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Starting my first 2DOF DIY motion rig

Discussion in 'DIY Motion Simulator Projects' started by Christian Doehl, Nov 2, 2020.

  1. Christian Doehl

    Christian Doehl Member Gold Contributor

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    My Motion Simulator:
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    Hi,

    yesterday tested with another USB Port and direct connection (not via USB-HUB) but without success. I testetd both motors in SMC3 for at least 5 min in motion mode without any trouble (but without load, just the rig) but when switching to AC within the first round left motor switched off during right turn.

    In my feelings its something related to the load. The problems seem to occur just in turns or hitting bumps and when seat is loaded (I'm just about 70kg :think). Again, Arduino, IBT2s and the wiring wasn't changed. Just the Motors and the PSUs???

    It's a bit frustrating at the moment.:confused:
  2. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    If the problem seems to occur just in turns or hitting bumps and when seat is loaded then try setting the Intensity Level in Game Manager to something like 95% and see if that makes a difference.
  3. Christian Doehl

    Christian Doehl Member Gold Contributor

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    It's already set to 70% without making a difference. By the way, I also testetd SMC3 motion mode with loaded seat --> motors turns off. So still SMC3 and SimTools cause the same issue.
  4. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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  5. Christian Doehl

    Christian Doehl Member Gold Contributor

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    I agree, thats likely what happens and yes the rig is balanced. What is different to the "old" setup: the motors are less "breaking", means i can move the lever by hand fairly easy, which was different with the old wiper motors.
    Yesterday it was in a right turn the rig moves to left side and, holds the position to the middle of the turn (feels like close to the limit of movement) and then the left motor stoped and the rig fall completly to the left side.
    I also changed the pots from single turn pots to unlimited turn pots (no hardstop but only 280° electrical effective). The gear is about 51 teeth on motor gear and 34 teeth on pot gear. The lever has roughly 160° movement, therfore I made this ratio to get best resolution from the pot.
    Just guessing now but maybe the less stiff lever (what I called less breaking of motor) leads to little overshoot which is in principle not problem for the pots because they are turnable unlimited, but when they reach their electrical 280° limit the voltage will drop down immediatly.
    This may be testable by using axis limiting to 25% or so, whalt do you think?
  6. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Axis limiting is not what you need.

    Effective use of torque with a lever falls off dramatically at anything over about 38 degrees up and down.
  7. Christian Doehl

    Christian Doehl Member Gold Contributor

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    But with axis limiting I thought I could test if this maybe the rootcause, or am I wrong?
  8. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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  9. Christian Doehl

    Christian Doehl Member Gold Contributor

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    Yeah I know, I'm just thinking if this may show if the pot runs to its limits. In case axis limiting is set to 25% and everything moves correct without the errors I can point the rootcause to be pot limits, then I will redesign the gears and solve it via hardware modification to set axis limiting back to full, axis limiting just for error diagnostics.
  10. Christian Doehl

    Christian Doehl Member Gold Contributor

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    Did some more testing yesterday, no success :(.

    But I think I can add some points to the failure description:

    Without load everything works ok. Motors can move up and down, no pot reaches the limit. Putting load on the seat the motors have to "keep" Zero-position and PWM signal level increases. When I now put additional force on one of the levers (push it down for example) the PWM increases and tries to drive the motor against the force direction (as expected). If this force is high enough (which is the case when seat is loaded and leans to a side, maybe in a turn) there are just few seconds the Arduino tries to work against and then stops the motors, but only if it has to work against higher force, if the force is low it works.
    Stopping is more or less the same behaviour as if the pot signal runs out above MAX LIMITS and switches the motor OFF but pot signal is still within the limits and the Motor is still ON (but effects are the same than MAX LIMITS). I have to restart SMC3 or unplug USB cable to reset the Arduino.
    Motor one keeps the PWM signal high for around 5sec bevor it stops, Motor 2 stays longer, something around 10 to 15secs.

    Im getting frustrated :sos.

    BR
    Chris
  11. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    As per my earlier comment have you ensured the levers don't go more than around 38 degrees up and down?

    Does a smaller CTC distance on the levers help alleviate the problem?
  12. Christian Doehl

    Christian Doehl Member Gold Contributor

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    Actually the levers still go more than 38° but the problem even occurs when lever is in Zero-position and I push down the seat . There is no big movement but in SMC3 you can see PWM signal increasing and when I keep to push the seat motor stops and stays until reset. I don't thinks it is due to lever angle.

    Smaller CTC means less force, maybe an idea.
  13. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    A smaller CTC means more torque to move the mass, less linear speed and less movement range.

    If the levers are exceeding more than 38° up and down then that will only exacerbate the problem.
    • Useful Useful x 1
    Last edited: Feb 19, 2021 at 11:04
  14. Christian Doehl

    Christian Doehl Member Gold Contributor

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    Sounds reasonable, I will modify the levers and test it. I expected the new motors with 240W instead of 60W to be strong enough to drive also the "longer" levers. But if this helps it would be great. Is there any technical reason why PWW signal stops if increased PWM level does not reach the target position within a time? Is this a timeout issue?

    BR
    Chris
  15. Christian Doehl

    Christian Doehl Member Gold Contributor

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    This weekend I modified the levers to realize a shorter CTC, what should I say, it works. Tested with AC on different tracks with different cars. On Nordschleife I have to set a lower Intensity level than on other tracks but thats fine. Now I'm able to drive with motion again, thanks noorbeast for the support.

    There is still the question to the reason. Why does an increasing PWM signal is causing an output shutdown when there is too much load on one side? I think the motor tries to reach a target which is not reacherd due to longer CTC and the load that pushes the motor away from target. For me it seems like a timeout that stops PWM output, is this possible?

    BR
    Chris