Toilet Bowl effect

I'm still very new to flying a Tarot PRO Hexacopter and APM 3.2.1 and its been fine up to now, I have about 4 hours of flying experience with out incident. I added my FPV components and was about 11 minutes into a perfect flight in Loiter mode and low wind and good weather conditions. While hovering my machine at approx 30 meters altitude it suddenly started a shallow Toilet Bowel effect and got progressive more severe, and then also lost complete control. I tried to activate RTL with no effect. I then switched to Stabilize but because I had pulled the throttle to zero for RTL my machine inverted and was heading for the ground at a rapid rate.  After applying full throttle I saved my machine from complete destruction with about half a meter above ground level.

My question is what causes Toilet Bowel effect and what should I do to fix it. Can antbody help please.

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  • Just flew my Tarot 690S for the second time and had an immediate toilet bowl in stabilize mode, lost control and tried several modes and maneuvers to bring it down until I finally was able to crash it.  I had recalibrate the compasses before the flight because I had repositioned the external pedestal compass.  I have no idea what happened.  I don't see any mechanical problems.  But the toilet bowl was defiantly occurring in stabilize mode.  Any thoughts???


  • Developer

     I then switched to Stabilize but because I had pulled the throttle to zero for RTL my machine inverted

    I noticed this statement. You should keep the throttle at mid stick (THR_MID) or just below when in an auto mode*, since if you need to switch to stabilize or other mode, the copter will either hover, or slowly descend. 0% throttle is motor cut.

    Auto Modes are modes that require other sensors to work (GPS/Compass/Baro etc..). They are kind of group like this in complexity Group1:{Loiter, Pos_Hold, Auto, RTL (any mode requiring GPS et..) }, Group2{Alt Hold, Land (when GPS fails)}. Stabilize is not an 'autonomous' mode so is the simplest.

    A good thing to remember is if any in the Group1 'Auto Modes' fails or isn't working as expected (e.g toilet bowling) the other modes in than group are not going to work. Group2 may work and give some assistance, Stabilize will always work unless you have a mechanical failure. If you keep your stick at mid throttle, a switch to stabilize will be easy and controlled landing. With the benefit  if you need to cut the motors just drop the throttle to zero.

    Hope that helps :)

    • Hi Bill

      Yes I am lucky I had altitude to attempt a recovery from 30 meters up. It took about 1 second to get to 10 meters and applying full power the machine flipped back the right way up. I am very new to flying so am learning the dos and dont's.  Am going thru the full setup and have a test flight tomorrow. 

      Cheers Henny

    • re-Stabilize will always work unless you have a mechanical failure

      Yes this should be the 'go-to' mode if your in doubt! I learned this the hard way... 

      • Good to know....

  • I apologize, for some of me recent remarks about the importance of magnetometer data to loiter, I overlooked the fact that there is no right or left built into a multicopter  and it can fly in any direction and frame alignment relative to desired course is necessary to go in that direction.

    I still contend that using a GPS for fine positioning within its 2D accuracy, is a futile exercise. The Horizontal accuracy estimate, is available from the GPS and could be logged.

    What is missing from the information is what is the expected accuracy from the calibrated magnetometer, and what size error can be tolerated, and how it is distinguished from a heading offset caused be crosswinds, a 5mph wind can cause a 45 deg offset in a multi moving at 5mph.

    Can it be guaranteed that with a properly calibrated magnetometer flying in the same local area, with no changes to the airframe, and equipment will not experience "toilet Bowling" in loiter?

    • Hi Clarence, Hoorah - you have seen the light! :) I am no professor of science, I simply read the manual. If you are experiencing the toilet bowl effect you need a compass that is calibrated and operating above an acceptable tolerance of interference. Is that a guarantee? In a way I suppose it is because if you calibrate your compass, and it is operating above the defined acceptable level of Interference, it holds its Loiter without toilet bowling.

      I hope Henry comes back, if anyone it would be him who could confirm whether calibrating the compass fixed his toilet bowling and his Loiter was acceptable.

      • Hi Sandy

        I believe my Toilet bowel effect was caused by the Lea-6 compass lead partially coming out of the APM 2.7 socket during the flight. I plugged it back in and re-calibrated the compass. Had 6 fantastic flights today without incident. My machine has almost no vibration, the compass is on a pedestal, with go-pro, FPV system and 2kg of batteries. It was very stable in gust wind conditions.  I am happy.

        Cheers Henny

      • I still am skeptical, it's not a bright light that I see. The code needs and uses the magnetometer data, but I did do the dance and calibrated my compass, and have seen inconsistent results.

        I flew a programmed course perfectly one day (practice), and the next day (demo) it flew nowhere near the programed path, circled wildly in the vicinity of a waypoint like it was lost, seemed to find its way again, and then would start a big circle at the next waypoint, I had to abort into stabilize mode. I assumed a bad GPS signal caused it, but now believe something else was probably the cause.

        • Have you tried to run your logs through mission planner or drone share to let it check for issues? It can be extremely helpful to diagnose what caused a bad flight. 

          I usually wait until I have a minimum of 10 sats and a1.2 HDOP before even flying. 

          I lost a quad that took me months to build and 2k in it. My last sight of it was whilst it toilet bowled away out of sight over Lake Huron. I guarantee it had a darn good sat lock and HDOP... what killed it was the compass wigged out. preflight checks was telling me compass offsets were high [ compass was too close to the electronics I bet because I had just moved it lower ] but I flew anyway. So I don't know how the code is written but I know the compass is VERY important. You would think the gps would have been enough to guide it home but it wasn't. A poor gps performance will give you sloppy flight paths. A lost compass will end worse. IMHO

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