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Son of OpenSimwheel - An Experiment

Discussion in 'DIY peripherals' started by RufusDufus, Sep 28, 2015.

  1. RufusDufus

    RufusDufus Well-Known Member

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    Hi All, I’ve been following all the interest in direct drive sim wheels for some time now and have always wanted one for myself although the price is more than I’m willing to pay. I truly believe they are worth the quality and fidelity they deliver, it’s just way beyond what I need.

    So I started to wonder if it was possible to build a budget version that gives some of the benefits of a direct drive wheel, perhaps with some loss in fidelity, yet outperforms the current consumer grade wheels such as the G27, TRS500, CSW, etc. One goal being to get at least 10Nm of torque out of the wheel feedback.

    ** SO FOR THOSE WHO MISSED MY POINT – I DON’T EXPECT THIS SIMWHEEL TO MATCH THE FIDELITY OF THE SERVO DRIVEN OPEN SIM WHEEL AND EQUIVALENTS **

    Hence my experiments begin…

    The closest ‘budget’ motor to a servo motor is a stepper motor. They have some of the highest torque per mass ratios of any motor and are common enough to be available at low prices. I had 3Nm NEMA24 stepper I bought for another project (AU$50) that never progressed so that seemed like a good proof of concept motor. If all goes well I’ll most likely move up to a 13Nm NEMA34 stepper for AU$170.

    The encoder was next. A good quality encoder can easily set you back $300-500. Seemed a bit much for a budget wheel. Some searching lead me to a cheapo (AU$17) Chinese encoder from ebay. It has 600p/r or 2400cpr, not brilliant but hopefully good enough.

    Now the stepper motor driver. Ideally I should probably just design my own controller but I’m lazy so I found a super cheap (AU$16) Chinese TB6600 stepper driver on ebay. Let’s see what it can do. Unfortunately these (and most) stepper drivers are open loop and don’t react well when you apply more torque than they are setup for – they start losing steps and get very jerky.

    To overcome this I will use an Arduino Uno to implement a closed loop torque control loop and hack into the TB6600 driver to make it work. Another cheap clone version for AU$10. So this requires the TB6600 to be opened, tracks cut, and components soldered inside and wired to the Arduino.

    Finally the interface to the PC. I will be aiming to use the excellent MMOs firmware. No point reinventing the wheel … oh wait I am… no point reinventing a brilliant PC wheel interface. The MMOs PC wheel interface can be found here: http://forum.virtualracing.org/showthread.php/92420-DIY-USB-Force-Feedback-Controller and is the one used in the open sim wheel projects.

    I have used my 3D printer to make a few parts to connect the encoder to the motor and the wheel to the motor. These could be fabricated in other ways but was easy for me to do it this way. These are the bright green parts in the photos.

    photo 2a.JPG photo 3.JPG photo 4.JPG photo 5.JPG

    Progress so far… I now have a basic torque control loop working. The cheap encoder is not as precise as expected however its positional accuracy is repeatable so I was able to compensate for the inaccuracy. It means the wheel will need to calibrate every power up though.



    I get over 3Nm out of this motor which puts it on par with a G27. There is more cogging than I expected at high torque. I think my torque control loop needs some more tuning. It may also be that I need a driver with more than 1/16 microsteps. At low torque it feels much like a G27 with only slight cogging noticeable.



    Still plenty more work, I'll keep you posted when any progress is made. :thumbs
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  2. RacingMat

    RacingMat Well-Known Member Gold Contributor

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    Great project! I wish you'll have the success you're awaiting!

    Could you please tell us more on this hack to convert "open loop" to "closed loop"?

    Here a link to calculate the maximal speed of a stepper motor http://www.daycounter.com/Calculators/Stepper-Motor-Calculator.phtml

    Here a french topic on your subject
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  3. Blame73

    Blame73 Yet it moves!

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    Really interesting project, looking forward to seeing wheel in action!

    Enjoy us with some video too! :popcorn
  4. RufusDufus

    RufusDufus Well-Known Member

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    Thanks for the links @RacingMat. Unfortunately google translate doesn't do a real good job of French translations - especially when they get technical. It is interesting to see others experimenting with steppers though.
  5. fzxj520

    fzxj520 Member

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    Great :thumbs This is what I expected
  6. sikjar

    sikjar Xiao Nie

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  7. Kirk

    Kirk Member

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    I have a whole bunch of those encoders, they are awesome for how cheap they are. It never occurred to me that they could be used for a wheel. I'm following this thread with great interest.

    While I already have a budget wheel (Logitech G27), but I'd LOVE to build a Tron bike sim someday, with force feedback on the handlebars. Being able to rig something up from parts found at a thrift store (broken bicycle) and a little PVC / fiberglass, well, that'd be quite awesome.
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  8. jaco73

    jaco73 New Member

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    interesting !! I continue to see as just: Thumbs
  9. RacingMat

    RacingMat Well-Known Member Gold Contributor

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    sorry for the short off topic
    I'm sure Kirk will open a dedicated thread if needed;)


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  10. RufusDufus

    RufusDufus Well-Known Member

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    Just a quick update. Testing is progressing slowly and looking promising. I have as yet not been able to eliminate the "notchy" sensation at high torque. I have tested alot of the individual components and am starting to believe it is coming from the cheap TB6600 stepper driver I am using.

    I will look into this further and let you know the results.
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  11. Archie

    Archie Eternal tinkerer

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  12. RacingMat

    RacingMat Well-Known Member Gold Contributor

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    Great!

    Are you talking about motor cogging?
  13. RufusDufus

    RufusDufus Well-Known Member

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    That is what it feels like, however I don't believe that is the cause. At the moment I think it is either my torque control loop or the stepper driver. Leaning more toward the stepper driver.
  14. sikjar

    sikjar Xiao Nie

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    Thank you for the update, following with interest :thumbs
  15. Evad

    Evad New Member

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    Following with interest.:) Would you be willing to share your arduino code?
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  16. Anders Nolberger

    Anders Nolberger New Member

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    I am also interested in any feedback on this. Is this driver any good for this purpose?
  17. RufusDufus

    RufusDufus Well-Known Member

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    The project has been on the shelf for a while. Hope to get back to it over Christmas.

    I can't comment on that controller as I don't read Chinese. As this is still in experimental phase I haven't yet worked out exactly what is needed for a properly working wheel.

    When I make progress I will be happy to post the details for anyone interested. :grin
  18. Evad

    Evad New Member

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    Hi Rufusdufus. I managed to get the encoder to work with the Mmos, as long as i pull the encoder signals high with the help of the arduino.

    Did You had to do that also or did you find an other way to get it to work
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  19. RufusDufus

    RufusDufus Well-Known Member

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    Sounds like you have progressed further than me, all my testing has just been with the arduino so far... but yes I used pullups with the encoder shown in earlier posts. I found a teardown of it on web... http://wemakethings.net/2014/05/26/rotary-encoder-teardown/

    What size stepper are you using?
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  20. Evad

    Evad New Member

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    Ha RufusDufus. Thanks for the link. That helped a lot. Im using a 34 zise stepper. Next goal is to make sense of the dir en pwm signal coming from the mmos.