Hi Guys,
So I have been working for a couple (few) months an this design it was a long held beleif of mine that ducted propellers would only have a detrimental effect on flight efficency. After discussing the dynamics
of a ducted fan and its effects on efficency I became aware of the potential for such a design. One of the largest hurdles was to create a duct design that would be light, durable and hold up to the forces applied during flight. We wanted to have a minimal prop/duct clearance but avoid any contact.
A carbon fiber design was the only logical solution. For all four props we were able to maintain the same or less weight. Also each duct was designed to hold two motors each. The clearance is <= 1mm.
We just had our maiden a couple days ago and I would say initial results were not bad. There is a lot of work to get the efficiency gains hoped for.
I am experiencing some problems that don't indicate a clear solution for me so I thought I would reach out for some insight from others.
On takeoff the aircraft seems to be fighting with itself. There are no clear indications of high or low PIDs such as jittering or sluggishness. What I notice is a constant yaw correction from the controller. At some points during the flight I will be attempting to correct or maintain a heading and the aircraft is steadily rotating regardless of my input. It also seems to have a noticable problem with altitude control.
I suspect there is some vibrations that could be aggravating the problems. I have looked at the accx, accy, accz values and noticed they did not look normal either. I noticed previous vibration readings in log files fell more in line with peaks and valleys. Here and more pronounced in previous tests the accx and accy are seperated quite a bit.
I will get some video tomorrow and post it to give a better idea of what i am attempting to correct. I have attached a test flight log that might contain more info. Currently param is default and works well on a non ducted quad with the same core components and weight. I am also getting a lot of errors like alt disparity, acc error. The horizon view also seems to keep getting out of level after many acc calibrations that seem to fix the issue temporarily.
Replies
I found that my ducted fans are more stable with lower settings.
I went to a controller with the capability to adjust gain from the transmitter while in flight, cuts down on trial and error. Just increase or decrease gain with the twist of a knob then enter settings when to my liking.
Ed
Hi Ed, which controller did you use that allows gain adjustment mid flight?
I was using a Multiwii Paris, I don't remember exactly how I did the mid flight gain adjustments. I was doing a lot of stuff with the 3DR tx-rx, back then.
Ed
I am replacing the controller to start with. I have always had great success with AC and the hardware. Pixhawk seems to me to be a very robust reliable controller and the Channel 6 tuning allows for the "in flight" adjustment of each PID value. I will try to see what lower p term does to affect flight stability.
Hi Sean, sorry for the ignorance - who do you mean when you say "AC" - did you mean 3DR?
But I can't help seeing the props mouted in the wrong order. In the picture above, the two front props both are ccw, the ones in the back cw. On a quad, the spinning direction should be alternating from motor to motor.
This would explain the behaviour you are experiencing.
With Regards
Marc
Good picking up on that. I don't even know if would have made it off the ground in that state. However I did check and all props are in the right orientation. That picture was during final assembly and it escaped me until after i had mounted the ducts that they were out of order.
This resulted in a very odd behaviour, but was clearly seen in the motor logs that half of the motors had to spin at 80% and the other at 20% to prevent yawing.
Here are the RCOU for channels 1-4
If you add yaw to this graph, you will wee that you have little yaw movement and maximum motor throttle changes. This clearly indicates a wrong mots/prop setup regarding order of motors and/or spinning direction.
Make sure you have selected the right frame type and run the motor tests so you can check the right order and spinning direction.
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