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Discussion Forum

Problems with Ducted fan design with standard PIDs

Started by Sean Headrick. Last reply by Ed Kirk 8 hours ago. 35 Replies

Hi Guys,  So I have been working for a couple (few) months an this design it was a long held beleif of mine that ducted propellers would only have a detrimental effect on flight efficency. After…Continue

Custom Autopilot development - Theory through Implementation

Started by Wil Selby. Last reply by Wil Selby on Saturday. 3 Replies

I started this project wanting to learn more about the ArduCopter software that was powering my APM board and 3DR Quad-C frame. I found …Continue

Tags: equations of motion, MATLAB, autopilot, Control System, ArduCopter

GPS err in altitude vs. flying a drone at low altitute 3 mts

Started by Darius Jack Nov 23. 0 Replies

Hi,I would like to study GPS err in altitude,since Cala suggested problems flying a drone at 3 mts altitude in agriculture.Laser Developer offers Lidar technology solution.Let me know your  opinion…Continue

Motor spin slow than others

Started by Cristian Rougier. Last reply by Khoa Vu Nov 22. 19 Replies

Hello, all , im working with APM 2.5, in X configuration, when i arm the APM, one motor (motor 4) spin slow than others 3.When i calibrate the ESC's in automatic mode, all spin with same speed and…Continue

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Comment by Andrew McKinstry on December 17, 2012 at 10:10am

Hello.. Shiny new hexa with all the toys about to leave bench (I hope).. however prop clearance issue! Or am I missing something.. 880 motors 11x4.7 props


Comment by avionics on December 9, 2012 at 9:45am



Hi Guys

I was in the middle of tuning for my Loiter and suddenly the quad started coming down out of control and crashed. Luckily no damage but it went out of control. this is the log i appreciate if any one can help and see what went wrong. thanks




Comment by avionics on December 7, 2012 at 8:16am

OK I got the Loiter going almost good. I had problem with my CH_6 knob on TX. fed the info directly from the ground station. all good for now. Thanks.


Comment by avionics on December 6, 2012 at 10:26pm


Randy thank you for the response. Frankly I dont really know what to look for in the log. any idea what i should expect in the log? sorry I have never done this before.

Comment by Randy Brazeau on December 6, 2012 at 11:38am


Have you reviewed the logs? That would be a good starting point to see what is happening.


Comment by avionics on December 6, 2012 at 11:04am
I have a H.A.L quad by hobby king with 1200kv motors and freshly assembled. It flies beautiful in stablise and alt Hold and when i try to loiter it doesnt hold its position. The GPS both LEDs are locked and steady before i start. It drifts and loses altitute very slowly. Tried playing with PIDs but no luck. I ran out of ideas appreciate if anyone can throw some light. Does the WP loiter config PIDs have any effect whilst on loiter or it is only for when on Auto mode? Thanks for the help in advance.
Comment by Chris Gough on November 29, 2012 at 1:36am

@Shayam, if you want to experiment with quaternions, DCM, euler angles, etc. you might want to check out the various pluggable AHRS subsystems in paparazzi.

Comment by Shyam Balasubramanian on November 29, 2012 at 1:24am

@Randy, Thanks for that nice explanation on accelerometer with quads! Now, my understanding gets better.

I would want to try out Quaternions once myself, it seems different people are having different opinion. My friend, who works purely on Quad uses quaternion. He mentioned to be that it was 'much' faster than DCM. But, since truth is one but scenarios differ, I will ask him if he can lend me some benchmarking ;)

Comment by Randy on November 29, 2012 at 1:15am

@Shyam re Quaternions,

     There's a thread by Bill Premerlani re DCM vs Quaternions.  My understanding is that they're equivalent.  II think perhaps DCM is faster but maybe not, i'm not sure.  I don't think it's as simple as one has 4 elements so it's faster than the other that has 9.

     When the copter/plane accelerates in any direction, the accelerometers sees this.  The problem is that we generally use the accelerometers to tell us which way is down.  So any acceleration of the copter/plane has the potential to throw off our attitude estimate.  Normally the accelerations are short-lived so they don't cause much problem but if they're long lived (for example you're constantly travelling in a circle) it can be a real problem.


Comment by Shyam Balasubramanian on November 28, 2012 at 3:51pm


Thank you for your thoughts on implementing quaternions. I have a question, quaternions are supposed to be faster as they use 4 elements unlike DCM which uses 9, and does not suffer gimbal locks (even DCM does not, but one should know how to avoid it there though), it must result in faster computation right?

And what does "the centrifugal (centripetal) force which can throw off the accelerometers" means?



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