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Compact Full frame, 2Dof with TL

Discussion in 'DIY Motion Simulator Projects' started by Rav3n87, Sep 23, 2020.

  1. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Gas struts have their pros and cons, read on from here to get a sense of the range of associated views and potential issues: https://www.xsimulator.net/community/threads/2dof-motion-simulator-build.6196/page-7#post-88210
  2. absyfadhel1

    absyfadhel1 Member

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    I have same problem as you , i have jerky motion when moving slow but at fast movment its great.

    so i want to add gas struts on front but i dont know how much nm should i buy like 100nm or more?, so if you add gas struts can you tell me if its helped you or not and which one have you installed?
  3. Rav3n87

    Rav3n87 Active Member

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    H
    Hi Mate,

    I have a few other issues to sort out atm, I have twist in my uni joint which is not helping the overall jerkyness, I will be rectifying that issue first and will retest to see how much improvement i get and go from there, I have some short 100n struts at home and they feel like they would almost be too strong depending on where they are mounted, when i get a chance i grab some for testing

    Thanks
  4. absyfadhel1

    absyfadhel1 Member

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    I have also twist on my rig shaft, i will check if i can make it stable, i check some post that maybe you need to add Motorcycle steering damper, like this



    but its to expinsive on my country about 120$ each one, also from the orginal site they dont ship to me .and i'm afraid to purchase it and not give any help.

    Thanks
  5. Rav3n87

    Rav3n87 Active Member

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    Yeah i saw those dampener units, I think they would work quite well to smoothen it up, but yes expensive!
  6. Rav3n87

    Rav3n87 Active Member

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    Update time...

    Oki doki now before I strip this thing and give up would somebody like to have a look at my photos and shed a bit of light on how I can fix/mask the backlash, other than the backlash it's feels great albeit needs a bit more refining in simtools but its close, I simply cannot and will not live with this bloody backlash!! It's off-putting and uncomfortable, turn it up no change turn it down no change, tried gas struts...nooopee that's a garbage idea, funnily enough slows the movement down to the point motors get hot when they are opening! Can't win!

    I'd like to think I'm reasonably smart and capable person but I'm at the end of my rope!

    Video also
    https://youtube.com/shorts/rojw_WAZw00?feature=share

    Attached Files:

  7. Radje748

    Radje748 Member Gold Contributor

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    This play is in several motors I have tested.... the way I solved it (almost)... is a combination of gas struts and springs between the up and down section to keep pressure on the motor arm....(but had to play to find the best position)....
    It is still there, but less notionable....
  8. itsumairu

    itsumairu Active Member

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    hello there. I really wanna know if the damper is significantly improve the motion, because its been a while I want to add this damper to my rig.
    especially because I find the cheaper damper on my country, for only $9 each.
    bee8d8b5-4d32-4c5c-9bc1-53a6e5115bf3.jpg
  9. absyfadhel1

    absyfadhel1 Member

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    This is DOFREALITY option so i think it can help with backlash , i call them and ask about backlash and they offer me two option :

    1. use damper (100$)
    dumpers.png

    2 : use SFU gearbox upgarde that can remove backlash completely (200$/1pcs)
    sfu-1024x747.png


    https://dofreality.com/options/


    this is cheap damper
    https://www.aliexpress.com/item/330...!sea!BH!1855950368&curPageLogUid=yUQpksmbEEvW
  10. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Backlash is common in wormdrives, this is about average: https://www.xsimulator.net/community/faq/wormdrive-backlash.293/

    The longer the leavers and inherent rig design leverage the more pronounced backlash is.

    A little bit of positive weight bias will help mask the back lash.

    Obviously you have more backlash in one wormdrive than the other, what you may consider doing is if they are new talk to the supplier, and if not open up the wormdrive.

    You will note only a small amount of the gear is repeatedly used for whatever lever range you are using, and it can wear the gear teeth, brass teeth can actually spread. So you could try moving the gear wheel and lever so you are using a fresh unworn part of the gear and see if that helps.
  11. Rav3n87

    Rav3n87 Active Member

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    Do you have any Photos of how you (almost) solved it?

    I contacted DOF reality and for me to use the SFU Gearboxes i would need 24v motors from them or someone else if i can find out exactly what they are


    Thanks Noorbeast, I have read the backlash Faq before, i understand that with longer leavers it is more pronounced, what do you mean by: "inherent rig design leverage" In my photos is there something you can see that would add to the problem?

    Yeah both of them are new from motion dynamics not sure why it has more backlash now than the other, They were both rather tight to begin with, perhaps i will open it up again and inspect,

    Not sure about adding more weight it does seem like a reasonable amount on them already, Roughly how much would you think you have on yours?

    Cheers all
  12. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    What I mean is that with a foot design rig, like yours, using fairly long levers that exacerbate backlash, the long design leverage distance from the motors emphasises that backlash even further. On a compact rig like mine a shorter CTC lever is used, there is still backlash but it is minimised.

    A small amount of positive weight bias may help, how much relates to the design, my compact rig uses just a tiny amount.

    You can actually hear the backlash of my compact rig at the extreme of motion here, but if you watch the top of the seat there is very little real impact on the actual motion, which remains fairly controlled:
  13. Rav3n87

    Rav3n87 Active Member

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    @noorbeast

    Do you think if i changed the lever mount to where it is in the rough drawing below it would help?

    It would add a little more down weight, Make the motors 90deg at rest, And i think i can change the ctc a little if need be to also help

    Oh also I got a quote back from DOF reality for the 24v motors and SFU units (2 of each) inc shipping it is just under $1500Aud, A little pricey but i think it would be worth it in the long run,

    Willing to make necessary changes atm to make it as good as it can be with what i have on hand though!

    I do have a question though regarding ball screws or the SFU units rather, Would they be easily back driven?
    Don't really want to end up with the same issue i had with the 25:1 gearboxes!!! that sucked!

    Cheers

    Attached Files:

  14. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    The suggested modification lengthens the inherent design leverage, reducing the load on the motors a little, so is worth doing for that reason, but I don't see how that helps the core issue of unwanted backlash being experienced by the user, it may help a little.

    The alternate to the SFU units would be to DIY linear actuators, which would be much cheaper.

    Being back driven or not relates to the ratio of what is being used, the 60:1 wormdrives I use can't be back driven. I did try 50:1s, initially when new they were not back driven, but once used for a while loosened up enough that the weight of the rig+user resulted in being back driven on my compact design. As you have found 25:1s are easily back driven. It is no different really with a linear actuator, its un-powered holding power relates to inherent friction plus ratio it provides.
    Last edited: Feb 9, 2023
  15. Rav3n87

    Rav3n87 Active Member

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    Ok @noorbeast I think i see what you mean, So realistically I'd be better off swapping the left and right motors to turn them around 180 and connect the rod to the next angled bar closer to the seat, Reduce the c2c as much as possible because it will require much less lever movement for desired platform angles, Which will have a side effect of placing a little more load on the motors albeit with a shorter c2c and also with the shorter c2c the backlash will be less pronounced?

    If you were going to build a Diy Actuator which design would you go with? I was using this project as a stepping stone project to get to an actuator based system in the future, Preferably 6dof so if i can get this working well enough for now i would be keen to look toward that


    Cheers
  16. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My thoughts are that you first try and make changes that reduce the impact of back lash, and once that is done rotate the gears in the boxes as the area you have been using has already likely been impacted.

    If you are planning a future upgrade save your money for that, you can repurpose these motors for things like motion driven harness, focus instead on optimising what you have for now.

    Reducing the CTC as much as you are comfortable with, as you lose movement range/speed, should help.

    A little bit of weight bias pre-load should help, you want to keep a bit of weight on if possible within design constraints.

    Don't over extend the range of lever movement, as it reduces effective torque and hence control.

    Moving the rods as per your image lessens the load on motors and should allow for a bit more weight bias on the levers, without straining the motors:
    [​IMG]
  17. Rav3n87

    Rav3n87 Active Member

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    OK Thanks mate, I'll get stuck into the changes and see how we get on from there!

    Cheers
    • Like Like x 1
  18. Rav3n87

    Rav3n87 Active Member

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    Update time...

    So I may have over reacted in my frustration!

    I think I've finally sorted it out, feels very close to what I think it should, which I'm guessing refinement is an ongoing process as far as the profiles goes,

    Moved the c2c to the closest hole and added tramp springs haha

    Backlash gone!!!

    Attached Files:

    • Winner Winner x 1
  19. Radje748

    Radje748 Member Gold Contributor

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    I am using these dampers....very cheap from Aliexpress, but do their job and easy to set the friction level.

    Attached Files:

  20. absyfadhel1

    absyfadhel1 Member

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    Hi, i want to ask you about the dampers, i just ordered 2 of them from aliexpress but i'm afraid that they will not help me in backlash problem, i got backlash and jerky in slow movement very annoying, any tips?