Newbie with Gremlin problems

Flyer70

New member
New to the forum here and this is my 1st post. I have quite a few drones sizes from 220 mm down to tiny whoops. My eyes are getting worse so I decided to get a Josh Gremlin and let FT build it for me. It arrived early this week and looked amazing. I hovered in my house and did some LOS in the back yard, I dumped it a couple times in the grass but no hard crashes. It has developed a couple of issues. It drifts back and right at a pretty fast rate. It also will spin the motors up to a higher rpm after I land. It will not go back down to my 1040 rpm idle rate unless I disarm it and re-arm. I can hover for a little bit and land, then the motors will start to spin faster all on its own before I disarm it.

After reading many other posts I thought maybe vibration in one of my ESCs was causing my drift issue. I started with #3 ESC and wrapped electrical tape around the frame to tighten it up, the double sided tape that was installed looked a little loose. Just taping up #3 ESC seemed to stop most of the rearward drift, it still pulls to the right pretty hard. Of course I tried tape on the rest of the ESCs but it still drifts to the right.

Here is everything else I have tried:

Moved the Spektrum diversity receiver off the FC and applied double sided tape between them...
Motors are calibrated, bolts tight and spin freely...
FC has current firmware, running stock PIDs...
Accelerometer calibrates fine and reacts to my manual movement of the quad in betaflight (drift goes away when flying in Acro but comes back when accelerometer is in use)...
ESCs have current firmware and are now double sided sticky taped and also wrapped in electrical tape...
My DX8G2 is set to 1500 centers, 1000 low, 2000 high, trims centered...

I have probably tried other things as well but are too many to remember. I keep leaning towards a bad accelerometer but it seems fine with manual movements in betaflight. I can't believe the FC can't take more than a couple dumps in the grass before the accelerometer goes out.

I am hoping someone else has had and fixed similar issues. I haven't even flown this more than an hour and am disappointed so far. All comments are welcome.

Steve
 

PsyBorg

Wake up! Time to fly!
To me the Accelerometers on the Femto don't seem to be the best. It seems to be highly susceptible to the drift you are experiencing. With the Gremlins being such a short wheel base the FC HAS to be nearly perfectly squared up and levl with the bottom plate. Mine sits a tad cockeyed but I know when I boot it up to hold a slight tilt to it if I want to fly in assisted mode which is VERY rare.

One of the things you should look at is how much your channels flutter when sitting perfectly neutral. Specially on analog gimbals. Your centers should be set to 1500 + or - 2 at the most. If the numbers are bouncing further then that you will need to add in some dead band compensation and that will help with drift and twisting issues. If you have twitching specially on the yaw axis look for things bouncing on the frame. Mainly the camera and the wires I cured mine early on by using motor case foam as a tilt and vibration pad under the camera and a piece of double sided tape between the camera and the frame.

I make it a point to calibrate my accelerometers thru the gui before I go out to fly. If you happen to crash in the field they can go goofy again easily. Set it as level as possible and use the stick commands to re-calibrate them. this has to be done in a disarmed state. The three profiles really come in handy for tuning and once that is done for various flight conditions like a more windy day or freestyle tune vs a race tune.

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