APM 2.6/2.7 without compass/GPS

I just build a new quadcopter using a APM 2.6 or 2.7 based flight controller which I salvaged from a crashed RTF drone (Quanum Nova Pro). I am also re-using the PCB which seems to have a Power Management integrated. Unfortunately I throw away the external compass/GPS module so I am trying to fly without them until I get replacements.

Obviously I had to disable all failsafes to get the FC armed without a compass/GPS.

I made my maiden flight today with the stabilize mode, and it seems to fly ok with following observations

  • with stick on center the drone drifts slighty to right and towards me. To keep it in place I need to manually compensate this, even without any wind. Is this a typical accelerometer miscalibration effect?

  • throttle control in stabilize is super sensitive. Just one ”click” more on throttle stick triggers fairly fast ascent, and vice cersa. How to calm this down?

I was also hoping to get AltHold working with my current configuration, since I assume it relies only on internal APM barometer and not on GPS/compass. However, i did some testing of AltHold mode while holding the quad from legs and the seems the motors where not spinning enough to even keep it in same altitude. When i tried to pull the drone downwards, it didnt increase the rotor speeds immediately. After this i didn’t have the confidence to test this mode in mid-air.

Should the AltHold work with my HW configuration?

Finally, how to get the beeps from buzzer? Is it external in APM? In that case it might be on my PCB and I am only missing some wiring.

You really need to post a flight log so we can see what is happening.
Turn on max logging, do a flight, and post it here.

The drifting you observed is normal.
You will never get it to stay on station in stabilise, too many variables, not just wind.

Throttle control IS direct in Stab.
Where is your throttle?
Half, 1/4, ?
Without a log and RCout being logged I cant tell what sort of power out we are talking about.

You won’t be able to tell how AltHold reacts from holding the quad.
You need to test it after you have set hover throttle to the correct values.

No buzzer unless you set up an external one of your own.


thanks for the swift response. I will do data logging flight, assuming I can figure out how to activate that and whether the APM FC supports even that without an memory card bay like there is in newer FCs.

I already reduced the “Climb sensitivity” setting in Basic Tuning menu to reduce the sensitivity of the throttle control. The effect was quite minimal, need to do some more tests.

However, I got the AltHold mode working and probably also the “Land” mode as well. This was really a unplanned test, let me explain what happened:

Before the flight, I added some wiring between the PDB and APM, using the original cables from the Nova Pro and using the same connector pins on APM. Pins A4, A5, A6 and A10 (if I remember correctly). This activated the buzzer on the PDB, but it also activated some other features which came as an surprise…

After taking of and flying for maybe 2-3 minutes (with a full 2200 mAh pack) in Stabillize mode, the quad started beeping very loudly in mid air. Immediately I noticed that the quad was descending gently and I had no throttle control at all, only roll&pitch control with right stick. I steered the drone to my landing point with FC controlling the descent.

After landing, I didn’t really know what happened. My theory was that the additional wiring enabled some additional features, maybe voltage monitoring (?), and some kind of failsafe was triggered which shifted the quad to a landing mode. I don’t have telemetry connected so I cannot tell what really happened, maybe the logs will tell more.

After this I made conclusion that if there quad can land autonomously it can probably also hold altitude. I switched to AltHold mode and did a take off using that mode. It fly nicely for maybe 10 seconds, but again the same landing sequence with beeping sounds was triggered so my testing in AltHold was cut short.

After this I didn’t want to make additional flights before I know what is happening inside the flight controller.

You can get logs no problem from that Flight Controller.

If you are using the PDB from the Nova it has a low voltage alarm at ~10.2V but there is no feedback to the FC to trigger Land Mode. It was likely just low on battery. Flying it to that point is not a good idea.

Personally I would throw that FC in the bin and replace it with one that runs current stable Arducopter. There are several that are very cheap and WAY more capable. I actually have a CX-20/Nova in mostly stock form that has been flying since 2014. It doesn’t see any use but it was my intro to Ardupilot so I keep it around for nostalgia’s sake.


thanks for the tips. However, I am pretty sure that the land mode was activated. I had zero throttle control once the buzzer started. Once the quad touched the ground, it also throttled back to zero the rotor without me touching the left stick. One of LEDs in the FC was also flashing, rather than being lighted consistently.

I think the Nova Pro had slightly different electronics than the original Nova. I can post some pictures if needed.

Which FC would you recommend, the Pixhawk?

Right,the Nova Pro has a full APM FC while the CX-20 had a bastardized version. You could be right and there is a low battery failsafe set on the FC but I’m not sure how it would receive the battery level to activate. I don’t recall if there is a power module in that vehicle. If there is then battery FS could work.

Yes, a Pixhawk or variant. The low cost Pixhawk option is one of the 2.4.8’s. Or you could use a F4/F7 board, there are several of those to choose from. I’m using an Omnibus F4 Nano and a Kakute F7 AIO in crafts. The later is a very nice FC for ~$50

I think it was actually the battery failsafe being enabled. Luckily the Dataflash logging is enabled by default, so I had some logs already stored in the FC. I am still learning how to use the Log Analyzer but I guess there is a Battery failsafe being triggered here somewhere in some of these flights:

Flight 47:

Flight 46:

After these flights I changed battery failsafe limit from default 10.5V to 9V, and did another test flight. Unfortunately I lost the orientation of the drone and mis-steered it to the nearby forest where it crashed. After some 30 minutes of searching, I was able to recover the drone (it had still power but there was no beeping / buzzing enabled so I assume it had unarmed itself somehow. Here is another log of that crash:

Now I need new arm or even new full frame and maybe a new motor as well. One arm had broken off during the crash and the motor wires were ripped off as well. So no more testing until some new parts come from China… :wink:

Yes, you are right. In the flight 47 log it clearly shows Vbat falling below the FS threshold and switching to Land mode. The last log ended abruptly probably when it crashed. Too bad about the crash, rebuild it with a better flight controller!

I ordered a Pixhawk 2.4.8 “clone” from Banggood, along with some other stuff. I read from some RCG thread that there might be some issues in some Pixhawks with some “residual power” being left in the circuitry, but I didn’t let that bother me.

Based on some general Googling, it am getting impression that there are clear division into

    1. FPV racing flight controllers with small size and limited GPS support
    1. Autonomous flight “optimised” flight controllers like Pixhawk and broader support to control additional hardware, gimbals, sensors etc.

Is this a correct impression?

Kind of…
Since Chibi-OS also many smaller boards, previously used for racing drones, are also supported by Ardupilot, like the Omnibus F4 Pro and the Kakute F7.