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Thread: New stick, with a car's uni joint and hall effect sensors | Forums

  1. #1
    Senior Member julian265's Avatar
    Join Date
    Dec 2005
    Here it is:

    It's based around a universal joint, part of a prop shaft from a car, $2 hall effect sensors (Allegro A1321EUA-T bought online from Farnell), and some 8mm cubic neodymium magnets for less than $1 off ebay. (And of course Leo Bodnar's BU0836 USB interface, which is mounted in the grey box)

    The automotive uni joint is suited to use in a stick - it's tough, is a pre-made gimbal, uses roller bearings with unnoticeable slack, has a square limit of movement, has a mounting flange, and pole to put a grip on, and it was reasonably easy to attach the sensors. I don't think this will ever wear out!!

    I measured the output from this hall effect sensor/magnet relationship, as fitted to this stick, and as you can see it's damn close to linear:

    Details regarding the use of the universal joint, and the hall effect sensor arrangement which achieved the above output, are written up in this PDF:

    But these pics summarise the essence of the angular sensing method. (hall effect sensor shown in blue, magnet is stationary for this axis, with one pole on the upper right face, and the other on the lower left)

    Pitched forward:

    Pitched backward:

    And the rudder pedals:

    And the rudder pedal's sensor:

    This is same arrangement as used for the stick. The pedal bar pivots on the large bolt and bearing, and the magnet is glued to it's top. The sensor is mounted on the pedal bar, and rotates around the magnet's vertical axis. One pole of the magnet is on it's front right face, the other is on it's rear left face. So in this view, the sensor is parallel to the magnetic field lines flowing around the magnet, and reads centered.

    This sensor/magnet arrangement is not new, it is an adaption of one I saw in a google e-book snippet, which used two magnets, with the sensor positioned between them. It turns out that there's no need for the second magnet, you can just use the field flowing around one of them, and mount it and the sensor on the axis of rotation.

    Edit - changed file hosting

  2. #2
    Senior Member WTE_Galway's Avatar
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    Oct 2002
    good solid engineering ... well done

    makes one wonder whether you could build a practical stick using strain gauges

  3. #3
    Banned ffb's Avatar
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    Feb 2008
    looks ideal ..... so when are you going to market them?

  4. #4
    Senior Member na85's Avatar
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    Feb 2007

  5. #5
    Originally posted by na85:

  6. #6
    Senior Member WTE_Ibis's Avatar
    Join Date
    Dec 2003
    I'll take two please.


  7. #7
    you can just use the field flowing around one of them, and mount it and the sensor on the axis of rotation.
    This is a very important discovery, I think a lot of DIY people will appreciate it!

  8. #8
    "car uni.joint used for bu836 flight stick" - i knew this would eventually happen one day. Thanks for posting, great motivation for my own projects!

  9. #9
    Senior Member K_Freddie's Avatar
    Join Date
    Dec 2006
    Very nice.. An added thought - you might want to add some toe caps and serrated teeth on the rudder pedals - you need these for those 'exciting' moments

    .. as well as sensors on each pedal so they can be used for differential braking.


  10. #10
    Senior Member julian265's Avatar
    Join Date
    Dec 2005
    Thanks for the complements!

    Galway, I guess the simplest method of using them would be one strain gauge on the front, and one on the side of the stick pole. Doing that wouldn't give you any movement, so you'd then need a sprung base (a engine's valve spring might be ideal). It sounds like a good idea, could be very compact, and has no movement around the sensors!

    Rnzoli, I have seen a few pics which might have used this method, but they lacked an explanation of it, and the orientation of the magnet, so I didn't understand it! Either way, it's been about a year since I started reading about hall effect sensing, and it's taken this long for me to to find a method I was truly happy with, albeit with two magnets!

    Freddie, I've had no problems slipping off the pedals so far, my wheeled chair is held near the stick post, and my legs place all their weight on them. I guess some side and top 'fences' wouldn't go astray though, especially to aid in settling my feet on them.

    I was thinking about brakes when I made the pedals, but IL2's lack of use of differential analog braking, and the desire to get flying again put me off including them! (It was hard enough doing the painting, and delaying flight for the sake of aesthetics!!) I'll build them in one day though.

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