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
Very interesting! Did you see a noticeable improvement in performance and/or efficiency when running in contra-rotating mode?
Did you just feed the shaft of the bottom motor through the middle of the top motor?
BTW did you play much with different distances between the 2 props? I've read that this is one of the most important things.
Sorry last question :) Why not just use standard config motors with props mounted to go in opposite directions? Or is the distance between them in that case too much?
I did it because it was a challenge and fun and I am pleased with the results. Very smooth when done properly and a great platform for Cinema and filming.
I did a number of designs, the best results has a bearing between the upper and lower props inside the lower part of the upper prop adapter and lower prop nut which I machined to accept a bearing.
I found the difference between the props to be no big deal, just don't get them to close. 10 inch props start getting noisy when less then an inch or so and loose thrust.
Your standard setup works very well, by far the easiest way to go. My reasoning had nothing to do with distance. The counter rotating design is complex and requires some extra effort. There isn't much to choose from in the market. It's pretty easy to convert two flat or pancake style motors into a counter rotating combination, A lathe is a must. Motors with larger bearings makes it easier to convert and a way to bolt the two stationary plates to a mounting bracket is essential.
Ed
i sould have described it as a dual motor setup as opposed to coaxial. The ducts are designed to hold either one or two motors. I had been interested in trying out some of those coaxial motors when I saw them start to be available. Do they operate on two independent speed controllers? Did you ever experiment with more aggressive pitch or higher Kv in the aft motors to deal with the increased inlet air speed?
The large shrouds create a substantial surface area which is effected by air flow and wind. With the extra power of two motor/props in each shroud it should fly better plus less weight per motor when doubled up. One of the things I wanted to try was to put a short shroud around one of my coax systems.
If it were my choice I would try a Y6 over the X8, simpler and less parts and I like the way a Y6 flies.
Each motor requires an ESC, I even used two ESCs paralled to a single control output on a tricopter since yaw is controlled by rotating the rear set of motors (motors rotating in opposite direction). Even paralled two motors rotating in the same direction set up as a Hex with 12 motors.
"Did you ever experiment with more aggressive pitch or higher Kv in the aft motors to deal with the increased inlet air speed?" This seems to be the most common question that comes up when talking about coax counter rotating motors. I just don't think it is necessary especially on a multirotor because of the torque. Just creates a real control nightmare.
The two videos attached below are my second effort at a multicopter, I was testing both coax motors and a my design of a tricopter with a rotating boom. Since I am not interested in going into business and selling I gave the rotating boom design to a manufacture who is more suited then me to do something with it. It is part of his line of equipment.
http://vimeo.com/30604209
http://vimeo.com/30604735
I also did some work with shrouded props, Y6's and a hex with 12 motors/props, 24 batteries.
Cool - is that the 'lady gaga copter' ?
Very interesting. I guess mine is actually kind of small.
Great work, nice looking quad. I have build several tricopters with ducted fans and one quad all with the same motor/prop rotation. I used thrust vectoring for yaw control, you can see in the video the exaggerated angle of the EDF's. I don't think that much angle is necessary but it works so well I left it alone.
My biggest problem with ducted fans is ground effect, needs several feet above ground to settle in and get good control. Other wise control is awesome, rock solid.
Ed
http://vimeo.com/41811715
Ed,
I noticed a tremendous amount of ground effect to be sure. It is a big quad and I am trying to keep it in one piece as I get it dialed in but I have noticed it calms down a bit over about 4-5 feet altitude.I added more vibration damping under the autopilot.
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