Copter-4.0.1-rc2 available for beta testing -- Critical Fix Included

I did three autotunes on two different quads with 4.0 and S-Port passthrough and didn’t encounter the watchdog bug in any of that message avalanche.
And now it dawned on me that while in 3.6.x doing an autotune would freeze the sensors, I definitely had pack voltage and current working throughout the tunes.

Does the “latest” Builds have this fix in them? Or do I have to build from source? Typically I have been grabbing the latest .apj file and upload it. And not 100% sure on how the RC builds work


Not sure what happened but after downloading the latest version of MP and installing Copter-4.0.1-rc2 I have lost all of my params. Doesn’t seem to like loading from an older param file with several errors.

Edit: Changing my frame type back to Hexa, loading 4.0.0, and grabbing the param file from a log download seems to have me back where I belong. I’ll give the beta another try.

Edit 2: Ok, the RC2 upgrade took that time. I very thankful for the param files included with log downloads. Saved my rear end this time. MP updated within minutes of my first download so wonder if there was a connection.

Edit 3: Looks like I will need to re-calibrate my compass though. Lost those settings.

Can’t wait to try out the circle mode!

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Thanks for the testing and feedback. It may be hard to reproduce. We only found it because the watchdog gave us enough details of the problem so we could track down the bug through “inspection” (i.e. searching through the code). We then made a temporary code change to replicate the issue.


Yes, the critical fix for the FrSky SPort Passthrough telem is include in “master” from yesterday so it should be in the latest .apj file.


Yes, I think the NeoPixel is included for all boards. There is a discussion thread here with some other users trying to get the NeoPixels working and they seem to be struggling so I’ve added this to our Copter-4.0 issues list so we will investigate and won’t forget about it.

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Thanks for the report and sorry for the parameters getting reset to their defaults. This happens occasionally (issue is here) although it seems to be quite rare. I’ve seen it myself once about 6 months ago and I was quite shocked but I haven’t had it happen again since even though I upload new firmwares all the time.

We think it happens when there is an error reading a critical marker that is placed at the start of the eeprom (where we store parameters). This makes AP think that the eeprom hasn’t been initailised and it wipes all parameters. We’re going to change this so it reads this critical byte multiple times to greatly reduce the chance of a parameter wipe.


No problem. Thought I was going crazy! Thanks for the heads up. :slight_smile:

Im getting this message in the Status window on MP, “EKF2 IMU0 forced reset”, several times. Im using the 4.0.1 rc2. I did not fly the drone, was just a bench test yet. Should I worry?

Flied 50 minutes today, all was good.

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Flew 1 hour today, with FrSky Passthrough, no issues. Here’s one of the logs:

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Sorry if this has been reported already, but I wanted to mention that I updated my 700 heli from 3.6.10 to 4.0.1-rc2 and it turned BATT_MONITOR off. After I realized this had happened, I turned it back on and all my previous BATT params showed up. AP is a CubeBlack.

@rmackay9 - for clarification - since losing my params due to this issue will reloading from a backup only require re-calibrating the compass, or will I need to calibrate the accelerometers again as well?

Not looking forward the to the compass dance with a 810mm drone, and recalibrating the accels again would involve removing the FC from the frame.


I think you shouldn’t need to re-do the accelerometer calibration if you’ve loaded the older parameters.

It’s possible to avoid the compass calibration as well by tricking the compass calibration check by temporarily setting the COMPASS_DEVIDx params to another value (like 999) and then back to their original value.

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The compass trick worked, but the FC is requesting an accel calibration now. Probably for the best, but I would love to see that little bug fixed. Back to the bench!

Edit: I needed to move the buzzer to a better location anyway! :wink:

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I wasn’t able to recreate the issue in which BATT_MONITOR parameter was reset to zero after upgrading from Copter-3.6 to 4.0 but from a look at the parameter conversion code I do see that in some cases it will set the type to zero. I’m wondering if you have a parameter file or log from before the upgrade that I could look at?

Sure thing, sent it over to you.

Since I haven’t done any night flying in a while, especially in cold weather, I calibrated my accels and took a test drive.

@Pedals2Paddles Thanks! I was able to change the diameter of the circle but don’t believe I was able to change the rate. Any chance this could be modified to change direction? I would almost prefer it started with no rotation and then a left or right stick would would determine direction and rate. I also noticed that on occasion it would lose yaw orientation. I am flying with spotlight so this is pretty easy to watch at night. Here is the log:

@rmackay9 I noticed a jump in yaw on takeoff which I had not seen before, and a change in yaw on quick decent, but this only happened twice that I could detect. We have a few inches of snow on the ground so was trying to get up in the air quickly.

It’s just a bit below freezing with about 6 mph winds, so just on the edge of uncomfortable. Foot warmers worked great, but note to self… my next laptop should not have a metal case. :wink:

You can change direction now. If you slow down to a stop and let go of the stick, you can then restart in either direction with the stick. It just won’t go past zero rate until you let go of the stick first.

You could set parameter CIRCLE_RATE for zero if you want it to start out not moving. It won’t move until you give it some left or right roll stick in either direction.


Today I did a test flight using the new circle mode and in principle I thought it didn’t work at all but I got used to the correct way to move the sticks I could see how amazing the new circle mode.

To understand how that flight mode works I did the following, in PosHold mode I raised the drone to a height of 10 meters and moved it away at a distance of 10 meters, then turned the yaw so that the copter’s nose points towards me, then activated The circle and copter flight mode starts to rotate counterclockwise, so we can see that the direction in which the sticks move takes on meaning.