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2DOF - one JRK has sloppy movement

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Jas, Dec 26, 2014.

  1. Jas

    Jas New Member

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    Hi all. Firstly, a big thank you to this terrific community for sharing your tips and tricks with us newbies, particularly earobbie and bsft. I must also thank the Simtools development team (RaceRay?) for their fantastic software.

    I’ve recently “finished” my first rig, being a 2DOF setup intended for space sim use. Thank you to Value1 for the quick development of an ‘Elite Dangerous’ plugin for Simtools – it is truly fantastic to see my project come alive after tinkering with it for so long. Wearing the Oculus Rift while playing Elite on the motion chair is an amazingly immersive experience!

    While there is plenty of tidy up work to be done, I’m hoping the community can help me troubleshoot a specific issue with one of the motors being a bit ‘sloppy’ during movement.

    But first, some specs:
    • 2DOF chair, inc 2 x Motion Dynamics 200W worm drives
    • 2 x Pololu Jrk 12v12 controllers
    • 2 x HP DPS-600PB 47A server power supplies
    • Decent POTs (about $15 ea from memory?)
    01_Chair.jpg 02_Worm_Drives.jpg

    Issue
    With the chair set to a ‘neutral’ position (using say the SimTools GameEngine - Output Testing tool), the left motor arm ‘sags’ when I sit in the chair. If I lean to the right side, the right motor arm barely moves and applies appropriate pressure to take up my weight.

    While still using Output Testing tool, the movements in the left motor are ‘sloppy’, and do not stop sharply. The right side motor moves much snappier and stops on a dime (see video).



    Some considerations:
    • The chair is as evenly balanced on the roll axis as I can get it
    • With the chair set to neutral (in say SimTools), I can easily move the left motor arm up and down about 10mm with my hand, while the right motor arm is much more rigid
    • The issue is present when testing with both the JRK config tool and SimTools
    • I’ve run the JRK config tool setup multiple times with no improvement in the left motor
    Is this something I can fix with say PID or deadzone settings in the JRK config tool (see below)? Or am I looking at a problem with the motor or POTs perhaps?

    Thanks in advance for any feedback you can offer.

    Left_Motor_JRK_Cfg.jpg Right_Motor_JRK_Cfg.jpg
  2. bsft

    bsft

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    grab each lever without power on it and see if one turns easier than the other.
    If one does turn easier, turn up PID on the D to 0.8 or even 1.0
    What gearboxes are you using?
    25:1
    60:1
    • Informative Informative x 1
  3. prodigy

    prodigy Burning revs

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    I would probably change the motor levers to something "beefier" - thicker, on the picture it looks like it started to bend already..
    And in the video your motors are moving the base of the floor, you could try putting anti-vibe rubber on the corners of the base, but then it shouldn't be on the carpet.. you can try though..

    Otherwise, very nice project for the first time :thumbs
  4. bsft

    bsft

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    my sim jumps a bit as well, especially when I am not on it
  5. Jas

    Jas New Member

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    With the power off, I'm not able to feel if one motor turns easier than the other - they feel about the same.

    Both motors were bought new, inc gearbox. I don't have the gearbox specs, so I'll email the supplier and see what detail I can get. Since the right motor appears to be working well, do you think the gearbox ratio is a consideration?

    I intentionally slightly bent the motor levers where needed for clearance, but I'll keep an eye on them.

    Indeed - the rig does jump around a bit with no-one on it, but is much better when someone is in it. After I get this issue sorted with the left motor, I'll look at beefing up the back end some more and probably adding some weight to settle it down a bit. (I don't think my landlord would appreciate a couple of tek screws into the floor).

    I'll play around, (learn), in the JRK config tool a bit more and see if I can stumble across something. Is there some way I can test the health of the POT?

    Thanks for your help.
  6. bsft

    bsft

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    Pot could be nuked yes, but not sure how to test it. Usually if the pot is wired wrong, it can just go crazy in the graph in the utility program.
    Do you have a spare pot to test on it?
    Also maybe swap the JRKS over to see if its JRK problem as well. But start with replacing the pot.
  7. Jas

    Jas New Member

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    Hi all.

    I've come back to this problem on and off but I haven't made much progress until now. After reading through this post, I reconfigured the problematic motor in the JRK utility again, in particular increasing feed back analogue samples to 1024, and dropping the P(roportional coefficient) value down to 0.14 (it was on 0.39). This has made the movement much snappier and minimises the sloppiness/overshooting I've experienced until now.

    I'm about to test in game - fingers crossed!
    • Like Like x 1
  8. Jas

    Jas New Member

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    Bugger - while the movement has improved greatly while the chair is unloaded, one side (left) still has excessive movement when I'm sitting in it. I'm starting to think the 25:1 gearboxes aren't up to the job - but it doesn't explain why the right side performs well (unless I'd somehow damaged the gearbox/motor on the left side early on in my testing.

    It seems my next step in troubleshooting this issue is to swap around parts (motors/gears/pots) to isolate exactly where the issue is - aahhhg.

    I welcome any feed back!
  9. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Just some random thoughts if you are confident you have gone over the JRK setup properly.

    It is easy to swap the motors over as a quick test, there is just 2 bolts holding them on the gearbox. Just be careful not to damage the rubber shock pads inside the two part coupler that joins the motor to the gearbox, they can be a bit fragile.

    As @prodigy mentioned earlier in the thread the motor arms and also mounts look flimsy, are you sure they are not moving, same with the pot mounts?

    How well balanced is the sim, did you balance it with the full frame foot plate in place and yourself in it, along with any controls?

    What is the CTC measurement on the levers and have you tried reducing the CTC distance?
  10. Archie

    Archie Eternal tinkerer

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    Just my <2cents> @Jas

    When I first got my motors (I have 25:1 boxes as well) I found one motor was very smooth to run and the other seemed to run a bit rough.

    I took the gearbox off the rough one and found the shock coupler (the rubber part @noorbeast mentions) was actually not seated correctly.
    I used a tiny amount of super glue on each rubber part (4 of them) to keep it in place and put the gearbox back on.
    I then ran the motor direct with 12v to "run it in" and it's much better now.
    I think sometimes the "gunk" inside the gearbox can get a bit sticky and giving them a run worked well for me....

    Might be worth a try....

    </2cents>
  11. bsft

    bsft

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    got photos of your sim? To see the design?
  12. Nick Moxley

    Nick Moxley Well-Known Member

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    Im gonna call pot mounts flexing or doing something they shouldn't be doing. And after looking at the pics in the first post, Im concerned about those motor's flexing the frame Big time also the fact the lever is already bent, Imo you need to do some re enforcing before going forward. Thing's flexing and bending isn't helping your issues.
  13. shannonb1

    shannonb1 Well-Known Member

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    I can 100% gaurantee that when you are on there with no upper support on that motor gear box you are getting no less then 1/2 inch movement in either direction. Could be more. That L Steel with holes in it will flex on its own. You would do well to provide a support bar between the two motors running horizontal.

    Here is a look at my rear:

    [​IMG]
  14. SeatTime

    SeatTime Well-Known Member

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    That setup should lock up solid and not move like that even with a not perfect PID and some rig flex. Is the JRK app showing any errors? Is your pot mounted securely and not rotating with the motor (seen this cause identical issues in the past)? Is the motor getting the current it needs (bad connections)?
  15. shannonb1

    shannonb1 Well-Known Member

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    I disagree that the flex wouldn't cause that. If the flex is moving the POT position you could certainly get that oscillation. I would agree to check all connections first though.
  16. eaorobbie

    eaorobbie Well-Known Member SimTools Developer Gold Contributor

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    My Motion Simulator:
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    I have had a simular issue in the past and it came down too the little hole I had drilled into the pot, one was nice and tight , which meant the pot move exactly the same time as the motor and other had a little slop, like 0.5mm this cause a mis cue in the motion , equating to nearly 10mm difference.
    Please check the pot and the way they are linked, any slop will cause a feedback position error, with any controller.
  17. Jas

    Jas New Member

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    Awesome feed back - thank you all!

    I'll get testing and let you know what I find.
  18. fusednova

    fusednova Member SimAxe Beta Tester Gold Contributor

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    I logged in to post a very similar problem. Both motors have a few mm play which causes some jerking. I had changed sampling to 1024 but will play with the coefficient.

    I suspect this thread will solve my problems - Thanks all! Alas, I must wait until Friday to test.