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Hall Sensors - Alternate mount - On the flange

Discussion in 'DIY Motion Simulator Projects' started by shannonb1, Feb 21, 2017.

  1. shannonb1

    shannonb1 Well-Known Member

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    Has anyone tried mounting their POT/Hall sensors on the actual pivot joint? Since converting from steal to 8020 I noticed that my flange joint, or rather my drive shaft conversion had plenty of space to drill a hole and mount the Hall sensor. You would need to drill a center hold in the u joint but this could be easily machine or you woudl weld on a piece of round tube with a guide hole in the side to lock it.

    My thought was that this would clean up the motor area even more.

    If you were to mount the stabilizer on the plate that corresponds with the pivot you could essentially make a triangle with a mount for the sensor.

    Im going to mock it up but I think I can print a mount. Ill share an image in a few minutes to this thread.

    shoot holes in my idea.
  2. shannonb1

    shannonb1 Well-Known Member

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    ok quick sketch, dont judge me....the red triangles would be 3d printed mounts....my UV Joint has a 4x4 plate this would mount to. The triangle point is where there would be a hole mount and then you would need to either drill a hole in the u joint or mount an adapter to slide it in similar to the joints we use now but attached generally to the motor.

    upload_2017-2-21_14-53-3.png
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  3. shannonb1

    shannonb1 Well-Known Member

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    Basic concept
    upload_2017-2-21_15-0-44.png
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  4. bruce stephen

    bruce stephen Hammer doesnt fix it, must be electrical

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    It would have to be a short pot i.e. 90degrees or less I'm guessing.
  5. shannonb1

    shannonb1 Well-Known Member

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    or a high res 360 hall
  6. Tim McGuire

    Tim McGuire "Forever a work in progress"

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    Theoretically there's no reason you couldn't do this, you might end up needing to do some math to back-calculate motor position from pitch/roll angle. You'd also need to know exactly how much roll/pitch travel you have available to use, and exactly how the geometry of your motors/pivot placement affects this.

    I've been developing a calculator application for sim building that does just this, and believe me, the math/geometry is actually a lot uglier than it feels like it should be :confused:
  7. SilentChill

    SilentChill Problem Maker

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    Good idea @shannonb1 it would work fine, you could easily just set it up with SMC3 set your limits and then do the same in Simtools no need for complicated maths, its just rotation at the end of the day and limits of your motor arms
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  8. Tim McGuire

    Tim McGuire "Forever a work in progress"

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    Right, I guess you could say that you don't necessarily need to know exactly how much travel you have if you're going to set it manually, but you'd definitely have to be sure not to have the motors trying to drive past +/- 90 degrees in either direction, which could happen if your sensor limit is set too high. You'd also have to program in some scaling factor for pitch vs roll, since usually the ratios of motor angle vs pitch angle and motor angle vs roll angle are not the same.
  9. SilentChill

    SilentChill Problem Maker

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    Very true, motors move opposite to each other for Roll I didn't think of that so we would control motors by DOF rather than individual axis hmmmm Easy to control for one DOF but not the other.
  10. shannonb1

    shannonb1 Well-Known Member

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    Have you built a sim and used the software before? I don't see anything you called out as relevant to the solution but Im trying to see if Im not getting what you are saying. The scaling is done in the JRK software/Simtools, not an issue. The pivot goes to a max and min in 2 directions and this is calibrated in the JRK software.
  11. Tim McGuire

    Tim McGuire "Forever a work in progress"

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    Right, sorry, I'm not the best at explaining these things. The max/min motor position would be a potential problem because the JRK no longer "knows" where your motors are. If you set your max/min pitch angle (from the pivot point), the feedback loop in the JRK should still do its thing, but if your desired max position is larger than the maximum travel that your sim can achieve, the loop would become unstable (the JRK is telling the motors to drive the sim to a position that they physically cannot, so they'll just keep on spinning). This wouldn't be too hard to overcome, as long as you set your limits properly like you said.

    The other thing is that (correct me if I'm wrong, I don't use JRKs) since you have one JRK controlling each motor, how exactly are you going to feed both of the sensor position/feedback signals into one JRK? Since in most cases we have both motors contributing to both pitch and roll (ie. moving only the left motor does not move the sim in only the pitch or only the roll direction, it's a mix of both), so unless you have the motors mounted such that only motor 1 contributes to pitch, and only motor 2 contributes to roll, you'd need to do some trickery in between the pot and the JRK to combine both feedback signals into a single one that could be fed into the JRK.
  12. shannonb1

    shannonb1 Well-Known Member

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    I dont think you get it.

    THe Hall sensor is still connected to the JRK. The idea is simply moving the sensor from teh motor arm to the pivot shaft on the rig.
  13. Tim McGuire

    Tim McGuire "Forever a work in progress"

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    Right, I understand that part, but which hall sensor will feed into which JRK? From the setup above, it looks like you have one hall sensor for pitch rotation, and one hall sensor for roll rotation. Unless you're using one motor for pitch only and one motor for roll only I don't see how you're going to set up the feedback circuit.
  14. shannonb1

    shannonb1 Well-Known Member

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    THere are 2 jrks and there are 2 hall sensors.
  15. shannonb1

    shannonb1 Well-Known Member

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    You understand the idea that essentially a drive shaft only pivots in 2 directions right? z and x axis. Therefore you measure distance +/- on the x axis and the same on the z axis.
  16. Tim McGuire

    Tim McGuire "Forever a work in progress"

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    Right, but you're not going to be getting the correct feedback if you just plug each sensor into 1 JRK.

    So if you have two sensors, one mounted on the pitch axis of the sim, and one mounted on the roll axis, and you hook them up like this:

    "Pitch Sensor" ------------> Left Motor
    "Roll Sensor" ------------> Right Motor

    When Simtools sends data to your JRKs telling them to "pitch the sim forward" the only your left motor will move, since it's the only one hooked up to the pitch sensor. Vice versa will happen if you tell it to roll. This will essentially result in your whole pitch/roll axis being rotated clockwise/counterclockwise by 45 degrees.
  17. BlazinH

    BlazinH Well-Known Member

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    The issue making this work with your current setup is you are using two motors that output the same dof’s at the same time. So unless the feedback is directly proportional to each motor, the controllers wont be able to tell what motor is producing what part of the movement. If two of the exact same motors always moved in sync with each other then this would not be an issue but that is never the case.

    If you want to try it anyway though an easy and effective way to mount hall pots is to simply epoxy a ¼” shaft collar to the end of the shaft (or pivot). If use of only one doesn't extend out far enough you can epoxy two or possibly more together.

    shaft collar.jpg
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  18. Tim McGuire

    Tim McGuire "Forever a work in progress"

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    @BlazinH Thank you, that's a much better explanation haha.

    Theoretically, if you had a stage in between to decode the different pot signals into a set of two motor positions, then you could make it work, but like I said above, the math would be ugly.
  19. speedy

    speedy Well-Known Member

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    Yes it is going to work ...
    theoretically you can pick any moving part and mechanically convert that motion into a rotating pot ...
    That's how some robot arms work ;)
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  20. shannonb1

    shannonb1 Well-Known Member

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    I dont thibk anyone commenting except you gets the concept
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