APM Copter 2.9.1.b has been released to the Mission Planner and is also posted in the downloads area.
2.9.1b is a maintenance release incorporating changes to 4 default parameters that have been optimized since 2.9.1 was released.  There are also 4 minor bug fixes.  There are no code function changes or additional features.
The changes are:
1) reduce default INS_MPU6K_FILTER to 20hz
2) reduce InertialNav Z-axis time constant to 5 (was 7)
3) increased max InertialNav accel correction to 3 m/s (was 1m/s)
4) reduce yaw_rate P default to 0.20 (was 0.25)
5) bug fix for alt_hold being passed as int16_t to get_throttle_althold_with_slew which might have caused problems if you climbed over 320m.
6) bug fix for throttle after acro flip (was being kept at min throttle if pilot switched out of ACRO mode while inverted)
7) bug fix to acro trainer to do with roll correction 
8) prevent cli from being entered more than 20seconds after reboot.
Users are recommended to:
    Update Mission Planner to 1.2.41 and
    Update their flight code to 2.9.1b from the Firmware tab on Mission Planner. There is no need to go through a new configuration process in the Mission Planner.


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Thanks Nathan, that was very useful, I found that enabling "Show hidden devices" in Device Manger and uninstalling Bluetooth devices that are no longer connected worked on one PC and even worked with a Bluetooth mouse installed, on another PC a Bluetooth mouse connected and it stays slow. I don't accept this is not a Mission Planner problem, plenty of other programs on the same PCs that have drop down COM Port lists don't do that. You can't see it when it runs fast but when it takes 30 seconds you can see it slowly scan for ports twice which as to be a mistake. Thanks for your help.

Hi Randy,

Done the Radio calibration. Turned on the RAW logs. Did live calibration for mag as well. Still the same symptom as before when in wind.

As for your question, loiter moves around, it's both the horizontal and vertical, and definately doesn't look a toilet bowl, but random move horizontally and vertically.

Often, when it hovers alright at Althold with no wind, as soon as the wind blows on it, it will either go up or go down, for like 2 meters, then re-adjust its position again. Is it my gain not high enough? Have flown in fully manual mode, P & I gain seems quite spot on already.

Attached new logs recorded hour ago, tried Stab, Alt hold and Loiter.

Hope you could spot something. And looking forward to the great V3!


I have got a problem to know when my copter is armed or not.

The APM is sitting inside a dome. So it's leds are hard to see. Some time ago I used to fly the mikrokopter which did spin its props when armed.

APM2.5 (and newest firmware) doesn't do anything. No motor-beep, no flashing bright light, no speaker sound.

Wouldn't it be possible to make the software show it's state more visually?

What do you mean? With the 2.9.1b code, and also with the V3 beta the buzzer double beep when arming and leds goes solid.
You can play with this define in your APM_Config.h to idle your motors even with the throttle to zero when they are armed:

#define MINIMUM_THROTTLE   130  // from 0 to 1000

Lately I have not tried but it should work, behaving like Mikrokopter board.

I guess 2.9.1b (the last official firmware the planer would flash)

How do I get the V3 beta?

On GitHub or in the latest planner inside "beta section".

Thanks for the this information. Will check it.

Yes I was a Captain for Bristow Helicopters flying IFR equipped North Sea heavy helicopters (Super Puma) and also have friends that fly SAR (Search and Rescue) helicopters with even better autopilots than we had. Ours were SFIM or Honeywell-Sperry full axis and supplied by Aerospatiale now known as Eurocopter. The Bell 212's used to a have a more rudimentary Bendix/Collins system. The SAR 212's had a much more fancy system.

When operating near the poles magnetic is totally useless so they don't use it. But of course the price tag was somewhat different, millions as opposed to a couple of hundred dollars which probably explains the accuracy!

I don't know to answer your question, maybe they didn't totally get a fix until we moved slightly. I just remember that they initialised while we were stationary. I doubt SFIM or Honeywell will tell you how they work, but you never know, it is always worth asking.

How do flight simulators work as they don't have magnetic inputs?

You can make LED extenders so you can mount them however you like, or if you hook up telemetry you can see the arm/disarmed state simply on a phone/tablet/computer


if wind blowing on it makes it climb or descend then in could be an aerodynamic effect but I'm pretty sure you have the foam over the bark right?  all APM 2.5s come in a case now with foam already installed over the baro.

I'm away from my computer today but will check your logs tomorrow.

very interesting.  I think I will have a talk with fridge who wrote the drivers to see what he thinks about this.  nice analysis!

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