Tarot FY650 yaw problem

[MadMonkey]

I'm finally to the point of asking for input

I built a Tarot FY650 a while back and have been chasing a yaw problem ever since.

Motors are Sunnysky X4108S 600KV with APC 12X3.8MR props. ESCs are ZTW Mantis 20A. I'm using 4S 4000/5400 batteries. Controller is a Naza V2.

I've tried every combination of gain settings I can think of to fix this and nothing works.

Pitch and roll are perfectly stable and spot on, no problems at all. At high gains it's very snappy and responsive with no stability problems whatsoever.

Yaw is another story.

When yawning quickly to the left or right (seems worse to the right), the aircraft will tilt sharply, diagonally. If I yaw right, the right front motor will rise briefly abd the aircraft will go unstable for a moment. It'll usually recover fine, but a couple of weeks ago I was doing a sliding pan across the field and it went almost completely out of control but I was able to stabilize before it hit the ground (using atti/GPS only).

Things I've done to fix it...

Balance was first. The gimbal and batteries are both on the same rails and can be slid back and forth for longitudinal balance and the battery can be moved sideways for lateral. I've tried centered, far forward and far aft CGs with little difference.

The measurements for the GPS antenna were double checked and correct.

All motors were re-aligned to make sure they're completely vertical.

I pulled the controller off and put it on my old testbed F450 and it worked flawlessly with Afro ESCs and crappy Turnigy motors, no yaw problems whatsoever.

(ETA: Also recalibrated all the ESCs to no effect).

Since this is the case, I believe this narrows it down to a motor or ESC issue. If anyone has any other ideas before I pull out the Mantis ESCs and replace them with 30A Afros, I'd like to hear them.

I considered a prop change because of the possibility of slow motor response, but with pitch and roll having no problems that doesn't sound like a likely answer.

Thoughts?

 

[Gator]

Have you checked your balance side to side or corner to corner? I used to have a yaw issue with my F550 and found I was heavy to the left rear, my front to rear was dead on. Now I check my balance front to back and corner to corner. (Alot easier with a hex.)

 

[MadMonkey]

Have you checked your balance side to side or corner to corner? I used to have a yaw issue with my F550 and found I was heavy to the left rear, my front to rear was dead on. Now I check my balance front to back and corner to corner. (Alot easier with a hex.)

I didn't try to adjust diagonal balance intentionally, but I had to have affected it with some of the lateral and fore/aft CGs that I tried, with little effect.

I can try again though.

 

[Old Man]

Mad,

I would be looking hard at an ESC on one corner that wasn't synced with the rest or not communicating correctly. If the problem is always one corner, swap ESC locations to see if the issue goes with it.

 

[MadMonkey]

Mad,

I would be looking hard at an ESC on one corner that wasn't synced with the rest or not communicating correctly. If the problem is always one corner, swap ESC locations to see if the issue goes with it.

I think I'll try this before completely changing out the ESCs to the ones I know are good.

I'm guessing it pretty much HAS to be either an ESC or motor issue. This is the first time I've used "pancake" motors on a smaller aircraft, I've built many other multirotors and this is the first time I've had this problem. Don't know if that's related though.

 

[Old Man]

A few bad FET's and you can have a seriously misbehavin'' ESC. Same results with a dead pole in a motor. I already know it ain't you.

 

[moonpie57108]

How about a hard punch out? Not that it's a Racecraft but to work that possibly bad motor, you should get a poor response from it under heavy vertical load.

Would think motor is also possible if esc swap does nothing. Could be a vibration at a particular rpm range getting back to the FC. Bad bearings or out of balance.

 

[MadMonkey]

How about a hard punch out? Not that it's a Racecraft but to work that possibly bad motor, you should get a poor response from it under heavy vertical load.

Would think motor is also possible if esc swap does nothing. Could be a vibration at a particular rpm range getting back to the FC. Bad bearings or out of balance.

Full throttle climbs are perfectly fine... every maneuver is great except for yaw.

Just a little while ago I finished swapping out the ZTW ESCs for the Afros that were on my testbed. And the results are in....


....exactly no change whatsoever. At least, no change I could see by flying in my small living room. Even in that space and being fairly gentle on the yaw, you could still clearly see the aircraft becoming unstable so I doubt that outdoors would make a difference.

The last thing I can think of to is swap out the motors to my crappy Turnigys and see what happens. Motors are pretty much the one thing that has stayed in place through this whole thing.

OM, sorry I wasn't clearer... I wasn't implying that it only happens to the front right (#1 on Naza) motor, I was just giving an example of what happens. The problem seems a little more violent to the right but it still happens to the left as well.

 

[moonpie57108]

Another thought, how is the flight controller mounted? Depending how it is mounted, maybe you are getting some movement on the yaw plane?

You could try going to a firm or softer mount, depending on what you are currently using:
firmer - would help if there is too much dampening in the current mount
softer - could help if there is a motor causing vibrations

Just thinking this might be a easier next try since you already had to pull all the escs and now looking at new motors. And it is the other thing that changed when you plugged the controller into another multirotor.

 

[MadMonkey]

Another thought, how is the flight controller mounted? Depending how it is mounted, maybe you are getting some movement on the yaw plane?

It's mounted with tough double-sided tape. I've always used that or hard mounting to standoffs for all my multis... that includes Naze, Multiwii, KK, Naza Lite, Naza V2, Wookong, A2, and others without ever having an issue like this.


Today's update is a giant FML. I'm guessing you know what that means.

Pulled off the Sunnysky motors, put on the Turnigy Park 450s... and...

exact.

same.

thing.

I am now at a loss.

I guess I'll reinstall everything back to the original setup and start over from square 1. My workshop door might have a fist-sized dent in it now...

 

[MadMonkey]

She's back together, and somewhat more cleanly than before, so I guess something good came out of this mess.

Now to start troubleshooting all over again.

I did notice something odd. This had never happened before... my idle speed was set too low in the Naza assistant, so the motors wouldn't spin up until I throttled up manually. One motor, maybe 40% of the time, would squeal and twitch a bit for a couple of moments before spinning up. I found that strange.

However, I had the Turnigy motors installed earlier with the same yaw wobble as before, so I can't for certain that this is related to the problem. It's certainly worrying though.

I'm tempted to order another motor just to test it out, but I don't have enough confidence that this could be a solution to try it just yet.

 

[violetwolf]

I keep coming back to the thought that your flight controller may not be perfectly level. Or perhaps the gyro chip itself may be soldered off level. Is this a new FC? Do you have a spare you could try?

 

[violetwolf]

That or there's some kind of mix programmed in your TX that you're not aware of? Maybe try creating a fresh model in the tx and see if the problem follows.

 

[MadMonkey]

I keep coming back to the thought that your flight controller may not be perfectly level. Or perhaps the gyro chip itself may be soldered off level. Is this a new FC? Do you have a spare you could try?

The controller case is itself definitely level, it's mounted directly to the top plate with the aforementioned double sided (thin) tape. I bought it new specifically for this aircraft. I don't think that it's defective because I tried it on my F450 frame and it worked perfectly... but with the F450's motors and ESCs, the same problem was present on the Tarot frame.

Now that I think about it, I used the same radio program for both, I didn't even bother changing it when I went to the F450 frame. So I don't think it's that. I did have a couple of mixes, but both were inhibited due to unrelated issues...

Since the F450 was fine and the Tarot was wonky with the same motors, ESCs and radio program, the first thing I'd think of is some kind of frame issue... possibly CG. But I've already messed with the CG! AGH!

I did have the GPS mast mounted to one of the booms to offset the weight of the video transmitter on the (diagonally) opposite boom. The mast is now mounted to the center plate just in case that could be part of the issue (though all the measurements were right).

I guess my next step is to go back to basics and start playing with the gains and CG at the same time and see if there's something I overlooked.

Also, speaking of details, I forgot to mention that the instability is temporary.... giving full rudder (yaw) to the aircraft results in instability for about 180-270 degrees, then the aircraft will stabilize and yaw as normal. Instability will again occur when stopping the yaw, but stopping is usually not as bad.

I'm going to mess with zip ties and weights and see if I can work this whole mess out. I might even do the same with my testbed aircraft and do some videos about it later on to see if I can help anyone with similar issues (assuming I get this worked out).

 

[violetwolf]

Ok. Have you looked at all the motors to make sure they are perfectly level? One that's out of alignment (twisted boom etc.) might have this effect.

And that's about all I've got at this point lol

 

[MadMonkey]

Ok. Have you looked at all the motors to make sure they are perfectly level? One that's out of alignment (twisted boom etc.) might have this effect.

And that's about all I've got at this point lol

Yeah, I did that before the whole experimentation process I just did, and also made sure they were level when reassembling this time.

 

[violetwolf]

Since the F450 was fine and the Tarot was wonky with the same motors, ESCs and radio program, the first thing I'd think of is some kind of frame issue... possibly CG. But I've already messed with the CG! AGH!

Yeah this is why I was thinking motor alignment myself. Def related to the frame if you're sure the FC is good.

At this point I'm almost 100% certain it's a vibration problem. Vibes are higher/highest when yawing as you are "opposing the motors" so to speak in order to maintain lift and rotate the craft at the same time. Also present at high acceleration / deceleration these multirotors tend to shudder.

You've eliminated everything else.

To bad it's not an Arducopter FC we'd have logs to look at.

PS: I just had a look at your original post.. it's a Tarot 650 which has smaller diameter booms and plastic clamps.. def more give on those frames (more shudder). Try one of those suspension mounts for the FC

 

[MadMonkey]

Welp, I fully reassembled the Tarot and got it test flown today.... same crap. I think I'm giving up on this frame. I haven't tried a suspension mount, but I'm not convinced that it would make a significant difference. I might give that a shot if I can figure something out though.

Any recommendations on a frame this size that'll take this power system? I really like the idea of this one because it's perfect for the gimbal, but.... ugh.

 

[Chalagi]

Try Arris hobby they have frames that I think are a little above what Tarot has to offer.

 

[violetwolf]

The Tarot 810 is an awesome frame, but their smaller ones definitely miss the mark.