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Question New SFX style build. USB dropouts. Cant fix.

Discussion in 'Motor actuators and drivers' started by Trigen, Jul 17, 2020.

  1. Trigen

    Trigen Active Member

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    Hello

    I got a new SFX 3 actuator setup. Im having severe issues with USB dropping out and failing. These are on hubs. Its fine if i do not enable the motors. Not long after enabling motors things will start to fail.

    My Pimax 5k+ will stop detecting the base station.
    Some but not all USB will stop working but still be detected.

    The cables are factory shielded. They are nowhere near the USB cables. At first the USB would just fail and reconnect continuously. I changed the socket and things are better. Enough to get testing. If i connect the Mega board to the same hub as the sound card i get a lot of noise.
    Its no doubt EMI since if i put a joystick on and select a box to put a button in it will fire random buttons when the motors are on. If i disconnect the wheel from the Simucube 2 pro i can hold it close to the motor with no issues but if i touch the motor or rig frame it will fire randomly. There's no direct connection with the frame from the motor either. If i place it on top of the SC2 it will fire a lot of buttons even when everything is disconnected from the SC2. Its almost centered in between the two motors. Touching different places on the frame has big or small effects.

    Another issue that may not be related is that when connecting a TM warthog stick trough an extension using a PC2 cable i will get shocks when touching the metal stick and the frame. If i ground the connection to the frame its fine.


    What i have done so far.

    Tried several different sockets that are on different power conduits.
    Tried moving cables around. Made sure no power are crossing the USB
    Grounded P1X frame
    Drivers are on a direct ground to ground metal stick. Also in the socket.

    Any ideas?
    Last edited: Jul 17, 2020
  2. Ads Master

    Ads Master

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  3. Thanos

    Thanos Building the Future one AC Servo at a time... or 6

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    Which controller do you use? Is it the AMC-AASD15A?
  4. Trigen

    Trigen Active Member

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    Im using an ardunio mega but actually. After a alot of trial and error testing it turned out to be coming from the USB extension cable. Must have been a short/grounding issue. Pimax still dropping the base station though so i need to tackle that
    Last edited: Jul 17, 2020
  5. Trigen

    Trigen Active Member

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    I am curious as to why the Pimax is so affected when its nowhere near the motor though. Seems like there's something going trough either the powersystem or USB
  6. cfischer

    cfischer Active Member Gold Contributor

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    I would get out the aluminum foil just to be sure. Super easy and then you'll know.
  7. Trigen

    Trigen Active Member

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    Ill look into that but im thinking its something different.

    Ive tested adding a couple of ferrite cores as some suggest but as i suspected it didnt do much. Basically as soon as a touch the HMD it looses tracking. While im no expert i think that means i completed the circuit to ground. I see a fair few report the same so how does one fix the issue? Seeing as using a different cable solved my other issues is only the Pimax cable to blame or is there something more underlying? How can i stop this from reaching my power system at all? I thought just being on a different circuit would be enough but seems not.
  8. cfischer

    cfischer Active Member Gold Contributor

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    Had the exact same issue with my vive. It was EMI. Took me forever to believe it. Not saying I'm right, but its an easy check.

    Seems unlikely to me that your skin is completing a circuit from the plastic case. But it can effect how EMI travels.

    By the way, who did you buy from that shielded your power cables? I have purchased servos from china twice. Both times I asked for shielded cables, both times they were not.
  9. Trigen

    Trigen Active Member

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    I was thinking about that yeah. Its plastic so it shouldnt conduct anything but thought there may be something transferring it anyway.

    I got a fairly good explanation on FB here which makes sense. Im going to try the ferrite choke he mentions in another post. 5 loops in FT240 31 Ferrite cores

    "the reason why it is worse if you touch the headset is because you become a giant antenna making the effect significantly worse. The correct ferrite cores act as a choke and the more loops of cable you pass through it, the more effective the choke becomes until at some point (around 5 loops in this case) the choke manages to surpress all of the interference while still allowing the intended signal to pass through. I have a pimax myself, I even use extended cables, I use the base stations, I have all sorts of other electronics hooked up to the rig, I use the SFX 100 and with the ferrite choke I get no trouble. Occasionally when you grab the sides of the headset it can for a split second still lose tracking but another loop of cable may reduce this but even when the SFX 100 isn't on, it can lose tracking for a split second when holding the sides of the headset because it physically blocks line of sight which is unrelated to EMI and is obviously not a problem. If I remove the choke while using SFX 100 I get total loss of tracking when touching the headset and sometimes it won't come back which confirms they work as intended.
    I wasn't the first person to find this solution but I have past experience using ferrite cores from designing hifi crossovers so understand how they work. This solution isn't a stab in the dark and it really does work.
    The shielded motor cable is a neat solution to reduce or eliminate EMI being emitted from the cables but it does not stop interference getting into your ring main, for which you need a big choke. It also doesn't stop EMI being emitted from the servo drives. The ferrite choke on your headset cable will always work regardless."

    Another one mentions he shielded the cables and grounded all the motor casings but arnt thoose grounded from the motors? Ill give that a try too in the morning to see. Never know.

    I got my motors from TwoWin store. It cost me 10$ extra per motor and added about 2 weeks to the delivery time.

    "
    Dear, Both the motor cable and the motor can be shielded, and the price needs to be increased by 10usd / pcs

    and the delivery time is relatively long, which takes about 15 days
    "
    https://www.aliexpress.com/item/32867802944.html?spm=a2g0s.9042311.0.0.36504c4d9YRq80

    At driver and cable on motor side of the connector

    20200717_233848.jpg 20200717_233956.jpg
    Last edited: Jul 17, 2020
  10. cfischer

    cfischer Active Member Gold Contributor

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    So worth it! Nice.


    By the way there are different ferrite cores for high and low frequency. The frequency that is emitted from servos is pretty low in the emi world. I opted for low freq ferrites on my system with great success.
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  11. Trigen

    Trigen Active Member

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    I gave the grounding another shoot as it was un drivable today for some odd reason. Took a wire from the motors to the frame and grounded the frame. Actually made things worse. Go figure. Then i soldered a wire on the base of the Pimax usb and tried. Still no go. Its all on the same grounding wire as i only have 2 sockets that are grounded in the kitchen. Disconnected the ground wire from the frame and things got about 80% better. Seems a bit odd but perhaps it needs its own wire, everything was on the same ground directly to the metal stick. I can live without Ferrites for the time beeing though
  12. Trigen

    Trigen Active Member

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    NOTE!

    Turns out all my EMI issues had one large source. Thank to the help of a guy in the SFX owners group on facebook we figured out the cable shielding was connected both to the motor and the driver causing a ground/earth loop. Once i removed the offending wire everything instantly became 95% better.

    Make sure there is no leftover that can touch the housing.

    Lesson is, always double check the factory shielding. I would not have a clue if it wasnt for the help though
    cut this.jpg
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  13. Trigen

    Trigen Active Member

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    The last thing i needed to do as i had some minor dropouts and button presses was to connect a ground from the driver to the P1X racing rig alu frame (only frame and it goes crazy) and then a wire from the frame to the usb like this. Make sure you got as much contact as possible at the hub. This grounded all my USB's and i can run the cables very close to the motor with no issues.

    usb last.jpg
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    Last edited: Sep 14, 2020
  14. cfischer

    cfischer Active Member Gold Contributor

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  15. Trigen

    Trigen Active Member

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    I noticed when i used noise from RPM (low rpm) on Pt mover that my Pimax 5k+ image was shaking double vision like crazy from EMI so i pulled another wire from the frame to the USB in the same manner as before and that solved it. Its on its own powered hub so i haven't tested when its connected directly to the computer or if grounding the entire computer to the frame of the rig will work but i think it will be about the same. Im unsure how isolated the motherboard is from the PSU and the grounded wall socket there.
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