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Questions - Help - 3DOF AC Platform IT Begins -

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by cthiggin, Feb 16, 2014.

  1. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    My Motion Simulator:
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    yep there is a double dip switch on the board.
    Which gives slot 0 SimAxe Admin , where you connect via a small app to set the settings for the SimAxe, then 3 slots to hold 3 different firmwares. And not added to code yet, but will come, board is already pin compatible for encoder support.
    Can switch through the firmwares without the need to stop Sim Tools or change SimTools.
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  2. speedy

    speedy Well-Known Member

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    My Motion Simulator:
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    ... that is a good point to admire :thumbs

    BTW I have 1 question for you Tom , late but to keep up with you ... Sorry:oops:, I didn't finish reading all the previous posts yet ...

    Is the center u-joint with a spring and can move in altitude ? like the car suspensions ?
    IF NOT ... you'll not get Heave and you don't want the base to be pushed up a little more by one of the motors without the other two are not following with same action on other direction "Unbalanced rotation around the u-joint" . So a push up or down force on the u-joint can break/twist the base or decrease motor torque
    Last edited: Feb 27, 2014
  3. cthiggin

    cthiggin Active Member

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    Eaorobbie,
    Thank you. IF I understand you, I would do initial programming - Say Firmware 1=Flight Sim - Firmware 2 = Racing? Suppose I am flight simming, quit, go have dinner, come back and want to
    race. Do I have to flip a dipswitch / or / just do it in the software. Just want to clarify.
    Thanks,
    Tom
  4. cthiggin

    cthiggin Active Member

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    My Motion Simulator:
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    Speedy,
    I am using a 1.25" spline shaft, 12" long and a spline collar to accept the shaft. Of course this will be centered and the spline shaft will connect to the u-joint, then upper platform.
    My up/down movement is +- 4" - same as crank arm shafts. NOW, I do "not" know if I will need a coil support spring or not - I've seen the platforms with and without the support springs.
    This "was" going to be an upcoming question when I got there. IF so, then I have a contact at a spring manufacturer that can make one based on my needs.
    The total amount of weight, based on my weight 218 lbs. + rSeat1 - monitor, etc. is going to be approximately 350 lbs. I know the motors and gearheads are strong at 117 ft. lbs. torque each, but
    I just don't know if I need one or not.

    ALSO, I'm waiting for you folks to advise if I need to move my "PITCH" motor in from 22" to the 16" like the other two motor/gearheads - so equal spacing is achieved for all three motors?

    Thanks for your continued interest and help.

    Have a blessed one.

    Tom
  5. speedy

    speedy Well-Known Member

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    That's very nice because you're already there :thumbs ... Sure you're going to need a spring to support all the wight needed to be like floating on the u-joint ... and spare the motors torque to tightly and powerfully move that wight ... So overall power coefficient and soft /quiet / fast movements are achieved ...

    IMHO ... leave the back motor distance as is "torque calculations are needed here for this 22" distance " ... as per the rectangular shape of the base with all loads are inside this 3' x 4' dimensions the back motor will acquire more power to pitch the whole load so more distance may be needed ... as @eaorobbie says a sketch drawing is needed !!!

    Or ... reduce that motor distance as you need and make another longer arm higher than the u-joint mounting point behind the back of the seat with longer push road to overcome the higher torque needed in the pitch direction .

    edit : just make sure that the spline collar will accept the 8" heave distance without any conflicts ...
    Good luck buddy :popcorn
    Last edited: Feb 27, 2014
  6. cthiggin

    cthiggin Active Member

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    Untitled-1.jpg Speedy,

    Speedy,
    Thanks. I will "leave" the Pitch Motor at 22" as you suggested.
    I am attaching a "rendering" so all can get a "rough idea" about the finished product. NOT TO SCALE.

    Maybe premature, but is there ANYTHING SPECIAL I need to tell the spring manufacturer when it's time to order?
    Thanks folks.
    Tom
  7. telfel

    telfel Active Member

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    Hi
    In your sketch, I think the roll motors need to inline with your centre pivot,
    Regards Terry
  8. cthiggin

    cthiggin Active Member

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    Hi Terry,
    Yes sir - they will be - again, I'm not an artist or don't know how to do a drawing, dimensionally speaking.

    Both Motor 2 and Motor 3 will be dead center of pivot, directly across from each other - Motor 1 is dead center to u-joint.

    Thanks for asking me on this....LOL - You'll notice "in red" Not to Scale, Reference Only...

    You guys stay with me on this build now - That way we can ALL achieve a really nice working "AC Platform".

    Tom
  9. telfel

    telfel Active Member

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    hi
    try using the free version of Sketchup, its easy to use and great for this sort of stuff.
    22 vs 16 x 4.jpg
  10. cthiggin

    cthiggin Active Member

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    Thanks Terry,
    I will download Sketchup, free version and check it out.
    I use Illustrator and Photoshop, but not a true 3D Drawing Program.

    Speedy likes the idea of keeping the Pitch Motor at back at 22" and the two motors across at 16" (from center of pivot) -

    Just for "my" information - what is your opinion -
    I really trust Speedy, but I can't get my head around "one motor" having a different +- angle . 14.3 for the two side (turn/heave) and 10.3 (pitch/heave).

    Thanks to all for educating me....guys, it's a blessing to have you ALL - Like Rene' says, it truly is a FAMILY here.

    Tom
  11. telfel

    telfel Active Member

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    Hi
    On the platform roll you have two motors push pull, on the pitch only one motor so perhaps thats why Speedy is suggesting the bigger dimension.
    Others may not agree with this, for car racing the greatest g force is in braking so how about mounting the pitch motor at the front, let gravity help with braking effect.
    regards Terry
  12. cthiggin

    cthiggin Active Member

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    Hi again Mr. Terry,
    Now even "me" can get my head around that and Speedys' suggestion (and yours) makes complete sense.

    If I move my PITCH MOTOR from the back placement to the FRONT PLACEMENT - ????
    Since my top platform is 1' longer - SHOULD I keep the distance from center of pivot to 22" - like it was in back - IF I place it at the end, then the distance from pivot would be 34", which is too large and would
    highly reduce my +- up/down movement. OR, better yet, should I mount BUT keep distance from center of pivot at 16", like the turn motors????

    I apologize to all of you who are kindly helping me out. I am not in a position to question your input since I know squat about what I'm asking. I just want to do it right the first time.
    Thanks friends!

    Tom
  13. BlazinH

    BlazinH Well-Known Member

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    Hi again Tom, It’s great that you have been getting some excellent advice and help since my last post. I will have to check out Sketchup myself.

    I think since you are wanting to use heave that you should start with that in mind as it is the most difficult to achieve. I assume you are going to attempt to make your balance point over your u-joint. With the motor setup you intend to use, your two roll motors will be doing almost all the heave if not all. Therefore, all your pitch motor will be doing for heave is to keep the platform level as the roll motors do the work. So we should start by calculating how many ft. lbs. of torque we can get out of the two roll motors. Since your gearboxes are rated at 117 ft. lbs at 1hp, and you are using 1hp motors, we can assume then you will get 117 ft. lbs torque from them although it also depends on the efficiency of your motors. Therefore x2 motors we will have 234 total. But your lever is 4 inches, not 12. So to convert the ft. lbs. to 4 in. lbs we will multiply ft. lbs. by 3. So the total theoretical weight you can lift is 702 lbs. or double your requirements. Just to note if all three motors were to share in the heave equally, the platforms balance point must be equally between the three motors. So you should be able to achieve heave without a spring. However, a spring will still make your heave work much better because the PID control won’t have to work as hard. The more equal the forces required to go up and down, the better it will be.

    With your setup, the mounting point of the pitch actuator is not a big deal. I would try to get the maximum pitch angle possible by mounting it closer to the u-joint. Even at 12 inches from the u-joint, you will be able to move 117 lbs. So when your platform goes forward or backwards, as long as the weight doesn’t go off balance more than 117 lbs one way or the other, it should work okay. At 22 inches it would move 214 lbs. but at the cost of maximum degrees possible. At 12 inches out for pitch, you will get +- 16.8 degrees pitch. Your roll motors at 16 inches do +- 11 degrees total. However in an 11 degrees roll, there will be no room left for the heave to work.

    So the math seems to work for 16 inches out for roll and 12 for pitch. But in the real world, this is one instance where math sometimes fails because not all factors are being considered, i.e. friction and motor efficiency. I would consider moving your roll levers to 12 out also though. This would give you +-15 degrees roll instead of 11. However, then you wouldn’t be able to go off balance over 117 lbs one way or the other for roll also. I don’t think this will be an issue though because 15 degrees will not off balance that much.

    Ps Anyone please feel free to check my math. I sometimes make mistakes!
    Last edited: Feb 28, 2014
  14. cthiggin

    cthiggin Active Member

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    22 vs 16 x 4[2].jpg BlazinH,
    Hey friend,
    Missed you today....Wow, what a dissertation AND you expect me to absorb all that, further more get my head around it???? Go figure.
    Thank you so much for the continuing education - I don't know why I waited so long to get this build started - guess fear of the unknown.....

    OK - Terry furnished the above chart in reply #49, above...

    If you'll be so kind as to humor me below, in making some observations and statements - and please affirm or correct me - please!

    ASSUMPTIONS:
    1. My motors and gearheads are very very strong and will lift a combined 702 lbs. , twice of the weight I will be carrying on the top platform - AT 100% motor/gearhead efficiency.
    2. Based on the 3' x 4' bottom platform (really not much room) - I have my mindset of having the two tilt motors and 1 pitch motor setting at 16" from c/l of u-joint - this would give me a +- 14.3 degrees - (identical on all 3) - again, based on Terry's chart.
    WHY: My gearheads are 10" long and motors are 12" long - so for each gear & motor, I'm dealing with 22" length - Again, 16" from centerline, ALL 3 would fit and still leave room
    for the electronics box.
    3. I will need to use a "center coil spring" for assist, due to all three motors not being equally apart and perfectly balanced - AND that it will ease load and PID will not have to work as hard.
    (I will need help on this in the very near future...just need to know what to tell the spring manufacturer)

    NOW, will my assumptions work AND are they acceptable - ???- - based on what I'm dealing with in space containment - AND the fact that through the firmware / and / software, it can be adjusted easily - re: eaorobbie on the previous page of this thread.

    BlazinH (and others) - please stay with me on this - "me" thinks were about there on this Chapter??

    Have a most blessed one.

    Tom
  15. BlazinH

    BlazinH Well-Known Member

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    Okay I did make an error in my math trying to take a shortcut that was an incorrect one for calculating degrees. I get 14 degrees using 4 rise at 16 out when doing it like Terry did but I'll take the sketchup math over mine for now. I was calculating by forming a triangle where Terry's sketchup shows a circle and I don't do this every day. I will have to research some more now to see if and where I am doing something incorrectly. However, we are pretty close to being the same now.
  16. BlazinH

    BlazinH Well-Known Member

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    I'm fairly confident my ft lbs calculations are correct though!
  17. BlazinH

    BlazinH Well-Known Member

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    Also I guess I shouldn't expect you to absorb that after I tried to read it for myself again! I need to correct one mistake I found in the ft lbs calculations when I was talking about 117 lbs one way or the other. I didn't multiply it by 3 to correct for your 4 inch lever so it should be 117 X 3 = 351 lbs. If all that is correct you have plenty of power to do the job.
  18. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    Thats why I build a test unit and physically see what it can do, then change and clean it up with a proper build. Or ya spend months researching something you can test physically in the workshop. This is what I have done for a living for the past 23 years, Fabricator, If you can dream it , I can build it, lol. Mechanically speaking.
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  19. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    I feel with the power you will have Tom the coil spring wont be needed, In 12v operation like Aldoz's unit we found it hampered the motion, as in dampened it badly. Myself design it to suit , IE measure the top parts wieght including driver now that is the wieght you want on the designed spring so it is 1/3 to 1/2 compressed and have it so you can remove it to test. What Aldoz found to work well, but took over 4 months to work out and serveral custom made springs too, in the end he found out it really wasnt needed with the winches and Jrks powering his sim. But once he had it right it was better.
  20. telfel

    telfel Active Member

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    Hi

    If your going with a centred support, have look at the converted hydraulic jack using an air tank, easy to adjust the the weight balance.

    regards Terry
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