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Question New 6DOF Build - Advice Needed

Discussion in 'New users start here - FAQ' started by duckdown, Jan 27, 2020.

  1. duckdown

    duckdown New Member

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    Hello,

    I have been reading through a lot of really cool projects on this site and am ready to do the research for my own build. Appreciate any help and suggestions in advance as I am very new to this. I have started to play around with the different tools on the site, but figured I would lay out my thoughts to get some feedback before going too deep down the wrong path. A bit of background and what (I think) I am looking for. I am not locked into anything yet, and could benefit from the experience here.


    Use: 65/35 dynamic flight sim (dcs, star citizen) / driving sim. If compromise needed, I would optimize for flight sims. This will be used almost exclusively in VR, with a small monitor for menus and testing

    Space: I have a play area that is roughly roughly 170cm x 170cm, which currently has an Obutto Revolution setup, so the new rig would need to fit within this box. The room has 10 foot ceilings, so height should not be a limiting factor relative to the base. I think that a max base diameter would likely be in the 140cm range


    Performance: I think I would like something with yaw +/- 30°, roll/pitch +/- 25°, heave/sway/surge +/- 150mm (I got these figures from looking at different builds and from the 6dof platform design tool). I believe that these angles are the max achievable in isolation, though in practice the achieved/combined angles would be less?

    Budget: $3,000-$6,000 USD. This is for the rig only, I already have the pc, vr headset and hotas/driving controls. Would obviously prefer to spend on the lower end, though I tend to be a "buy once, cry once" person. So willing to play for quality components if they make sense in the context of performance and reliability. But definitely don't want to overspend for unnecessary capabilities.

    Hardware: This is still very open. Hopefully my goals and budget will help narrow the choices. The only point of which I am fairly certain is that I would like to use an AMC-AASD15A controller if possible with whatever motor/actuator hardware used. Regarding motor design and choice, I would like to prioritize motor speed and reaction time. A secondary consideration is rig noise. Would be nice to have a quieter rig, but again performance would be the main driver.

    Software/Controls: This is important. I do not know how to code, but can usually figure things out, within reason. I would like to build something that uses commonly used tools that forum members have tried rather than having to use something proprietary.

    Timing: Next 3-12 months. Planning to research and plan over the next 60-90 days and finish the project within the year. Might be willing to wait for Chinese tariff resolution if things seem to be making progress and there's a meaningful impact to project cost.

    Given the above considerations, I think that I should build a 6DOF traditional platform, rather than a recessed rig. I believe that a sunken build might not be right for me given my space limitations and preference to prioritize angles of deflection, but perhaps I am wrong here?

    I am very interested in the FDM/Grigory type build, with lever arms rather than actuators, given the compact footprint:



    https://www.xsimulator.net/communit...ct-and-no-linear-actuators-220v-servos.11839/

    https://www.xsimulator.net/community/threads/wkom-6dof-ac-servo-motion-platform.13725/

    Do you guys think that these could work given my desired angle of deflection and responsiveness performance? Related, I saw some Thanos and some other folks exploring an FDM build on Discord, but unsure of developments. This could be an ideal solution.


    Questions: I have many, but I think my main question is related to the performance of an actuator vs. rotating lever arm driven platform for my desired rig. Once I can get a sense for the pros/cons, I can choose a route and will be able to make some more choices regarding the project design.

    Wow, that was long. Almost as excited to design and build this as I am to use the finished product!

    Thanks again
  2. Ads Master

    Ads Master

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  3. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    Have a look at some of the existing compact 6DOF projects: https://www.xsimulator.net/community/faq/list-of-6dof-projects.179/

    In VR less is more, you don't necessarily need huge actuator movement, but you do need very fast and accurate movement.

    Actuators are more effecient than rotary motors with worm gearboxes. Design decisions may also come into play as to what best suits your project.
  4. Thanos

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

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    My Motion Simulator:
    AC motor, Motion platform, 4DOF, 6DOF
    The latest firmware of AMC-AASD15A addresses the math calculations for easy configuration of rotating actuators(planetary gearboxes), and all have been verified on very large scale flight simulator (160:1 double gearbox):




    A small scale 6DOF would be much easier!
    There is a push to persuade PT-ACTUATOR to create easy to put together kits that include the hard to make mechanics ( arm-rod, universal joints, top - base modular frame etc...). We'll see.

    Thanks
    Thanos
  5. duckdown

    duckdown New Member

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    Looking at the other projects, it seems the rotary motor is the way to go for compact design.

    If I want fast and accurate movement for a VR environment, is there a preference between an actuator or rotary solution?

    When you mention efficiency, what does that mean in a practical sense for a build? Will I need more power to get the same performance out of a rotary setup vs. an actuator? Or will I need to spec more powerful motors in order to make up for mechanical inefficiency in a rotary system relative to an actuator build?
  6. duckdown

    duckdown New Member

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    That sounds great, I would be interested in a PT-ACTUATOR kit.
  7. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    Depending on the ratio you may want to allow between 10% to 50% loss for worm gears and the greater the gear ratio the higher the % loss is: http://www.meadinfo.org/2008/11/gear-efficiency-spur-helical-bevel-worm.html
  8. duckdown

    duckdown New Member

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    A bit of an update.

    Spent the last couple of weeks researching and trying to learn how to use CAD software.

    I think I have settled on some of my basic design parameters. I am going to build a radiating, crank arm 6DOF platform with a steel base similar to the Grigory build but with extending support legs.

    The rig will be built with 80/20 or similar t-slot extruded aluminum. Likely using 40mm x 40mm profiles. I also looked into 1.5”x1.5” profile, would be a bit cheaper and about 4-5kg lighter than the 40mm profiles, at the expense of stiffness.


    Motor: LiCHUAN 90ST-M04025. 1kw, 4Nm, 2500RPM.

    Gearing: LiCHUAN PLF90. Ratio undecided, see below.

    Controller: Thanos AMC-AASD15A

    Open questions:
    - The upper platform diameter is to be determined, but I am going to size it so that I can achieve pitch/roll in the 20-25 degree range.

    - How much linear velocity should I be targeting? I have seen some posts that mention 250-300mm/s as ideal. Want to confirm that linear velocity is taken at the end of the crank arm? As mentioned, I will be using this rig for dynamic flight sim and driving sims.

    - Gearbox choice. My calculations are below, but I think that given the motor choice and rig weight, I have a lot of leeway in gearing choice. The gearbox specs show 94% efficiency, is that realistic? Curios what the folks who have completed a build would choose for gearing in this case.

    - Assuming my calculations on linear velocity are correct (they seem high) and the setup is not torque constrained, is there a preference for choosing torque or velocity? Will I be able to use firmware/software to slow down a rig that is too fast or jerky while maintaining torque? Or is it preferable to have less velocity and more torque? I will have several bolt holes in the crank arms, so I should be able to make additional adjustments there.

    Is there any reason that I should not bolt the supporting rods directly to the rig chassis? I was thinking of adding two side “wings” to the rig chassis to complete a virtual or inline upper platform anchored at the base. The alternative is to attach the chassis to a steel upper platform, similar to the Nisch build.

    Overall, having fun with this. Pretty sure the motors are overkill at this point, but want to build in some extra margin, as I can see this thing evolving over time...those G-Seats look pretty cool ;)

    Thanks again for the help

    Calcs.jpg Base.jpg
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    Last edited: Feb 14, 2020
  9. Thanos

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

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    My Motion Simulator:
    AC motor, Motion platform, 4DOF, 6DOF
    50:1 gearbox will provide a good balance between speed and load ability. You can always slow down the max speed (max RPM parameters in the AASD-15A servo drives).

    This 6dof has 50:1 gearboxes for example:


    Thanks
    Thanos
  10. duckdown

    duckdown New Member

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    Think I am getting close to finalizing my upper platform design. I am probably going to use a steel upper platform with some 8020 extruded aluminum for the steering wheel mount and monitor mount using this build as a model:
    Upper Platform.jpg
    I have a question about mounting points and how they impact the performance of the 6DOF rig. The ideal mounting points for the upper rods straddle points A1, A2 and A3. However, given space constraints with the main rails, I won’t have enough room straddle A2 and A3. If I mount at A1, B2 and B3, (non-equilateral triangle) will that cause motion/calculation issues? I am guessing that B2 and B3 will be offset about 1” (25.4mm) from A2 and A3. Alternatively, I can build a little tail and mount on the equilateral triangle B1,B2,B3.
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  11. duckdown

    duckdown New Member

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    Received the Thanos controller in the mail this week (Thanks again, Thanos).
    Thanos Controller.jpg


    Servos and gearboxes are inbound.

    Controller case is being printed as we speak: https://www.twitch.tv/twitchtvleech (FYI, the guy printing my case can give advice on printing, settings, etc., but his print queue is full and he cannot accept any additional work).

    Still have a lot of decisions to make, but at least the parts are moving.
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  12. duckdown

    duckdown New Member

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    Even more goodies showed up on the doorstep today.

    Servo and Gearbox.jpg
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  13. duckdown

    duckdown New Member

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    Getting closer to pulling the trigger on a build. Existing draft attached. I ended up going back to a traditional upper platform that will support an extruded aluminum rig. The extra rails should help me to mount the rig and adjust the fore/aft to find an optimal balance for the servos. Made a small modification to the Grigory build with extendable feet in green, I want to keep the smallest footprint possible.

    6DOF Draft.jpg 6DOF Draft_1.jpg

    The lower platform radius to the crank arm extensions is 442mm, the upper platform radius to the mounting extensions is 318mm.

    I just saw kaitila's new build (https://www.xsimulator.net/community/threads/6dof-project-750w-ac-motors-1000w-servo-motors.14477/), which is a great mod to Grigory's build. The support feet might be a simpler and better solution than the route I am going. I need to stop browsing this site and get on with it, lol!
  14. duckdown

    duckdown New Member

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    Made some adjustments and simplified the support feet. Rather than having extendable feet, I added extra mounting holes so that I can have a wider or narrower stance, depending on rig stability.

    The original plan was to do the fabrication with a friend, but the Covid-19 situation has changed that. Now likely going to send the plans to a local maker, with one of my gearboxes so that precision measurements can be made for the crank arms and motor mounts.

    I would take the attached motor mount and crank arm diagrams as guidelines, they will be slightly different based on the gearbox spindle and mounting hole measurements. The gearbox key spline measures is 1.25", but I am trying to figure out whether I can make the crank out of a standard 1" billet or if I need something wider.

    Any suggestions or improvements would be appreciated before I push the button.

    Attached Files:

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