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HelicopterMain Discussion › Actual Servo Speed Under Load
09-11-2007 03:02 PM  10 years agoPost 21
tchavei

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Portugal

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Eagletree sells little cheap sensors that you can place between each servo to be tested and their logger. I think you can however only record one servo at a time with the usb micrologger. I'm not sure about their more advanced systems

Tony


--------------------
"Perfection and patience usually walk side by side..."

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09-11-2007 03:11 PM  10 years agoPost 22
SSN Pru

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Taxachusetts

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Couldn't you just stick an amp draw meter on a servo and record that during a flight, then use the scale method to reproduce the amp draw?
is there an echo in here?

Stupidity can be cured. Ignorance is for life!

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09-11-2007 05:07 PM  10 years agoPost 23
AceBird

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Utica, NY USA

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I bet the load on the servo could be calculated after taking some in flight current readings on one cyclic servo.
That is probably the only method you can use to estimate the load with out the use of an onboard load cell. Once you find that number though it will not be accurate for everyone’s use. There are way too many variables such as headspeed, blade choice, linkage arrangement, TX programming, available horsepower from the engine and even the gearing itself. Finding the max torque load will only answer one question. Will the performance be affected? That will not necessarily tell you if the servo will stand up for the long haul.

In this case of servo selection I think experience is the best choice selector. The question could be asked two different ways: What would you use for this application or what would you not use for this application? Having a simple chart of good choices and bad choices based on experience would be a great help for beginners.

Something like this is a prime example:
There has always been a rumor that top Futaba pilots choose the 9351 over the 9451 because under load the 9351 was actually faster.
Without getting into brand names any “good” servo that is identified will have specifications that could be duplicated for torque and speed. However now that digitals are becoming so popular the simple specification of torque and speed is not gospel. Digitals with out a doubt have higher torque and speed values but do they last longer? The bottom line is experience will tell.

Ace
What could be more fun?

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09-11-2007 06:07 PM  10 years agoPost 24
JKos

rrProfessor

Redondo Beach, CA

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> Digitals with out a doubt have higher torque and speed values but
> do they last longer? The bottom line is experience will tell.

Just how many years of experience does it take on a given servo? We have been using some of these servos for quite some time now.

- John

RR rules!

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09-11-2007 06:46 PM  10 years agoPost 25
DS 8717

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Here wishing i was somewhere else

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Almost 10 years now.

YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED

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09-11-2007 08:34 PM  10 years agoPost 26
AirWolfRC

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42½ N, 83½ W

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The main question remains unanswered.
What are the torque requirements in actual use ?

Only then can an intelligent choice be made.

I'm hearing Dimension Engineering and Eagle Tree Systems but does anyone have any numbers ?

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09-11-2007 08:57 PM  10 years agoPost 27
SSN Pru

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Taxachusetts

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The main question remains unanswered.
What are the torque requirements in actual use ?

Only then can an intelligent choice be made.

I'm hearing Dimension Engineering and Eagle Tree Systems but does anyone have any numbers ?
thats is what this post is about. No one has numbers. We are discussing feasible ways to get the numbers we need....

I knew it would only be a matter of time before he came into this thread...

Stupidity can be cured. Ignorance is for life!

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09-11-2007 09:18 PM  10 years agoPost 28
Chopper

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Stow,Oh- oops, I mean St Louis, nope Stow again,

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I didn't notice the voltage for the test. The 9451 servo is rated at 6V where the 9351 is not. (Not to say you can't run the 9351 on 6v.) The servo times are based on 60 degree transit. Full +12 -12 collective would require about a quarter of that time (depending on the heli). With higher voltages, and dividing the servo difference by 1/4 transit time, the difference becomes almost imperceptible.

The loads on the system will change with blade design as well. The bolt hole placement and CG of the blade will have a noticable effect in the loading. There are certain blades out there (of a certain non-color) that will actually strip the servo gears of some servos. Other blades will not ever come close.

I have been preaching "the right combination" for a long time. This is another one of those cases. There is not one item that you can put on a heli that will not affect the performance of another item on the heli.

If you are running the higher load blades to the extremes, the stronger servo may be better for you. If you have a high flybar ratio, and if you have more temperate blades, the higher speed servo at a higher voltage may work best for your set-up and flying style.

Lots of variables that need to be accounted for in this excercise.

Paul Soha is a free agent now. Wow.

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09-11-2007 09:20 PM  10 years agoPost 29
Rockohaulic

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Canyon Country, CA, USA, 3rd Rock from the Sun

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Well, I was just getting to that!

Since many of us use 6 volt systems, this is what the numbers look like:

As you can see, and as everyone knows, 6 volts buys us a lot more performance. If our actual in-flight loads are less than 70 (for me that means on a 50 size helicopter), then we can save some money and get the Hitec 6975 servo. However, if our actuals are 70 or above, we are better off with the Futaba 9351.

Mythbusting: One small misconception is that a 90 oz-in servo can handle 90 oz-inches of torque. Actually, it's exactly the opposite. The rating of 90 is the stall torque. What that means is that the servo will work up to 90 oz-inches, and then it stalls out. Of course, as the load approaches 90, it starts to get very slow!

Saturday morning I flew my helicopter in my pajamas
How it got in my pajamas I'll never know

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09-11-2007 09:22 PM  10 years agoPost 30
JAGNZ

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Auckland, New Zealand

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I just overspec my birds then I know servos are not the limiting factor...I am the limiting factor.


Jason Greenwood

www.3dheli.co.nz

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09-11-2007 09:25 PM  10 years agoPost 31
AceBird

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Utica, NY USA

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The main question remains unanswered.
What are the torque requirements in actual use ?

Only then can an intelligent choice be made.
Well as I said you are going to get wildly varying results if you perform the measurements on multiple machines with multiple pilots. But suppose you get a value like 59in-lbs of torque would that mean that a servo with 60 in-oz of torque is good enough? I don’t think so.

Ace
What could be more fun?

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09-11-2007 09:27 PM  10 years agoPost 32
JKos

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Redondo Beach, CA

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Chopper,
I'm on your ignore list for some reason. I would like to ask you few questions about comments in your post, if you don't mind.

Thanks,
John

RR rules!

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09-11-2007 09:39 PM  10 years agoPost 33
AirWolfRC

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42½ N, 83½ W

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He's not going to see your post.

I agree with his formula and conclusions, as far as they go.

BUT, real world numbers are still needed, as many as can be had.
. . . . to see where on the chart we fall.

The sun is going to urn out of fuel too, in a few billion years . . . .

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09-11-2007 09:48 PM  10 years agoPost 34
Nick Jones

rrKey Veteran

anderson

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Chopper,
I'm on your ignore list for some reason. I would like to ask you few questions about comments in your post, if you don't mind.
There now he will see it

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09-11-2007 09:48 PM  10 years agoPost 35
Rockohaulic

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Canyon Country, CA, USA, 3rd Rock from the Sun

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Oops, ignore the last chart. I just noticed that the Hitec 6975 is a bit faster at 70...

Saturday morning I flew my helicopter in my pajamas
How it got in my pajamas I'll never know

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09-11-2007 09:58 PM  10 years agoPost 36
AirWolfRC

rrProfessor

42½ N, 83½ W

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A nomograph with torque on one axis and speed (º/sec) on the other axis can show the same thing.

speed for a 150ms servo is 60º/0.15 = 400
speed for a 200ms servo is 60º/0.20 = 300 . . . . etc

Draw a line for each servo and see what side of the lines you are on for a given torque to see which servo is faster.

BUT life is never that simple.
The site http://www.teaser.fr/~osegouin/aeromode/servos.phtml indicates that servo response is not linear . . . . but close enough.

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09-11-2007 10:00 PM  10 years agoPost 37
Chopper

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Stow,Oh- oops, I mean St Louis, nope Stow again,

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Sorry if I had someone on my ignore list. It would have been purely accidental.

Paul Soha is a free agent now. Wow.

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09-11-2007 10:18 PM  10 years agoPost 38
AirWolfRC

rrProfessor

42½ N, 83½ W

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I knew it was there, I finally found it, a previous thread on this topic,
http://runryder.com/helicopter/t325262p1

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09-12-2007 06:27 PM  10 years agoPost 39
Rockohaulic

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Canyon Country, CA, USA, 3rd Rock from the Sun

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And even more info on Tail servos...

Even the 6965 at 4.8 volts kicks the 9254 butt at 30 oz-in load. Only problem is - how much load does a tail servo see???

But even at half the rated load of the 9254 (20 oz-in), the 6965 at 6 volts has caught up!!!

Saturday morning I flew my helicopter in my pajamas
How it got in my pajamas I'll never know

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09-12-2007 07:15 PM  10 years agoPost 40
heli3000

rrNovice

Germany

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120 and 140 CCPM

So it would be actually better to use a 120CCPM swashplate because the two servos in the front will move faster than the single servo? This will cause interaction I think.

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HelicopterMain Discussion › Actual Servo Speed Under Load
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