Thought Id test RTL behavior on my VTOL. I initiated an RTL while in FW flight 500mts away. It appeared to be heading for the deck with no attempt to transition. Im sure I have some setting wrong but cant see where. QRTL alt is at 40 but it got almost to the ground before I recovered to FBWA. Also I think it was probably heading for a rally point that I set. Perhaps my rally point had 0 altitude set. Can that be seen in the logs?
Any guidance appreciated.
Hi Vince,
There are probably ways to extract rally points from the *.bin file. The easiest way would be to read out any rally points from the flight controller with the MissionPlanner via USB cable.
From the log file alone, however, you can already clearly combine that a rally point with an altitude lower than 20 meters must have been the descent target, otherwise (if approaching the home point) the return transition would have already taken place in Q_RTL_ALT (40 meters).
Furthermore, the approach course after triggering QRTL does not lead to the home point, but slightly away from it to the open field.
It is not quite true that you initiated RTL, because you triggered QRTL directly via the RC transmitter. If you had triggered RTL, the VTOL behaves depending on what is parameterized in Q_RTL_MODE parameter (0,1,2 or 3)
Wiki: Return to Launch — Plane documentation
Rolf
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Everyone’s favorite WebTool will extract rally points.
Indeed, in this case it had zero alt relative to home.
1 0 3 5100 0.00000000 0.00000000 0.00000000 0.00000000 53.40465830 -0.97952130 0.000000 1
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Thanks Rolf. Unfortunately I uploaded another mission before investigating this QTRL behavior so Im not sure if I put a rally point, or what height I set.
Yes it was a typo about the QRTL. I just want a safe behavior if I loose the link (I had a lot of experience of this with my CRSF issues).
I was reading the RTL documentation before posting and think I have set everything for the right behavior. I guess I must have set my rally height to zero as the documentation advises about this.
Would it not be a good idea if the firmware ignored the rally height if it it set below the RTL_ALTITUDE?
I will test again soon.
Thanks Peter. Whoops about the rally height. Would it not be safer, in the case of RTL, to ignore the rally height if below RTL_ALTITUDE?
If you define “safer” as not crashing into the ground then sure. However if you define “safer” as not breaching your local altitude restrictions then no. As with most things we can only do what the user told us to, we cannot guess what they really meant because we don’t have enough information.
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@iampete My bad, big time—how on earth did I miss that?!
@Vince_Hogg
You should first consider which of the RTL procedures available for VTOLs are suitable for an RC failsafe and your own flight routes. To be honest, it doesn’t make sense to me why you need a rally point only a few metres away from the home point. What Q_RTL_ALT is for a homepoint as a target point, is the altitude of the rallypoint for rallypoints! In your flight you should have specified a rally point altitude of 40 metres to achieve what you wanted.
However, with rallypoints you lose the option of returning higher up in RTL_ALTITUDE if you are further away. With rallypoints as destination points, you fly back at the current altitude.
Rolf
I use rally points because I arm and takeoff from the corner of my garden which has tall overhanging trees. While there is a small gap above, I don’t trust a non RTK gps to find it, so in the unlikely event of RC loss I would prefer to have it land in a clear space. Im well aware of the tall trees to the south and power lines to the east so its imperative I can trust the RTL behavior. 12 months ago I was having RC drop-out on about 50% of my flights (on a quadcopter) when using Crossfire so I got paranoid.
You can see here why I dont wish to do an automatic return to the home point.
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@Vince_Hogg Amazing, the airfield directly behind the garden! Congratulations. A quadplane precision landing system for landing right in front of the house between the trees would be a blast. And trackable antennas on the roof for FPV and data transfer 
Sorry if I have to double-check because you forgot a rally point with a height of 0. Just to be on the safe side, if you use rally points, the altitude is the target altitude for RTL or QRTL. Also, the distant aircraft does not climb to RTL altitude when it returns, but remains at the current altitude until it begins its descent to the altitude of the rallypoint when approaching. If there are high obstacles on the flight route, this should be taken into account in my opinion.
A thousand good flights
Rolf
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Thanks @Rolf
My fixed-wing flying was difficult while the field was in crop, and in any case was never suitable for undercarriage, which was the driving force to design a VTOL. I just used the motors I had but its right on the limit in hover flight and in recent hot days is not able to hover in turbulence when returning with lower batteries, redulting in some premature landings. Working on a new VTOL but cant settle on a layout.
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