1) Does the Pixhawk need to be at the CG of the copter (a la Naza)?
2) Does the GPS need to located in front of or behind the FC or can it off to the side as long as it is pointing in the same direction?
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Wow really nice looking ti-copter. Looks very sturdy.
How far away from the pix did you mount the gps? What kind of offsets did you get? Where are you esc's? thx
The ESC's are in the arms. They are HobbyWing X-Rotor 40A (no 30A option), but are still light weight. Motors are KDE 2814XF-515. AUW is ~3000g with 10000mah Multistar 10c battery. I should have bought 2 5200 (then will be 20c) because the 10c rating is overrated, actual in my experience is probably 4c. They work ok but definitely not for hard throttling once the voltage drops below a certain point because it can set off the battery FS.
After much experimenting with props, I was forced to switch from economical APC MR props to TM style CF; 15x5.5 Tarot on bottom and 14x5.5 no-brand on top, soon to be T-Motor 14x4.8 to attain a lower pitch.
It started with a 3DR GPS to test from my Y6B, then bought a CSGShop Neo-M8N. I don't recall what the offsets are, but interference is ~10%, was <5% but I didn't like the super long mast so shortened it up.
The weather has been so miserable the last few weeks, flying is on hold, plus I'm getting INAV alarms by the hundreds. Others are getting them, but no answer as of yet to what is causing it. If you have any suggestions, feel free to post. http://diydrones.com/forum/topics/csgshop-neo-m8n-is-giving-pm-erro...
The next copter won't be a co-axial I'm really liking the Steadidrone SIKS to go with these motors, and putting lower kv on this boat anchor on 6s.
One more question: I've read that twisting wires is good to prevent noise. Which wires should be twisted if any?
Here's how it ended up, but the wires are more organized now. So far everything works fine, vibration is very low and GPS/Mag is performing well, compassmot @ 1.7%.
And the power area. I wonder if it would be a good idea to secure a thin piece of aluminum or copper under Pixhawk?
If your receiver is in the same orientation you should be fine, but if your aircraft rotates the antenna to be pointing to or from your receiver you'll be toast. That's why generally both tx and rx are vertical: in LEVEL flight, any compass direction you point you'll have great signal. unless you're flying almost exclusively directly above yourself, I would not recommend the horizontal orientation.
In regards to the original post, Gary is right. You want it at the roll center (which is ALWAYS the CG, no matter what) but if you're off center then there will be some coupling of angular rates causing accelerations. As he says, this isn't a big deal, and the reason why is that accel data is typically used to reduce steady state error (leveling it off) when angular rates are typically negligible.
Thanks for the replies.
One more question, a bit off topic but since 3DR 915 telemetry is connected to Pixhawk, will positioning the antenna horizontally out the side of the craft negatively affect it's range? I think it will, yes?
Hi DG,
Generally speaking it is desireable for the Pixhawk to be mounted on the roll center of the copter which generally corresponds to it's C/G (assuming the CG is symmetrically between the prop centers.)
However mounting it a bit forward or back from center does not seem to have any deleterious effect.
Clearly Gyro response should be the same, but there will be some difference in accel effect since you are now actually moving the flight controller slightly up and down when you pitch it.
I have my Pixhawk about 3 inches forward of center and have not experienced any noticeable effect.
On my Hoverthings Flip FPV Pro Gimbal Quadcopter this is to more easily balance battery weight with camera and gimbal weight on a dead cat and end up with the CG where it belongs symmetrically centered between all the props.
The Pixhawk is between the battery and the camera.
The Gyros have the most effect in nav control in any case and the small amount of pitch motion on the accels has not had any identifiable consequence.
Best Regards,
Gary
Yes, it is best for the pixhawk to be as close to the center of your copter as you can get it. For the GPS, it just needs to be pointing the correct direction. To a reasonable degree it can be put wherever you need to to get it to fit.
Heres the install instructions for the GPS module. No mention of positioning requirements other than keeping it away from other components.
http://copter.ardupilot.com/wiki/common-installing-3dr-ublox-gps-co...
Also, dont forget to calibrate compass and accelerometer each time you change their position on your copter