Zor

Hi again rmh,

NOTE to oher readers ___
Please do not read this for the main purpose of plastering Zor some more.
If these subjects are of no interest to you , just skip and ignore Zor.

Using the edited version which you did at 09:34 (AM).
and considering the following part of it ___

Keep in mind that I am still considering that I am a learner from well knowledgeable fellows like you.
Plese kindly correct me where, when or ifI am misunderstanding.

I presently understand that the position of any servo is determined by the width (time duration) of the pulses and that this is so in both PTM and PCM. That time duration is from 1 milisecond (ms) to 2 ms with 1.5 ms as the center position (neutral).

I am not aware that this changes whether we have frames of 44 ms, 22 ms or 11 ms.
I think some decimals are involved but we can neglect them for our present purpose.

Some thinking follows ____
Time has to be reserved for pulses up to 2 ms. In one second we can have only 500 pulses.
If a frame is 44 ms we can have 22.73 frames in one second.and 22 pulses max.in a frame.
If a frame is 22 ms we can have 45.45 frames in one second and 11 pulses max in a frame.
If a frame is 11 ms we can have 90.91 frames in one second and 5.5 (?) pulses in a frame.

This leads to think that with an 11 ms frame it wouldnot be possible to command more than 5 servos in one frame and some algorithm would have to distribute commands to some servos in alternative frames or avoid to send a command if the comand has not changed.

I can even think of commands being distributed to servos only when a change is desired.
I do not know how this command distribution is functioning and it may even vary from manufacturer to another manufacturer (designers).

The main part of this discsussion at this moment seem to be the speed of servo response attributed to average voltage stated (if I understand well) as varying with the frame rate. I interpret this as more frames, more pulses; more pulses, more average voltage: more average voltage, more average current; more averag current, more torque andfasteracceleration of the servo motor resulting in a sooner deflection of the control surface (elev, rudd, etc...) .

Now I am the rudder servo ___

I am being commanded from 44 ms frame from a 9 channel transmitter
I receive just about 22 frames each second .
Being 9 channels and each pulse never exceeding 2 ms, that takes only 18 ms. I wonder if 44 minus 18 means that 26 ms is useless or does that 26 ms is all occupied by overhead (management of the pulse distribution to the servos) .

Now how is it different if the frames are 22 ms instead of 44 ms ?
It now seem to leave only 4 ms for administration of the pulses.

Do i (me rudder servo) receive twice as many pulses per second compared to the 44 ms frames ?
Is that an explanation for my average voltage to have doubled ?
Well perhaps the peak voltage has not changed but it is given to me twice as often doubling the average.

Back to Zor not being a rudder servo ___
I have done a fair amount of research about all this subject. You better believe me since I am so stupid as wanting to understand some more.

Things that are still not clear enough inmy mind are ___
What does the modulation envelope on the carrier actually looks like ? In PCM for example.
How does the receiver manage the distribution of the pulses to the servo signal lines ?
How many command pulses does a servo receive each second ? Is it one per frame ?
Does the rate of pulses differ due to the method of distribution by the receiver ? Such as if only correction pulses are sent.

I have read lots of stuff but so often ambiguous, sometime contradictory or as the old expression "turning around the bush" .

It will take time. Someday I will get a reasonble mental picture and then the whole thing will change.

Hee! Hee! Lots of fun and every little gain is a pleasure but not for everyone.

Zor

StevL

According to Billy who is a HiTec employee (he may own the place, I have no idea) their 79XX series servos are 12 bit and capable of up to 4096 resolution (they are programmable so your could pick the 2048 if you like).

Just passing along info I was told. Go buy a 7955 and have some fun....

Steve

rmh

IF the info was all sequential- and it is NOT in the 2.4
in old stuff, it was

Zor

Sorry, what you say is not clear to me.

Zor

Zor

I went and looked at the 7955 which included some info about the 5955 as well.

Sorry I do not have $114.95 plus tax and may be plus custom dutys and custom services charges to buy a 7955.

I did not find there any information about the mechanical resolution of the output shaft.

It seems that what they are talking about is the electronic signal that the servo can accept at its electrical input.

I will give up for the moment about finding the information I have been looking for.

I am not trying to be hard headed.
I have not yet seen clear information about the servo output shaft resolution and i cannot see small potentiometers in the transmitter and in the servos resolving 5900, 4096, 2048 and even 1024resolution.

I have not seen the nature of the voltage on the cursor of the potentiometer in a servo but I have seen it in a ransmitter and it is a DC voltage.as seen on my DC oscilloscope.

I will try that again using a digital voltmeter to observe the readings but I have a problem with that because I only have a digital voltmeter that shows only twodecimals above two volts. That would detect only 1/100 of a volt of variation and with a source varying betwen 0 and about 8 volts would not be able to dissect even 1024 variations.

Anyway there is only 6 screws to open the transmitter again. .

Ya ___I am having fun in my frustration .

Zor

.

AndyKunz

Back in the old days, the servo signals went out over the air using PPM. Your understanding of PPM (a serial method) is pretty good.

Today, they go out digitally as a packet. That packet gets decoded by a micro, and if the micro programmer wanted, he could have made all the pulses go out to the servos at the same time. Not a good idea from a power loading point of view, but very possible. We are not limited to the shift-register operation of days of yore.

The rate that the servos are refreshed can be totally independent of the frequency that packets are transmitted over the air.

Andy

Zor

Andy,

Thanks a million.
I fully understand and can visualize what is going on.

I had suspicions but did not dare ask.

Zor

rmh

Why not ask? I did not mean to be abrupt -Andy described the present setup which is not a straight time line -as you had assumed
As for all discrete steps you were looking for I can only say -you won't SEE them
A good analogy is like watching a super high speed camera shot -
when played back, even very slowly,You will still see the motion as a constant thing -not steps.

Zor

rmh,

You wee very helpul and I can only thank you in writing.
I wish I could do more.

Many in the forum were also very helpful and I pass to everyone my gratitude.

Zor

baronbrian

My Feedback: (13)

I have a question zor- what do you have that needs less than .02" movement? do you have a 3D ship with huge throws that is difficult to trim? That is the only thing 512 resolution has ever hurt me on. really except for trim purposes I think that 32 steps each side of neutral would be enough to fly just fine. I'm sure the QQ or Chip could out fly me using a 1024 system if they were using a 64 step one. I truly believe that going from 1024 to 2048 was mostly marketing. the increased speed of the newer systems that the pilots could feel they attributed incorrectly to the increased resolution. But just like increasing a camera a few MP makes people think that the new model is better, I don't believe that 2048 made a significant difference in people's flying, which is the true measuring stick in the end. Even with more Megapixels, if you look at all but the best pilots flying, is going to look out of focus up close. and a better camera isn't going to help them, only taking more pictures will. Your servos are fine, your radio is fine, go out and use them!
Aren't metaphors fun?

rmh

the "resolution" is detectible.
A strange thingtho- the biggest change in the feel of accuracy came when I switched from my 72 mhz to the then new 2.4 and the DX7 tx
Many modellers felt that 2.4 was "just another frequency -like 27 -to 72 .
Actually th entire transmission is done much differently
surfaces which needed duplicate inputs get them- not one lagging the other.
The models inmmediately required more expo to get same damping .
also response at extremely small corrections - notably better
Would I go back to 72? and the old transmission setups ?
No way
would I go back to glo fuel?
NO way

Zor

Hi Brian,

I oten inserts text in red in the original text to assure correspondance beween my writings and the original.
I am trying something diffeent now to avoid the red text that some do not like.
I have broken your text in paragraph so that each of my paragraph below correspond to yours above.

1 - I have nothing that needs a high degree of resolution. When I read about this 2048 and particularly when someone wrote that he had some servo capable of 2048 resolution it did not make sense to me.
I got curious about what I could detect with my DS821s and made some test.
I have a small electric Fly Dragon that flys very well on 27 Mhz and I measued only 20 steps each side of neutral. No matter how fast a control surface can be moved, by the time the aerodynamic force has acted on the airplane mass and produced a result (change of attitude) we are far away from responses in miliseconds.

2 - I also think that marketing people have made a big fuss about stressing these resolutions.
Photography has been one of my hobbies for decades. I used to have a dark room and develop my own color 35 mm slides. I wanted a digital camera and waited months to learn enough to take an intelligent decision. Considering my finances, I bought a Kodak Z612 with many bells and whistles that I stil have not all used in 3 years. It has five resolution setup 6.0, 5.3, 4.0, 3.1, and 1.1 MP. I use 1.1 and have much smaller file sizes and all the definiton I need. I have no need to print photos 40" x 30" .

3 - i did quite a bit of studies recently to increase my knowledge of the modern radios. I have both 72 Mhz and 2.4 Ghz. I am not building gigantic models. I am happy with 5 to 7 feet wingspan that I can carry all assembled in my old van. I fly for my own pleasure and in remembrance of my career as a pilot. I am not trying to show off detailed cockpits and minute details. Over the early years I have developed my own techniques of gluing and covering and still work the same way.

For me being a hobby is to work in leisure times when I feel like it. I will havethe old designed Spectra sailplane ready to go in the spring and have all kind of experiments I plan to do with it.

Thanks for your good support and a post that makes lots of good sense.

Zor

Zor

Hi rmh,

i can easily visualize that, with very light weight models and and a pilot that has very quick physical reactions anddoing precision flying, that a change fom 512 to 1024 might be detectable by the pilot.
This assumingthe same model and setup.

I came up to 2.4 Ghz more by experimental curiosity and partly to keep up with the fellows at the flying field. Part of my interest in the hobby is not only to learn how to use the stuff but also how it works and function.

I am limited in funds and do not spend money on ARFs, RTFs and similar. Spending as much time as I can at the flying field is not my goal. I used to fly quite a bit in nice winter days but no more.

It is always nice to read you. Thanks.

Zor

bem

My Feedback: (1)

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Hi,

Well, I retype everything now I tried to send:

DX8: It has been some problem with this radio, make sure that the radio you buy is fixed. I think the safest way is to just send in the radio to be sure it will be fixed, if in doubt.
http://www.horizonhobby.com/Products/Default.aspx?ProdID=SPM8800#quickSupport
Other then that I'm sure it is a fine radio.

8FG: Futaba has been in this field for many many years, 8FG is light (I like that) but perhaps little plastic (but not "cheap"). Stick tension is little weak for my taste, plenty of mAh battery in transmitter. Software upgrades seems to add many great features - very soon there willl be an upgrade to 8FG - see below from European Robbe/Futaba 2011 catalog). Futaba digital brushless servos are rather expensive (if one prefer them) and also their receivers are rather expensive(but you can buy 3rd party receivers now that is Futaba compatible - FrSky and Orange have some). FASST seems very reliable. I have a Futaba 2.4 GHz radio myself, 14MZ, and I'm pleased with Futaba. Good luck whatever You may choose.
http://2.4gigahertz.com/systems/futk8000.html
http://2.4gigahertz.com/index.html

/Bo

Zor

You surely are not alone. I have not succeeded to find what the timing is.

Now I save my text before any attempt to post if Ihave more than just a few lines.

Zor

baronbrian

My Feedback: (13)

Hey Zor- I have a servo resolution experiment going on right now that is giving some very interesting initial results. photos and a report tomorrow once I crunch the numbers. Good luck sleeping tonight now...

Zor

Anxiously awaiting any information on what you are doing , with what and any results.

Zor

garyr1

Futaba Fasst is the way to go. This company DOES have a superior 2.4 Tx/Rx link, well proven industrially for years.
Simply put, they know what they are doing in 2.4 spread spectrum technology.

Failures and unexplained glitches at our field are virtually always Spektrum. Not JR, unless a spektrum receiver is involved.

I absolutely love the JR 9 channel and would have it if they linked to Fasst technology like they do in europe (c'mon you N. American distributors...get with the program here!)

I don't care about $100 either way on the radio package. The all up price of our kites in the air dwarfs any modest price differences.

RELIABILITY is really, really key. Don't get hung up on a programming 'trick' or glitzy features that sell equipment but don't fly your airplane better.

Spektrum stuff seems to constantly have a varied collection of glitches, brownouts, lost binds, etc...not to mention a few recalls here and there.
No question Spektrum is doing a great job packaging for the BNF entry and interemediate markets...super selection and prices. Can't beat them there.

BUT....I constantly hear of little things going on at the field with the Spektrum crowd.
The Futaba guys are up there flying, not on the ground fiddling, or collecting pieces.

I have both, so I'm not speaking from one side of my mouth.

IMHO, for whatever it's worth... RELIABILITY!!!!

baronbrian

My Feedback: (13)

O.K., Here are my results on a standard JR 517BB servo that is about 10 years old. each click of sub trim did result in movement from the servo, as did each click of trim on the radio face. the sub trim made smaller incremental movements than the mechanical trims on the face did. Testing was done with my x-347 JR transmitter. I should have my 10x back from service this week, and I may repeat these tests.

The first thng I did was enter a new model on the transmitter, and then set the travel adjustments on the elevator channel to 150% to make the changes easire to see. Then I took an old servo case top and got the dremel out to make a window so that I could see the gear train move while in operation. at 150% travel, the servo appeared to have exactly 60 degrees throw on each side of neutral, about 120 degrees or 1/3 of a full circle total.

Gears for the 517 are as follows: output (servo horn) gear has 38 teeth, the secondary gear has 12 on the top half that meshes with the output gear, and 49 teeth on the bottom. the third gear has 11 teeth that mesh with the secondary gear and again 49 on the bottom. there is a forth gear as well as a small pinion gear on the motor inside the servo, but Those ratios were not used or noted.

After making a mark on the third gear with a sharpie (see pic) I set the mark to start at exactly where it is overlapped by the secondary gear, and then started counting clicks of sub trim untill the third gear made exactly one full revoulution. It took exactly 109 clicks of trim for that to happen. then I took that number and multiplyed it buy the gear ratios.

38/12=3.166

3.166x49=155.166

155.166/11=14.106

this means that for every revolution the output gear makes, the third gear tuns 14.106 times.
But we found that the total sweep of the output arm isn't a full circle but rather 1/3 of one, so in a 120 degree sweep of the output arm the third gear rotates 14.106 / 3 = 4.702 times

so the third gear rotates 4.702 times in a full sweep, and it takes 109 clicks of subtrim to rotate the third gear once, so 4.702x109 is the resolution of the servo which equals 512.518. the x-347 is a Z-pcm radio, meaning it's maximum resolution is 512, so this servo came out perfect. "
the end of a half inch output arm would move 1/3 of the circumferance of a 1" dia circle, or 3.14159"/3= 1.047196" in those 512 steps, or .0020" per step.

But remember that at the top when I said that one click of the mechanical trim created more movement than the subtrim did? well it turns out that the gimbal only has the resoulution of the mechanical trim, providing the servo 128 steps each side of neutral, or 256 total as it is moved back and forth.
this is what I thought was so interesting, that the radio did not provide it's own maximum resolution to the control surface in flight.

Add to that the fact that the throttle has 12 steps abouve and 12 below the half throttle position (25 discrete positions) and that the pots that control channels 6 and 7 are racheted to give 40 positions each, and one quickly realizes that you don't need that much resolution to fly a plane.

baronbrian

My Feedback: (13)

that was because the first servo that I used was from my crashed pile and had a damaged pot. the servo that was used in the above post was perfect.

Zor

Brian Dorf,

I appreciate very much your post #69 because it makes good exercise for the brain cells __

I note that your transmitter had a claimed resolution of 512 and you ended up with a minimum servo motion of 0.002 inch by the method you used to figure things out.

It puzzles me a bit about the 109 increments of the sub trim but the figuration you did is good.

As you may be aware in my case I actually put a dial indicator right on the servo horn at the 1/2 inch radius and also concluded with 0.002 inch.

I was using however a 1024 claimed resolution transmitter which should have showed me a 0.001 inch movement of the servo arm (horn).

At this stage I can only believe that the servo resolution is limited by the ability of the potentiometers in the transmitter and in the servos to resolve a higher resolution and thus limit the available servo resolution.

Until anyone comes out with facts and figures I remain satisfied with your figures that match mine and are in agreement.

We had one more of many opinions and claims in the forum that the claimant does not return to explain or prove what he wrote.

Zor

Radimani

Just FYI. Do you know this stuff?
http://www3.towerhobbies.com/cgi-bin...FVSEARCH=jm912

baronbrian

My Feedback: (13)

here are a few replys to you reply....
Remember, the .002" of movement was the smallest movement that I could accomplish with the sub trim function. the mechanical trim as well as the gimbal would only give half of that resolution, which would mean .004" would be the smallest movement that I could get during flight. If your transmitter also gives half of its resolution to the gimbal and trim (I have no idea if this is true) then the minimum movement would be .002" during flight, however subtrim on your radio should yield .001" of movement. let us know.


If it takes 109 clicks of subtrim to make the third gear rotate once, then you can use that number along with the gear ratio to find resolution.


_______________________
I can't wait to repeat this test with my 10X, the trims on that radio have adjustable sensitivity dependant on the user. you can program the trim to have any where from 1 to 10 clicks of subtrim per click, so max resolution should be available in flight, or 4 times better than the 512 system can achieve without going into the radios programming. this would yield the .001" that you were seeking. also interested to test how many steps each side of neutral the gimbal provides, not that that matters as much. the resolution is really only important when it comes to trimming a plane.

Also of note is that I did try the test on the JR 8231 digital servo, but with the signal going to the servo arm 6 times faster that with the 517 servo, I couldn't tell if the arm had moved or if it had moved 1 step or three... (the human eye can see about 50 Hz which is why our household electricty runs at 60Hz. if the electriciy were 45 or 50 hz we would be able to see the lightbulbs flickering, which they are doing anyways...) Also I didn't have a case top for the 8231 servo that I was willing to sacrafice for this experiment, if anyone has one to send me (your 821 case will work, Zor!) I'll test it to.

Zor

Many countries in the world are using 50 hertz .

brenthampton79

So if i understand right the futaba 8fg can do like 8 proportional channels plus two on off, like an optokill switch, and retractable landing gear, as long as you have a 14channel rx, which i do have one. so its basically a 10 channel with 8 proportional channels right? If so I'll get rid of my 10c and get one of these