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    James Barker, Aug 5, 2025
    #11