1. Do not share user accounts! Any account that is shared by another person will be blocked and closed. This means: we will close not only the account that is shared, but also the main account of the user who uses another person's account. We have the ability to detect account sharing, so please do not try to cheat the system. This action will take place on 04/18/2023. Read all forum rules.
    Dismiss Notice
  2. For downloading SimTools plugins you need a Download Package. Get it with virtual coins that you receive for forum activity or Buy Download Package - We have a zero Spam tolerance so read our forum rules first.

    Buy Now a Download Plan!
  3. Do not try to cheat our system and do not post an unnecessary amount of useless posts only to earn credits here. We have a zero spam tolerance policy and this will cause a ban of your user account. Otherwise we wish you a pleasant stay here! Read the forum rules
  4. We have a few rules which you need to read and accept before posting anything here! Following these rules will keep the forum clean and your stay pleasant. Do not follow these rules can lead to permanent exclusion from this website: Read the forum rules.
    Are you a company? Read our company rules

Question Simulator Math

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by mprofitt, Aug 26, 2017.

  1. mprofitt

    mprofitt Member

    Joined:
    May 27, 2014
    Messages:
    37
    Balance:
    230Coins
    Ratings:
    +14 / 0 / -0
    I am currently in the planning and design phase of a motion platform build. Using the FAQ, SimCalc, and other resources, I have what I believe is the math required for a successful build. Please provide a sanity check and input on the following math.

    Known Values
    Lever CTC: 200 mm
    Mass: 160 kq

    Newton force required to move specified mass
    Speed of Movement (a): .5 m/s
    Mass (m): 160 kg
    Newton Force Required = ma: 80 = 160 * .5

    Newton force of 80 is required to move 160 kg mass at a speed of .5 m/s

    RPM required for given velocity and CTC lever
    The RPM to Linear Velocity formula is:
    v = r × RPM × 0.10472
    RPM = 23.87 = .5 / .2 / .10472
    Where:
    v: Linear velocity, in m/s
    r: Radius, in meter
    RPM: Angular velocity, in RPM (Rounds per Minute)

    23.87 RPM is required at the motor to produce .5 m/s of movement with a 200mm CTC lever

    Torque required to lift mass with 200 mm CTC lever
    Torque = F(r) = 80 N x 0.2 m = 16 Nm
    Where:
    F: Newton Force
    r: Radius, in meter

    16 Nm of torque is required at the gear box output.

    So the final conclusion as the math shows, I will need 16 Nm of torque at the gear box to lift 160 kg at a speed of .5 m/s. I will add 25% to make it 20 Nm to compensate for system loss. I understand that as the angle changes from the 90 degree position, more force is required. I will probably rerun the calculations with the current angle at 30~45 degrees to ensure proper force at both ends of the cycle. I also ran these number through SimCalc and had very similar results.

    upload_2017-8-26_14-20-3.png

    Any and all input will be greatly appreciated.

    mdp
  2. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

    Joined:
    Jul 13, 2014
    Messages:
    20,461
    Occupation:
    Innovative tech specialist for NGOs
    Location:
    St Helens, Tasmania, Australia
    Balance:
    144,596Coins
    Ratings:
    +10,741 / 52 / -2
    My Motion Simulator:
    3DOF, DC motor, JRK
    A 200mm CTC lever is too long, you trade linear speed at the cost of torque. Most use 40-60mm on high power DC motors.

    It takes 9.8N per kg to counteract gravity.
    • Agree Agree x 1
  3. momoclic

    momoclic Active Member

    Joined:
    Sep 23, 2014
    Messages:
    215
    Occupation:
    Retraité
    Location:
    Nantes - France
    Balance:
    2,761Coins
    Ratings:
    +115 / 1 / -0
    My Motion Simulator:
    DC motor, Arduino
    It is equally important to know for what purpose these calculations are made: 2-3-4-6DOF?
    As the case and the type of mounting the load is distributed ...
    • Agree Agree x 1
  4. Zed

    Zed VR Simming w/Reverb Gold Contributor

    Joined:
    Apr 4, 2017
    Messages:
    1,044
    Location:
    USA
    Balance:
    5,828Coins
    Ratings:
    +1,042 / 4 / -0
    My Motion Simulator:
    2DOF, DC motor, JRK
    Yep, because dead lifting and accelerating a mass by brute force is very different from tipping a mass that is mostly supported by something like a U-joint.
  5. mprofitt

    mprofitt Member

    Joined:
    May 27, 2014
    Messages:
    37
    Balance:
    230Coins
    Ratings:
    +14 / 0 / -0
    noorbeast,

    Thank you for your reply and input. I agree with you the CTC lever is probably way to long. I am just using this length as an example for calculation purposes only.

    My plans are to use 3 phase AC motors.

    I agree I did not account for gravity and should add that to my calculations. Where in the system do I add the 9.8N per kg? Will this be added to the Newton force required to move the mass? ie. At 160kg, in my previous calculation, I have a Newton force of 80. Should the Newton force look like this?

    acceleration = .5m/s
    mass = 160kg
    gravity = 1568 = 160*9.8

    Newton Force Required = g+ma: 1648 = 1568+160 * .5

    If this is the case, the torque required at the motor just went through the roof.
    Last edited: Aug 27, 2017
  6. mprofitt

    mprofitt Member

    Joined:
    May 27, 2014
    Messages:
    37
    Balance:
    230Coins
    Ratings:
    +14 / 0 / -0
    momoclic,

    Thank you for you help. I am planning on a 3DOF style of motion simulator based on a equilateral triangle base with the motor / gearboxes distributed at 120 degrees with the center of mass in the center of the triangle.
  7. mprofitt

    mprofitt Member

    Joined:
    May 27, 2014
    Messages:
    37
    Balance:
    230Coins
    Ratings:
    +14 / 0 / -0
    Zed,

    My initial plans are not to have a center supporting spring with a u-joint. If my calculations prove to require motors and gearboxes out of my budget, I will reconsider the design to incorporate the center supporting spring.
  8. Zed

    Zed VR Simming w/Reverb Gold Contributor

    Joined:
    Apr 4, 2017
    Messages:
    1,044
    Location:
    USA
    Balance:
    5,828Coins
    Ratings:
    +1,042 / 4 / -0
    My Motion Simulator:
    2DOF, DC motor, JRK
    Hey @mprofitt, I wasn't meaning any comment on your sim. I was just expanding on what momoclic was saying. You hadn't even said what you were building I believe. Not until a post after or so.

    I've not done a hard calculation for my rig. Doing more what others have done and what was successful. It was just a general comment.
  9. mprofitt

    mprofitt Member

    Joined:
    May 27, 2014
    Messages:
    37
    Balance:
    230Coins
    Ratings:
    +14 / 0 / -0
    I understand Zed and I appreciate your assistance by asking me all the right questions. I have about a $5000 budget, maybe a little more if needed. So I am hoping to forgo the center support spring with powerful enough motors and gearboxes. This is why I want to be precise on the math so I don't have to buy any more than needed.
    • Like Like x 2
  10. Lodewijk

    Lodewijk Member

    Joined:
    Feb 25, 2012
    Messages:
    32
    Occupation:
    Engineer
    Location:
    South Africa
    Balance:
    597Coins
    Ratings:
    +5 / 0 / -0
    My Motion Simulator:
    4DOF
    Hi mprofitt,

    One problem with your calculation is that you are using a velocity ( speed) of 0.5 m/s in the place of acceleration in Newton's equation. Force (in Newton) is mass (in kg) * acceleration (in metre per second squared, wich I write as m/s^2)

    If you want to accelerate a force of 160 kg at 0.5 m/s^2 you need 80 kg*m/s^2
    kg*m/s^2 is the S.I. Unit for Newton. Put another way, if you apply 80 Newton to 160 kg, you will increase the velocity of that mass by 0.5 m/s every second. If the mass starts of at rest (0m/s) it will have a velocity of 0.5 m/s after 1 second, 1 m/s after 2 seconds, and so on.

    The 9.8 (m/s^2) is the gravitational acceleration of the earth. If you want to keep a 160 kg mass suspended in the air, against the 9.8 m/s^2 gravitational acceleration of the earth, you must apply 160 kg * 9.8 m/s^2 = 1600 Newton or 1.6 kN (kiloNewton) hence @Zed 's comment about lifting vs tipping a mass.

    Your calculation is therefore spot on, if you want to accelerate a mass upwards at 0.5m/s^2, you need approximately 1680 N.

    My planning on my motion simpit is to support everything as close as possible to the combined centre of gravity so that i will mainly be tipping the mass. I've also seen people using bungee chords ant the likes to help lift the mass.

    Sorry for the long winded science lecture, but I hope it helps.
    Last edited: Aug 28, 2017
  11. mprofitt

    mprofitt Member

    Joined:
    May 27, 2014
    Messages:
    37
    Balance:
    230Coins
    Ratings:
    +14 / 0 / -0
    Lodewijk,

    Excellent input and I think I see things more clearly. I am in the process of redoing my calculations using gravitational acceleration. I will post for further input when I complete. I just want to make sure I get this right so I do not buy bigger equipment than need and that everything I buy will perform as calculated. Again, thanks to all for the input.

    mdp
    • Like Like x 2
  12. momoclic

    momoclic Active Member

    Joined:
    Sep 23, 2014
    Messages:
    215
    Occupation:
    Retraité
    Location:
    Nantes - France
    Balance:
    2,761Coins
    Ratings:
    +115 / 1 / -0
    My Motion Simulator:
    DC motor, Arduino
    From my point of view, there is no point in starting acceleration calculation!
    This type of calculation is part of the dynamic. Few of us are able to carry out this type of study given the number of variables ...
    In my reasoning I leave my own requirement and tries to integrate the many experience easy to consult on the WEB.
    These experiments include, among others, that good simulation requires crank rotations between 40 and 80 rpm for the automobile, probably less for the aircraft.It is obvious that with 80 rpm and the couple that goes well we will have better accelerations than at 40 rpm.
    As my system wants to be dynamic I multiply by 1.5 my load, which seems acceptable.
    With this I determine the stroke I require of the connecting rod-crank system
    .Depending on the static load, I determine the torque and calculate the length of the crank arm.
    Starting from the RPM and the race I calculate an average acceleration.

    Note that the worm gear units generally have a yield of only 0.5.
  13. Lodewijk

    Lodewijk Member

    Joined:
    Feb 25, 2012
    Messages:
    32
    Occupation:
    Engineer
    Location:
    South Africa
    Balance:
    597Coins
    Ratings:
    +5 / 0 / -0
    My Motion Simulator:
    4DOF
    On the one hand I agree with @momoclic that imperical "design" is a good starting point. If something has been done hundreds of times and works well, go with that idea.

    On the other hand, I also think its good to have some idea of the forces you're working with. When I get to the detailed design stage with my motion platform, I will definitely want to check forces, member stresses etc, to make sure I'm not under sizing something. There are however a few problems with this, for example:
    • What would be an acceptable rate of acceleration?
    • How much must be allowed for losees due to friction etc?
    • What about dynamic effects, for example, you're platform is moving down, and you want to reverse that movement and accelerate upwards
    • Etc etc
    Still, having some knowledge about the forces, moments, shears, wattages, rpm and budget is probably a good idea :think
  14. momoclic

    momoclic Active Member

    Joined:
    Sep 23, 2014
    Messages:
    215
    Occupation:
    Retraité
    Location:
    Nantes - France
    Balance:
    2,761Coins
    Ratings:
    +115 / 1 / -0
    My Motion Simulator:
    DC motor, Arduino
    Lodewijk is perfectly right!
    What I'm suggesting is that in any project, whatever it is, you have to determine the target first. What is the objective?
    Simulating a simulator is not a target, it's far too blurry.
    -What simulation: auto - airplane - both
    - With which movements
    - With what means (technical, financial, skills)
    - etc.
    Then we analyze what has already been done and choose our own options.
    From this moment on, we move on to the calculations to check if his ambitions are up to our means...
    In fact I was talking about method and pragmatism. ;)
    • Like Like x 1
  15. mprofitt

    mprofitt Member

    Joined:
    May 27, 2014
    Messages:
    37
    Balance:
    230Coins
    Ratings:
    +14 / 0 / -0
    I have not recalculated the math yet but plan to this weekend. In the mean time, I have been working on a SkectchUp drawing of the simulator configuration I have in mind. the motors will be, I am guessing, about 1 HP AC motors. Please provide input.

    Capture.PNG


    [​IMG]
  16. Lodewijk

    Lodewijk Member

    Joined:
    Feb 25, 2012
    Messages:
    32
    Occupation:
    Engineer
    Location:
    South Africa
    Balance:
    597Coins
    Ratings:
    +5 / 0 / -0
    My Motion Simulator:
    4DOF
    @mprofitt will this be flight or racing sim?

    I'm thinking your motors might need to be closer to the centre of the platform (sort of under the seat base), but I must admit, I hav'nt really given these steward platform type systems much thought. I'm thinking more along the lines of a balanced frame type setup which will take a lot less force to move.