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[Guide] How to check for prop wear.
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ABeardedItalian
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Video Instructions


Written Instruction
The first thing we need to do is Disable "Flight Data Sync" within DJI FLY. When your flight information is synced with DJI your .Dat files are erased, we need to preserve these files as they contain more information then the flight log.



    1 On your Android/IOS device navigate to your internal storage (My files on android) and find the DJI folder.
    2. Open the DJI folder, open the Gov5 Folder, open FlightRecords, open MCDAT folder.
    3. Find your most recent flight or the .Dat file you would like to examine.
    4. Upload it to your PC/Mac
    5. Download CSvView from datfile.net .
    6. Install CSvView.
    7. After installation CSvView should open, navigate to where you stored the .Dat file.
    8. Open the .dat and wait for it to load.
    9. Select Motor speed from the options below after the .dat has loaded.
    10. A new window will open with the RPM Information of each motor, here we can Analyze the information and look for prop wear.

Here's grahamjohnson10's Known "Motor Speed Error" Graph.

The Dark Blue line is REAR LEFT and the Tan/Yellow line is REAR RIGHT
We can see that Rear Left is the motor that triggered the "Motor Speed" warning, we can also see that the Rear Right is also experiencing increased RPM's. These values should be closer together, see grahamjohnson10's second chart after the props have been replaced.



(Note: The Rear motors will always work a little harder then the front due to weight distribution.)

Here you can see the RPM Values are much more in line with each other, a closer grouping indicating a healthy performing mini.

If we look at my Graph:



It's easy to see a deviation has started between the front and rear motors and  that both Rear motors are experiencing Increased RPM's. Note my Rear Left is just marginally worse then my Rear Right. Looking at the Peak RPM and the grouping of the lines I don't think my mini is ready for prop replacement just yet. If I had to take a guess my mini will see the "Motor Speed" warning on the Rear Left first, how long before my mini is within that threshold is anyone's guess.

I hope this helps others and opens the door for more discussion, that previous thread is a mess and too few data points being shared. Let's stop guessing and review everyone's Dat files, lets see how many other mini's are "Soon™" to be experiencing this issue.

2020-4-30
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Deucalion
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Thanks for this write up.
2020-4-30
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fans1cafe718
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Thank you very much!
2020-4-30
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120ccpm
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Nice post, simple and clear. You might want to add that rear motors will show higher RPMs than front motors, because there's a bit more weight on the rear of the AC.EDIT: this is incorrect, if anything there is a bit more weight (5-6g) on the front.
2020-4-30
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Occams Razor
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Nice description of using CSvView.  My last flight looks similar to your graph however you need to overlay the AC's yaw with the RPM's. There are times where your right motor's RPM exceeds the left's and visa-versa so some of those differences will be associated with yaw.  Look at how close the rear RPM's are at the beginning and end of your graph where it looks like you are gaining and losing altitude.  Your rear left and right rear prop RPM's may be more closely aligned than you think.
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crash1sttime
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Very informative, I will be definately looking at my DAT files after each flight from now on.
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djiuser_Ek3oes1nLuai
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thank you very much
2020-4-30
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ABeardedItalian
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Occams Razor Posted at 4-30 08:27
Nice description of using CSvView.  My last flight looks similar to your graph however you need to overlay the AC's yaw with the RPM's. There are times where your right motor's RPM exceeds the left's and visa-versa so some of those differences will be associated with yaw.  Look at how close the rear RPM's are at the beginning and end of your graph where it looks like you are gaining and losing altitude.  Your rear left and right rear prop RPM's may be more closely aligned than you think.

The more evenly mixed area's are from take off/landing, I do a pre flight check and after flight check. The big "Peaks" are when the mini was "stopping" from flying full forward in Sport mode. So the motors experience the biggest peaks in rpm as the drone is decelerating.

I don't know how to enable Yaw, maybe someone could point me in that direction but here's the some more options toggled.

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fans1cafe718
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ABeardedItalian Posted at 4-30 08:47
The more evenly mixed area's are from take off/landing, I do a pre flight check and after flight check. The big "Peaks" are when the mini was "stopping" from flying full forward in Sport mode. So the motors experience the biggest peaks in rpm as the drone is decelerating.

I don't know how to enable Yaw, maybe someone could point me in that direction but here's the some more options toggled.
Yaw is rotating clockwise or anti-clockwise....in a steady hover is best.

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ABeardedItalian
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fans1cafe718 Posted at 4-30 08:49
Yaw is rotating clockwise or anti-clockwise....in a steady hover is best.

haha I'm aware of that, I was talking in CSvView how to toggle the Yaw overlay.
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fans1cafe718
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...also...you will always get props disparities if machine is in mouvement...I think no wind and steady hover should reveal defect props more accurately.
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fans1cafe718
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ABeardedItalian Posted at 4-30 08:55
haha I'm aware of that, I was talking in CSvView how to toggle the Yaw overlay.

Lol...ok...sorry bud
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Occams Razor
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ABeardedItalian Posted at 4-30 08:47
The more evenly mixed area's are from take off/landing, I do a pre flight check and after flight check. The big "Peaks" are when the mini was "stopping" from flying full forward in Sport mode. So the motors experience the biggest peaks in rpm as the drone is decelerating.

I don't know how to enable Yaw, maybe someone could point me in that direction but here's the some more options toggled.

I don't see a way to add Yaw using the CsvView tool.  However, when you see the difference between the left and right rear RPM's and you see a corresponding difference between the left and right front RPM's then you are most likely yawing and that may not necessarily indicate a problem with the props.   A good test is to fly the drone in a straight line at maximum speed to identify a differential between the left and right rear RPM's.
2020-4-30
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hallmark007
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I just have a feeling you will see similar results with all dji drones, maybe jjb has logs from other craft.
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BudWalker
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ABeardedItalian Posted at 4-30 08:47
The more evenly mixed area's are from take off/landing, I do a pre flight check and after flight check. The big "Peaks" are when the mini was "stopping" from flying full forward in Sport mode. So the motors experience the biggest peaks in rpm as the drone is decelerating.

I don't know how to enable Yaw, maybe someone could point me in that direction but here's the some more options toggled.

Try IMU_ATTI(0):Yaw

2020-04-30_10-42-47.jpg
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ABeardedItalian
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fans1cafe718 Posted at 4-30 08:56
...also...you will always get props disparities if machine is in mouvement...I think no wind and steady hover should reveal defect props more accurately.

I can't do anything about the wind but I went out and did just this, hover, flew forward 500 feet and backward. Fwd was 18.7mph, Bkw was 28.3mph, no yaws, spins, rolls.

Up, Forward, Back, Down.



I've enabled height, pitch, and mode check. You can see the whole flight was in Sport mode, you can see when I was hovering and when I was flying full pitch. You can also see a small elevation drop in the graph and video, I think this still looks pretty good. The grouping could be tigheter but the deviation isn't as sever as others have been, I'll keep flying and report when I recive the Motor Speed error.


Here's the video of that flight:


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ABeardedItalian
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Yeah I found it later, when I was scrolling it would jump 4 values at a time so I kept passing it.
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Deucalion
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ABeardedItalian Posted at 4-30 10:08
I can't do anything about the wind but I went out and did just this, hover, flew forward 500 feet and backward. Fwd was 18.7mph, Bkw was 28.3mph, no yaws, spins, rolls.

Up, Forward, Back, Down.

New props? Old Props?
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ABeardedItalian
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Deucalion Posted at 4-30 10:10
New props? Old Props?

These are still the original rear props, my front right props have been replaced sometime in march with a one of my three extra sets that was included. So technically all original props since the extras are as old as the original.
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JJB*
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hallmark007 Posted at 4-30 09:13
I just have a feeling you will see similar results with all dji drones, maybe jjb has logs from other craft.

Just checked few of my dat logs,  front and rear props rpm are close together.

Interesting thought this #1 post, but hard to check if you do no see other parameters and flight conditions.

Guess best results and comparison between yout own flights is flying in the same condition; like no or less wind and flying 100% forward only into the wind.

Checking not your own flight is difficult as rpm excursions between props are seen in rapid yaw moves, makes it hard to draw conclusions.

But if one blade RMP is over the whole flight a lot (how many) higher than it make sense to suspect that blade.

cheers
JJB
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djharrisx
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Thanks for a very helpful and informative post. The information about how to get and install CsvView is particularly useful.

However, there is an alternative workflow that might be considered, especially if like me, you find using the Sync app for AirdataUAV much more convenient if it scrapes the files from the DJI server. While I can't speak for Android devices, the iOS Files app makes saving a copy of the DAT file to a safe place trivially easy. I generally do this as my first action after packing the drone away following a flight.

I appreciate there may be many reasons why folk want to keep their flight logs off DJI's servers, but as the auto upload doesn't kick in immediately, you have plenty of time to copy the DAT files before they are lost.

Thanks again for the information.
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hallmark007
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JJB* Posted at 4-30 10:43
Just checked few of my dat logs,  front and rear props rpm are close together.

Interesting thought this #1 post, but hard to check if you do no see other parameters and flight conditions.

My suspicions are that this exercise needs to be much wider and as you say maybe need to see or introduce other flying parameters.
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Zbip57
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120ccpm Posted at 4-30 08:26
Nice post, simple and clear. You might want to add that rear motors will show higher RPMs than front motors, because there's a bit more weight on the rear of the AC.

"rear motors will show higher RPMs than front motors, because there's a bit more weight on the rear of the AC."


I'm curious where that idea came from.  Has anyone actually measured the exact weight distribution, and how?

I don't have scales accurate enough, nor the patience to construct jacking devices to fit precisely under each motor.  So I tried this simpler method.

I didn't want to permanently mark up the top of my Mini, so I taped a piece of paper on it and, using a straight edge aligned with the motor centres, drew crossed lines to mark the geometric centre between the four motors. (img-01 & img-02) The "X" is located about 11/16" ahead of the top edge of the "d" in the "dji" label. (img-03)


Then I suspended the Mini from a string with the knot centred over that "X". (img-04)  It looks to me as though the Mini actually is sliightly nose heavy. (img-05)

The Mini hangs more level if the knot is moved about 1/4" ahead of the "X". (img-06 & img-07)  I didn't measure it exactly, but this whole method is only approximate.




img-01

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img-02

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img-03

img-03

img-04

img-04

img-05

img-05

img-06

img-06

img-07

img-07
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fans1cafe718
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Zbip57 Posted at 4-30 11:53
"rear motors will show higher RPMs than front motors, because there's a bit more weight on the rear of the AC."

We need a reference point (Datum) as in any aircraft it's different.

This info needs to be provided by DJI.

In airplanes or helos, this info is provided in the pilot's manual and it's located in the "Weight and Balance" section.

You cannot make up the center of gravity yourself.

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hallmark007
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Zbip57 Posted at 4-30 11:53
"rear motors will show higher RPMs than front motors, because there's a bit more weight on the rear of the AC."

I think there was a presumption that battery would make MM rear heavy, excellent test and something else to add to the mix.
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ABeardedItalian
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Getting more curious I decided to replace my rear props with my replacement spares. I was honestly expecting to see a huge difference but I'm guessing since my mini was never one of the effected ones it won't be as dramatic as others.

Here's the original Rear Props:


Here's the replaced Rear Props:


I can see that the distance between the Rear Left and Rear Right has gotten closer but the gap between Front props and Rear is still very much the same.

Here's the two overlapped, the grouping has gotten better but the deviation from front to back is the same.


I'm going to reinstall the original props and test once more but "If" my replacements can be called "good" then my original props aren't far out of spec.
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hallmark007
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ABeardedItalian Posted at 4-30 10:08
I can't do anything about the wind but I went out and did just this, hover, flew forward 500 feet and backward. Fwd was 18.7mph, Bkw was 28.3mph, no yaws, spins, rolls.

Up, Forward, Back, Down.

Having tested in sport mode just after FW update through one full battery my findings and I posted on another thread.
At altitude 30m sport no wind sport mode full elevator stop, craft lost approx 1m alt before regaining gps height.
At altitude 1.5m sport mode full elevator stop craft gained approx .5m before regaining correct gps alt.

I done many tests and results were almost identical .
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fans1cafe718
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ABeardedItalian Posted at 4-30 12:08
Getting more curious I decided to replace my rear props with my replacement spares. I was honestly expecting to see a huge difference but I'm guessing since my mini was never one of the effected ones it won't be as dramatic as others.

Here's the original Rear Props:

Thx for great infos...
...rears are at a slight angle...that may explain higher revs...I don't think it's the extra weight.
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Zbip57
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hallmark007 Posted at 4-30 12:07
I think there was a presumption that battery would make MM rear heavy, excellent test and something else to add to the mix.

It looks like the camera and gimbal hanging at the front very nearly perfectly counter-balances the rearward placement of the battery.

The first time I hung it from a string like this it was even more dramatically nose-heavy,  Then I realized I had forgotten to remove the gimbal cover.  D'oh!

These photos were taken with the Mini in its flight trim; micro-SD card in place, battery installed, gimbal cover removed.

I suppose the piece of paper with the "X" taped to the top has a negligible effect on the centre of gravity.  Maybe it's only nose-heavy because of my "If found, please call..." label stuck near the nose.
  
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ABeardedItalian
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I'm charging the battery right now, the original props are now reinstalled. Once I get some juice I'll go repeat this test again, I'm also curios now if I should change the front props and see what if any effect that has.
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Occams Razor
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ABeardedItalian Posted at 4-30 12:08
Getting more curious I decided to replace my rear props with my replacement spares. I was honestly expecting to see a huge difference but I'm guessing since my mini was never one of the effected ones it won't be as dramatic as others.

Here's the original Rear Props:

When going forward, the rear propellers will have higher rotation to achieve the pitch. When hovering, all 4 motors will be closer in RPM's.  Your charts seem to reflect this so everything looks as it should.  Nice job on all of the analysis.
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Zbip57
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fans1cafe718 Posted at 4-30 12:16
Thx for great infos...
...rears are at a slight angle...that may explain higher revs...I don't think it's the extra weight.

"And yes, rears are at a slight angle...that may explain higher revs...I don't think it's the extra weight."

None of the motors are level.  The rears are canted outboard, and the fronts are canted rearward.

I have no idea what the exact angles are, I'm just eye-balling this.  But they look to be near the same amount of tilt away from horizontal.

Angles.jpg
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Deucalion
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I measured mine, and the CG is as Zbip stated and the motors are all equidistant from it, within a few mm. Could the rear props be getting and prop wash from the front props?
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Zbip57
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Occams Razor Posted at 4-30 13:06
When going forward, the rear propellers will have higher rotation to achieve the pitch. When hovering, all 4 motors will be closer in RPM's.  Your charts seem to reflect this so everything looks as it should.  Nice job on all of the analysis.

"When hovering, all 4 motors will be closer in RPM's."

That makes sense.

"When going forward, the rear propellers will have higher rotation to achieve the pitch."

That doesn't make sense.  The aircraft's attitude will change whenever the props rotate at different speeds.


The rears need a higher rotation speed only when changing the aircraft's pitch angle forward.  If they maintained that difference in speed the aircraft would continue pitching ever further forward while doing a front flip.  In steady-state forward flight the propeller speeds should be equal to maintain the desired fixed pitch angle.


Similarly, if the left-side rotors are turning faster than the right-side rotors the aircraft would roll to the right.  Unless the speeds are equallized the aircraft would continue rolling.

Yaw is induced by slowing (or speeding) the two clockwise rotating props while simultaneously speeding (or slowing) the other two counter-clockwise rotating props.  If the one set is slowed by the same amount as the other set is sped up, the aircraft will continue to generate the same amount of total lift to maintain altitude while yawing.  Once the props speeds are matched again the yaw stops.


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fans1cafe718
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Zbip57 Posted at 4-30 13:25
"When hovering, all 4 motors will be closer in RPM's."

That makes sense.

You are correct to assume rear props high revs would dip the machine...that would be in a hover...however...in forward flight...the flow of air should induce a steady altitude...with minor adjustments always, of course....it's kinna like traction through air....
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fans1cafe718
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Zbip57 Posted at 4-30 13:07
"And yes, rears are at a slight angle...that may explain higher revs...I don't think it's the extra weight."

None of the motors are level.  The rears are canted outboard, and the fronts are canted rearward.

Forward tilt (when in motion) is less demanding than horizontal/sideways tilt (engine wise)
Think of AIR as WATER.
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Occams Razor
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Zbip57 Posted at 4-30 13:25
"When hovering, all 4 motors will be closer in RPM's."

That makes sense.


That doesn't make sense.  The aircraft's attitude will change whenever the props rotate at different speeds.

Did you mean attitude or altitude?  If you meant altitude then it will not change.  Think of it this way, when the rear propellers have a higher rotation speed than the front props then the AC will tilt forward.  When the front end of the AC is pitched downward, some of the thrust created from the propellers will be converted into forward thrust which moves the aircraft forward and some thrust is downward thrust which will maintain the altitude.  The FC knows the exact combination of front and rear RPMs to keep the AC at the right pitch to achieve a forward speed and maintain a certain altitude.   When flying backwards, the same concepts apply and the front motors will spin at a higher rate than the rear props to achieve an upward pitch of the front end of the AC.

The rears need a higher rotation speed only when changing the aircraft's pitch angle forward.  If they maintained that difference in speed the aircraft would continue pitching ever further forward while doing a front flip.  In steady-state forward flight the propeller speeds should be equal to maintain the desired fixed pitch angle.

Again the FC knows how to balance the RPMs of all of the motors to maintain the required forward pitch and not flip the drone.  If all of the propellers maintained the same RPM, the AC would level out and there would be no forward thrust.
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120ccpm
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Zbip57 Posted at 4-30 11:53
"rear motors will show higher RPMs than front motors, because there's a bit more weight on the rear of the AC."

I actually measured it with a scale (0.1g precision, or so it says), but what you did makes a lot of sense and seems to contradict my measurement... let me double-check.
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Deucalion
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Here is my first test inside the house. I set the drone on the floor, started motors, lifted off, hovered for a bit, yawed CW for a couple revs, hovered, yawed CCW for a couple revs, hovered, landed, picked the drone back up. Notice that even though I am yawing CW or CCW, there is very little to see in the RPMs. It looks like I am hovering the whole time. Which is why I added the Gyro to make sure.

HoverInHouse.png
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fans1cafe718
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120ccpm Posted at 4-30 14:23
I actually measured it with a scale (0.1g precision, or so it says), but what you did makes a lot of sense and seems to contradict my measurement... let me double-check.

...Do you have the exact Datum point?

It is measured in all 3 (three) axis.

It really would be interesting to have the official measurements on this.

...but, lol...it's just a toy/hobby...but still...curiosity is insatiable
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