Can you solve unknown triangle from shared hypotenuse?

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Discussion Overview

The discussion revolves around the challenge of determining the centrifugal (C) and tangential (T) accelerations from accelerometer readings on a rotating plate, where the accelerometer axes are not perfectly aligned with the C and T directions. Participants explore whether it is possible to extract these values given the constraints of the setup.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if it is possible to solve for C and T, suggesting that the readings from the accelerometer could be used to determine a unique acceleration vector that can then be decomposed into radial and tangential components.
  • Another participant argues that it is impossible to uniquely determine C and T, stating that any pair of C and T can satisfy the conditions if plotted on a semicircle, implying an infinite number of solutions.
  • Some participants discuss the relationship between the accelerometer axes and the radial/tangential directions, raising concerns about the alignment of the axes and suggesting methods to re-orient the plate to improve measurement accuracy.
  • One participant acknowledges that while calculating the magnitude of C and T is straightforward, it leads to a range of possible solutions rather than a unique answer.
  • Another participant expresses appreciation for a suggestion to re-orient the plate to help clarify the alignment issue, indicating a potential path forward for resolving the measurement challenge.

Areas of Agreement / Disagreement

Participants generally disagree on the possibility of uniquely determining C and T from the given setup, with some asserting that it is impossible while others explore potential methods to clarify the measurements.

Contextual Notes

There are limitations regarding the assumptions made about the alignment of the accelerometer axes and the conditions under which the measurements are taken. The discussion does not resolve the mathematical steps needed to fully address the problem.

FGD
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My question comes from an accelerometer attached to a rotating plate. C and T are the centrifugal and tangentinal accelerations. X and Y are the accelerometer x, y axis readings. The x and y axis are not perfectly aligned with the C,T accelerations and are rotated by some arbitrairy unknown angle. I can get the magnitude of x, y which should be the same as C,T. (I think). But then I would like to know the amounts of T and C in each of the x, y axis. With all that said, is there a way to get the values of C, and T? Thanks in advance..
Solve_C_T.jpg
 
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You cannot solve for C and T. If you draw a semicircle with H as the diameter, then any pair of C and T with the right angle vertex on the semicircle will work. So there are an infinite number of C,T pairs that satisfy your condition.
 
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FGD said:
But then I would like to know the amounts of T and C in each of the x, y axis.
With all that said, is there a way to get the values of C, and T?

It seems that the posted diagram and your question are not very well related.

Could you add the x and y readings of the accelerometer to determine one unique acceleration vector, which could then be decomposed into radial and tangential acceleration vectors?
 
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phyzguy said:
You cannot solve for C and T. If you draw a semicircle with H as the diameter, then any pair of C and T with the right angle vertex on the semicircle will work. So there are an infinite number of C,T pairs that satisfy your condition.
Thank you for confirming there is no solution. I was hopeing there would be some way I did not know about to figure this out. :)
 
Lnewqban said:
It seems that the posted diagram and your question are not very well related.

Could you add the x and y readings of the accelerometer to determine one unique acceleration vector, which could then be decomposed into radial and tangential acceleration vectors?
I guess I could have drawn the diagram with the right angle corners together and the hypotenus as the magnitude. I thought drawing it the way I did would be less confusing. Thanks for the advice.
 
Getting (C^2+T^2) is trivial, but then you have an arc of possible solutions...
 
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I think what you are saying is that
neither the x-axis nor the y-axis of the accelerometer is directed radially
(and the other is not directed tangentially).
Is it that the z-axis of the accelerometer is translated from the z-axis of the disk?
Presumably, your plate is horizontal.

Are you allowed to re-orient the plate so that it is vertical but not rotating?
You could manually change the angular displacement of the plate
so that the y-accelerometer reads zero, and the x-accelerometer reads g.
You could then mark up the plate so that you know where the x-axis points.
You could repeat for the y-axis.
 
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robphy said:
I think what you are saying is that
neither the x-axis nor the y-axis of the accelerometer is directed radially
(and the other is not directed tangentially).
Is it that the z-axis of the accelerometer is translated from the z-axis of the disk?
Presumably, your plate is horizontal.

Are you allowed to re-orient the plate so that it is vertical but not rotating?
You could manually change the angular displacement of the plate
so that the y-accelerometer reads zero, and the x-accelerometer reads g.
You could then mark up the plate so that you know where the x-axis points.
You could repeat for the y-axis.
Yes you understood the issue I was having with alignment. Your idea is really good! With that I should be able to tell more or less the exact position and orientation of the x,y axis. Smart idea! Thanks.
 
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