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TM TCA Boeing Yoke Roll Axis Sensor Upgrade

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After having acquired my own TCA yoke I decided to investigate the reason for the roll axis issues reported by some of the users. The first thing to check was the roll axis sensor as some of the users were reporting a strange dependency of sensor operation on the external magnetic field (which shouldn't be the case with a properly designed sensor).

So after the disassembly I was very much surprised to see the roll axis sensor to be designed around a single AH49E chip which is a simple "old-style" analog Hall-effect sensor. There is a couple of issues with this solution:

1. AH49E is reacting to a magnetic field strength variation in any direction relative to it's body. When a small round diametral- magnetized magnet is rotated close to it, the field strength change is non-linear in relation to the rotation angle. Which means that the yoke's reaction to roll axis rotation is stronger near the center and becomes weaker close to the rotation extremes. Of course it can be compensated in the sim by choosing a non-linear response curve, but in my opinion having a sensor with a non-linear response and no internal compensation for it is simply not right.

2. The magnet is not too strong, so the output signal swing for a full side-to-side yoke rotation is mush less than a sensor power supply voltage. When the yoke internal calibration is performed, the signal is- well- 'amplified" digitally within a yoke controller to match the controller's reference signal voltage swing (from 0 to full power supply voltage). Unfortunately any "noise" (magnetic or electric) that might be induced to the sensor circuit/ connecting wires (that are quite long) will be amplified as well increasing the roll axis sensitivity to the external interference.

3. As AH49E is sensing any changes in the adjacent magnetic field strength, any external ferromagnet object near the back of the yoke handle will create a disturbance in the roll axis; the same goes for the stability of the internal magnet. In some cases this might require a yoke re-calibration.

My solution to this issue is the replacement of a simple Hall-effect sensor by a different type specifically designed for registering an axis rotation. In my opinion the best DIY option here is AS5600 from AMS. The main features of the chip are:

1. It is reacting to a degree of magnetic field rotation in relation to a chip's upper/ lower cover. The signal is directly proportional to the rotation angle with a very good linearity.

2. AS5600 offers a very simple internal calibration routine which adjusts the sensor's output signal swing (from 0 to power supply voltage) to a full rotational angle required. This means a much better immunity to the external "noise".

3. AS5600 is not sensitive to the magnetic field strength variations so the external ferromagnet objects do not influence the sensor operation. Also there is no need of a periodic yoke re-calibration.

In practical terms the option that I've chosen was to use the ready-made AS5600 board available from Amazon or eBay (also from AliExpress). It has all the external elements needed and the size allows to fit the board into the existing opening in the roll sensor base without the need of any mechanical trimming of either the sensor or the base. The board requires soldering one additional jumper to set the correct power supply voltage. Here is the set of pictures showing the mod. After removing the existing sensor and mounting the new board the new sensor needs to be calibrated internally but it's a very simple procedure not requiring any additional tools.

Having done the mod I'm quite happy with the results. If any of you are interested, I'll be happy to provide the additional details.


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Thanks for the info. It falls along the original post here. Good to know I can order some parts if the magnet fix I'm using stops working. 



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53 minutes ago, Wise87 said:

It falls along the original post here.

Yep; actually your post was one of those triggering my investigation- thanks for that!😀.

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