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APM 2.5 by a newbie

Started by happyal, Wednesday,September 11, 2013, 22:40:15

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Hello everyone,

I have bought a APM 2.5, GPS, external compass, OSD and a few other bits. I thought I would start a new thread to ask some setup questions, share my build process and document a fairly new copter pilots attempts at getting this control board working. I am currently flying a F450 with a KK2 board and it';s flying really well, but I want to move to a board with GPS functions.

Before I got the board I read the wiki, and I started to watch videos on youtube about the setup. I watched quite a few videos but this is the one that I followed when I setup my board.

Setup seem to go fine, everything on the screen is level. Compassmot was 2% once I moved the external compass away from the ESC';s (where I mounted it first time). Here is a picture of the completed multirotor. It has changed a little as I have changed the compass location and I have mounted the GPS high too.

Normal flying in stability mode works great, it';s unbelievably stable and so easy to fly. It is a little titchy, as it goes back to level as soon as you lift of the sticks, but I think this is a slight settings issue.

I';m having problems getting the GPS functions to work. It does get a lock, etc. but when I switch on a GPS mode it goes off in a random direction. I tried holding it, running it up and turn of GPS Hold mode. I noticed that it would give wrong messages to the motors, i.e. if I lifted the front, instead of giving more power to the rear to get it back level, it would give more power to the front? I have made sure that the compass is the correct direction (checked against a real compass), and the APM board is correct and calibrated. Does anyone have any idea what I';ve done wrong?

Once it stops raining here, I will post my log files up and make sure it';s not a vibration issue. I also haven';t been waiting for a good GPS fix, could the problem be as simple as not waiting long enough?


If its flies in ';stable';, then its not a motor wiring problem.
Could be a number of things - logs help. Firstly - you want to check that you';re getting a good GPS lock with an HDOP below 2 (or 200 if you';re looking in MP). If you don';t get that - it could be some interference - for example, my JR RX interferes with GPS quite a bit, so I had to separate them by 6cm or so.
If you';re getting a good lock, then check your vibrations - turn on IMU logs and check your vibrations. Does alt-hold work well? I';d try that before loiter..

Tony Campbell

GPS can take 10-15 mins the first time its switched on and outside to fully download all the info it needs from the sats. It has to download a surprising amount of info. Once that has been done, it takes 3 -5 mins on first startup of the day to get its proper fix. Although it will get a 3d fix fairly quickly, it really needs 7 or more sats to get a really good fix and will wander about a lot until it does finally settle down.

Neil R

My learning curve on lengthy GPS settling was reinforced by doing a simple switch on outside with the lap-top still connected (presumably easier if you have telemetry).  I was amazed how far your present position jumps on that Mission Planner Google-Maps page in the settling period. Suggest you try it and see how well yours is settling.


Quote from: rickp on Wednesday,September 11, 2013, 22:47:56 Does alt-hold work well?

Yes Alt Hold works great too.

I left GPS on in the house for about 30 minutes (I see from the threads it';s not a true measure), it did get a lock, but it was still jumping around a lot. I will do the same outside once it stops raining.

Tony Campbell

If you can, get it in a position outside, with completely clear sky visibility all around. Doing it in the house may get you a 3d fix, but it most certainly wont have downloaded all the info it needs from all the sats. And just like has been mentioned, if you have telemtry, use it to determine the holding pattern to ensure a good fix. Once you have allowed the gps to initialise properly, you';ll see a huge difference in the ';wander'; on screen. I';ve seen it jump 20 metres or more on screen, before it settles down. I reckon that, thats what your issue was. Keep at it, it';ll come along nicely  ~~


What GPS module do you have? As others have said, you really do need to get a good first fix and after that allow a 3 minute period before first flight of the day.

Also, have you set the compass magnetic declination? That is important too.

It sounds like you';ve got your APM nicely tuned to your air frame.

Sent from my C6603 using Tapatalk 4

"Its better than bad, its good"

Current FCs: Pixhawk, APM 2.6, Naza M V2, Naze32, Flip32+ CC3D, KK2.1.5
Aircraft: miniMax Hex, DJI 550 (clone) TBS Disco, 450 Firefly, 250 Pro, ZMR250, Hubsan X4, Bixler 2


Quote from: Tony Campbell on Wednesday,September 11, 2013, 23:05:23
Doing it in the house may get you a 3d fix

...but with most of the signals coming from reflections off the walls, with ';interesting'; consequences. Also, be careful with geofencing - if it';s enabled, it';s enabled, even if indoors, so if the position appears to move outside your geofence boundary doue to a dodgy indoor fix, off it will go on a quest for ';home';, wall, furniture or people be damned!


I would stop looking too hard at the gps for now  .
and go back to the compass and double check its pointing the wright way.
if so ,have you check your vibration levels in the logs?

if not do this next because most APM issues come from vibration .
How have you attached the APM to your frame ?

I run 3 frames  all with APM2.5    and 1  as a external compass all run well (touch wood).
I now use 1 layer of http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26457 under the APM and found it to be by fare the best for removing vibration.

Anyway if you can post your logs it may help
Good luck


Quote from: Hands0n on Thursday,September 12, 2013, 07:37:35
What GPS module do you have?

Also, have you set the compass magnetic declination? That is important too.

The GPS is this one: Mediatek-mt3329 v2


I currently don';t have a separate UBEC, I have read that this GPS likes a separate UBEC, I do have one on order.

I have not sent my compass magnetic declination, I have left it as auto.

Quote from: dazza22 on Thursday,September 12, 2013, 08:21:14
How have you attached the APM to your frame ?

At the moment it';s attached using Velco

Tony Campbell

Like the majority of us, I think you have fallen prey to that man thing, ';take it out the packet and plug it in';.
Hey, we';ve all done it with something at one time or another!!!

You really should mount the apm (you do have a case for it?) by something a bit better than velcro. The reasons for this are that firstly, velcro will allow slight movement on all axis. This will give problems with level readings. Secondly, velcro most likely isn';t the best at vibe absorbtion. Get some heli gyro mounting pads. They have adhesive on both sides and are about 3-6mm thick. Cut some 8-10mm squares and stick them to each other, two high. Stick these little towers to the four corners of the underneath of the apm case and then mount it to the frame as close to the centre as poss. This (at least for me), gives good vibe absorbtion and has the added benefit of raising the apm up away from the electrical and magnetic noise of the frame and all wires, motors and esc';s. Then you will have to balance all of the props, including hubs. Once you have that done, balance the motors. Then, using the logs ( you';ll find some good stickies on this site), to determine your vibration levels. Once you';ve got those, post them up and we can all see if you need to do anthing else vibration wise.
As far as setting your compass, I';d really recommend using the declination website to set you declination manually.
Also, please make sure that you do the compassmot and the ';compass dance';, making sure you do it outside if you can. It works much better than doing it anywhere near household wiring and central heating pipes etc. So......lots for you to do!!! Something else that sometimes gets overlooked is to make sure all cables are secured to the frame. Lots of vibes can be created by loose wiring, transferring the vibes straight to the apm case. Oh, nearly forgot..... I found that sticking a couple of self adhesive wheel balancing weights to the top of the apm case, increases its mass, allowing it to be less affected by some of the vibes. You can usually cadge a couple of freebies from a tyre fitting place.
If you approach this the right way, you';ll actually enjoy it and learn loads about how and why the apm works. Its certainly not a plug and play FC, but once set up, it works really, really well.

I';m sure there';ll be loads more help and suggestions coming your way, so try to absorb it all and should you get stuck, we are just a message away.  ~~


Thanks Tony for the information in the post.

I will take your advice and order the anti vibration foam from Hobby King now.


Also I will manually set the compass declination and go through the calibration routines again.

I';ll post logs when I can :)

Thank you all again for your help. It';s so nice for a newbie like me to get the benefit of your experience.p

Tony Campbell

You are very welcome mate. The tips I';ve given you are just the very basics. Hopefully they will help. Just one point though...... the anti vibe foam will help, but the main thing is to reduce your vibes by balancing as much as you possibly can. The last update of the APM firmware was superb, but in doing so, it made balancing props and motors absolutedly imperative. As virtually everyone on here will tell you, nearly every flight issue with the APM since the new firmware was released, has been traced to vibration issues. To be honest though, balancing doesn';t take long at all. Good luck  :beer2:


Quote from: happyal on Thursday,September 12, 2013, 11:16:57

Thank you all again for your help. It';s so nice for a newbie like me to get the benefit of your experience.p

There is a lengthy thread here http://www.multi-rotor.co.uk/index.php?topic=4006.0 That may help you a little. As Tony says, vibration at source is your biggest enemy with APM 2.5 and 3.0.1 firmware.  They use the ACCelerometers to help with Altitude Hold and other auto modes more than ever before (like a kind of inertial damping).  And it works very effectively indeed.

I have published a pair of APM log charts near the end of the thread where you can see what the Arducopter team suggest is "acceptable" vibration levels for X Y and Z compared against what I was able to achieve simply by balancing the Propellers and their Hubs.  Since then I';ve worked on the motors to reduce the vibration even further.  But before I did any of this vibration-elimination work the APM was very unpredictable and near impossible to control. 

Once you';ve reduced the vibration to as little as possible then you may be able to dampen whatever is left by fitting various materials between the APM and the air frame.  I went for Moongel, cut into four and double layered at each corner of the APM case (also worth getting one of those if you haven';t). 

"Its better than bad, its good"

Current FCs: Pixhawk, APM 2.6, Naza M V2, Naze32, Flip32+ CC3D, KK2.1.5
Aircraft: miniMax Hex, DJI 550 (clone) TBS Disco, 450 Firefly, 250 Pro, ZMR250, Hubsan X4, Bixler 2