Coaxial DoDecakopter

[Craig]

Guys -

I am inches away from deciding to use these 6 coaxial arms, six BL 1.2's, and six more motors to build a coaxial, 12-motor MK because,well . . . Why not!?

The thing I'm thinking aboutnow is motors. Rather than spend $240 on six more Roxxy motors (all out of stock except in Germany), why not use some of the cheap knock-around motors that some of the guys are using on their non-mk build, as detailed in the non-mk forum?

$15/motor sounds good to me, and since all six motors would basically be 'redundant' . . .

What am I missing?

[3rdeyepro]

Are you going to use 2 hexa power boards then stack them?

[Craig]

I would like to, but whereas I am pretty sure that I will be upgrading all 12 ESC's at some point, I'm just going to strap these six on the arms.

I guess I need to learn how to install the 'special software' to be able to address motors 8 - 12.

[Crash]

I would like to, but whereas I am pretty sure that I will be upgrading all 12 ESC's at some point, I'm just going to strap these six on the arms.

I guess I need to learn how to install the 'special software' to be able to address motors 8 - 12.

You remind me of that German guy in the 1700s. He strapped 16 Turkeys to his arms and wanted to fly.
I think his name was Einfach zu Fup-d-up.



//Just yanking your chain of course Do a google translate.

Or I'll do it: Easy to Fup up.

Have a safe weekend!

[Craig]

Well, I spent a lot of time researching motors, and I cannot seems to find any that meet my criteria:
A) Draw less than 25A max
B) Closely match the revolutions per volt of the Roxxys (1100 rev/volt)
C) Can accept a 4S battery

I'm sure they are out Ther, but since Crash called me a turkey or something, I guess I'll just go with the Roxxy's  . Holger is the only one with them in stock, so i will need to wait another couple of weeks.

I found two guys on the DE site who had started the switch to a coaxial dodeca, but could not find evidence of a successful flight. They did, however, direct as to how one should create an mkm file for configuration of the second six motors. I think they are mistaken, though. They direct that each arm should have motors running in opposite directions. That is, they say each arm should have a counterclockwise and clockwise spinning motor on it. But if that were the case, then it would seem that the craft would have no ability to yaw (because all arms would be in equilibrium). So I will design mine such that motors on top and on bottom rotate in the same direction.

I am also wondering about power now. I wonder if it would be better to run two 4S 5aH batteries in parallel (eq. One 4s 10ah battery) or if instead I should just connect the 'bottom facing' ESC's and motors to one battery, and connect the original six (along with flight electronics) to the other battery. I am leaning towards the latter option, only. Because it seems that I would be asking for trouble by having 12 motors sucking juice from those little pads on my original hexa power distribution ring.

Lastly, what is a good way to determine allowable (or at least recommended) payload once I get this thing built?

I can't wait to try it out! I wonder if it will vibrate itself into oblivion, or if instead it will be so smooth . . . I also am eager to see what sort of flight times I can get from such a monster!

Curse this all-consuming hobby!!

[Crash]

I think they are mistaken, though. They direct that each arm should have motors running in opposite directions. That is, they say each arm should have a counterclockwise and clockwise spinning motor on it. But if that were the case, then it would seem that the craft would have no ability to yaw (because all arms would be in equilibrium). So I will design mine such that motors on top and on bottom rotate in the same direction.

In the yaw mixer the clockwise motors get a 64 (or is it -64?) The counterclockwise motors get the opposite value. That means that during a yaw, one motor will speed up and the other will slow down. That causes yaw and neutralizes lift at the same time on each arm. There's probably a real good aerodynamic reason for it also. What happens when both props that spin in the same direction get in perfect sync with each other?

[Craig]

Excellent point! I guess I kept thinking that the FC would only be addressing six 'points of action', but of course it will have full control over all 12.

And, I have done the math, and it turns out that if I had proceeded with my 'swing the motors in the same direction' plan, and the props got in perfect sync with each other, it would irreparably damage the space/time continuum.  Well, ok maybe not, but your point is well made - thanks for the feedback!

[andyman]

I applaud your enthusiasm.  With all the talks of stalled motor, fried BL controllers, and sudden flips, having 12 motors up there seems like risky business.  Just be careful with that i2c bus.  By the way has any one investigated the impedance problem of a 12 way i2c bus?  Seems to me like theres a lot of potential for signal degradation due to transmission power reflection since nothing is impedance matched as you split the signal. 

andy