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JADs 6dof with ballscrews

Discussion in 'DIY Motion Simulator Projects' started by JAD, Feb 25, 2018.

  1. JAD

    JAD Member

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  2. noorbeast

    noorbeast VR - The Next Generation Staff Member Moderator

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    My Motion Simulator:
    3DOF, DC motor, JRK
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  3. hannibal

    hannibal Active Member

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    My Motion Simulator:
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    interesting!!! jeez, i learn something everytime i visit these forums...
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  4. wannabeaflyer2

    wannabeaflyer2 Well-Known Member

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    My Motion Simulator:
    2DOF, Arduino, Motion platform, 6DOF
    Kangeroo = Dimension engineering add on Board for sabertooth Motor controllers which allow Encoder feedback and a whole raft of other options when used with their Controllers . :)
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  5. JAD

    JAD Member

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    Well Im back!
    Now Im up to the point in the build before I collapsed the rig earlier this year.

    The new bearing block has improved the wobble but not entirely.
    I'd call it servicable, but only just.
    At this stage, Ive lowered my standards just to keep going with it.
    I think it will be fine long term, but I will upgrade these actruators eventually. I'll wait to see what breaks first.

    As you can see in the vid, there is a bit of wobble at some points of rpm and extension.
    Im driving this manually with the mouse, its not connected to simtools yet.


    Ive also got the Simucube running with the mige servo motor and an old set of G27 pedals.
    Ive had a few runs of it with my Pimax 5k+ just to get a taste of what this whole project is about.
    No motion yet, just enjoying the FFB wheel and pedals.

    IMG_20190728_172031.jpg IMG_20190728_172043.jpg IMG_20190728_172056.jpg

    Right now, Ive just been running the front pair of actuators to setup the Kangaroo properly.
    With a bit of help from Dimension Engineering, I was able to tune by mechanical stops,
    then engage the single bottom limit switch to act as a homing point on every startup.

    The aim this weekend is to have it all running on Simtools and FlyPT's interface.

    Hopefully next post will be a video of full motion.
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  6. JAD

    JAD Member

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    Didnt quite make it to up and running.
    I had two problems.
    The easy one first :
    On one of the Alu tube's, the ballscrew end bearing that floats up and down internally at the free end, became damaged probably while doing a crash limit tune that was too strong.
    The outer bearing race became loose just enought that it would bind internally against the side walls of the tube and lock up fully.
    I think a combination of a cheap bearing that was already a little too loose and too much bump power on the tune.
    I recommend a bump power of 5% - I had 15% and maybe that might have done it.
    At 5% bump power, it was still able to lift the rig with 90kg in the seat (my tuning test weight) during the tune.
    It only needs to bump once during tuning. After that, back to using a bottom limit for homing on every startup.
    So hopefully this is an outlier.

    So a bit of surgery to extract the ballscrew
    IMG_20190810_145248.jpg

    It took about 3-4 hours to make another one. I should be able to get it done to 2 hours if it happens again.

    That was the easy problem.

    I'll give the next problem its own post.
  7. JAD

    JAD Member

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    So at this point I have fixed the damaged tube, and tuned up 2 sets of gear all succesfully.
    I can drive the actuators properly and the encoders all register properly.
    I can set limits using the Describe software and drive them manually over serial connection just fine.

    Now for the 3rd set, I have this problem that I've spent a full day of testing trying to figure out.
    I was hoping that just writing up the problem would help me diagnose the issue but Im still stuck.

    So I sent of a query to Dimension Engineering hoping they could help.
    I dont think its a problem with their equipment, I think its something on my side.

    Now Im putting it up to the good folk of xsimulator to see if anyone has any suggestions.

    Below is the query I sent to DE.
    Sorry, its a long one, hope it reads ok to understand what Ive done.
    There is a video of the problem at a link in the description below.

    Hi Support,
    Im struggling with an issue and and thought you might be able to give me a few clues.
    I have a 6dof motion platform setup, so 3 sets of sabertooth, kangaroo and 6x motors+encoders.
    2 sets are working fine, I have set them up successfully, tuned and all ok.
    Just having trouble with the 3rd set.

    Its not a problem with the Sabertooth 2x60 or the kangaroo. Some of the troubleshooting has shown that these are not the problem. Its something on my side that has completely puzzled me and thought you might have come across the problem before.

    A description of the problem:
    I have a Sabertooth 2x60, connected to 2 motors and encoders connected by gears.
    I have reset to default in Describe, uploaded, restarted the sabertooth, reconnect in Describe and I check that it is in independent mode then I go straight to the pretune window without changing anything.

    At the pretune window, I drive channel 1 motor forward, the channel 1 encoder increases correctly, but also channel 2 encoder moves.
    When I drive channel 1 motor reverse, channel 1 encoder decreases correctly, and channel 2 encoder stays idle correctly. So in summary for channel 1 motor drive, in reverse its fine, in forward it moves both encoders.

    When I drive channel 2 motor, encoder 2 moves correctly, encoder 1 stays idle correclt. ie no crosstalk.

    A video of the above description here


    If I mechanically decouple both encoders from motor, I can spin each manually, and they register correctly in the pre tune window with no cross talk.
    With encoders still decoupled, I drive channel 1, and channel 2 encoder increases like before even though the encoder 2 is decoupled and stationary.

    If I disconnect power lead to channel 2, and leave both encoders connected, then when driving channel 1, encoder 1 moves correctly, encoder 2 is idle correctly. I can also manually spin both encoders and they both register correctly. So it appears to recreate the odd behaviour, both motor power leads have to be connected.

    Some other troubleshooting I have done :

    -I connect all the same hardware directly to another set of working sabertooth/kangaroo and I get the same behaviour. When I return the working sabertooth/kangaroo to original, it goes back to working normally. This alone tells me that its nothing to do with the kangaroo/sabertooth and something down the line I have added.
    -I have a spare encoder and swap this in on both channels one at a time and same behaviour as the description above
    -I swap for another set of extension leads for encoders and power to motor (from a working set) and same behaviour which tells me the extension leads are OK.
    -I ensure all the extension leads for encoders and power are separated in case they interfere.
    -I have 1k pull up resistors on all the encoders. These have been working ok in the other 2 sets.

    My next troubleshooting check is to disconnect everything fully upto the terminals of the kangaroo/sabertooth. Then connect 2 different motors and a second set of encoders (when they arrive in about 2 weeks). I'll give this a run and see if the same problem exists.

    In the meantime before I do this last test(while I wait for the encoders) I wanted to check if you have come across something like this before and could give me any clue as to what it could be.

    Attached are a few photos of the setup
    IMG_20190811_151526.jpg
    IMG_20190811_151426.jpg
    I need to add to the troubleshooting list (I sent DE another message), that I took this sabertooth/kangaroo and hooked up one of the good running sets of leads, motors and encoder and this worked fine. So another reason I believe the problem is not with the sabertooth/kangaroo.

    Last edited: Aug 11, 2019
  8. JAD

    JAD Member

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    Here is a marked up photo of the setup that might help someone give me a clue.
    setup Page 001.jpg
    setup Page 002.jpg
  9. JAD

    JAD Member

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    All good now with some help from Dimension Enginnering,
    I was pointed to problems with screening and grounding.

    I noticed the problem only occured when the body of the encoder was electrically connected to the body of the motor.
    The encoder body is connected to the cable shielding, and I didnt connect the cable sheilding to anything at the Kangaroo end.

    I also have the situation where each actuator assembly is electrically isolated from the frame of the rig.
    So I guess my problem is some electrical noise making its way to the body of the motor which passed to the encoder body and cable shielding.

    So Ive connected up electrically all the actuator bodies to the upper and lower frame.
    Now all 6 cable shields, encoder bodies, motor bodies and main frame are connected and the problem has gone away.
    But at this stage the ends of the cable shielding at the Kangaroo end are not connected to ground anywhere.
    Im guessing this merged network of electrical mass has damped the electrical noise?

    Maybe I should be connecting the ends of the cable screening to ground on Kangaroo or ground on the house circuit but so far so good so I'll leave it as is.
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  10. Pierre Lalancette

    Pierre Lalancette Lalancelot Gold Contributor

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    My Motion Simulator:
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    Noise in the ground. That's a tough bug to find. Glad you did.
    So, all is good now, right? You are flying away in your sim.
  11. JAD

    JAD Member

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    I had it all running on Simtools manually with heave only before I ran out of time last Sunday.
    I'll be back at it this coming weekend and will hopefully post a video of full motion.
    Ive got some catching up to do on reading some threads on axis setups for 6dof.
    • Like Like x 2
  12. JAD

    JAD Member

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    Milestone Reached!
    We have motion with LFS and Simtools.
    Its raw, unfiltered, untuned, untamed but its rocking and rolling!

    I got a bit ahead of myself and jumped in boots and all into VR and made myself sick in 5 mins.
    I've got to start working through the tuning process and looking into motion compensation before I try that again.

    I managed to get a video.
    I rushed to get this done in case something would break and I have no proof of life.
    Sorry about the potatoe webcam, its a very old one. I'll look around for an upgrade soon.

    Now the fun begins with tuning.

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  13. JAD

    JAD Member

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    Has anyone succesfully performed surgery on a pimax cable?
    I pinched mine in the actuator when it was homing!
    Ive sent off a request to Pimax for a replacement as I dont like my chances of patching this up.
    IMG_20190901_200927.jpg
    IMG_20190901_195100.jpg
  14. noorbeast

    noorbeast VR - The Next Generation Staff Member Moderator

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    My Motion Simulator:
    3DOF, DC motor, JRK
    Ouch :(

    I have a spare Pimax cable that had some sparkles, you are welcome to it if you PM me your details.
  15. JAD

    JAD Member

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    Here are some other accessories added to the sim this weekend.

    An old G25 shifter. I just discovered I cant hook this up directly to the Simucube so Ive ordered a Teensy and will follow this advice found here to hook it up.
    https://www.isrtv.com/forums/topic/...ith-h-pattern-sequential-and-handbrake-modes/
    A swing away keyboard.
    Hung a monitor from the roof to be closer to me when seated. The other monitor was too far away for me to see numbers when tuning.
    And some vive wand holders. One for motion compensation and the other just to store it somewhere when sitting in the rig.
    IMG_20190901_215526.jpg IMG_20190901_215502.jpg
    I had only just barely got motion compensating working when I crushed the Pimax cable.
    So I havent really had a proper go of it yet to see what vibration issues I might have.
    I did have a huge stutter with the image though which I need to look into.
    I'll have to sort this out next weekend with the original Vive until the Pimax cable is fixed or replaced.
  16. JAD

    JAD Member

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    Thats great! Thanks for the offer.
    I'll PM you now.
  17. Pierre Lalancette

    Pierre Lalancette Lalancelot Gold Contributor

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    6DOF
    Is the Pimax still working?
    If yes, don't touch the cable and used it, until you got a new one.
    If not, cut it and repair it. I see 10 wires. What do you got to loose?
  18. JAD

    JAD Member

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    No, it was failing as soon as it was pinched. The USB chime was cycling on and off.

    The small wires are smaller than Ive ever seen. It will be a challenge to splice these.
    I will have a go soon but I can delay it for now thanks to @noorbeast who kindly sent me his old cable which I received yesterday.
    Ive put in a Pimax helpdesk ticket asking about a replacement as I cant find a way to purchase these on their website.

    @noorbeast, you mentioned this was the cable that gave you trouble with sparkles and Pimax replaced it but its interesting that for me its no problem. I cant detect any visual defects.
  19. noorbeast

    noorbeast VR - The Next Generation Staff Member Moderator

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    My Motion Simulator:
    3DOF, DC motor, JRK
    Test it on a black screen, like a loading screen, the sparkles are noticeable there, but the cable works OK.
  20. JAD

    JAD Member

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    I'll check that out