Working on the next revision. Here's what's coming:
- Moving imu and baro calibration to the arming sequence, anything else?
- Simple mode with alt hold?
- Tridge's max motor fix for Hexa's and Octa's
- A new Octa setup from Hein for better performance.
Please fire away with any suggestion or issues. Mostly looking for fixes and improvements to existing features so we can finalize this version of the code and move to the next generation.
What's done so far.
todo move ground start to first arming
added ground start flag
moved throttle_integrator to 50hz loop
CAMERA_STABILIZER deprecated - now always on
renamed current logging bit mask to match APM
lowered NAV_LOITER_P to 1.0
increased NAV_LOITER_D to .6
added MASK_LOG_SET_DEFAULTS to match APM
moved some stuff out of ground start into system start where it belonged
Added slower Yaw gains for DCM when the copter is in the air
changed camera output to be none scaled PWM
fixed bug where ground_temperature was unfiltered
shortened Baro startup time
added MA filter to PID - D term
decreased Nav_WP_ kI term
fixed issue with Nav_WP integrator not being reset
RTL no longer yaws towards home
Circle mode for flying a 10m circle around the point where it was engaged. - Not tested at all! Consider Circle mode as alpha.
Enclosed is where I'm at so far. This is fly
Ok cool. That's what I wanted to hear.. Looking forward to your video!
Propeller size (inertia is proportiaonal to the square of diameter) and motor torque is an important factor i think, even more than ESC update speed as soon as the frame is in the heavy lift size.
Processor power is important as well for best results, because PID closed loops are simple and efficient, but not optimized for best dynamics.
Prop efficiency is something that starts to become very noticeable with heavy lift quads. My latest design is 35% more efficient than it's predecessor. No matter how many times you do the calculation a quad comes out on top in comparison to a hexa or an Okto. The others are absolute non starters in that race. Having the props below the arms is a big improvement as aerodynamic drag is a square law. Mounting the props close to the backplate reduces overhang and thus vibration also. Lift efficiency is almost a function of how much diameter you can absorb the available power into. The thrust velocity should be matched to be just above the airspeed that you will fly at. So if you fly at 100 mph then you need a small toothpick prop with a high pitch angle. but in our case we need a slow moving high volume of air movement i.e. large dia small pitch angle and wide blade profile. a 14x4.7 came out on top when testing on my motor dyno. It was also the top performer on Holgers tests. Better stabilization from a high degree of efficiency does not always follow. A little less dia. can smooth out the response if the pid settings are not great.
I am considering mounting my props on the underside of my octo frame. Main reason I went for the octo configuration was for redundancy. When carrying expensive equipment I just appreciate that extra peace of mind. I am really curious to see how the inverted prop mount will affect my efficiency. That translates into longer battery life correct?
Could you explain how having the props below the arms offers increased efficiency?
The low pressure air that flows into the top side of the prop. swept area comes in from all directions especially from the sides. It does not really notice the laminar flow arm. The thrust side of the prop. converges that flow inwards and therefore at greater dynamic pressure. As that flow is a square law i.e. double the velocity and get four times the drag then you are effectively using your own thrust to push the model downwards due to the less than ideal profile of a square arm. I cant remember exactly how much additional lift that gave but it multiply it by 4.
There is one other factor that starts to play a role and that is due to the center of aerodynamic pressure created by the lifting propellers. If the center of mass is significantly lower, then the motors will need to work a lot harder to stabilize the model. This is because the low center of mass wants to swing about like a pendulum when there is a lateral movement. I have two models here one with a high thrust line and one with a low thrust line. guess which one gives 35% more duration.
Thanks for sharing. That is incredibly interesting! I love physics! I think that switching my props to the bottom side would really be beneficial in my case because I carry heavy equipment under and having the props closer to the CG would be more stable. I never considered that. Thanks again!
Is there any reason one could not mount two opposing motors pointing downward and the other two upward? Then all four props could be the same without the need for pusher props.
Yes, props are designed to spin a certain direction, you simply can not reverse the direction the prop spins....
as Don said, you cannot simply flip a prop and invert it's rotation. The props are not simetric, they are build to rotate in one way. If you want to use 2 motors counter rotating each other, you'll still need CW and CCW props on both, with the bottom one flipped regarding to the motor (pushing air down).