Auto-Mission without BARO = EK2_ALT_SOURCE was on 1

I wanted to try my first mission with a new TR600 Heli with ArduCopter 3.6.0-rc2 and the Pixhawk 2.1 last Saturday.

During earlier tests I changed the EK2_Alt_SOURCE to use my LIDAR only which is nice because it will not be effected by the blades close to the ground ( pressure). After 3 tests I wanted to do my first mission but forgot to change the EK2_ALT_SOURCE back to 0. My WPNAV_SPEED was set to 5.5m per second. The mission was created with different heights per way point. I have done many missions with different aircraft’s but never touched the parameter EK2_ALT_SOURCE before. Now what happened:
After way point 5 which was higher than the LIDAR can measure ( about 30m above ground) the Autopilot was waiting for the confirmation of the next way point height. The Baro was disabled and the Lidar out of reach so the Helicopter climbed and climbed at 5.5m p second. The Heli was not moving in X and Y but in Z only.
I found it strange because my highest point of 100m over ground was not in that area where the Heli was at that time. I watched for few seconds and than checked my transmitter, could not find a fault.
When I looked up again I could not find my Helicopter but it was clearly to hear.
I switched to RTL and waited, but it kept climbing. (FS was set finish mission first)
The sound was fading and I immediately looked at my tx again and set my collective pitch to about 45% and changed mode into stabilize. I could here the blades barking instantly. They do that when the Heli gets minus pitch and coming down. Now I was worried that the Heli is coming down to quickly and starts tumbling. So I took my time and a couple of minutes later I could see a tiny Helicopter above me. I managed to get the Heli down safely and about 20meter above ground I switched to RTL and this time it worked and the Heli did a nice auto landing at the spot where he had taken of for his first mission. That lucky outcome took a total of 13 minutes.

The photo above was taken by the onboard camera at 2460 feet above ground, not legal here I know. Not done on purpose.
I will get my new FrSky Horus x10 ready quickly to get my Pixhawk Telemetry onto that big color screen of the transmitter. The laptop in my van ( Arial on the roof) is useless when time is important to react and do the right decision.
Be careful with the EK2_ALT_SOURCE parameter. Make yourself a big note to read your changes and don,t forget like me!!


Fred, do you have any sort of FPV on your heli? FPV has save me from these mistakes more than once - I shouldn’t admit that.

As I was reading your blog post it came to mind that this going to be the most epic RC heli autorotation ever done :grinning: Which is what I probably would’ve done in that instance - switch to FPV flying in autorotation as I know then it’s coming down stable. Even plenty of time for an engine restart as you pass thru ~300 feet :grinning:

Awesome tale and great advice! I bet you experienced a few moments that were, err, unconfortable …

Something similar happened to me a few years back. I was playing with a ridiculously over-powered “racer” MR I had built, 6000 watts of power. Tested static and in the yard, all good. Go to airfield to test some more and get some good speed, all good at first until at some point I switch to loiter, next thing I know it shoots up like a rocket at an incredible speed and becomes a dot barely visible then completely out of sight. All within what appeared to be an instant and before I had time to say “what the …”.

I freaked out and switched to stabilize and got it to slowly descend until I could see it, then land. In my case it was a typical case of excessive vibration, accelerometers aliasing and reporting no upward acceleration when it was climbing up, so controller kept asking for more upward speed. Later log analysis showed it went up vertically at close to 60mph!

Stabilize mode is our friend, one tends to never forget these sorts of episodes! :slight_smile:


That’s a beautiful picture though. What are those hills towards the sun that look like giant tailings piles from an old mining operation? They seem to be on both sides of that reservoir and I don’t see any other geological formation in the photo that looks like that.

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You did get a great picture out of the ordeal and didn’t lose the aircraft. You lucky guy. Good job staying in focus. I would have had to change my shorts for sure.

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Hi Chris,
I do not have FPV installed yet just my Sony action cam FDR-X3000 underneath the Heli.
The photo is a screenshot out of a total video in 4K taken during that episode.
What you can see in that photo is rolling sheep and cattle farming country formed first by the last ice age and than corrosion over time. That water is a natural inland little lake. To the right you can see the coast of the Pacific. If you keep flying in that direction you will end up in South America, only if you can make it.
What you see is the surroundings of my private flying field next to that river.

You might like to know that this is going to be enabled by default. In my experience this has some very positive effects near ground, on MR’s and also on my small 450. Still have to test it on the E700.

Hi Luis,
I appreciate your link to the ground-effect-compensation.
There was a specific reason for disabling the BARO in my case.
Chris Olson had offered me to try his default parameters who he claimed will work with any Heli of the 550 to 700 class. Because I have told him about my new build I took that offer for trying.
To be really sure nothing will interfere with my first maiden take off I looked that EK2_ALT_SOURCE parameter up which will disable the baro.
Only for my first lift off I wanted that.

The default values from Chris are working just perfectly for my Heli. I went to the next step to get the perfect throttle curve for this Heli. After 3 very successful tests with ALT HOLD and LOITER I wanted going to the next step and doing a mission. Than I forgot to change the EK2— param. back to = 0.

The Heli is landing very gentle by itself and has no bouncing what so ever. No ground-effect-compensation needed.

If any Heli-flyer knows that his new Heli is hardware wise healthy and good trimmed out with a pitch gate and went through Accel-calib. and Mag-calib., I would recommend and trust the Chris Olson default values.
I have not changed anything yet. I like that gentle behavior of my Heli with those values from Chris.

That’s good to hear, Fred. That’s another one those settings have worked well in. The eventual goal (if possible) is to maybe have those settings as the new defaults in heli. And make a heli tuning page that only has to adjust a few items for “pilot feel” and/or a bigger/smaller heli that may have a different mechanical configuration that requires going into the settings and “tuning” the old way. We have gotten more feedback from users that the settings work really well, and don’t cause anything bad to happen. And they turn on a little bit of ILMI that many users are failing to set, which improves the heli’s hovering and handling characterstics. They use feedforward as the primary method of rate control with just enough P-gain in the rate controller to damp the controls but make it super-stable for our high-speed users.

It took me almost a year to arrive at that combination that I determined works well in almost any helicopter.

Yes, I agree those values should be the defaults in Heli.
Again, thank you what you have done for all Trad. Helicopter lovers.

Hi David,
thank you for your reply.
I was keeping my nerves because I knew exactly where the Heli was even I could not see him.
It would have been a totally different story if the Heli would have been to far away and not above you and you can’t see him.

Just a final note regarding the video.
Because it was a beautiful calm day the 4K video is stunning. The Heli was not only climbing straight up. Every few seconds the Autopilot was yawing the Heli 90 degrees without my knowledge.
In the west you can see the mountain range with snow cover and to the east the pacific coast as well a city, the rural land with the all natural hills, a river and water-filled depressions.
I always have a camera on board and a head-cam when I am testing. That help,s me to identify problems easier, with the addition of the log-files of course.
But it is illegal to fly an RC aircraft at that high altitude in this country.
I don’t want to be blamed I did that high altitude on purpose.
I will not be putting that video onto YouTube for that reason. Sorry for those who have contacted me.

Fred it is understandable that a flight control system malfunction caused it, and your experienced saved it.

I also have a Sony X3000 camera now and trying to figure out the best way to mount it. It has a 1/4-20 tripod mount and I may use that to bolt it to the mount on the heli. I typically do not use a gimbal but I do have a couple homemade tilt mounts with a tilt servo that I may try to adapt it to.

Chris, the mechanical lens anti-shake system in the Sony camera is very effective. I know during use of the camera for different purpose on a stick.
Under the Heli I always use a 3 axis gimbal because of the smooth yawing which is nicer to look at in the video. I never have used that camera with the Heli and fixed mounted. Can,t tell how effective the mechanic. anti-shake is doing with those kind of vibrations. Good luck.

My rigid mounts still have a “jello plate” with the rubber balls. I got tilt servos on two of them. I just don’t use the gimbal usually because I snap stills, not video, and the gimbals can’t take the wind load at high speeds on Section surveys. Make a high-G “ag turn” on the end of a pass and accelerate back to 27 m/s for those mile-long passes and I get about 10 nice shots of the bottom of the heli until the gimbal’s IMU recovers from it.

That makes sense for not using a gimbal.

I’m able to use a regular gimbal for low-altitude where I fly at 22mph and the speed can’t be much higher to prevent over-flying the camera. But it’s not necessary even for that. I could use one of my servo-operated tilt mounts, or a rigid mount like this homemade one that I have on the heli right now:


It has a lead weight on it to prevent sudden camera movement on the rubber balls. I’ve had problems with those rubber balls ripping right out of the holes on high-G turns so I got plastic zip ties thru them now to prevent that.

With a different bracket I think I can put my Sony X3000 on this mount.

Chris, just to your interest I want to show you how my Sony X3000 is mounted under my Heli.
Cables not tidied up because I am still testing.

Thanks for the photo Fred! It looks like you are using the 1/4-20 tripod mount bolt hole, which is what I planned on using instead of a clamp bracket to hold the camera.

Have you experimented with the PWM trigger using the multi/HDMI port? Or do you use the WiFi app?

Yes, I am using the tripod mount of the camera. Nothing else at the moment. Just turn the video on before takeoff and stop manually when the Heli has landed.
When I am happy with everything I go in further connections.
I am just on my way of a next flying test because the suitable weather is rare in our winter.