S800 Arm's carbon fiber wrapped

K

ksrimoungchanh

Member
with all the post about the S800 arms vibrating, has anyone done any custom work on their S800 frame to stiffen it up or something?

I am thinking of wrapping a sheet of carbon fiber around the arms all the way out around the ESC. wondering if anyone has done similar? is it worth it or not.

Today, my S800 was flying awesome and several spectators, just pointed it out and so the idea started flowing.

KS
 

BorisS

BorisS

Drone Enthusiast
Hmmm one would have to test it and than its a long way just for that. Completely wrapping it would mean that you create a big surface area under the prop resulting in performance loss and additional vibrations created by the thrust. If this eventually works out in less vibrations is hard to tell.

I was thinking of reinforcing them only on the side but after seeing what the zen muse can do I lost motivation to reduce the vibrations since I don't have any on the cam anymore.

Boris
 

K

ksrimoungchanh

Member
well, I had a different experience that got me thinking.... I was up about 200ft, and I started it down, but for some reason, I was in a hurry to get it down faster, so I kept bringing the throttle down, down, down, pass the 10% and somewhere high, you can see all the motors quit, it just slowly started rolling on it's side.

I was quick and slowing push the throttle back up above the 10% and it started and swiveled back in the correct attitude and kept coming down.. everyone was thinking I did that on purpose..:) I said.. "just testing". After that, I was thinking what concerns should I look at. Any stress on any arms, rotors that may fail in the next few flights?

I was afraid that when it swiveled back in mid-air to catch itself, it did it pretty quick. I am glad the battery was velcroed and wrapped, I also had the datalink velco'd and it did not move either.

I had 2 6000mah betters and it felt like it was too heavy to be doing acrobatics... :) not sure the arms would like that. I don't plan on "testing" that feature anymore.

KS
 

T

Tahoe Ed

Active Member
There was one arm that had been modified with a 1/4" CF strip under the arm that appeared to be glued on the same way the center CF rib is. Together they formed a "T" on the arm. This appeared during the esc recall. The guy sent his arms in and got this one single modded one back with the other 5 regularly configured. DJI has never commented on this.
 

J

jes1111

Active Member
Gluing pultruded CF profile to the top, bottom and sides would seem the easiest way. Rectangular or half-round profile - cheap and easy. Clean surfaces with isopropyl alcohol, use slow-setting epoxy, apply pressure moderate for first few hours at least.

Boris - I'm intrigued by the Zenmuse's vibration isolation - where is this happening? i.e. given that we know the arms of the S800 are flapping about like crazy, where does the vibration "stop" - at the Zenmuse mounting? After that? Do you think the vibration attenuation is entirely mechanical or is the gimbal cancelling it out with servo movements as Denny suggests?
 

BorisS

BorisS

Drone Enthusiast
jes1111 said:
Gluing pultruded CF profile to the top, bottom and sides would seem the easiest way. Rectangular or half-round profile - cheap and easy. Clean surfaces with isopropyl alcohol, use slow-setting epoxy, apply pressure moderate for first few hours at least.

Boris - I'm intrigued by the Zenmuse's vibration isolation - where is this happening? i.e. given that we know the arms of the S800 are flapping about like crazy, where does the vibration "stop" - at the Zenmuse mounting? After that? Do you think the vibration attenuation is entirely mechanical or is the gimbal cancelling it out with servo movements as Denny suggests?
Click to expand...

Jess i would be on that one with Denny. Done and tried enough vibration isolation on big birds and the small FPV thingis I can't believe that those rubber balls that dji are using would be enough to kill the vibrations. And even when i managed to get clean pics on the other birds, some of it would come back when I realyl push the birds ! Zenmuse S800, and i am not treating it good pushed it couple times now full stick from left to right, I don't see anything !

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yeehaanow

yeehaanow

Member
I think the Zen is fast enough to cancel out vibes. I saw this on one of the early test videos on a super windy day with the windmill. The s800 was vibrating so much you could see the landing skid moving around in its rubber grommet!

IMO- The only way to solve the twisting arms is with a tubular shape. Any additional flat piece is still going to twist. It might help it from bending up and down a bit.

While testing each arm for vibrations individually, I found significant differences between arms. As in, one arm maxed out at .35 G's and another was at 1.2 G's. Turns out it was due to the prop, even though it was properly balanced. I tried many experiments and could not get that one prop to run smoothly. The s800 design makes it really easy to test each arm. :)
 

J

jes1111

Active Member
BorisS said:
Jess i would be on that one with Denny. Done and tried enough vibration isolation on big birds and the small FPV thingis I can't believe that those rubber balls that dji are using would be enough to kill the vibrations. And even when i managed to get clean pics on the other birds, some of it would come back when I realyl push the birds ! Zenmuse S800, and i am not treating it good pushed it couple times now full stick from left to right, I don't see anything !

View attachment 8062
Click to expand...
If you were to run the motors with the S800 strapped down to the ground and put your finger on the gimbal itself, would you feel any vibrations? That's the question :)

I think the Zen is fast enough to cancel out vibes. I saw this on one of the early test videos on a super windy day with the windmill. The s800 was vibrating so much you could see the landing skid moving around in its rubber grommet!
Click to expand...
I'd agree it would be possible for the motors to be fast enough to cancel vibes - what I can't understand is how DJI would be measuring vibration at that level with sufficient accuracy and lack of "noise" to send meaningful "vibration cancellation" commands to them. Accelerometers are noisy little things - on their own (and in this price range) I can't see how they'd be capable of this.

I wouldn't dismiss the "rubber balls" - they look "deliberate" to me and DJI has certainly injected some high level engineering expertise into this.
 

J

jes1111

Active Member
yeehaanow said:
IMO- The only way to solve the twisting arms is with a tubular shape. Any additional flat piece is still going to twist. It might help it from bending up and down a bit.
Click to expand...
I hear you - but it's the interface between the applied CF piece and the arm that would supplement the rigidity. Unidirectional CF doesn't want to stretch, so as long as the bond was good (and continuous) it would prevent/reduce deflection of the arm (is it plastic?) in any direction that would require applied CF fibres to stretch.
 

BorisS

BorisS

Drone Enthusiast
Next flight i will just mount a go pro like this. If there are no vibes we know its the rubber balls, if there are some we can keep on speculating :)

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BorisS

BorisS

Drone Enthusiast
one thing is also strange the GCU must be a much more advanced device than the IMU of the WKM itself. In normal FPV mode the Zenmuse has issues keeping the pan straight 100% pointed to the nose of the copter. The reason behind that is that the actual position info comes from the WKM compass. When you switch the zenmuse into second mode what ever its called were its controlled pan nick roll from the radio, it will holds the pan 100% what ever you set it to before. Its independent of the copters position thus only relying on the info of the GCU Zenmuse IMU.


FPV mode, fakes the pan and moves back to a aprox. position.


Min 1.33 operator moved it a little but copter was flown full forward and yaw and it holds perfect, when independent from the WKM Compass,

Interesting will be based on the knowledge testing they have down with the zenmuse GCU what the next generation WKM/FC will be capable of doing !

Boris
 
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BorisS

BorisS

Drone Enthusiast
by the way this is the vibration situation of my s800 with a go pro mounted to the center plate :)

 
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J

jes1111

Active Member
For sure the requirements for a gimbal controller exceed those required for MR stabilisation. Gyros are accurate but they drift - so you have to add at least 3-axis accelerometer and some clever maths to keep the gyro drift down. But then you introduce the dreaded horizon drift because the linear acceleration (from sudden and high-g movements) biases the estimation... and so on, round and round in circles ;) - so you introduce more sensors (mag, barometer, etc.) and fuse all the data together - but up goes the cost and complexity. And/or you use more expensive sensors that have better characteristics - and then the complexity of the maths goes ballistic. :)

There's no doubt IMO that DJI either farmed out the development of the Zenmuse or acquired some fresh (and serious) talent internally - the electronics side of the Zenmuse is significantly higher level than their (current) FC.
 

J

jes1111

Active Member
BorisS said:
by the way this is the vibration situation of my s800 with a go pro mounted to the center plate :)

Click to expand...
Is there any evidence that the Zenmuse performs equally well on any other frame? It occurs to me that these bendy "cream cheese" arms might actually be deliberate. The vibration on them looks to be relatively low frequency - perhaps they are deliberately wobbly to absorb the high frequency vibration which the Zenmuse couldn't cancel. Just a thought :)
 
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BorisS

BorisS

Drone Enthusiast
There is this guy on rcgroups who during the whole mc and esc dilemma of the s800 gave up on it and mounted it on his home built (no frame kit) hexa or
Octo. His result are the same.

Boris
 

A

Acmach5

Member
Have S800 users had arms break in flight? I feel that this video above makes the vibes look worse than they actually are. I don't care how well balanced your props are. When they are spinning opposite directions and constantly changing speed for flight you are going to get some shakes. I gotta say if the arms are of poor quality and breaking thats one thing. If they are designed to have some give I'm ok with that. It's been working well for Boeing for quite some time now in their wing design. If you consider any successful modern aircraft or building, they generally have some flexibility designed into them. What DJI needs to do is some stress testing and post the videos showing at how many pounds of pressure the arms break.
 

kloner

kloner

Aerial DP
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