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12-15-2011 10:36 PM  9 years ago
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Charlie R

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Lafayette Ca

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servo Typ
I am installing (3) BLS255HV and a BlS256 in a 700n and I am wondering what to tell my CGY 750 is the Servo Typ ?
Are they both DG :760 ?
Thanks for your help in advance .
Charlie R
Helicopters are a mass of rotating metal fatigue surrounding an oil leak !
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12-15-2011 11:00 PM  9 years ago
gorn

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Western Australia

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no they are both not.

The 255 is 1520, the 256 is 760
For the love of the hobby
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12-16-2011 01:00 AM  9 years ago
Charlie R

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gorn
In the swash basic 1520 is not a choice either DG 140hz or DG 285hz ?
For the tail there is a 760 choice .
Thank you for your help !
Charlie
Helicopters are a mass of rotating metal fatigue surrounding an oil leak !
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12-16-2011 02:41 AM  9 years ago
brian94066

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285hz
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12-16-2011 03:47 AM  9 years ago
Charlie R

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brian94066

Thanks !

Charlie
Helicopters are a mass of rotating metal fatigue surrounding an oil leak !
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12-16-2011 07:01 AM  9 years ago
GetToDaChopper

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the numbers 720uSec & 1520uSec refer to the servos "pulse width" and the numbers 140hz & 285hz refer to the servos "frame rate", two completely different things, a good fbl controller will let you set both instead of a less than optimal default setting.......

EDIT changed termanology
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12-16-2011 07:29 AM  9 years ago
Phaedrus

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For reasons that I do not understand the 750 now has the 140Hz & 285Hz choices for the swash servos. The rudder still has 1520 & 760. They state in the v1.2 instructions that the 285 selection = 1520.AMA Leader Member
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12-16-2011 08:43 AM  9 years ago
GetToDaChopper

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i wonder how they fig that ? in my skookum software they give you a choise of "200Hz, 250Hz, and 333Hz frame rate" with the 1520uSec pulse width and the same "200Hz, 250Hz, and 333Hz frame rate" with the narrow 760uSec pulse width, the "pulse width" & the "frame rate" don't seem to be directly tied together.

here's this from Spartan
The servo position is controlled by an electrical pulse or variable duration which in electronic terms is called pulse width. The pulse repeats at constant intervals and this repetition frequency is also known as frame rate and is represented in Hertz (Hz). The majority of RC receivers will produce a frame rate of around 50Hz which means that they will instruct the servo where to go 50 times each second. The position of the servo horn is defined by the pulse duration. For a typical RC servo a pulse duration of 1520uSec means that the horn should be at the mid-point of the servo travel. If the pulse duration becomes shorter or longer the servo horn will move clockwise or counter-clockwise respectively.

As gyros evolved it was apparent that 50Hz was not enough to achieve the desired performance as the time intervals between pulses were too long. So manufacturers starting pushing the frame rate up. JR gyros went to 250Hz and Futaba pushed as high as 333Hz. This allowed the gyro to talk to the servo more frequently but the position command remained the same (1520uSec still means mid-point).

Then the GY601/611 gyros came along with the non standard 760uSec system which is also known as "narrow pulse". With this system the servo travel mid-point is at 760uSec as opposed to 1520uSec. In theory by shortening the pulse to half it can reach the servo faster and therefore the servo can react sooner. In reality the benefit is negligible as the savings are less than 1mSec. Considering the inertia of the motor windings and the helicopter as a whole 1mSec does not give any practical benefit and very likely this system was only implemented to tie specific servos to these gyros.

So when buying a new tail servo the important things to look at are speed, torque and capability for high frame rates. With the exception of the older JR servos (8700G etc) most new digital servos will work at 333Hz. This includes all Futaba digital servos and therefore the S9254 will work as good as the S9256 since they have the same torque and speed spec but perhaps a little hotter due to the lack of metal case.

Added (March 2009)
As gyro technology evolves Spartan RC has introduced a new 560Hz servo pulse mode in the V2 firmware update of our gyros. This higher pulse frequency is only possible when using narrow pulse (760uSec) servos such as the S9256 and BLS251. Because the servo position is updated 68% more frequently this system has the potential to deliver smoother tail response and more consistent pirouette rates.
looks like "560Hz servos" might be the new hot ticket soon ?
idk what do you guys think ?
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12-16-2011 02:24 PM  9 years ago
Phaedrus

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i wonder how they fig that ?
It seems to me that what they mean is if you are using 1520 servos then use the 285 setting. Not sure if there is anything else to read in to it.
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12-16-2011 02:41 PM  9 years ago
Wave

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Illinois

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For reasons that I do not understand the 750 now has the 140Hz & 285Hz choices for the swash servos. The rudder still has 1520 & 760. They state in the v1.2 instructions that the 285 selection = 1520.
The reason is simple.

Everyone moaned and complained that there cheap servo's that they were overvolting were getting hot when using the CGY 750, because the CGY outputs a LOT of correction data.

So Futaba simply gave them a way to cool things off. Thats also why they added "head response".

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12-16-2011 02:51 PM  9 years ago
GetToDaChopper

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It seems to me that what they mean is if you are using 1520 servos then use the 285 setting. Not sure if there is anything else to read in to it.
but not all 1520uSec servos run 285Hz so i guess that means thats a default setting that futaba uses with 1520uSec servos ?

you would think futaba would run servo faster than 285 if they could, like at my tail servos speed which is 560Hz, thats way faster than 285Hz........
Everyone moaned and complained that there cheap servo's that they were overvolting were getting hot when using the CGY 750, because the CGY outputs a LOT of correction data.
i can believe that........
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12-16-2011 03:06 PM  9 years ago
gorn

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I understand what the differences are between pulse width and frame rate.
I misinterpreted which one he was asking about.
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12-16-2011 03:16 PM  9 years ago
Phaedrus

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S. Orange County, California

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All I know is that the directions that came with mine with v.1.2 software said to use the 285 setting in swash if my servos were 1520 servos. That seems to work.

BTW - Ben Minor noted in one of his threads that the servo setting appeared to have little to do with the setting. It was mostly an issue of over voltage to the servos. i.e. unregulated 2S lipo for servos not HV rated.
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12-16-2011 06:05 PM  9 years ago
GetToDaChopper

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if DrBen said it, then there's little doubt it's true.     ▲
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12-16-2011 06:37 PM  9 years ago
Dr.Ben

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To clarify, long before 1.2 was released, there was a beta version of the firmware with an added parameter for different driving frequencies for the cyclic servos besides the so-called analog rate and 285Hz (that's what the "digital" drving frequency was in pre-1.2 firmware was a default) for digitals. With all else kept constant in situations where servos were overheating, lowering the driving frequency to less than 285Hz did little to reduce the issue. Results of background testing with this firmware were consistent with what guys found in the field when they tried to no avail the so-called (at the time) analog mode for the cyclic servos when they had servos running to warm. Head response works by adjusting the data stream to a level a given servo type or brand is able to handle. That parameter along with strict avoidance of overvolting servos have been the ultimate solution for those who have had issues with servos running too warm.

1520uS/285Hz are the correct settings for all Futaba digitals being used for cyclic control.

Ben Minor
Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA
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12-17-2011 07:34 PM  9 years ago
GetToDaChopper

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leave it to the Dr to to have the correct diagnoses !

it makes this sport we love that much better becuase of him !

thanks Doc !!!
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