Hello,
I ran across this thread over at google code drones discussion and would like to bring attention to it, hoping 3DR chimes in and can clarify if indeed the rear blades need to be swapped (and documentation updated to reflect this). You will notice on your Y6 that if you yaw, it induces a pitch change. Here is a portion of the discussion where a solution is found:
Problem definitely solved : it was caused by the rear arm propellers arrangement (reversed compared to the front arms).
Here is how i did solve it :
- put a pusher prop on the rear arm upper position (instead of the normal one)
- put a normal prop on the rear arm lower position
- exchange ESC outputs for those two motors and reverse spinning directions
So now i have an Y6 with the 3 pusher props in upper location on the three arms.
No more Yaw / Pitch coupling at all.
This is confirming what i thought, a thrust asymmetry is induced if a propeller tandem is reversed on a arm.
The probable reason :
On a coaxial setup the two propellers of a same arm do not have the same efficiency. During yawing, we are accelerating three propellers, and slowing down the three other ones.
The problem is that the vertical thrust result is not the same if one arm has a different prop arrangement : rising the speed of the lower prop is more efficient than rising the speed of the upper prop.
So if two arms of the Y6 frame have pusher props in the up location, and the other arm have the pusher prop in the lower location, then when yawing one side, we produce a different vertical thrust on the rear arm compared to the front arms, because we are not speeding up the same arm propeller. This is causing a pitch derivative coupling.
The coupling is only derivative because the induced pitch unleveling is compensated by the APM accelerometers as soon as it is detected but with a small delay.
So the definitive solution is to put the three pusher props in the same location on the arms. That's it.
I think that reintroducing a top bottom ratio is not the solution, at least not without a more complex motor mixing to avoid axis coupling.
Olivier.
If a simple change can increase stability, I think it's really worth looking at and addressing.
Replies
Hi all,
Brendan already posted my summary.
Basicly 10's on the top and 11's on the bottom are ever so slightly more efficient. However, the lower motor and esc tends to get hot and the copter isn't as agile. Tests by others apparently showed that using different props top and bottom results in less control during motor out situations.
I personally recommend 10's top and bottom for performance, reliability and simplicity with very little compromise in efficiency.
thank you for taking the time leonard, it is much appreciated.
hi!
Sorry to hear about your bad luck. I had a lot of issues myself when I ordered my kit a few months ago, (wrong ESCs, bad motors, badly soldered components) sad to read it's still going on.
The truth is no one knows and I have yet to find a definite answer.. basically have to try different configurations and see what works best. Leonard (one of the devs) was supposed to be getting a comped Y6 & different prop configuration around christmas time to use his in-depth knowledge to find the best prop config. I have no idea what happened with that - I hope he reports back!
Ok Tried doing the prop change thing, but ran into a few issues :
1. we changed all the esc-apm wires, (apart from 4 I think), according to this thread. When changing the frame to 10, during the motor test the motors would spin in a "all over the place" sequence. When I change the frame back to 1, only then did they spin Right top then bottom, Left top then bottom, Back Top then bottom.
Can someone confirm the motor numbering now, and the correct order they must spin in again for me please?
2. I am unsure about the A vs B firmware implementation. Do I load a new version of the firmware? If so which esc wires do I change, and does the motor sequence change too?
3. Once we changed the props, and took it for a flight, the y6 flew ok, even in strong wind, but the only thing that seemed weird is that the yaw stability has gone for a ball. The Y6 will sometimes spin around in windy conditions instead of holding its heading. do you think this could be Yaw Pids that need adjusting, or related to the above. She flew rock solid and great yaw holding before the prop swop experiment.
TIA
Wessie
Thanks phillip! That was the issue - flying very well now after re-configuring the motors. only thing I do notice with this new config is that if you are hovering then give a high throttle, it seems to yaw slightly - otherwise no complaints! I would definitely suggest making the change to any Y6 users.
Looks like the new Y6 configuration was included in the 3.1 release which is great news. Has anyone tried this yet on 3.1? or have been flying the new configuration (motor mapping with all top props CW, bottom pros CCW)? any feedback would be helpful
lots of proper tests here.. http://www.pulsosystem.com/u39m-280.html
Any update to this?
One key factor that no one has mentioned is that the Y6 uses differential propeller sizes on the upper and lower rotors to achieve greater efficiency (+10%-20%). If you use all of the same props, swapping the directions could make sense to remove any pitch/roll coupling.
However, none of the Y6 copters ship this way. What happens if you have three smaller upper rotors and three larger lower rotors? Well, you end up with a torque differential. In an equal power output state to the 6 motors, the aircraft will have a tendency to yaw in the direction of the smaller motors. That causes the smaller rotors to speed up, and the larger rotors to slow down to maintain yaw stability. You will also have difficulty yawing in one direction and overpowered yaw in the other. This also upsets the co-axial flow of air through each arm if they are matched for efficiency, which could remove the efficiency benefits of differential propellers in co-axial arrangements.
This change could potentially induce very complex and detrimental control interactions in pitch roll and yaw that may or may not be able to be solved in software. I would be very careful in making changes like this using the more efficient prop differential configuration.
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