Align T-Rex 500 with flight controller Matek H743 Wing V3, and Hall effect RPM sensor Graupner.
Immediately after takeoff, two noticeable drops in main rotor rpm occurred, followed by immediate landing.
I would like to analyze the flight log, which I’ve attached, to understand the cause of these drops in rpm, but I’m unable to. Can someone please help me?
Thank you.
Today I wanted to take a flight, and during takeoff I had the same problem with the engine rpm dropping. Looking at the flight log, I noticed that the RPMs were very high at times.
I’m attaching the flight log: https://drive.google.com/file/d/1LiWwajFMiOEzu-GFZf31F6SvdKQ-elh0/view?usp=drive_link
@Ferrosan che ne pensi?
Thank you
Ciao Walter,
Da quello che vedo hai vibrazioni su y elevate, il che mi fa pensare a qualche problema elettrico e/o meccanico tra sensore e board.
farei un check su:
1)cablaggio e relativa connessione alla board
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From what I can see you have high vibrations on Y, I can see a relation between vibes and rpm reading going off rails.
I would check:
wiring and connection to the board.
secure mechanical attachment of the sensor to the helicopter frame
Ciao, ho controllato il fissaggio sia del sensore (incollato ed avvitato al frame) sia della Fc al frame ed eventuali giochi nella maccanica: tutto regolare. Ho controllato il cablaggio sensore/FC: ok. Ho deciso di sostituire il sensore. Potrebbe essere che le vibrazioni sull’asse y non siano la causa, ma la conseguenza di un errato funzionamento del sensore?
Hi, I checked the attachment of both the sensor (glued and screwed to the frame) and the FC to the frame, and for any play in the mechanics: everything is fine. I checked the sensor/FC wiring: OK. I’ve decided to replace the sensor. Could it be that the vibrations on the Y-axis aren’t the cause, but rather the result of the sensor malfunctioning?
Rapid changes in commanded motor torque could increase vibrations though I would expect to see tail wagging if that was the case. I have had issue with overly aggressive governor tune causing tail wagging though that heli vibrates a lot in all axis 
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Hi Walter, I don’t think this is the case. In the first flight log you shared vibrations were already on the high end and the sensor malfunctioning only appeared later in the flight.
Hi Ferruccio,
I replaced the RPM sensor, but the result remains the same: constant variations in engine RPM. I’ve checked all the mechanical parts and can’t find anything loose. All the wiring also seems fine. I don’t understand what could have happened; until last Saturday, it was running great.
I’m attaching today’s flight log: https://drive.google.com/file/d/1P_X3I4tBmX3Msr2KDUXQFVSRoAMaQxd1/view?usp=drive_link
What can I do?
Thanks
Could be as simple as that.
If you haven’t already done so, I would check continuity on your signal wires with a multimeter.
If you can get your hands on one, maybe with an old analog unit so that it’s easier to see any quick intermittent connection when you move the wires around.
Sorry to hear that. Little difficult to debug further without hands on. At this point I would suggest to try and connect and configure the rpm sensor to another pin of the FC- this way we can rule out soldering issues on fc pcb. Also, for now, set RSC MODE to 3 (throttle curve) .
I don’t know why the previous message wasn’t published. Thanks to the diagnosis from Ferruccio, we found the problem. A bad contact, which resulted in a power interruption to the servo controls, was causing the rpm to drop. I reset all the contacts, and today I tested it, and everything works perfectly.
Thanks Ferruccio
