Questions & Answers - 3 DOF AC Platform - 4th DOF - Is "this" Feasible???

Hello to all my friends here -
You all have been so kind and informative (saving my butt really) - In my progressing 3 DOF AC Platform Thread - and my Thread - "Questions & Answers - 3 DOF AC Platform" -

My Lord guys, the information you have freely given in both of my threads have been a dream come true...
THANKS to all of you.

NOW - I have a question about "Adding a 4th DOF, Sway/Yaw - IS it feasible the way that I have "worked it out"????

OVERVIEW
One of our current members here has a thread about his build, adding "Sway" - he used a turn-table on the front end and from what I'm reading, it's working great.
1. I do not have the "bug" to build a 6dof - time, money, age, just don't.
2. My 3Dof AC Platform will about give it all to me, which I'm satisfied with -
3. After following this members thread, laying in bed and "brain-storming" (dangerous), I said, heck man,
"me thinks" I have it figured out??????
4. Searched and FOUND an Industrial Grade Turn-table device - it will hold 5000 lbs + . It's made like a
battleship - and it's not that expensive at all. SO, on with the "Feasability".
5. The MAJOR PROBLEM, my 3rd DOF, HEAVE, utilizes a 1 1/4" Spline and Spline Coupler, Assist Spring,
and ABSOLUTELY will NOT move in reference to Sway / and / or Yaw.
HOWEVER, I can put the TURN-TABLE between the base platform, and the Base for the Spline Tube, Spline Shaft, Assist Spring, U-Joint - THIS WAY, (again, "me thinking") there is NO interference and the platform can now HAVE SWAY!!!!!! Turn-table is just "sandwiched" between the two 1/4" steel plates.
PROBLEMS I NEED ANSWERED
1. The "rod-ends" / or / HEIM's - will STILL be attached to the BASE PLATFORM - along with the motors/gearheads - and I THINK there is enough movement in the Heims' to allow a +- 3" to 4 " SWAY/YAW movement.
I would Need to MAKE SURE the Heims are facing forward to allow more freedom for left/right rod movement.
2. IF this is doable, how much torque would I need to move the total platform, left & right. I do not know
how much force would be present since the turn-table is running on 1/2" steel ball-bearings....probably not much, but again I will have 425 lbs MOVING LEFT / Centering / MOVING RIGHT.

SUMMARY
I really need your thoughts - suggestions to make changes - or just tell me I am starting to drift into "La-La" LAND....

Thanks for taking the time to evaluate my thoughts - Your help would continue to be highly appreciated.

All of you have a most Blessed One!

Tom

@cthiggin Pardon me if I'm dense but are you wanting to get sway by only using the three motors you have or will you be adding a fourth?

I too am not sure how you plan on setting this up. But if you plan on having the motors on the bottom layer, the sway in the center layer and the sled on the top platform then I think there is going to be a problem. The base layer motors will be static while the center layer changes the attitude of the top layer. This means that as you sway sideways the bottom motors do not move and this will result in your top platform being rolled to the left or right, or even pitched forward and backward.

BlazinH & Historiker,
GREAT - that's what I was hoping for....

I was "going" to add a 4th dedicated motor, JUST for the sway function.

Here was my logic (which evidently was wrong) -
Yes, the motors would be "static" on the base platform - BUT I "thought" that I would have enough side-to-side PLAY in the heim joints to accommodate the sway, regardless of pitch/roll/heave
positions - SO, PLEASE confirm that my thinking was WRONG - that's what I want and NEED to know - NICE concepts do NOT always become reality!!!!!

I know I "COULD" make a larger support frame, sitting on top of the turntable - that I could mount the three motors on, then there is no interference PERIOD - but that's a big undertaking -
at least 3/8" plate steel to sit motors/gearheads on for stability -

Again, PLEASE confirm so I can either proceed further / or / forget it and move on.

THANK you,
Tom

PS - Historiker - I completely understand what your saying - if the sway motor moves say left, AND I'm in a pitch mode / or in a roll mode - THEN the heims would lock up causing an unstable platform.
Again, "me thought" that there would be enough side-to-side movement in the heims to accommodate this????????

THAT'S WHY I HAVE TO ASK QUESTIONS - I just "brain-storm" too much -

Hi Tom, It is not the play in the heim joints that is the issue, it is the length of the connecting rods, they do not change. So when the top platform is rotated to the left the connecting rod will change attitude resulting in a lift or drop of the platform where it is connected.

I guess you could use software to automatically compensate for this but that is way beyond my abilities to figure out. Something like x input in sway motor results in y input to the other axis motors in order to keep the correct orientation. The software designer would need to know the exact dimensions of the hardware being use, connecting rods, levers, platform mounting locations, etc etc.

The way I got around the issue was to have my base layer the traction loss layer with the other axis mounted to the middle layer. Since you are using very beefy motors already why not use the same setup? You would need the center pivot and then a few castors around the perimeter. This would also allow you a much greater range of movement on the yaw axis. I think you are going for yaw considering your PDF showed a center mounted pivot?

My brain is already fried for today so I'm not visualizing your setup very well right now! However, I still think everything on the turntable is the way to go if you decide to do it.

Yes, that is what I was trying to explain as well.

Another option, and I know this adds even more money to the project but since you are already talking about four AC motors why not go all in and do 6DoF? It would have everything that you desire for a flight sim platform as well as a racing platform. You would need to change from heim joints to u-joints to get it smooth though. I am finding this out myself.

Hello again Historiker,
I am "completely" on the same page with you friend. It is NOT the heim play - it's the Rod Lengths -
THIS particular method I "brained up" is NOT FEASABLE and will NOT Work.

My platform base is completely finished - welded - top MDF'd , bolted down, well, the whole works including my center steel plate to accommodate my spline shaft / assist spring /etc.

BlazinH - It's just too much trouble to acquire a 3/8" piece of steel large enough to accommodate 340 lbs. of motors/gearheads - and place them on a dedicated layer above the turntable.

Gentlemen, I highly appreciate your taking the time to point out the "obvious", which I did NOT take into consideration. Thank you for NOT letting me crash and burn here.
It's a pleasure with all of you guys....you just "got it together"...

Have a blessed one,

Tom

PS - as they say on MythBusters - this one is "BUSTED"!!!!!

Now I have a question for you @cthiggin . Why does it have to be a 3/8" piece of steel large enough to accommodate 340 lbs. of motors/gearheads? Can you spare a few inches in additional height? Wood is a great building material with the proper engineering! Is there any way you could deal with that?

BlazinH,

We MUST add the Sprine/Spline Shaft / Spline Collar / Pipe Receptacle / 2x - 1/4" x 9" x 9" Steel plates at top of Spline Shaft / U-Joint -
ALL combined - PLUS a 3/8" steel plate, that would roughly be 2.5' x 3' - add them together, ALL very close to 1000 # - At that weight, (for "me) - I would only use steel - no wood in the equation.
Even with great engineering, I'm just afraid that with the movements, and AGE, wood would lose some properties and then I would be confronted with flexing.

To do this BlazinH, just too much of a labor/cost issue for the returns I would get.

With finished platform / and at maximum travel UP - the SimPlatform is 27.5" off the ground - which, for me, seem too high, but have I have NO choice but to live with that -
With my "huge" gearheads, assist spring, - well, all that encompases the build - it just takes up vertical real-estate....

Thanks so much for your thoughts and most of all, your help.

Tom

Sure thing! If it’s not worth it, it’s not worth it. And I think a lot of us have to live with tradeoffs we wish we didn’t have to make! Only suggesting an idea here anyway. Yes, wood will deform much more quickly then steel of course. But if you can get a few years use on the cheap with a well thought out design, then it’s usually cheap to fix also. It’s just a little hassle to deal with every now and then. You wouldn't want to risk something that could break and cause injury though! But to each his own, right? Also, while 1000lbs. sounds like a lot, if you distribute it over you’re 2.5’ x 3’ = 7.5sf then that’s only 133 lbs per sq. ft. That's less than you apply on the floor when you're walking on it for what it's worth. Take care my friend!

ps Unless you only weigh 133 lbs or less now that is!

BlazinH,
THANK you. Your absolutely correct in the weight/sq.ft. ratio.

IF I had really good help - I would do it with steel - My son and son-in-law just can't wait for Pop/Mr.Tom to get this platform finished, but I've asked them to come over and help with cutting steel on a chop saw / or / grinding - CRAP - it's like asking them for a million dollars - always an excuse - and my grand-sons are just too young to help at this point....plus it's not safe for them - 4 & 6 years of age....but they do loves' their "Pop'.
Now when it comes time for ol' Pop to do some simming, I'll do it when they're not around. My grandsons will use it WITH ME when they stay over. When these two "big ones come over", I promise I'm going to tell them I'm having software issues. I know HOW to deal with that issue - Rewards are measured by the amount of expended effort - they will have no reward for a LONG Time.

THANK you for showing and allowing me to see the "BIG Picture"..........and your advice was not taken in vain. Appreciate you and ALL you do for the forum.

Have a blessed one,

Tom