GPS offset?

ArduCopter Copter 3.2
1

Hello all

I had a thought today that I cant find a good answer to. I have a 650 quad with Ap2 with external GPS and compass. The GPS is mounted on a stand in the rear center.

My assumption is that it should be in the middle of the craft at the center of gravity? If so… Is there a input to tell the board that its mounted x centimetrs to the rear? Or… am I dead wrong?

T

2

I don’t think there is although I would like it if there was. My last configuration had a GPS tail and it rotated about the Gps in loiter.

sent from my phone so apologies for any typos

3

Good point. I will check if mine does that too. I guess it should be moved to the center in that case.

  • I just had a second thought reading your comment, I am planning to do video and stills with this build. And if it is so that it rotates around the GPS - perhaps its a good idea to have the GPS above the camera instead? Anyone with thoughts about that?

Still hope for that offset setting, kind of like to keep it in the rear.

T

4

I think ideally you need the GPS as close to centre as possible as that’s the point used for any GPS fix. I built a Tri for a friend and when flying it in PosHold when he comes off the sticks you can see the frame almost pendulum (under braking) with the GPS receiver as the fixed point.

On my quad the GPS was mounted up front so yawing while in loiter produced a spiral rather than a spin. After moving the GPS to near the COG/COT the yaw now produces a nice spin.

5

[quote=“MrTeeJay”]Good point. I will check if mine does that too. I guess it should be moved to the center in that case.

  • I just had a second thought reading your comment, I am planning to do video and stills with this build. And if it is so that it rotates around the GPS - perhaps its a good idea to have the GPS above the camera instead? Anyone with thoughts about that?

Still hope for that offset setting, kind of like to keep it in the rear.

T[/quote]

From a transportabilty point of view i really liked the rear mount. other than yawing on the spot i didn’t have any issues.

What altitude and distance from the things in shot are you going to be. unless very very close the offset yaw won’t be noticable.

Thinking about how the problem would be solved in the software isn’t just a matter of adding or subtracting a hard number for the gps position. The code woul need to use the compass data and translate the offset based on the heading. With the newest generation 32 bit based brains this is probably achevable, but could end up in problems if a compass isn’t accurate enough or interfered with. It could end up with toilet bowling on steroids as offset could be wrong and also changing, on top of any toilet bowling there would be without the offset.

For normal video type work I don’t really see the offset gps causing an issue.

I am currently using a folding mast, but may go back to having a tail. Its just far less fuss for transport and setup.