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DIY 2DOF with Traction Loss to come.

Discussion in 'DIY Motion Simulator Projects' started by p00ky, May 7, 2020.

?

How foolish am I?

  1. Very

    0 vote(s)
    0.0%
  2. Beyond measure.

    0 vote(s)
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  1. yellofella

    yellofella Member

    Joined:
    Aug 8, 2011
    Messages:
    56
    Occupation:
    builder
    Location:
    UK
    Balance:
    270Coins
    Ratings:
    +29 / 0 / -0
    My Motion Simulator:
    3DOF, SimforceGT
    Hi @p00ky
    Here is a few answers to some of your questions and a couple of pointers/advice for you.
    Ok so you mentioned that the motors were turning off when they reach the clipping point. This is most certainly the SMC3 disabling the motors when they reach the motor off value in the code. ( motor off value is slightly before potentiometer max/min value and used to stop mechanical damage to the sim rig) Try to use less motor angle by clipping it in the SMC3 software
    You mentioned that one of the pins on the Arduino uno has blown. My advice would be to get a new Arduino and set the blown pin one aside for other projects as you don't know what other damage has been done inside it. It controls a mechanical device that could harm the user if not controlled properly, not worth the risk for a few pounds imho.
    Now the advice.
    The potentiometers and wire that you are using are surely going to give you problems down the line so ill mention it now to save you some agro/frustration later. The cheap pots will give you proof of concept and are ok to setup with but realistically you wont have a good sim with them. My advice would be to use some high end hall sensor pots from bourns ect. They are about £20 each but are well worth it. The cheap pots you are using are very noisy as the wiper moves inside it where as the hall sensor pots are contactless so therefore noise less.
    They will wear quickly on a sim rig and the noise spikes will get worse and that's if you don't break the end stops first. Hall sensor pots don't have mechanical end stops so cant be damaged in the same way, my advice is invest some money into getting them.
    You will need to use shielded cable to connect the pots otherwise you will get loads of emi energy from the motor coupling to the pot wires causing loads of noise on the analog sensor leading to vibrations on your sim. I suggest to get an unused usb cable and cut the ends off to use the wire. Connect the outer shielding of the cable to ground at the Arduino end only to avoid ground loops.
    Back to the frame. Id leave it as it is if the welds appear strong enough for now as you will probably be changing/adjusting things as your sim develops and your sim building knowledge/experience grows. Ive had 3 revisions of my frame now due to upgraded parts and modifications that ive made and this will probably be the same for you so you could sort any suspect welds then. If you keep going back and changing things you will never go forward in the project. At the stage you are at with the build things like tidy wiring, good welding and appearance are not important. Focus on safety and getting a working sim then all the other bits are part of the r&d.
    If you got any questions then tap me up as im always happy to help a fellow uk sim racer and remember be proud of what you have created buddy.
  2. p00ky

    p00ky Member

    Joined:
    May 4, 2020
    Messages:
    42
    Occupation:
    Self Employed Laser Cutter
    Location:
    Wales
    Balance:
    70Coins
    Ratings:
    +17 / 0 / -0
    My Motion Simulator:
    2DOF, Arduino
    Hi thanks for that wedge of advice :) Certainly hall Effect pots will becoming & I did replace the arduino. A kill switch would be a good idea & i'll defintely try the sheilded USB cable for the pots, as there is a little jitter there :D Right now however I'm trying to work out my design flaw and I think I've found it. I think I missunderstood how the crank angle effected the available torque & as it stands I think I have loads of torque going up (and at the top of the swing) but very little at the bottom, Im about to move the rod mount position by a small amount, which should at least get me closer to where I need to be. I'll post some SMC3 util pics soon enough and then evryone can have a good laugh at my trouble :D
  3. yellofella

    yellofella Member

    Joined:
    Aug 8, 2011
    Messages:
    56
    Occupation:
    builder
    Location:
    UK
    Balance:
    270Coins
    Ratings:
    +29 / 0 / -0
    My Motion Simulator:
    3DOF, SimforceGT
    Hi buddy
    Not sure I completely understand your problem reading the description that you posted but ill try to help if I can. Posting some pics of the problem or a quick video might help.
    Firstly buddy no one on this site will have a good laugh at your trouble. Were a community here and try to help where we can. We all started somewhere and have made most of the same mistakes that you will make along your sim building journey and only offer help and advice.
    Ok back to your sim. When you refer to crank arms we on this site tend to refer to them as lever arms. The connecting rods are the piece between the lever arm and the frame. Looking at your pics I see the lever arms are not in the right place which may be your problem. The leaver arm needs to be as near to 90 degrees as possible to the connecting rod when the motors are in the centre position as this should give you even torque each way.
    Hope this helps
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  4. p00ky

    p00ky Member

    Joined:
    May 4, 2020
    Messages:
    42
    Occupation:
    Self Employed Laser Cutter
    Location:
    Wales
    Balance:
    70Coins
    Ratings:
    +17 / 0 / -0
    My Motion Simulator:
    2DOF, Arduino
    Ah yes, Lever Arms :) & yes after a long day of messing, grinding things off & rewelding them into a better position I've managed to cure at least some of my afflictions. You got it in one. When I first started the build I knew the Lever arm to push rod angle should be 90 but along the way I decided that the CTC Rest Angle should be at 45 degrees :/ One half of the brain didn't know what the other half was up to I guess. I then welded the bar that the Push Rod connects too slightly away from where it was suppose to be ( I put that down to to much haste at the end of a long day when I was first welding stuff together. So yes, yesterday I kind of realized what I had done & when I pumped the figures into SimCalc it turns out that at the end of the stroke I only had about 20Nm of pitch/roll torque. Now I must admit I'm a little lost on the whole Newton Metres, I get what they are but how many is enough is lost on me :D Anyways, I figured out where the bar should have been welded & corrected the Lever to Push Rod Angle in SimCalc & it jumped upto 138Nm for Pitch torque and 114Nm for Roll torque. Now again, I don't know how great that is over all but it's a lot better than 20 & Im only a small chap of about 9 stone.

    With all of that done it's made a huge difference. Before I couldn't set the Clip Input to anything, as if the motor hit it, it would stall at the bottem of the Levers swing. Not turn off but become unresponsive. Now I can set it and it does what it's suppose too which is nice. I'll do a post of SMCUtil at somepoint as I still get some weirdness there. Kp is lower than 300 Ki can't be set above 1 with out mad osscilations, Kd doesn't seem to have any effect and nor does Ks but that's for another day.

    One quick question though. If my rig is powered up before I open SMCUtil, it will jump around the room for a while even if it's in the Home position (as in dead centre and level). Is that normal? If I remember to wait and only power it up after SMCUtil has started, no bouncing at all. No such effect with SimTools itself.

    Oh and another quick mention, more for the general build post than anything to comment on. My neighbour let me borrow a second battery so I could try running the rig at 24v and it would just osscilate badly all the time. There didn't seem to be any chance of tuning it out. 12v just seems to work much better.
  5. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

    Joined:
    Jul 13, 2014
    Messages:
    14,681
    Occupation:
    Innovative tech specialist for NGOs
    Location:
    St Helens, Tasmania, Australia
    Balance:
    108,555Coins
    Ratings:
    +8,879 / 43 / -2
    My Motion Simulator:
    3DOF, DC motor, JRK
    Disregarding mechanical loss, to know what Newtons it will take to move something it will be Mass (kg) x Acceleration (m/s) = F (N). So to move 100kg at 0.7 m/s needs 70 N. It takes 9.8N per kg to counteract gravity. Keep in mind there is significant mechanical loss in things like the gearbox, depending on the ratio you may want to allow between 10% to 50% loss for worm gears and the greater the gear ratio the higher the % loss is: http://www.meadinfo.org/2008/11/gear-efficiency-spur-helical-bevel-worm.html

    Here is a lay person guide to PID tuning, hopefully it can help you regarding some foundational understanding, rather than just enter random numbers: https://www.xsimulator.net/community/faq/a-laymans-analogy-guide-to-pids-pid-tuning.219/
  6. p00ky

    p00ky Member

    Joined:
    May 4, 2020
    Messages:
    42
    Occupation:
    Self Employed Laser Cutter
    Location:
    Wales
    Balance:
    70Coins
    Ratings:
    +17 / 0 / -0
    My Motion Simulator:
    2DOF, Arduino

    Thanks noorbeast. I did find you making the coment about newtons last night some where else on the site. I guess it's one of those... "If I had a penny for everytime some one said they don't understand Newtons" :)

    As for the PID, I shall take a look. I have tried to get my head round them in the past but the knowledge never stays with me sadly.

    Anyways, thanks for your help.
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