Posted by Wayne Jones on August 14, 2012 at 6:43am
I need help please. I have made a couple of custom hexacopters. My favorite frame shape is the U-shaped Hexacopter. Unfortunatley I am not arduino gifted. Fortunately I do have the DJI wookong. They have a nice custom motor mixing table which makes any custom frame design easy to program, all you need to do is to write in the motor percentages.So my question is how can I change the motor power percentages in Arduino code to do this?
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the motor factors were my best quick guess versus optimal thought given the prop directions:
CW CCW
CCW CW
CCW CW
but, prop rotation does not alternate (CW to CCW to CW to CCW) as on other ships. i'm not sure if this matters in terms of noise or effienciency.
is there a solution if the props alternate is in the following?
CW CCW
CCW CW
CW CCW
if there is, then all the props move the same direction when passing each other.
what are your thoughts on this?
Joe Gordon > Forrest FrantzOctober 16, 2015 at 8:52pm
I have mine setup with alternating prop rotation. as in your second case. Vertical thrust factors would be the same in both cases. Torque factors for yaw might vary but I am not sure the code accounts for varying arm length. My assumption was that keeping sets of arms of equal length from COG to opposite rotation would produce the best balance.
I am not seeing any ill effect of this setup. Seems to fly well.
I would think this would be best for efficiency since prop tips and airflow would be moving in the same direction. I would expect this to be secondary to the overall effects of prop size and RPM etc particularly if these is a significant distance between prop tips. Also any turbulence due to props moving in opposite direction would seem to be minimized and these could be somewhat quieter although I am not sure if this is a big effect.
pitch and roll motor factors are affected by arm length (radius to CG axis).
yaw is only affected by rotation direction and the radius of it's rotating mass around itself. thus yaw motor factors can be altered to remove coupling between roll and yaw and pitch and yaw.
you may have minor coupling between roll and yaw where yaw will also impart a bit of roll and roll will impart a bit of yaw.
i don't understand how a U can can each arm the same distance from CG. can you send me two things:
1) the x/y coordinates for the left arms
2) the roll, pitch, and yaw motor factors for each motor (this will tell me if there is coupling
Joe Gordon > Forrest FrantzOctober 25, 2015 at 3:22pm
Forrest,
I have worked on the the calculations a bit and done some cross checks.
I have added a Excel add in to allow me to use the Moore-Penrose Pseudo Inverse method to calculate the motor command factors for non symmetrical copters (also works for standard symmetrical configurations).
And redone the coupling check calculations and verified with standard HES X configuration.
There alternating motor rotation has a solution. Form my config it shows the minor pitch lift coupling I expected but for the case where the middle motors are on pitch COG it shows no coupling on any axis
Latest rendition with labels added to all three sheets.
Some corrections to coupling checks that I somehow messed up
I am trying to figure out whether the yaw should be normalized to the highest yaw value or the highest overall value. I think probably the highest yaw but currently is normalized to highest value in output matrix.
Replies
did you have the quad, hex, or octa worksheet. the hex worksheet need more optimization. the other two are good.
The CustomHexaCAD spreadsheet. I am using the U Hexa tab.
Are there issues or just improvements you are noting for optimization?
The motor matrix values corresponded to my calcs very closely so I think these are good.
Working on compiling now but running into some issues with errors = but first time on this computer so I guess to be expected.
the motor factors were my best quick guess versus optimal thought given the prop directions:
CW CCW
CCW CW
CCW CW
but, prop rotation does not alternate (CW to CCW to CW to CCW) as on other ships. i'm not sure if this matters in terms of noise or effienciency.
is there a solution if the props alternate is in the following?
CW CCW
CCW CW
CW CCW
if there is, then all the props move the same direction when passing each other.
what are your thoughts on this?
I have mine setup with alternating prop rotation. as in your second case. Vertical thrust factors would be the same in both cases. Torque factors for yaw might vary but I am not sure the code accounts for varying arm length. My assumption was that keeping sets of arms of equal length from COG to opposite rotation would produce the best balance.
I am not seeing any ill effect of this setup. Seems to fly well.
I would think this would be best for efficiency since prop tips and airflow would be moving in the same direction. I would expect this to be secondary to the overall effects of prop size and RPM etc particularly if these is a significant distance between prop tips. Also any turbulence due to props moving in opposite direction would seem to be minimized and these could be somewhat quieter although I am not sure if this is a big effect.
pitch and roll motor factors are affected by arm length (radius to CG axis).
yaw is only affected by rotation direction and the radius of it's rotating mass around itself. thus yaw motor factors can be altered to remove coupling between roll and yaw and pitch and yaw.
you may have minor coupling between roll and yaw where yaw will also impart a bit of roll and roll will impart a bit of yaw.
i don't understand how a U can can each arm the same distance from CG. can you send me two things:
1) the x/y coordinates for the left arms
2) the roll, pitch, and yaw motor factors for each motor (this will tell me if there is coupling
Forrest,
I have worked on the the calculations a bit and done some cross checks.
I have added a Excel add in to allow me to use the Moore-Penrose Pseudo Inverse method to calculate the motor command factors for non symmetrical copters (also works for standard symmetrical configurations).
And redone the coupling check calculations and verified with standard HES X configuration.
There alternating motor rotation has a solution. Form my config it shows the minor pitch lift coupling I expected but for the case where the middle motors are on pitch COG it shows no coupling on any axis
Torquw factors
1.000
Motor Command factors
Coupling Check
grea
I have added an octocopter sheet and it is working well. I need to add code generator for 2 added motors.
Matrix calculations now happen automatically once add in is loaded in Excel.
Made some changes to the graphic copter display to dynamically update motor number and prop rotation on graph.
Doing quad sheet next.
Latest rendition with labels added to all three sheets.
Some corrections to coupling checks that I somehow messed up
I am trying to figure out whether the yaw should be normalized to the highest yaw value or the highest overall value. I think probably the highest yaw but currently is normalized to highest value in output matrix.
I believe this would limit yaw authority.
JSG ModCustomHexaCAD2.xlsm
Use this file Found same reversal of sign in Oct and Hex sheets.
Now changed.
Also put the S octo input into sheet and comes out with no coupling solution.
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