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Seat Harness Tensioner Questions

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Zed, Jun 15, 2017.

  1. Zed

    Zed VR Simming w/Index Gold Contributor

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    I've decided to add a harness tensioner as I build my rig. I've looked around and @SeatTime's servo tensioners seems a popular design.

    Do those designs essentially put the motors into stall at full force? Has anyone used a gearmotor with an output arm with a spring in tension to pull on the straps? The reason I was looking at a spring is because Hooke's Law says that the force will be linearly related to spring extension. Instead of motors going into stall, and maybe I'm misunderstanding the servo designs, a gearmotor and output arm could set the tensioner force just by setting position. As long as the gearmotor/arm had the torque to pull the spring to full extension, it wouldn't stall and sizing would just be proper spring tension to get the proper force range with output arm and motor torque enough to get that range of spring tension.

    The only thing I can think of is that pulling against a spring is a bit unrealistic. Maybe add a hard limit to the spring extension so that at some point you hit the worm gear lock kind of like pulling on a regular seat belt?

    Has anyone else tried this? I've done searches but so much gets buried and hard to find so apologies if this is reinventing. I'd be thankful to get pointed at other examples.
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  2. Ads Master

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  3. SeatTime

    SeatTime Well-Known Member

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    I don't know how popular my design is, as I do not know of anyone else that has built one o_O. They are a great addition to a sim. There are lots of different ways to build them, I think a worm gear motor would be quite good, but I was concerned about the weight of using them in my rig. I have not needed to use a spring, but could see were it could be necessary depending on the design/setup. In my setup my body/seat-mount/padding are the 'spring', with the range of motion set to stop damage to myself or more likely the servo - it does pull down hard (the seat-mount is design to flex at high loads)- which is why I use powerful servos - 2 (soon to be 4) x 73Kgcm, but you need that for the realism:D.
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    Last edited: Jun 16, 2017
  4. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
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    FI. you can see the rubber mounting in the picture below - and note that my harness straps are connected to the servo via velcro. Good luck with your build.

    Seat Harness Tensioner mounting.jpg
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  5. pab61

    pab61 Member

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    I'm planning on doing pretty well what you suggested, but using 3Nm steppers rather than servos. If I get it done before you do (I'm probably about a month to six weeks away from getting it up and running) I'll let you know how it goes.

    PB.
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  6. Zed

    Zed VR Simming w/Index Gold Contributor

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    @SeatTime - Thanks and very cool! You are going to four servos for seat tensioning? One for each strap on a four point system or to get more pull on the top straps? If it's for tensioning four straps, do you miss tensioning on the bottom straps? I guess that's an obvious question if you are adding tensioning there.

    At 73 Kgcm, about how much pull does that work out to be? I don't have a scale for how big those drums are. Brilliant idea on the Velcro! I was wondering how to handle over tensioning.

    @pab61 - thanks! Looking forward to hearing and if I get it going first, I'll let you know. I was checking out springs today and am thinking something around 20 pounds pull at two inches of extension would be in the ballpark. We'll see how it goes if I'm guessing the proper pull range right.
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  7. SeatTime

    SeatTime Well-Known Member

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    FI: you need a 6 point harness - I was able to just add a crutch one (extra point was already available on the Camlock) to my current Sabelt harness. If you don't have this extra point, the Tensioner may waste travel in pulling the hip belt up.
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  8. pab61

    pab61 Member

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    I'm wondering why it needs to be 6, wouldn't 5 point achieve the same thing (I can see why 4 point wouldn't work)?
  9. SeatTime

    SeatTime Well-Known Member

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    It's more comfy ;).
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  10. pab61

    pab61 Member

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    Ah! :) Yep, I reckon you're right!
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  11. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
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    Just to let you know - in the never ending pursuit of simulation perfection (and possibly lower cost), I have moved on to another pressure system design :rolleyes:.
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  12. Zed

    Zed VR Simming w/Index Gold Contributor

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    I hadn't even thought about the top straps needing a counterpoint for when they pull! Thanks for the heads-up on that!

    Since it sounds like you were considering a tensioner on each of the waist straps, did you miss the waist strap tensioning? I was thinking of mounting a gearmotor under the seat near the post to minimize the inertia moment, connecting the spring, and then connecting individual ropes between the other end of the spring and each seat strap using little turning pulleys. I was going to use the rear bay of my lower platform for the electronics (not mounted yet but test fitted in the photo) but am now thinking I could put the gearmotor and spring there and move the electronics into a box. That would take all inertia off the seat and if I route the ropes next to but located around the post, can make the added force mostly symmetrical and of no consequence for the motion stuff. Work to do...

    Wouldn't have started down this path if it wasn't for the people here talking up seat belt tensioners. Damn you all... :grin

    image.jpeg

    Curious what your new design is, @SeatTime. Definitely one to keep an eye on! :thumbs
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  13. SeatTime

    SeatTime Well-Known Member

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    Certainly so many ways of doing this each with their own advantages/disadvantages. Agree, you need to keep you seat inertia down, and remote as much equipment as you can off it. As such, amazingly we are thinking of a similar solution :), although slightly different execution ;)- will be interested in seeing what you come up with and how it differs from mine. Don't proclaim to have all the answers and really won't know if it is a improvement to my current system until I build and try it :think. Good luck :thumbs.
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  14. Zed

    Zed VR Simming w/Index Gold Contributor

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    And good luck to you! It's always fun to see how others do things and try to learn from them. And you are very right about lots of ways to do things. Curious what you are up to... :popcorn

    I ordered some ball bearings today and am planning on 3D printing turning blocks to hold them. Since I'm building with 80/20 strut, they will bolt onto the strut with the bearings both parallel to the strut as well as 90 degrees to it. I got one of the 50 rpm MakerMotor gearmotors since it should have about 48 pounds of pull at about a 5 cm C-C with almost three inches of throw. I also ordered a hobby horse spring with a max load of 48 pounds so I'm hoping it's a good match. After the spring I'll split to the lap belt and shoulder harness ends.

    I think the MakerMotor will fit next to my shaker plate amps where I was going to put my USB hub. Will know better once I get it in hand. It's power supply will go where I was going to put my outlet strip. Fingers crossed it fits like I hope it will...
    Last edited: Jun 17, 2017
  15. Zed

    Zed VR Simming w/Index Gold Contributor

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    @SeatTime - I ordered a pack of 10 bearings from Amazon and went to work on a turning block design. Learned more 3D printing tricks to split the frame into two pieces to clamp the bearings in place. Also did a curved face on a ring to keep the rope more centered that will fit on the outer surface of the bearings.

    The frame has a ridge along the bottom to help lock it into position in the 10 series 80/20 strut. Where the top and bottom clamp together I added keyways at either end to lock the top to the bottom in register and the bolts hold the two halves to each other as well. The center post for the bearing has a mating hole in the top half to support it at both ends.

    With the pulley ring having a bigger diameter than the width of the frame, rope can enter and exit at all sorts of angles to turn rope 180, 90, or all sorts of other angles as needed. I'll also need blocks with the pulley perpendicular but haven't designed that yet. I think I'll need eight blocks total the way I'm thinking this will go. It's just which version where with my seat frame. All in all very pleased and think this just might work.

    Seems a lot of effort for some simple blocks, but it's too easy to make parts exactly as needed. No bearing in the block. Not here yet... :thumbs

    image.jpeg image.jpeg image.jpeg
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  16. Zed

    Zed VR Simming w/Index Gold Contributor

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    In the same vein, bolt-on, two-piece, snap-together seat belt guides. They are basically thinner and wider turning blocks. Same design for the most part but to hold the belts captive and in proper position, and feed them around the frame.

    image.jpeg
  17. Zed

    Zed VR Simming w/Index Gold Contributor

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    @SeatTime, some progress here. Should be a lot more this weekend. Got parts in and am building again though still waiting on some key ones for the motion part.

    In the mean time, been printing pulleys (still need to print the pulley faces) to do the rope turning to keep all the weight on the lower frame. Made both center and offset designs to turn the pull from horizontal to vertical - that will get more clear when I lace it up. Got the motor and it fits perfectly where I was going to put my USB hub. Printed up a drill guide and will mount the motor when the mounting studs get here (delayed). Need to use studs as those are the mount for the tensioner motor Hall sensor too.

    Printed a box that will bolt to the frame right next to the tensioner motor, holds the power supply for it (hoping its powerful enough but plan on limiting in the JRK setup), and also mounts a fan for forced-air cooling the JRK heat sink and power supply. Using the same bottom board cooling as on my motion motor JRK units. Heat sink is a bit tall but that's what was available.

    Getting there. Doing all the wiring and component mounting this weekend. Looks like it's going to work just fine. Got a cheap Tanaka 5-point harness for all this to pull on. All the belt guides are printing now to hold the belts all in proper position. The hobby horse spring may end up being a little strong but only one way to find out.

    Cheers!

    image.jpeg image.jpeg image.jpeg image.jpeg image.jpeg image.jpeg image.jpeg image.jpeg image.jpeg
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  18. Zed

    Zed VR Simming w/Index Gold Contributor

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    Got the harness. Can now add the strap guides.

    image.jpeg
  19. Zed

    Zed VR Simming w/Index Gold Contributor

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    I think I'm going to extend this clamp up to enclose and protect the JRK but this shows the clamping of the JRK onto the thermal pad material and onto the upper heat sink. The final piece will have vents but will use the same kinds of tabs to push down on the JRK board at the edges.

    image.jpeg image.jpeg
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  20. Zed

    Zed VR Simming w/Index Gold Contributor

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    Protective but lots of big vents just in case cover added to the clamp. Tested with the power supply wired up and the air flow is fine through both the top and bottom. Now to install.

    image.jpeg image.jpeg
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  21. ferslash

    ferslash Active Member

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    i did not understand well your sistem (my fault) but, your 3d printed stuff looks grate, i really liked your jrk box.

    keep posting, it looks grate

    fer
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