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Your Opinions Please on X/Y Motor Distance on Quads

Cyberdactyl

Misfit Multirotor Monkey
#1
As some may have seen, I have an ultra bright LED module I can attach to my tricopter.

Currently, I am building a dead cat/H frame hybrid, and I would like to also be able to use the LEDs on it. So I angled the booms to fit.





However, I have a slight concern the hybrid's from-to-back/side-to-side spacing ratio which is 0.73%. I am worried the pitch is going to be hyper sensitive. I realize I can use a crapload of expo on the elevator, but I was wondering if anyone thinks I will run into any other sort of freaky handling?
 

xuzme720

Dedicated foam bender
Mentor
#2
I doubt it. It looks like the same spacing ratio as the true H-quad as opposed to an I-quad. So, pitch will be more sensitive but if you know that going in, a little tuning should take care of that, either with expo or stick scaling...Looks like it will be fun!
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#3
CD,

That's gonna be a nice flying spotlight ;)

You're right the physics should make it more sensitive in pitch axis, but as long as your CG is good, board is centered, and your motors are level, I'd think your control board can dial that down for you (or dial up the roll throw to match, physics allowing).

Remember that board is flying the copter, you're just telling it "how to" in setup and "where to" in flight.

B̶T̶W̶,̶ ̶m̶i̶g̶h̶t̶ ̶w̶a̶n̶t̶ ̶t̶o̶ ̶p̶u̶s̶h̶ ̶t̶h̶a̶t̶ ̶K̶K̶2̶ ̶b̶a̶c̶k̶ ̶a̶ ̶b̶i̶t̶ ̶t̶o̶ ̶g̶e̶t̶ ̶i̶t̶ ̶u̶n̶d̶e̶r̶ ̶t̶h̶e̶ ̶C̶G̶ ̶(̶C̶G̶ ̶i̶s̶ ̶a̶t̶ ̶t̶h̶e̶ ̶c̶e̶n̶t̶r̶o̶i̶d̶ ̶o̶f̶ ̶t̶h̶e̶ ̶m̶o̶t̶o̶r̶s̶,̶ ̶r̶i̶g̶h̶t̶?̶)̶

edit -- scratch that. didn't realize that was a front on shot. Gyros/accels are just about right. my bad.
 
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Cyberdactyl

Misfit Multirotor Monkey
#4
Thanks for the input. Yea, I suspect it will fly fine. I don't think there would be a real problem with stability until the X/Y ratio approached 0.6 or an Y/X of 1.6 or more. After 0.4 or 2.5, I suspect you would then approach the issues you might encounter with a bicopter.
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#5
If I'm understanding the dynamics correctly, most of the bicopter issues are from touchy CG balance -- you pretty much need to nail the CG to the line between the motor shafts. For a quad, you've got a box between the motor shafts, and the closer to the center the more even the prop-loading.

You've still got a fairly spacious envelope there, and shouldn't be hard to keep the front/rear CG in a happy place, so long as you can counter-balance the gear on the front. but even narrower, your prop spacing will force you to keep the "happy place" large enough it's easy to hit.
 

Cyberdactyl

Misfit Multirotor Monkey
#6
Also with a standard configuration of all the rotors being in the same plane, and not offset or overlapping, and having something larger than a non-zero prop radius :p, you can't get the ratios too far from 1 in either the X/Y or Y/X.