Awhile back there was a thread about putting the props below the CG in order to get a more stable design. Now on my plane I can get most of my quads weight above the CP......But Is it enough to count? Im going to attach a photo with one prop up, one prop down. Let me know what you guys think......
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This thread is a few weeks old, so my comments might now be unnecessary now...
Moving the CoG above or below the thrust plane will diminish maximum torque about the centre of mass and thus reduce the dynamic response to attitude perturbations. It won't actually make the quad more stable with regards to exogenous forces (such as wind gusts)... just less sensitive to small variations in thrust from the motors (so perhaps easier to control in manual flight). A good transmitter with an exponential rate on the stick would be a better alternative.
If you want to enhance stability in hover, tilt the motors toward the central vertical axis of the quad. You'll suffer a slight decrease in maximum thrust, but introduce a natural balancing moment whenever the attitude is perturbed away from level. You'll obviously need to re-tune your control loops to accommodate the changes to linear and angular accelerations at various throttle settings.
I think it's an interesting idea to try as well. I'll keep tabs. I wanted to build my Octo this way, but as it's ultimately designed to be a camera ship, I just couldn't make it work out practically.
Well, it looks like you would be shifting the plane of the props by as much as 2 inches. I would guess that would make a noticeable difference, but I don't have any test data to back that up. Also, you would be lowering the CoG by shifting the weight of the motors and props. At least it appears that you can flip the rotors without too much trouble (on my frame, the props would hit the bottom if I did the same change.). If you continue, it would be great to hear if the difference was significant. Not sure how to approach measuring "significant" in this context.
I was thinking that too, but there is a half sphere plastic dome that covers everything on top.
I think that will make a little difference but a much bigger difference would be to mount the battery (usually the heaviest component) on the top of everything instead of underneath everything.