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Very jittery yaw on my newly built Gremlin

#1
I just finished building a Gremlin. First quad I ever built other than a tiny whoop. I went with the 1106 red bottoms and 20A ESCs.

Everything seems to work for the most part, except it jitters a lot in what appears to be the yaw. Here's a video: https://youtu.be/ibZ86yR6MK4

I think I might have fried the FC with my soldering iron. There were some wires and connectors pre-soldered on it which I had to take off but I was having a hard time with it. I think I held the iron on for too long and heated the whole FC too much. It's my first time soldering haha :rolleyes:

That being said, the accelerometer works just fine in betaflight. Could this be an issue with my settings in betaflight? Has anyone experienced this before?
 

French

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#2
If that’s the first time you’ve ever soldered, congrats on just attempting something so tiny.

I don’t own a gremlin with the femto FC, but I’ve read that yaw twitch is normal if the flight controller isn’t taped down well. You may not have fried anything! Hopefully others here can give some pointers. There is also a 15 page gremlin thread with lots of info - http://forum.flitetest.com/showthread.php?33056-Flitetest-DIY-Gremlins&highlight=Gremlin
 
#3
Thanks French. I'll try putting another piece of double sided tape under the FC and see if that works.

EDIT: Okay I got working! The issue was vibration after all. I loosened the screws on the motors and the jitters went away. The screws kept coming loose though so I put a little piece of electrical tape under each motor to dampen the vibrations and then didn't tighten the screws quite as much. Now it's working just fine!

I'm so glad I didn't have to buy another FC haha
 
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PsyBorg

Fly Angry
Mentor
#4
Yes congratz on working thru this issue. Specially the solder work as that is not the easiest task even for seasoned electronics people.

Gremlins are extremely sensitive to vibrations. The yaw twitch is a sure sign. Double sided foam tape helps but also things to watch for are camera vibrations where it bumps up against the frame. Loose wiring wobbling around and hitting the frame is another cause, and finally the long battery wires swinging free can cause issues. I run the balance connector between the main wires on the battery and give them a twist to secure it before I plug it in.
 
#5
Thanks for the help. My VTX is pretty loose so I'll try securing that better too. It's good to know that yaw twitch is a vibration issue.
 

AkimboGlueGuns

Biplane Guy
Mentor
#6
I'm having the same problem. I'm going to try trouble shooting tomorrow when I have a more experienced quad pilot at hand to help. I'll report back with any findings/fixes.
 
#7
So I got the jitters to go away... when flying indoors. I put some double sided tape under the motors to dampen the vibrations and hot glued the VTX so that it wouldn't be so loose.

The weird problem is when I take it outside it still jitters. Take it back inside... it works again. The only thing I can think of is that the cold must be affecting it somehow. The temp outside is low to mid 40s F. Does cold usually mess with accelerometers? Or maybe the cold is affecting the rigidity of the quad and making the vibrations worse? Seems like a longshot :/

Lowering my PIDs like PsyBorg suggesting in another thread seemed like it helped a little bit but I might be imagining it. I'll play with the PIDs more after work and see how that goes.
 

PsyBorg

Fly Angry
Mentor
#8
Actually that was the wrong way to go. As all this is a learning process (as you are finding now) I was mainly a KISS user. The Gremlin was my first time in Beta Flight. Most older control software's were very short in their effective range. Beta Flight scaled theirs differently and it has a HUGE range where a quad will fly.

Where older software would allow effective changes from 3 (30) to 5 (50) depending how the scaling was done Beta flight can fly between 30 and 100 plus on some quads to get the performance needed. Very light settings are effective in doors with no wind or out doors for speed and very loose freestyle. To be accurate pids will go up in value and will need to be matched to each build to get it to fly good.

What I originally thought was good in low range was actually very sloppy for targeted flight like the small gates I am working with now.

Finding rates you are happy with should be the first thing you do on the stock set up for the Gremlin as it has a short wheel base and needs a lot less to move around then you would think for very precise control. I have not posted my newest settings yet as I am still fighting weather for time outside to refine them.

Here is the current set up for gate runs in the video below. Note everything seems to be in increments of 5 which is how I work into things then refine tighter once I find a limit. Pay attention as well to your min throttle. I find the Gremlin to be lacking in low end power when coming out of a loop or trying to fly in ground effect with any form of stability. I am running mine I think now at least 30 points above min throttle where in set up you get them to spin smoothly.

Also keep in mind I am flying on 3s with an all up weight of 147g

gremgatepids_small.jpg


You seem to be focused on full size quad "soft mounting" techniques. While that may help with jello it is not curing the yaw twitch issue. The yaw twitch is a vibration where something is hitting the frame (just like if you were flicking it with a fingernail). Which means it can be a loose camera or antenna hitting the frame, a wire from your vtx or receiver hanging down and bouncing on the flight controller or the balance plug on the battery flopping around and striking the main power connector. Its a one shot random thing that causes the twitch each time contact is made.
 
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#9
Thanks for all the help Psy. I'm still just baffled at this point though. I've hot glued the FC, VTX, and Rx so that nothing moves and I've wrapped the loose battery wires - including the balance connector - in the rubber band for the battery. The ESCs are held down with electrical tape. Still, it flies perfectly inside but jitters outside. I think it must be possessed!
 

French

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#10
What’s your I gain (middle numbers for PIDs) and how windy is it outside?

I gain will let the quad compensate for external forces, like wind. It may be low.
 

PsyBorg

Fly Angry
Mentor
#11
Using foam tape to shock mount the FC and then hot gluing it tight again defeats the purpose.

Instead of all this back and forth post up some pics for various angles and video as well as a screen shot of your pids and rates like I did please. I want to see the video so we can determine what the conditions we are fighting look like. The yaw twitch is pretty obvious but inside or outside should not be effecting it so I think we are talking two separate issues.
 
#12
Yeah I glued down the FC because someone else on YouTube had a similar issue and that worked for them. https://www.youtube.com/watch?v=sCLuLCvlvFE

Through all my testing the only thing that really seemed to have an effect was loosening the screws on the motor. I had some thicker foam left over that FT sent me with my stuff (A black piece with some adhesive on one side - TJ didn't use it in the build video as far as I could tell so I'm not sure what it was supposed to be for). I cut that into squares and put it under each motor. Now it works, even outside!

This still seems weird to me though so I'll try to get some better pictures and video. Unfortunately it's dark by the time I get home from work so it'll probably have to wait until the weekend. There's lamp outside that I've been flying around but I don't think it's bright enough to get good video.

That being said, there's almost no wind in the spot that I'm testing in. It's a pretty small, enclosed space with the building on one side and trees on the other sides. We'll have to see how it performs when I take it to a larger space.

Anyway I'll try to get back with some better pictures and video this weekend. My friend's Gremlin that we just built does the same thing to a lesser extent so I'll try to get a video of his.
 
#14
It's been a while since I updated this, sorry. I've been flying my Gremlin with no issues ever since I put that foam under the motors so I've pretty much stopped investigating this. In case you're still curious: I'm running Multishot. I might switch over to Dshot soon if I feel motivated so that I can get turtle mode and use my motors as beepers. Does Dshot sometimes cause issues like this?