H520 Spinning around (yawing) in flight - intermittent fault

[Whisperit]

Hello,
I test flew on of my H520s yesterday after repairing a broken chassis and a few minutes into the flight when it was hovering it started spinning around really fast. I could slow the spinning slightly by using opposite rudder control and after a few seconds it stopped and I flew it straight back home at low level.

I had not remembered to re-calibrate the compass, although the sensor state did show green. Not sure if this could be the reason thought. I could fly it again, calibrating the compass first, but I'm reluctant to risk it until I ask some more expert people on here first.

Anyone else experienced this or know what the problem might be? What would I look for in the log to tell me what the issue was?

Spin was about 1 revolution per second.
Aircraft kept fairly level during the spin.

 

[arruntus]

Could be something from the stick, dirt maybe?

 

[WTFDproject]

I had not remembered to re-calibrate the compass, although the sensor state did show green.
Anyone else experienced this or know what the problem might be?
What would I look for in the log to tell me what the issue was?

The symptoms don't match a compass issue. I doubt that's the problem.

Ignoring the possibility (for now) that the issue is related to the recent rebuild, the most likely issue is corrosion on the control stick pots. This can be easily checked by opening "RC Monitor", and looking as the associated scale (J2) as you move the left stick in Yaw. The scale should not move unless you move the stick. When you move the stick, the scale should move smoothly and match the amount you move the stick. If rabbit/turtle (K3) is in full rabbit, the J2 scale should go all the way from top to bottom as you move the stick. And when you release the stick, the scale should return promptly to center, with no "slow" spots, especially as it nears the center. You can move other sticks around to get a feel for what "normal" looks like.
Check the sticks first, then let us know what you find. We can move from there towards a resolution.

 

[Whisperit]

Thanks for the suggestions. The Yaw control stick is working perfectly according to the RC Monitor. I have been using this transmitter with another H520 for a site survey without issue. But, it did actually get a fine dirt-dust covering on it, from a nearby field that various tractors were working on. How would dirt affect the stick?

I think it was spinning too fast for it to have been a control stick problem (the spin seemed faster than the maximum you can make the H520 yaw using the yaw stick).

Will the logs be able to show anything? What should I look for?

 

[Whisperit]

Hi,
I'm having a problem downloading the flight log from the H520 to work out the spinning problem. I've got Datapilot loaded up on my PC, I plug the H520 into the USB port from the microUSB socket on the bottom and the drone fires up, but every time I press Download the log status turns from Available to Error.

Tried it several times now on different logs, and with my other H520 aircraft, and I haven't been able to download a single log!

Anyone know how to solve this?

 

[Whisperit]

Well, this is slightly embarrassing. I flew the H520 again, having calibrated the compass this time, and it was fine - no spinning around at all. Then, as I came into land, I noticed a problem with one of the motor arms - see photo!!

In fact, two of the arms were loose, the carbon tubes had become detached from the inner orange bracket. I always check the arms are locked up, but never thought to check whether they tilted around on their own.

The aircraft flew like normal on this flight, just shows the job the control system can do to keep things stable. I assume the previous spinning around happened when the arm first tilted, and then after a few seconds of spinning the control system compensated.

Another thing to go on the pre-flight check list....

 

[arruntus]

Well, this is slightly embarrassing. I flew the H520 again, having calibrated the compass this time, and it was fine - no spinning around at all. Then, as I came into land, I noticed a problem with one of the motor arms - see photo!!

In fact, two of the arms were loose, the carbon tubes had become detached from the inner orange bracket. I always check the arms are locked up, but never thought to check whether they tilted around on their own.

The aircraft flew like normal on this flight, just shows the job the control system can do to keep things stable. I assume the previous spinning around happened when the arm first tilted, and then after a few seconds of spinning the control system compensated.

Another thing to go on the pre-flight check list....

The important thing is that you've found the problem. Do you remember hitting your arms or being forced into transport? It could be a manufacturing problem.

Having the motors well placed is fundamental, up to half a degree of deviation can cause problems and excessive battery consumption precisely because of what you have said. The controller has to compensate and in this case that's precisely the strongest point of the H520, it has a very good stability.

 

[rconiv]

The symptoms don't match a compass issue. I doubt that's the problem.

Ignoring the possibility (for now) that the issue is related to the recent rebuild, the most likely issue is corrosion on the control stick pots. This can be easily checked by opening "RC Monitor", and looking as the associated scale (J2) as you move the left stick in Yaw. The scale should not move unless you move the stick. When you move the stick, the scale should move smoothly and match the amount you move the stick. If rabbit/turtle (K3) is in full rabbit, the J2 scale should go all the way from top to bottom as you move the stick. And when you release the stick, the scale should return promptly to center, with no "slow" spots, especially as it nears the center. You can move other sticks around to get a feel for what "normal" looks like.
Check the sticks first, then let us know what you find. We can move from there towards a resolution.

I actually do have this issue with my left controller. It also won't spin up the blades because it sticks at around 25 percent. If I move the stick in any direction it is quickish till around 90% then it slows down, and it is really sluggish returning to center. It fails the calibration test. I think it has been failing for a while, because the unit has been touchy to control either of those axis for a while. I had seen a suggestion to blow some air in to the holes that the rubber grommets cover in the back, but didn't do much, and I don't have contact cleaner. Am temped to open up the unit so I can see how things are looking on the back end of the controller. The right controller works fine, is quick when the control is moved, and going back to center.

 

[WTFDproject]

Yes, it would be best to take the rear cover off and try to get something in the pots to help clean them. Alcohol sometimes works if you don't have any contact cleaner.

 

[rconiv]

Yes, it would be best to take the rear cover off and try to get something in the pots to help clean them. Alcohol sometimes works if you don't have any contact cleaner.

Do you just spray in to the assembly, or should some of it be taken out first?

 

[WTFDproject]

You don't have to remove anything other than the back of the controller. Spray mostly towards the back side of each of the four potentiometers. On most, there is a small hole that lets a little get inside where it can do some good. Some older models don't have the small hole, so you are just trying to get a little in around the shaft. Then exercise the sticks to help remove the corrosion.

 

[rconiv]

You don't have to remove anything other than the back of the controller. Spray mostly towards the back side of each of the four potentiometers. On most, there is a small hole that lets a little get inside where it can do some good. Some older models don't have the small hole, so you are just trying to get a little in around the shaft. Then exercise the sticks to help remove the corrosion.

Thanks, I got a hold of some of the cleaner, and sprayed it in the back hole, and per suggestions some on the front, and moved the controller around a couple time in all its directions, and then ran calibration, and it is happy now. Thanks for the help.