I plan to do what is called a "pull" to made changes to the custom code regarding custom shaped copters.  

This change in code would only impacts irregular shaped quads, hexas, and octas when the pilot specifically opts to go custom versus the default (the standard X or +).  You have a custom quad if the:

o aspect ratio <> 1 (length is different than width).

o rotors are non symmetric around the

   - forward axis (y) going through the center of gravity (CG)

   - sideways axis (x) going through the CG

   - vertical axis (z) going through the CG

o has a front that is more open for a camera

o deviates from the pictures of a a + or X for the quad, hexa, or octa

o this includes ships described as spider, V, H, U, 88--88, C, etc.

o motor spin direction(s) are different than the pictures

o your CG is pushed somewhere else besides the centroid of the motors.

The advantages of going custom is that the motor factors will be tuned to the coordinate/spin system of your copter versus the coordinate/spin system of the regular copter.  They will fly better.  Pilots will probably not notice small deviations nor would they see significantly improved flight times.  Large deviations might be noticed and provide noticeable changes in flight duration.

Please reply with the motor number (the out-pin number on the APM), coordinates of the motor, and rotation direction of each rotor.  For example,

the owner of this copter would reply (motor number, x, y, CCW/CW):

o 1 (400, 200) CCW 

o 2 (-250, -200) CCW

o 3 (-400, 200), CW

o 4 (250, -200 CW

[note:  no need to tell us your units of measure just so long as you are consistent in measuring; say mm or inches]

Please note:

o The center of gravity of any quad spider or V is not necessarily where the bars cross.  The bars typically cross behind the CG.  .

o The CG is the center of the coordinates or (0,0) where x=0 and y=0

If you decide to participate by replying, the idea is that you will be able to access your custom motor factors without having to compile firmware.  No promises at this point.  First we see what's out there.  But if you do reply, it's far more likely that your design will be implemented in the library.  

If you have any questions or difficulties in doing this, let me know so I can help.

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Replies to This Discussion

Currently the code doesn't allow you to modify the mix matrix directly, and also doesn't support a throttle factor in the table. I hacked the code to for my V-Tail design to add the throttle factor (since the rear props are angled) and am quite pleased with the result. 

I think the best solution would be to have a custom frame mode in mission planner that lets you populate the mix matrix (including a throttle factor) to your liking. You could then use an external program to calculate the optimal factors based on geometry. 

You photo above looks like it assumes all props are level and on the same plane. I think the general case would have a z axis value and a pair of angles to indicate tilt for each prop:

love the photo and thanks for the parameter suggestion on throttle

totally agree that the parameters should be in MP

will try to find out the possibilities of that for APM and or PX4

did this die or what?

I'd be interested in learning more.

I'm working on an H frame type.  (actually more of a capital letter I )

Can someone answer a question on the I or H design versus the X?

So obviously there is not difference in an I, H, or X in terms of motor location.  All three frame types can locate the motors where ever you want them.  So this question is in regard to frame design.

- H has two motor masts plus a central beam.

- I is simply a sideways H.

- X has two motor masts.

The advantages of the X over the H and I are:

- Frame weight as the motor positions can be supported with less frame material

- Motor to motor stiffness as lifting of one motor immediately lifts the two adjacent motors without the forces acting through a 90 degree joint.

- Wire weight as wire runs to the motors are shorter

- Frame stiffness as the X easily becomes, with the electronics platform, a series of triangles versus a series of rectangles.

So what are the advantages of the H and I?

In order to get the attention of the design team, we need to show them that there are many of us. 

Hi Forrest,

All the H I tried and have self-built were not behaving as good as the X :

-twist forces in the central body of the H

-yawing issues

So why H ? pure hype & fashion I guess (some say to have props out of the way when filming)

that is my impression too.  guess they don't realize that changing the X angle does the same thing.

Forrest, Have you made this change or do you still plan to make it?  I am building a quad using a Flip FPV Pro frame.  After reading all this stuff and looking at the frame, testing its stiffness, I think that I would benefit from configuring it as an H to get the props rotating so that they assist with the yaw.  I also think that this change your propose would help because this frame's aspect ratio is not 1:1.

Do you plan to add this to Mission Planner? Would this be some sort of beta build? How would I get it?

We need to get the attention of the development team to make the motor factors variables so that they can appear and be edited in mission planner.

But, the good news is as long as you keep the shape rectangular, you can make the adjustments to the roll and pitch P(ID) for the same effect.  Normally the two are linked.  Change roll P to .15 and pitch P also changes to .15. There is a check box that you can uncheck.  Then adjust the two individually.  My guess is that you will only have to make the P (not the D or I) different.

The only problem for a quad comes when you make a trapezoidal shape.


Is this possible now in their latests releases?



- Under Config/Tuning

- Extended Tuning

- Right below Stabilize Roll P, you will see a check box marked Lock Pitch and Roll Value

Uncheck that box.  Then tune as required for your rectangular ship.  The Pitch and Roll P values should end up approximately proportional to Mass x Distance^2.  If mass is evenly distributed, then simply D^2 from the hub to the rotors.  But report back as to what you find out.  The working relationships might be different.  We are all learning here.



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