Optimize your vibration levels with unsuspected technique (thx Forrest Frantz for that)

I finally did the test of hard fixing the APM case to the frame, thus not having two separate masses with vibration dampening materials in between, as before (i.e. : frame/props on one side and APM on the other side).

This is explain by Forrest Frantz in a post I made earlier about moongel use here:

http://www.diydrones.com/group/arducopterusergroup/forum/topics/hot...

and in more details here:

http://diydrones.com/forum/topics/vibration-isolation-and-dampening...

 

I have to say that I felt on my bottom when I saw the results : TWICE less vibrations with this method WITHOUT any moongel nor any other vibration dampening techniques. JUST ONE SINGLE mass (APM fixed on frame directly).

Look at this graph that shows ZACC within plus or minus 0,1g which is twice less than the best +-0,2g I had with moongel combined with rubber bobbins and/or silicon gel. It is measured on the exact same aircraft (except moongel was removed and rubber bobbins were replaced by hard pylons). APM is stcked to the plate with NON foam double sided tape (hard double sided tape, as I did not want to drill screw holes in the APM plastic case).

Not only have I less vibration but I will also get better control on the craft since I get rid of the lag effect of dampening materials.

 

I confirm thus the theory of Forrest Frantz. It works for my frame.

It would be nice if others could confirm this also on their frame.

I publish this UPDATE after the information about 200hz dangerous vibrations came out thanks to the debate initiated of this post: the APM and its integrated sensor's hardware have a limit (due to low processing power limiting sampling frequency - that should be solved with the more powerful PX4 hardware) in such a manner that all frequencies of 200hz (and multiple of) will impact the APM control (accel) and will go through the 20hz software filter, undetected (thus noise id processed instead of valid signal, possibly creating catastrophies). As there is no way to analyze in a  log AccelZ graph if you get these 200 Hz frequencies on your arducopter, it is necessary as a precaution to use dampening technique(s) to eliminate these high frequencies (even if the AccelZ log seems to show low vibrations by direct fixing APM on the frame). 

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Hi Forrest,

You might want to see this.. lot of experiments and configuration with different flight times and possibilities here:

http://thequadcopterguy.blogspot.nl/

Regards..

Hi Forrest I have just built a 3dr y6 and I mounted the AMP hard on the carbon fiber plate with thin 3M double sided tape. I ran the compassmot and have readings of 8 and 9 on the two test I did. Then I flew the copter for the first time with Raw enabled. When I looked at the vibrations I feel they were pretty good. So far the copter flies great. I tried using your excel sheet and could't get it to work. I will attach my to logs the first was just a hover in stabalize mode the second I tested my alt hold mode as well. Here is a shot of my copter.

Greg

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hale Mary ... that thing is beautiful!  Never seen such clean work.

It's getting late.  my brain died (nothing new).  so will look at it tomorrow.  thanks for sharing.

Thanks for the kind words, I do custom computer installations for a living and its all about making the wires pretty. I learned from my helicopter days that you need to keep your wires off the sharp edges of the carbon fiber and the neater you keep things the less mishaps you have. It's easy to see things out of place when things are neat. I have some more work to do on the ESC's but wanted to make sure it flew first LOL. I have not tested Loiter yet and unfortunately we are having what is called Santa Anna winds this week end so I think I am grounded. 30 Mph sustained with gusts to 60 Mph. 

Greg

must have been really tired last night ... didn't notice that these are .rlog

do you have .log files from the flight?  you should see a date followed by .log

Here you go. I understand what the TLog is which is the telemetry log file. Could you please educate me what the difference between Log and Rlog is?

Thanks

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Beautiful Tri ... great vibration and stability numbers.  Thanks for sharing Greg!

From here, you can tune pitch and roll (turn off link the two) and see if you get improvement in stability.  But watch for a trade.  The X2 was tuned like a cello, but being nearly 2 meters long, you could see the tiny vibrations, so relaxed it a bit.  This is your first flight.  The best hover is under the horizontal bar on the vibration chart and shows where the statistics are derived.  Also, the macro doesn't print the graph in the correct order (biggest numbers first, in your case, z then y, then x) so to see them you sometimes have to right click on the graph and choose data source then click on the z and use the arrows on to the right to move it to the first spot, etc.

Also, your signal to noise proxy is 3.  That's good too.

Also note the orange area that tells you your THR_MID.  Set that to 593 in MP and next time it will hover at about 50% throttle.

Can you try launching the macro again, now that you know you go after the .log and let me know if the macros fails?  Please report the error message if it does.  Getting this to work in an international community will be interesting.

"you can tune pitch and roll (turn off link the two)"

I am not sure I understand what you mean here. Are you referring to the Lock Pitch and roll values check box as seen in this screen shot of my config? I had my mid throttle set at 600 and changed it down to 593 per your suggestion. Both those logged flights were not done in real calm winds as I would have liked so the stable hover was not as good as I would like. Those two flights were numbers 2 and 3 on the new copter also my number 2 and 3 on a multicopter so this is all new to me. Thanks for the help. I am glad my patience during the build is paying off in smooth flying so far. I will try the excel sheet again and let you know what happens. 

Greg

yes, the checkbox.

careful though using it.  every time you go back into that page, it is checked even though you unchecked it before.  it caused a crash on the X2.  my PIDs are unlocked for two reasons:  aspect ratio of the prop layout is twice the width (y) than length & uneven distribution of mass in x/y with mass further away from CG in y.  in any case, my y P ends up being about twice the x P (and off the chart huge).  While tuning live, i made a change to the y P and (not paying attention) it immediately changed the x pid making it about twice what it should be, which as you can imagine immediately sent it into an uncontrolled and wild crash.  your PIDs might end up the same, but it's good to check.  Generally only the P of the PIDs might be different.

I tried the excel sheet again and did make some progress. First I found in your file config data tab the logdirectory path. I have installed mission planer in a different folder than default so I copied the log files to match the path your sheet is expecting. When I viewed the macros and clicked on main and hit run it asked me to select my log file so good start. Then it gave me this error message. I have Raw logging enabled and you were able to run my two logs so not sure why it sees no data. Do I need to be on a specific tab when I run the macro? There seems to be some sample data in the sheet is this ok? 

Thanks

Greg

Forest since I still am not able to load my log file into your excel sheet I am going to provide you another log with a flight I did today. Please take a look at my vibration graphs. Today I tested the Loiter again and the RTL for the first time. Loiter was rock solid!! I couldn't be happier with how stable and solid it sat in one place. Alt hold worked pretty well but I believe the baro was being affected by the bright sun on the right side of my copter. As soon as I turned it to the left 90 deg it would drop a few feet. I did a test of the baro last night with my flash light and that right side was the side the flash light would change the alt by as much as 2 meters. Today I blacked out the inside of my APM case so I expect that to be more stable now. Going on to my RTL test when I switched into that mode it climbed to the alt it was supposed to and moved back to the home position at altitude really nice. When it reached home position but before it started descending the copter started bucking in place, more so on the second test. I let it be and it started the decent and settled down a lot on the way to 2m and it hovered rock solid there. Can you help me figure out what the bucking is all about at the top of the home way-point before decent? 

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This is how it looked, which is really nice for active flight.

Bucking ... causes.

The best way to solve that, if you haven't all ready, is to understand what happens in RTL.  On the return leg after the elevation climb, the ship is traveling at a rate through the air set or adopted by you in the parameters. Once it gets close to the home location it slows down and tries to maintain that x/y earth coordinate for five seconds per another series of parameters that you set or adopt.

So there are a whole set of tuning parameters that could be the cause.  How to know which ones?

The first thing to do is to eliminate that the cause is the roll and pitch PIDs. Once eliminated, you can then focus on Loiter and Alt-Hold PIDs.

Manually fly the copter with speed to a position and aggressively stop it at that location (sort of what like RTL does).  Do this by flying to that position using pitch only and then by using roll only.  If the copter doesn't buck like you saw it do during RTL, then the cause isn't the Roll or Pitch PID.

If it is roll or pitch PID, then the first suspect is that the P is too high.  The second suspect would be that the D is too high.

If it isn't pitch or roll PID, then post a question to the general community (don't use the unassigned catagory) with a snappy title like Bucking Copter during RTL ... HELP!  Explain like you did above and what you have tried that doesn't work.  Other people have a lot more experience on this than me.

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