DJI S800. Uncommanded yaw after adding Secraft Anti-vibration arms.

[Benjamin Kenobi]

Hi there,

Well, first problem I've had with my S800 since I bought it back in April. Had over 100 flights and no issues.

I decided to add the Secraft anti-vibration arms, not because I have vibes but to strengthen the arms for the future. Why oh why mess with a perfectly working system? So, first test flight and I got uncommanded yaw (about 45° to 90°) a number of times. Also had drift to the right as if input and had to use aileron trim to get the single flashing light which means no input. Very odd as all calibrated and Tx monitor showed normal values as usual.

Of course on the bench, removed trim and all fine again. Checked logs but don't fully understand them. I'll post them if someone feels they can interpret them.

The obvious course of action is to remove the Secraft kit and go back to how it was.

I did notice the yaw happened when I hit the wind above the tree line. It was up to 14mph which is normally fine but zero on the ground.

I was thinking maybe the arms are slightly magnetic? The extra weight means I have to up the gains a bit?

During yaw, my sticks had little effect at slowing the rate of yaw which was disconcerting. I also noticed that the CCW motors were warmer than the CW ones (M1,3,5).

I've seen this problem mentioned before but the threads were never resolved.

The footage I got was fantastic as usual because the location was awesome. It was only when I tried to do some 360° panoramic photographs to stitch together that it became a little annoying as usually it's so locked-in.

Cheers!

 

[Eco]

"I was thinking maybe the arms are slightly magnetic?"

You re-calibrated the Compass right?

While I have no direct experience with the Seacraft kits, it seems that it could be possible that the thrustlines have been changed with the installation of the arms. It may just be a matter of ensuring uniform torque on the fasteners of the seacraft arms.

You'll be able to see if it's a compass issue vs a thrustline issue because if it's a compass issue, and you don't manually stop the yaw, the motors will be more of a uniform temp. If the thrustlines are off, and the autopilot is attempting to correct it, then you'll notice the motors that spin in one direction or the other are warmer than the others.

 

[Carapau]

A couple of things. Firstly, vibes can have some quite interesting effects on the system. Now that you have changed the arms, you have also changed resonant frequencies, frequency damping characteristics etc. So, try a different location for the IMU or a different mounting pad for it and see how that goes. For me, chaining the mounting pad turned a twitchy octo into and uber smooth beast, despite all the props and motors being very well balanced. If it flies, it vibrates. As for why the CCW motors might be warmer, it could be that all of you motors are just a bit off dead centre meaning that the CCW are having to work a bit harder to keep the aircraft on point. If you have an IOSD, look at the logs from a flight where you do nothing more than hover. If the motors are off centre (and as much as .3 of a degree can have a noticeable effect in terms of the log), then you will see higher revs on the CCW motors. If you don't have and IOSD I would seriously consider getting one as this becomes your 'black box' and it makes diagnosing problems possible. More importantly, you can often catch a potential problem before it becomes a real problem.

 

[Benjamin Kenobi]

Hi mate, thanks for your reply. And your first post!

I re-calibrated the compass naturally. I think my gains were a little low but that doesn't explain the CCW motors running warmer. So that does indeed leave thrust lines.

I'm gonna try again tomorrow in the wind to see if it's made any difference. On the log the CCW motors were running a little faster. I was waiting for the blisters to heal from putting the secraft stuff on (there were many screws!) before trying to check the tension. I guess one motor slightly askew could cause the issue.

Need to sort it for upcoming jobs so might just remove the adapters anyway as everything was running perfectly before. I was just trying to future proof the arms against wear and tear. Silly me.

Cheers Eco!

PS - How'd you come up with that name?

 

[Scott Drysdale]

Likewise the yaw issues remain unresolved for me as well.... but am using a custom RCT800 Hex with S800 landing gear and DJI antivibration kit for the camera and 2 axis BGC system. In my case the Hex yaws ccw when the wind is from port side and cw when the wind or breeze is from starboard side. Also there tends to be yaw when I hover closer to ground level...... all so mysterious. But I have a theory that the cross-sectional area of the HEX from port or starboard side creates a weathervane affect when the camera/battery crosssectional area are not centered according to MR center of gravity.... same way that the rooster silouette wind pointer works on the old barn roof!!!

 

[Benjamin Kenobi]

Looks like we all replied about the same time. In answer to some of the questions, my IMU is on the anti-vibe upgrade on the landing gear. And I think I mentioned that the logs did indeed show a greater RPM on the CCW motors. The yaw did happen in cross wind just above the tree line. I have my IMU hole covered with some foam to stop static pressure build-up caused by wind hitting it. I want the IMU V2 but they've been out of stock for a while.

I honestly think it was low gains and one of the motors being slightly off. I guess I'll find out tomorrow if it's not too windy (bit of a storm here in the UK). I've always had really low gains to be honest so it was about time I upped them. I've been using 100% on the attitude. Been fine in wind up to 18mph but a bit wobbly. The zenmuse always makes the footage look super. I've gone for 140% now. Kopterworx uses 170% with a similar setup. I think the manual recommends something ridiculously high like 200% (don't quote me on that).

Anyway. Speculation at this point. If motors come down unevenly warm tomorrow off comes the secrafts and in the for sale section they go.

May the force be with you!

 

[Benjamin Kenobi]

Hey guys,

Well I just removed the Secraft bits and all back to normal again. Flew in 15mph wind gusting up to 20mph and everything was spot on again.

I decided to remove the Secraft anti-vibe arms after reading this post:

http://www.multirotorforums.com/sho...ns-when-above-100ft-but-fine-when-below-50-ft

I had similar symptoms although this OP decided it was nothing to do with the anti-vibe arms he added although his problem started the first flight after adding them. Go figure.

They'll be in the for sale section soon. £120 inclusive of p+p.

Cheers!