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Old Jul 22, 2012, 04:02 AM
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Originally Posted by janoots2 View Post
My hexa lost full power today in the middle of a shoot and fell to the ground like a rock for no reason at all. I spent half the day rebuilding it and nervous as hell to try and complete my commitment tomorrow. Please dji fix this well reported issue!!!!!!!!!!!!!
Quote:
Originally Posted by janoots2 View Post
Wkm, maytech 30, avrotos, 8fg w/sbus. Had a full battery and was only about 30 seconds into the flight when the power motors just stopped dead. Flew about 16 flights earlier without issue, would esc cutoff matter with a full charge?
If you were in the middle of a shoot have you got the footage when the motors stopped, might help us seeing it to help diagnose what happened!

Which version firmware you using?

Which setting have you programmed in to your ESC's?
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Old Jul 22, 2012, 04:31 AM
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Originally Posted by IconFlyer View Post
I'm back on 5.08 and flying rock solid as before. The slow yaw problem is back and it's driving me crazy. The copter yaws very slowly CW after about 3-5minutes of flight. I checked and rechecked motor angles and they are within 1 degree of vertical. I think the problem may have to do with motor heat. The motors on the bottom are clearly going to pulling more amps(they are 5-10 degrees warmer than the top motors) due to the fact that they are running in the downwash of the top propellers. I think what happens is as the bottom motors heat up, they somehow lose effieciency and start running at lower RPMs causing the copter to rotate CW(since the top motors continue to run at nominal RPMs CCW). Did any one experience this behavior before? Would a customized motor mix solve this problem either by dropping the throttle % of the bottom motor or by making a mix that makes each individual arm either CW or CCW(so I can use vectored thrust from tilting the motors)?

I'm running 8 Carbon bird motors and at full AUW(3KG with a 500g 5000mah battery and fake camera load of around 500 grams) the copter is pulling 34 amps., that's 4.5amps per motors which is around 50% of the motor capacity(10amps).

Any advice would be much appreciated!!


I had kind of the same problem with my Naza Y6 - and I changed the rotation of the motors: http://www.rcgroups.com/forums/showp...ostcount=11523

The problem is that the lower motors are affected by the top motors and thus have lower efficiency. That's why a coax config only have about 78% efficiency compared to a flat hexa.

I would suggest changing on the WKM:
M1->M5 & M5->M1 and the same for the aft motors: M3->M7 & M7->M3.
Don't forget to change the props .....

Now there are just as many motors turning CW+CCW on top as on the bottom.

This same basic princip worked very good on my Naza Y6 and may work equally good on a X8 - worth trying IMHO.

IF this doesnt work you have ruled out the motor/prop combination .....
Do you have a Scarab Octo?

tritan
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Last edited by tritan; Jul 22, 2012 at 04:40 AM.
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Old Jul 22, 2012, 05:32 AM
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Canada, QC, Laval
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Originally Posted by Tahoe Ed View Post
I finished my S800 today so if the weather cooperates I will go and do some flying. I will let you know if it crashes. I am on v1.30a and 5.12a.
You are a brave man ED. Good luck to you.


Cheers
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Old Jul 22, 2012, 05:43 AM
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Canada, QC, Laval
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Originally Posted by Adidas4275 View Post
you have a S800 and a flexacopter?????????????????

damn man! that is some serious frame awesomeness
hehehehe. what is wrong with that I got the same.
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Old Jul 22, 2012, 06:44 AM
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Originally Posted by tritan View Post
I had kind of the same problem with my Naza Y6 - and I changed the rotation of the motors: http://www.rcgroups.com/forums/showp...ostcount=11523

The problem is that the lower motors are affected by the top motors and thus have lower efficiency. That's why a coax config only have about 78% efficiency compared to a flat hexa.

I would suggest changing on the WKM:
M1->M5 & M5->M1 and the same for the aft motors: M3->M7 & M7->M3.
Don't forget to change the props .....

Now there are just as many motors turning CW+CCW on top as on the bottom.

This same basic princip worked very good on my Naza Y6 and may work equally good on a X8 - worth trying IMHO.

IF this doesnt work you have ruled out the motor/prop combination .....
Do you have a Scarab Octo?

tritan
thank you very much tritan, I'm glad to see that I'm not crazy
What I understand from your suggestion is to change the mix between CCW and CW motors top to bottom so not all top or all bottom motors are either CW or CCW? But basically you're saying to keep each arm as a CW/CCW combination correct?

I was having the same idea when I asked the question about motor mixer so that each arm has a set of either CW or CCW motors/props on them. This way I can twist the arm a few degrees to make the vector of that trust support the torque created by this arm. I've been doing this on my quad setups all along and it makes perfect sense and really improves the yaw behavior.

My X8 is a ScarabOcto based with a small modification to the motor mounts to make them easier to service and replace(I use rusty's motor mounts and Quinton's frames )
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Old Jul 22, 2012, 06:47 AM
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Originally Posted by hexa View Post
If you mean the copter yaws slowly to one side after letting go the stick.
if so you need to angle tilt some of your motors to one side. I can't pick the info off the top of my head, this problems some times happens with heavy lift hexa and octos,

go here for better understanding
http://www.mikrokopter.de/ucwiki/en/AngleAdapter
thanks hexa, yes if the yaw stick is at neutral, the copter very slowly starts yawing CW. That's other than the high gain like behavior of of rotating a few degrees against the direction of last yaw command(so command right, then neutral, I get a slight rotation to left as if it was a helicopter with high tail gyro gain). I will try the motor mixer change idea and twist all the arms like I did on my quads, I think this should solve the issue.
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Old Jul 22, 2012, 06:50 AM
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I think you can change top to bottom motors as long as they are on the same arm. So you can move m2 to bottom and m5 on top. Am I getting this right?
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Old Jul 22, 2012, 06:59 AM
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Originally Posted by tigar View Post
I think you can change top to bottom motors as long as they are on the same arm. So you can move m2 to bottom and m5 on top. Am I getting this right?
I think changing top to bottom motors only is a good idea because basically the motors responsible for maintaining the yaw torque on a certain direction are not all on the same top-bottom side. The problem is because lower mottors are less effecient the more they heat(I guess) the more they need to run to maintain their torque direction authority. If they get a little help from the top motors the load is more evenly distributed top-to-bottom interms of yaw torque. This is my theory at least of what happening with co-axials. More gain on the WKM could solve the problem but you're just sacrificing a few %'s of efficiency. I don't know how coaxial setups work on other controllers but I'm guessing it's better to have this top-to-bottom CW/CCW mix(I know HFP is like WKM, but multiwii is different).
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Old Jul 22, 2012, 07:50 AM
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Originally Posted by IconFlyer View Post
thanks hexa, yes if the yaw stick is at neutral, the copter very slowly starts yawing CW.

Yes, beacuse all top motors have higher efficiency than lower and want's to turn CW, this make sense to me.
My theory here is that if you have an unlucky combination of motor/prop/distance between coax motors etc etc this can happen.
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Old Jul 22, 2012, 07:55 AM
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Originally Posted by tritan View Post
Yes, beacuse all top motors have higher efficiency than lower and want's to turn CW, this make sense to me.
My theory here is that if you have an unlucky combination of motor/prop/distance between coax motors etc etc this can happen.
Yes but as I noted this only starts happening after the motors get running for few minutes and get to their steady running temperature. So if I fly for a couple of minutes, land/rest for a minute, then fly again this doesn't happen. I think the magents lose some strengh or something upon heating?? the motor case temperature is always under 50degrees so it's not too high but I guess the slight difference between top and bottom motor power is the key..again just a theory
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Old Jul 22, 2012, 07:57 AM
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Originally Posted by IconFlyer View Post
thank you very much tritan, I'm glad to see that I'm not crazy
What I understand from your suggestion is to change the mix between CCW and CW motors top to bottom so not all top or all bottom motors are either CW or CCW? But basically you're saying to keep each arm as a CW/CCW combination correct?
Yes, without making a new motor mix in WKM, just change the ESC cables.
Please note that I haven't done this on a X8, just my Y6 but the princip should be the same, and in fact it "should" work better for you as a X8 is more symmetrical than an Y6.

Quote:
This way I can twist the arm a few degrees to make the vector of that trust support the torque created by this arm.
Yes if you will need it after the mod I did, maybe you won't have to as the torque on the arms will be equal (after the mod).

Quote:
My X8 is a ScarabOcto based with a small modification to the motor mounts to make them easier to service and replace(I use rusty's motor mounts and Quinton's frames )
Thanks, could I ask for some links?
EDIT: found them

Tritan
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Last edited by tritan; Jul 22, 2012 at 10:41 AM.
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Old Jul 22, 2012, 08:02 AM
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Originally Posted by IconFlyer View Post
Yes but as I noted this only starts happening after the motors get running for few minutes and get to their steady running temperature. So if I fly for a couple of minutes, land/rest for a minute, then fly again this doesn't happen. I think the magents lose some strengh or something upon heating?? the motor case temperature is always under 50degrees so it's not too high but I guess the slight difference between top and bottom motor power is the key..again just a theory
What if you switch your motors, top to bottom and bottom to top?
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Old Jul 22, 2012, 08:17 AM
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Originally Posted by tritan View Post
What if you switch your motors, top to bottom and bottom to top?
I will actually start with that without touching anything else...I'm sure this will help. I would like to eventually get to the point where it's not just torque causing the yaw but also a little bit of thrust. This made a huge difference for me on quads...I could finally do smooth 360 panoramic pan shots in the middle of the air(e.g. see 2:09 [text]http://www.youtube.com/watch?v=-vTfP4XfPJ4&feature=player_detailpage#t=130s[/text]) without worrying too much about throttle/pan/roll because the motors where not having to change rpms dramatically to make the yaw movement happen. I will do the tests tonight and will report.
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Old Jul 22, 2012, 10:57 AM
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Originally Posted by IconFlyer View Post
I will actually start with that without touching anything else...I'm sure this will help. I would like to eventually get to the point where it's not just torque causing the yaw but also a little bit of thrust. This made a huge difference for me on quads...I could finally do smooth 360 panoramic pan shots in the middle of the air(e.g. see 2:09 [text]http://www.youtube.com/watch?v=-vTfP4XfPJ4&feature=player_detailpage#t=130s[/text]) without worrying too much about throttle/pan/roll because the motors where not having to change rpms dramatically to make the yaw movement happen. I will do the tests tonight and will report.
Didn't work for me (see my post couple pages back). Just tried. I swapped M2 <-> M5 on WKM, changed rotation direction and swapped props.
Yes yaw behaviour became more soft and controllable which is good but still it yaws when you move. Rock solid while hoovering.

The only reason I can imagine is that one motor or ESC over/under revs when changing rotation speed and WKM is unable to compensate. This produce a yaw impulse and copter continues drifting in this direction which results in flying by arc.
When static it compensates....

Anyway I'll continue to use this new scheme on my copter. Thanks for a good idea.
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Old Jul 22, 2012, 11:03 AM
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Originally Posted by slo_dave View Post
I've emailed him recently and he quoted me $15 shipped for a 4" round CF plate ..
It's basically the backplate from the CF spinner he sells pictured here:

http://www.ebay.com/itm/ws/eBayISAPI...X:eRTM:US:1123

Perfect size for a GPS shield... if thats what your looking for
Why don't you get yourself a sheet of 1.5mm carbon that way you can cut it yourself.
That's what I did I bought 4 sheets and I have some extra for future uses.

Cheers
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