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Questions on sensing bellcrank position

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ChrisSarnowski:
Hi Kim,

I have some engineering questions for you.

1) What sensor device do you use for bellcrank position? I did a brief search and didn't see any hall effect angular sensors as small as yours and with as few wires (pins).

2) I see you have ball bearings for the bellcrank shaft, which must smooth out any sensor position noise. How come the hall effect sensor is not rigidly assembled into the bellcrank shaft passage way? That must add to noise and inaccuracy.

3) Do you have to calibrate the bellcrank range of motion? (seems like an obvious yes). Do you do that just once at home?

4) What is your sampling rate on bellcrank position?

Thanks
Chris

pmackenzie:
Hi Chris,
    just heading out the flying field, but I can answer all of your questions tonight.

  In regards to question #2, the hall sensor is held in place accurately. Not quite rigidly since we used goop to locate it in the inner tube. :)

  If you look at the pictures Kim posted I can try to explain.

   The bearing caps are bolted to the inner spar sections for the take aparts.
    The outer races of the bearings are a light press into them.
   The crank is mounted to a tubular shaft that runs on the inner races. The tube rotates with the crank and the magnet assembly.
  The bearing caps also have a smaller ID support in the centre. This holds the aluminum tube that has the Hall sensor located inside it.
  When you install the hall sensor in to the tube it has to be aligned vertically with the magnets and also rotated so that neutral bellcrank is also "zero" for the sensor.

  The software can be adjusted to correct for things being out a bit , but for best dynamic range you want neutral to be as close as possible.
  The Vertical position and neutral can both be easily set "live" by looking at servo throws and a neutral LED on the controller.
   Vertical position is not too critical, the "sweet spot" is fairly large since the sensor is much smaller in diameter than the magnets.
 
  If that doesn't explain it well enough I can try to do up a drawing.

  It might have been simpler to make the sensor rotate with the crank and have the magnets fixed, but then the wires would be subjected to constant flexing.

Pat MacKenzie

MikeCoulombe:
Good info Pat

Why not have the sensor assembly tube attached to a slotted adjustable plate on the top of the wing?

I do have a question, may have been asked before but, if you loose line tension, does the bell-crank return to neutral?

Mike

Kim Doherty:

--- Quote from: MikeCoulombe on September 01, 2013, 09:20:08 AM ---Good info Pat

Why not have the sensor assembly tube attached to a slotted adjustable plate on the top of the wing?

I do have a question, may have been asked before but, if you loose line tension, does the bell-crank return to neutral?

Mike

--- End quote ---

Mike,

The components we used were what was handy, what could be repurposed and what could be machined in time. We simply needed to see if this concept would work and it did. Next time we can take more time and make it more elegant. There is no access to the top of the wing. It is firmly glued into the fuselage. The stem was adjusted by rotating the magnet block.

We had a rudimentary form of return spring (small foam pads) to keep the bell crank from being hard over and staying there. As yet we have not decided on how to do this as we go forward. I'm thinking of trying some 1/4 flat rubber.

Kim.

MikeCoulombe:
Okay, so it works where to now?

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