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Main Discussion > SERVOS: An in depth look - Part 2
 
 
JKos
Elite Veteran
Location: City of California in the state of Maryland

Bad Karma,
You must consider the magnitude of the x values being used and the magnitude of the result before you can say the 1e-9 is "tiny". Look at the values of x. For example, at 1000 mA the magnitude of the terms are (in order)...
1, 20, 81, 7.3984

The x^3 is 1.8% of the result in this case so not really as "tiny" as 1e-9 might suggest. Ok, maybe drop the x^3 term but certainly not the x^2 term.

> its straight enough for most uses

You must not be a scientist or engineer. As a EE, I'd say it's not even close to straight.

- John

MSH Protos
04-16-2008 12:21 AM
 
 
Bad Karma
Veteran
Location: UK

Ofcourse its close to straight, actually I am training to be an engineer, but I would for our purposes just treat that as a straight line from (100,7)
04-16-2008 12:26 AM
 
 
AirWolfRCrrProfessor - Location: 42½ N, 83½ W -
You want polynomials ?
Chew on this,

±Yt = t/0.20(0.29690x^0.5 - 0.12600x - 0.35160x^2 + 0.28430x^3 - 0.10150x^4)

That describes the shape of your rotor baldes (NACA-00xx series where t=xx)
04-16-2008 12:27 AM
HOMEPAGE  
 
 
bstock
Veteran
Location: Easton, MD.

Very very Cool !!

Thank you for doing this... and for sharing it with all of us!! Two of the best threads I have Ever read!!

Keep the analysis coming guys. I am learning just as much from that.

I am fairly clear in what the data is telling us... but your analysis is helping make it make more sense.
04-16-2008 01:39 AM
HOMEPAGE  
 
 
Rockohaulic
Elite Veteran
Location: Valencia, CA, USA, 3rd Rock from the Sun

Very cool!

So now that we know that a realistic flight envelope torque can reach 70 oz-in, can you set up something to check the servo speed of the BLS451 and some other popular servos at that load???

That would be very cool data!

And it would be neat to see if it correlates to my graphs that I have posted on RR...

I got a helicopter for my girlfriend,
It was a good trade!
04-16-2008 01:52 AM
 
 
playfairKey Veteran - Location: Rochester, NY -
Quote 
...actually I am training to be an engineer
I guessed it!
You sound just like my old math professor, who lived in the world of assumed-infinitesimally-small pieces that made everything fit nice and cozy. (JK, really!)

I only used the 3rd order because it looked like it described the curve better, and it was just a "mouse click away".
Now you guys are bringing back unpleasant college memories!
Ends up that a second order would have been fine. Of course, Excel will change the values to fit the curve, which isn't the same as dropping terms.
FWIW, Below is a new graph with the curve in black, and 3 different orders of polynomials shown in dashed colors. The measurement error is more significant than the differences.


Rockohaulic, the R90 with single collective servo hit 70, the eCCPM Stratus got about half. I think the speed info you're asking about can already be found on an earlier chart.

I didn't rush to post this very first video of my Raptor 90, but it does have some merit as far as dedicated vs. shared servo duties.

Raptor 90SE collective servo torque (44mb wmv)

I also have the data from my Pantera 50 and will assemble after this nice weather spell if it looks interesting.


The sky is our canvas
04-16-2008 05:46 AM
HOMEPAGE  
 
 
the Wasp
rrProfessor
Location: Vt

Playfair,, may I suggest a new test with both Mccpm & Eccpm helis using the same servos, batt regulator,, then do a graph to show what heli was harder on the servos ..

Jim
Buzz Buzz Buzz
04-16-2008 06:18 AM
 
 
JlerchSenior Heliman - Location: Parrish, Florida -
OK playfair, how are you mixing the data into the video? I ask as I wrote some ugly code in VB.net to do this, but haven't taken it very far. I'd rather play with the heli than write code, so what product are you using?

BTW, Here is one of my videos:



And a graph of the data in the video: (still to rich, never hit target temp of 235f till end of flight...)



James Lerch - ManateeRC Member - Blade 400 - Raptor 60 - Lots of sim time
04-16-2008 03:06 PM
HOMEPAGE  
 
 
Bad Karma
Veteran
Location: UK

As I said, in this case I wouldn't bother, most of us are smart enough to use battery packs and servos beyond "up to the job" so drawing a little more current than we expect isnt really an issue except for those out there who get by on batteries that are not fit for purpose.

Eg I run a Hitec 5985 on collective, it develops 10.4Kg/cm of torque, I could get away with half that, but I dont, and I run two packs in parallel, even one can deliver enough current to power everything, but I dont.

So, I dont really care if I am drawing 1001mAh instead of 1000.

Its not like peoples lives are dependant on whether the servo draws 1000 mAh but not 1001 for a given torque load.

Some things you do have to be very precise on because there are requirements that must be hit or failure occurs, but this isnt one of them, close will do.....
04-16-2008 03:25 PM
 
 
RPMATLANTA
Senior Heliman
Location: Cumming GA

YOU GUYS JUST MADE MY BRAIN HURT!

I am a little confused but I find the info facinating!

Take offs are optional! Landings are not!
04-16-2008 05:27 PM
 
 
Heli_Man_Bob
Heliman
Location: Miamisburg, Ohio, US

This is great now I can explain to the wife why I need those new servos here honey look at the numbers who could argue with that.

All kidding aside I would be interested in the results for the Pantera as there has been arguments as to what servo is good enough and that a lsser servo is fine because there is less load per servo in this type of swash setup.

Thanks for posting this interesting analysis.
04-16-2008 05:44 PM
 
 
Rockohaulic
Elite Veteran
Location: Valencia, CA, USA, 3rd Rock from the Sun

Playfair,

Quote 



Rockohaulic, the R90 with single collective servo hit 70, the eCCPM Stratus got about half. I think the speed info you're asking about can already be found on an earlier chart.

I am assuming that the value at the bottom of the graph is speed to 60 degrees in miliseconds???

I got a helicopter for my girlfriend,
It was a good trade!
04-16-2008 05:57 PM
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

playfair,

doesn't the R^2 value in the "curve fit" used in excel show you how closely your fitted curve matches the data curve?

My college professors always wanted to see that value along with any fit curve equation...

Nice work with the servo info though. I am sure you could be working for years to come on analyzing all of the servos available. you should start charging people to analyze their servos

If you avoid failure, you also avoid success.
04-16-2008 06:31 PM
 
 
S Bell
Senior Heliman
Location: Nova Scotia Canada

Without getting complex it is easy to reason that 3 servos doing a pure collective movement on the same rotor would be each loaded 33% of the mCCPM single collective servo provided with the same servo arm length, same servo control axis rotational travel for the same blade angles.

Because setups vary and blade pitch to servo rotation preferences I think most of the data could yield different servo tasking. The mechanical speed of the system is a factor.

For a true comparison the total workload during a similar flight with the same servos in equally agile machines using the same rotor system and with the same rotor head throws (cyclic and collective blade angles.

Just a few quick thoughts on the matter, I'm sure there are more factors.One thing is basic to reason, the single collective servo will naturally draw more electrical current and require more servo torque. If you run low collective ATV with a long servo arm in a R-90 for increased pumping speed you'll need a stronger servo.

Stephen

Raptors are everywhere
04-16-2008 06:37 PM
HOMEPAGE  
 
 
playfair
Key Veteran
Location: Rochester, NY

Jlerch,
What I did was copy the data from the saved logger file into Excel.
I wrote a program in LabView that "plays back" the data rows in 125ms intervals as it was recorded. Used a screen capture video program to make a video of the data, then used Premier to blend the two.
What got cut out from the videos was a "pitch pump" at the beginning and end to sync. Yes, it was a major PITA!

I really like your data capture, and may be able to send you a similar video file if you mail me the raw data.

Rockohaulic, I'm not sure which graph you're referring to? If you look up a torque on the flight graph on the first page, you can look up the speed on the graph in the other thread.

umdpru, I can't go there, it's been far too long since doing that stuff in school! You guys are killing me with your math knowledge... I'm just glad I got to see it all come out, in a heli forum of all places.


The sky is our canvas
04-17-2008 02:21 AM
HOMEPAGE  
 
 
Jlerch
Senior Heliman
Location: Parrish, Florida

Quote 
Jlerch,
What I did was copy the data from the saved logger file into Excel.
I wrote a program in LabView that "plays back" the data rows in 125ms intervals as it was recorded. Used a screen capture video program to make a video of the data, then used Premier to blend the two.
What got cut out from the videos was a "pitch pump" at the beginning and end to sync. Yes, it was a major PITA!

I really like your data capture, and may be able to send you a similar video file if you mail me the raw data.

Actually, your system seems more complicated than mine. Perhaps I should work on cleaning mine up and sending it your way. The goal for mine was to load a video file and an FDR file. Select what data you wanted displayed, then use a scroll bar to get the data and video in sync with each other.

The only problem I'm having at the moment is when saving the resulting combined video file, I can't figure out how to get it to save in any other format than uncompressed raw AVI files (which turn out to be HUGE)

James Lerch - ManateeRC Member - Blade 400 - Raptor 60 - Lots of sim time
04-17-2008 04:47 AM
HOMEPAGE  
 
 
w.pasman
Elite Veteran
Location: Netherlands

Finally someone that has finally gives real input on the ever returning question about how much torque is really used there

Great info, many thanks! Video visualization also very nice.
04-17-2008 12:34 PM
HOMEPAGE  
 
 
w.pasman
Elite Veteran
Location: Netherlands

umdpru
I think you are confusing r^2 with the variance. The r^2 here is not the variance.

Jlerch
Your height measurement often sticks at 0 and does not exactly follow the real height variations either. Sure you got this calibrated right?
04-18-2008 07:59 PM
HOMEPAGE  
 
 
Jlerch
Senior Heliman
Location: Parrish, Florida

Pretty much, however I haven't done the calibration on the alt sensor yet as I don't wan't to dig the electronics out of the heli and wire them up so I can get the required 20degree temp swing.

I did momentarily think of putting the heli in the deep freezer, but I figured my normally tolerant wife would not appreciate that :-)

James Lerch - ManateeRC Member - Blade 400 - Raptor 60 - Lots of sim time
04-18-2008 08:04 PM
HOMEPAGE  
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

w.pasman,

Nope, not confusing anything. The R-squared value displayed via excel on a fit curve give the user an indication of how well the fitted curve actually fits the data.

If you avoid failure, you also avoid success.
04-18-2008 08:49 PM
 
 
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