Roll of Death

[simonbethke]

This is an issue, that was reported recently like 4 times in a row in the german forum fpv-racing-forum.de.

The catchy name "Roll of Death" shall describe the issue that results in this experience: A pilot tries to do a roll. The roll works perfectly, but when trying to stop it, the copter starts to accellerate the roll. This always results in a crash.

I already discussed this a few times on the betaflight slack group and we found that this is not caused by the FC.

Observation: BlackMarlin12 reported, that the issue did not occur again after switching off damped light.

Theory: When having throttle at zero during a roll, the props are on idle speed. I think it could happen that the props on one side of the copter eventually start spinning backward due to the airstream. Furthermore, I think that BLHeli might be not prepared for backward spinning props if no 3D setup is used.

However, either active braking (which would support the damped-light observation) or the command to spin up the prop in the correct direction will result in the prop spinning up in the wrong direction. Ofcourse this will lead to a PID-Feedbackloop which will max the speed of this prop in milliseconds.

I already explained this theory to several people but nobody was able to give good pro or con arguments. Just all people gave it the mythbusters "Plausible" tag.

Material: From BlackMarlin12

• Setup: Emax Nighthawk HX200 Emax RS2205 2300kV Littlebee 30A: 14.4 Blheli SP Racing F3: Betaflight 3.1.5 X4RSB + Taranis X9D Plus Tattu 4s 1300mah 75C HQProps 5046 Tri-Baldes Durable
• Screenshot of BLHeli Suite: http://fpv-racing-forum.de/attachment/6482-escsettings-png/
• Video of the roll-of-death: https://www.youtube.com/watch?v=knyxufqSGqo
• Betaflight Blackbox: https://drive.google.com/open?id=0B0Ya5032OOsAdTM1RzdSRkJKT2c

From xrayevo

• Betaflight Blackbox: https://drive.google.com/file/d/0B0XBXkpws0FCQlB2UTA2VVBRdDA/view

From SignalSpirit

• Setup: Frame: Storm Loki X3 Motoren: T-Motor F20 4100 kV ESC: Racerstar 4 in 1 20A FC: Omnibus F4 Pro Kamera: HS1177 VTX: Unify Pro Race RX: Lemon RC Sat mit langen Antennen Antennen: Lumenier AXII Propeller: DYS XT30453
• Screenshot of BLHeli Suite: http://fpv-racing-forum.de/attachment/6422-img-20170219-wa0001-jpg/
• Video: https://www.youtube.com/watch?v=DhliWhDe4yU

[simonbethke]

Oh no. I posted wrong Material. I will fix it now.

[simonbethke]

Material fixed.

[BlackMarlin12]

Hi, I'm affected by te Roll of Death. It would be nice if there's someone who can help us.

[simonbethke]

Dear developer of blheli, what is your prefered channel for communicating issues related to blheli. Being a Softwaredeveloper myself, I very well understand that you might not want to jump on this immediately. However, I would really like to read at least a first oppinion from you.

[sskaug]

Generally these issues are better covered in forums like RCG. And generally, increasing min_throttle, increasing timing or increasing demag comp helps against such issues. All these things have been widely discussed in forums. And unless you have a badly wound motor or an ESC that tends to reset in flight, one or more of the above should fix your issue.

[simonbethke]

Thanks for the quick Response now. So

[simonbethke]

The cancel Button instead closes The issue and posts The comment...

[cubitusclaudius]

Interesting. I'm just having such problems, and was wondering if dshot_idle should be changed (dshot600 in my case). This value doesn't exist no more under configuration tab, but is still in the CLI. I raised it up and it deemed to get me rid of the problem : I first raised it to 6.5 (it was 5.5%) and tried a lot of flips and rolls without problem, except on my last lipo where it came back again. so I raised ti to 7.0% and till now no more desync... but I just flew 2 lipos since then...