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(Ask)Things to consider to build 2DOF

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by DonCorleonez, Mar 21, 2014.

  1. DonCorleonez

    DonCorleonez Member

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    Hi,

    This is my first post here, after wandering around this great forum, i'm planning to build my own motion platform. From my browse thru this forum i find some great design and system, i have few question regarding building this platform :
    1. What to look in wiper motor specification for 2DOF simulator (how much V, Amp, or nM)? (because i want to look for in car scrap yard)
    2. What is differences of :
    - Putting the motor in front, below seat, or slightly in the back of the seat?(because i see some of the design in here have different positioning of motor)
    - Use of connecting rod, shorter rod (connect to platform) or longer rod (connect to shoulder level in seat)
    Whether there will be different configuration of motor setting, driver setting, or axis setting from above two aspect?

    Thanks in advance
  2. Ads Master

    Ads Master

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  3. bsft

    bsft

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    wiper motor, must earth isolate and large passenger car is good, 12v.
    Or something like these http://www.motiondynamics.com.au/worm-drive-motor-12v-24v-200w-180-rpm-20nm-torque.html or ebay substitute
    Control boards http://www.pololu.com/catalog/product/1393 , one per motor.
    Motor placement depends on your height and weight, space you actually have to place the sim.
    Best is shoulder mount seat mover at rear, but other setups will work. Best sketch something up, or dig through the threads and get some ideas on design.
    Cheers, David.
  4. Historiker

    Historiker Dramamine Adict Staff Member Moderator Gold Contributor

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    Hi Don (or should I say GodFather?) :)

    It might be easier to ask what is your budget? You can go expensive and get some very good equipment or go as thrifty as possible and get lessor quality parts that will still do the job. I assume the mention of the scrap yard indicates the latter budget?

    1. I have not used wiper motors in my sims but I have played around with them in the shop and read many of the projects here that use them. The general consensus is as BSFT mentioned, 12v. You want as beefy a motor as possible, many people are having great luck with large truck wiper motors; the type found on big SUVs and cargo haulers, etc. There are several motor/gearbox combinations to be found on Ebay for a reasonable cost that might be better than wiper motors. Some will point out that output RPM is vital as well, the faster the output RPM the more the sim will rattle your teeth ;) This is very true, but my 10 RPM motors rattle my teeth very well, lol. You can see an example of this in my thread about my 2DoF platform here in the forums. I posted a video yesterday. You might also look into winch motors, pioneered by Eaorobbie several years ago, winch allow you to move heavier loads (pun intended).

    2. The motor placement is key to getting the most out of your sim. Think of a lever and fulcrum from high school physics. The longer the lever/further away from the fulcrum you are the less effort you need to move a load and the larger that load can be.But also the less movement you get in the load.

    cl1lever.gif

    The lever is the connecting rod from the motor and the fulcrum is the pivot under the seat.

    Many people prefer to have the motor placed either behind the seat far enough to have an effective lever with which to lift the load (I need a very effective lever indeed, lol) or far enough forward to accomplish the same thing. This is why you will see motors a foot or more behind the seat with long levers connected to outer shoulder area behind the driver. The more theangle (further back the motor is) the more angle you have on the fulcrum (the pivot under the seat). You will see some shoulder mounts far apart from one another and some closer, the further apart they are from one another the more force they can assert on the fulcrum and move a heavier load (again, like me :) ) side to side (roll). The motors have to pivot not only forward and back but also side to side.

    Eaorobbie has a graphic floating around here someplace that shows a very good placement of the motors in relation to a shoulder mounted setup. It recommends 60 degree mounting for the connecting rods. I used these dimensions myself on the two 2DoF platforms that I have built and it works fantastic.

    Any way you set up your main two Axis they will be doing the same thing, providing tilt either side to side (roll) and forward and backward (pitch) so the mounting method really doesn't matter as long as it gets the job done to your satisfaction.

    Another bit of advice, a cheap method of providing electronics for your project is an Arduino UNO micro controller and Chinese MotoMonster dual driver board, this will provide control of up to two motors. Together they cost about 40.00 (ebay from China) and work great. I and many others here use them with very good results. If you can afford it (100.00 per motor) the JrKs that BSFT mentioned are excellent. Almost plug and play. The Arduino requires you to load a code (only once and then never again) but there are several sources of code here in these forums. The three that I have experience with all work very well indeed. Look for threads by RacingMat, Prilad and RufusDufus. Let me know if you are interested in that path and I will find the links for you.

    Sorry for the wall-o-text, keep asking questions. Everyone has their own opinion of what works best and with so many sources you should be able to figure out what you want.
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    Last edited: Mar 21, 2014
  5. DonCorleonez

    DonCorleonez Member

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    thank you mr bsft and mr historiker
    with your explanation plus information in forum, i almost complete the understanding.

    i have another question, how do you guys calculating centre of gravity?
    and how about use of springs attached to moving platform and base platform?
    for connecting between motor and potentiometer, i have some refferences
    1. (use of lever)
    2. the one like racingmat has
    3. or maybe another suggestion
    what do you think about it?

    i think for start i will use wiper motor, ard uno, and moto driver.


    Sent from my iPad using Tapatalk
  6. bsft

    bsft

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    to work out best centre of gravity, build the top frame with seat and wheel and pedals on it, thats if you go full frame, or just the seat frame, if you go seat mover.
    Sit on it and with the help of someone else, sit the frame on a broom handle and roll back and forth till you find a sweet spot for balance, mark it, and thats your pivot balance point.

    Dont use springs, they will reduce motion and put extra load on the motors. Set the frame up properly with motors connecting as high as you can so you avoid use of springs to help balance or otherwise.

    Feedback on pots, yes Mats will do, you will get about 60 deg turn or so of the pot and a good way to stop it breaking.
    Or you can do this
    2014-03-01 15.51.51.jpg
    2014-03-21 11.39.01.jpg
    Drill a hole in the back of the motor shaft to the size of the pot shaft, now, as you will be using about 160 deg, a single turn pot will do or even better a 360 deg turn single pot or hall effect 360 deg. Why 360 deg continuous? If you make a mistake or the motor lever throws too far, you dont break the pot.
    And you will get better resolution for feedback.
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  7. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    Method above in the video is one of the better ways to mount a pot specially if you going to use the ard , if the motor runs away because the ard has locked up or lost its signal then the pot will never be turned a full 360 deg and break but the resolution on the feedback is low. To increase this resolution which results in a nice motion on the sim you need to use as much as the pot as possible.
    I now use 180 deg hall effect connect in the same method pictured below.
    DSC00208.JPG

    They are directly connect to the shaft of the motor that drives the lever.
    I used heli gear on my winchs with mutiturn pots for even better resolution of the motion.

    But there is a couple of other that can be done to make the sim faster and the motion more aggressive.
    Use less of angle in actual lever movement, most try to use near 180 deg and I only use 90 deg so my sim will reach its max and min twice as quick, plus the motors running at 180-150rpm depending on 14v - 12v power supply, real teeth rattling speed, or to compare a big jump and landing in Dirt3 results in me having to catch my breath again because the seat knocks it out of me on landing. Must remember I don't use a foam, sprung seat, way to heavy for me to use on a sim, I use baja buggy , rota formed plastic seats, less than 3kg with little padding , you feel every little movement nothing dampened in the seat. Ya want motion why dampen it. I love to rattle and roll.

    All things to consider building a sim.

    The CG point that we use is not the exact cg of the sim , but has been found the easiest way to place the pivot in the right place.
    Have you top for you sim free of base with everything on it that you will use and you in it too. Place it on a bit of pipe or something round like a broom stick, now have a mate slide it back and forth over the broom stick till it seems to balance over the pipe/stick.
    Now mark that location and we now have a cg point in one plane, this is the centre that you need to mount the pivot too and of course in the middle of the width but that can depend on whats hanging off the sides , keyboards, button boxes , etc. all change this point. Its all about balance so that the motor works evenly when it shifts the sim up and down , with out it the sim will move one direction faster than the other. Bad motion in game. All things to consider in design and building.
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  8. DonCorleonez

    DonCorleonez Member

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    Thank you guys, such a magnificent support:cheers

    What about height of Sim (motion platform and base platform), how to determine the height is it depend on height of the uni joint or some calculation?

    @bsft about motion dynamic motor, what characteristic that we're looking from motor that you suggest?because I'm afraid that i have to find equivalence of that motor in Indonesia
  9. bsft

    bsft

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