servo torque rating?
04-26-2003, 12:46 PM
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servo torque rating?
i was just wondering what good are the torque ratings and torque servo calculators if the gears tend to strip on some servos (like the HS-225BB) thus not able to handle the specified loads? 
see:
http://www.rcuniverse.com/showthread...919&forumid=27
how are the servos rated/ tested? under real life stresses test or what...?
can anyone enlighten me on that?
THNXX
see:
http://www.rcuniverse.com/showthread...919&forumid=27
how are the servos rated/ tested? under real life stresses test or what...?
can anyone enlighten me on that?
THNXX
04-26-2003, 09:42 PM
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Exactly!!!
I brought up this point a few years ago. I asked if someone could give me an example where the surface didn't have enough torque to operate correctly and strips didn't count because that would mean that the servo didn't fail.... the gears did. I didn't get a response, just plenty of people telling me that I needed to use high torque servos, or the gravity gods would get me.
Guys 10 years ago were flying giant scale planes with futaba s148 servos, and they worked fine. Now we have all of these high torque servos and all, but the torque is only as good as it's weakest link, the gears. Maybe the higher torque can strip the gears .024/sec faster
Dan
Guys 10 years ago were flying giant scale planes with futaba s148 servos, and they worked fine. Now we have all of these high torque servos and all, but the torque is only as good as it's weakest link, the gears. Maybe the higher torque can strip the gears .024/sec faster
Dan
04-27-2003, 01:49 AM
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Try This Test
Here's a test you can do... Get a pair of binoculars and get somebody you trust to fly the airplane or fly the plane and get them to watch. Roll the plane into Knife and watch the rudder...if the servos are not strong enough you will see blowback. High torque digital servos are an ***extreme*** improvement. The difference in feel is noticeable instantly. The difference in the ability to precisely put the control where it's been commanded and keep it there is also noticeable. You don't get that spongy feel with them. The plane goes where you put it when you put it there is the best way I can decribe it. With a good quality digital there just is no comparison. Try the test above...I did...you'll be suprised at what you see. It's hardly scientiffic, but what is shown is real clear.
04-27-2003, 12:02 PM
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servo torque rating?
Cap, i am glad someone thinks like me (always reasuring)...
i was figuring out what servos to use in my Patriot, and using the torque calculator, all surfaces should be OK with standard servos (under 40 oz/in)
so using mini HS225's should be more than adequate, since their torque rating is 55oz/in (more than the standard servo), but then i read their gears strip under conditions a regular servo should handle...
if the gears of the HS225 can NOT withstand their max torque under real life conditions, i see two possible problems:
1- BAD design: all components of a servo should be FAILING approx. in the same torque range (for obvious reasons)
2- the rating methods do NOT simulate conditions under real use of the product ; example the loads are being applied very gradually in a linear mannar hardly representing their real life applications (a marketing strategy to "up" the servo torque rating compared to the competitors...
in any case, the ratings then mean NOTHING and the torque calculator is just a techological gadget that most of us really like to use...
back to square one...
where can i buy metal gear set for the HS225's?
and is it worth the trouble?
i was figuring out what servos to use in my Patriot, and using the torque calculator, all surfaces should be OK with standard servos (under 40 oz/in)
so using mini HS225's should be more than adequate, since their torque rating is 55oz/in (more than the standard servo), but then i read their gears strip under conditions a regular servo should handle...
if the gears of the HS225 can NOT withstand their max torque under real life conditions, i see two possible problems:
1- BAD design: all components of a servo should be FAILING approx. in the same torque range (for obvious reasons)
2- the rating methods do NOT simulate conditions under real use of the product ; example the loads are being applied very gradually in a linear mannar hardly representing their real life applications (a marketing strategy to "up" the servo torque rating compared to the competitors...
in any case, the ratings then mean NOTHING and the torque calculator is just a techological gadget that most of us really like to use...
back to square one...
where can i buy metal gear set for the HS225's?
and is it worth the trouble?
04-27-2003, 02:55 PM
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servo torque rating?
You left off number 3 and perhaps the most important.
The smaller the physical size of the servo requires proportionately sized gears. If you are using smaller servos to save weight or because it just looks cool to see tiny servos in a big wing then you are kidding yourself, because that big wing has a correspondingly large control surface to move and keep in place at speed in manuvers. The small servos are designed for small planes with small control surfaces. The purpose of high torque small servos in not that it will move a huge control surface, but rather, that it will move the small control surface it was designed for in a COMMANDING way, and keep it where you tell it to be. A large surface requires a servo not only with the torque needed, but also the more robust gear traine needed to stand up to the load imposed by the control surface size, speed of the plane(wind resistance/drag), and the amount of control surface deflection which has been commanded. There is a lot of math and physics to support this, but the math is way too involved for this forum and not really needed to understand the principles.
The reason we used standard servos 10 years ago for large scale planes is because that is what we had. Most of the really big planes back then were designs like the Piper Cub, or Taylor Craft, or something similar. These were relatively slow flying aircraft. If it was a warbird, it was flown in a scale manner and the standard servos were okay there also.
Three D flying and Extra 300s and the like werent an option. Only the guys on the raw edge were even thinking about building planes like the three D jobs that are so prevelant now. They learned the hard way about standard servos with nylon gears on high performance aircraft through plane losses and servo gear replacements etc. They are the ones who demanded of the radio manufacterers the metal geared, high torque, high speed digital servos we use today. The reason they still cost so much is due to the radio builders need to recoup their R&D bucks and it is a relatively new technology and a sellers market. The technology is soon to change again. Any time you see a flyer ganging three or four digital 8411's or such together to get the command needed to do the manuvers he wants the plane to do safely, you can bet that he wishes there was a single, 450 oz in digital servo available. There are some coming on line now but are way pricey for all but the flyers who are a pro level or wanting to go there.
My opinion, hope it adds some insight.
blabree
The smaller the physical size of the servo requires proportionately sized gears. If you are using smaller servos to save weight or because it just looks cool to see tiny servos in a big wing then you are kidding yourself, because that big wing has a correspondingly large control surface to move and keep in place at speed in manuvers. The small servos are designed for small planes with small control surfaces. The purpose of high torque small servos in not that it will move a huge control surface, but rather, that it will move the small control surface it was designed for in a COMMANDING way, and keep it where you tell it to be. A large surface requires a servo not only with the torque needed, but also the more robust gear traine needed to stand up to the load imposed by the control surface size, speed of the plane(wind resistance/drag), and the amount of control surface deflection which has been commanded. There is a lot of math and physics to support this, but the math is way too involved for this forum and not really needed to understand the principles.
The reason we used standard servos 10 years ago for large scale planes is because that is what we had. Most of the really big planes back then were designs like the Piper Cub, or Taylor Craft, or something similar. These were relatively slow flying aircraft. If it was a warbird, it was flown in a scale manner and the standard servos were okay there also.
Three D flying and Extra 300s and the like werent an option. Only the guys on the raw edge were even thinking about building planes like the three D jobs that are so prevelant now. They learned the hard way about standard servos with nylon gears on high performance aircraft through plane losses and servo gear replacements etc. They are the ones who demanded of the radio manufacterers the metal geared, high torque, high speed digital servos we use today. The reason they still cost so much is due to the radio builders need to recoup their R&D bucks and it is a relatively new technology and a sellers market. The technology is soon to change again. Any time you see a flyer ganging three or four digital 8411's or such together to get the command needed to do the manuvers he wants the plane to do safely, you can bet that he wishes there was a single, 450 oz in digital servo available. There are some coming on line now but are way pricey for all but the flyers who are a pro level or wanting to go there.
My opinion, hope it adds some insight.
blabree
04-27-2003, 03:34 PM
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servo torque rating?
Originally posted by blabree
You left off number 3 and perhaps the most important.
The smaller the physical size of the servo requires proportionately sized gears. If you are using smaller servos to save weight or because it just looks cool to see tiny servos in a big wing then you are kidding yourself, because that big wing has a correspondingly large control surface to move and keep in place at speed in manuvers. The small servos are designed for small planes with small control surfaces. The purpose of high torque small servos in not that it will move a huge control surface, but rather, that it will move the small control surface it was designed for in a COMMANDING way, and keep it where you tell it to be. A large surface requires a servo not only with the torque needed, but also the more robust gear traine needed to stand up to the load imposed by the control surface size, speed of the plane(wind resistance/drag), and the amount of control surface deflection which has been commanded. There is a lot of math and physics to support this, but the math is way too involved for this forum and not really needed to understand the principles.
The reason we used standard servos 10 years ago for large scale planes is because that is what we had. Most of the really big planes back then were designs like the Piper Cub, or Taylor Craft, or something similar. These were relatively slow flying aircraft. If it was a warbird, it was flown in a scale manner and the standard servos were okay there also.
Three D flying and Extra 300s and the like werent an option. Only the guys on the raw edge were even thinking about building planes like the three D jobs that are so prevelant now. They learned the hard way about standard servos with nylon gears on high performance aircraft through plane losses and servo gear replacements etc. They are the ones who demanded of the radio manufacterers the metal geared, high torque, high speed digital servos we use today. The reason they still cost so much is due to the radio builders need to recoup their R&D bucks and it is a relatively new technology and a sellers market. The technology is soon to change again. Any time you see a flyer ganging three or four digital 8411's or such together to get the command needed to do the manuvers he wants the plane to do safely, you can bet that he wishes there was a single, 450 oz in digital servo available. There are some coming on line now but are way pricey for all but the flyers who are a pro level or wanting to go there.
My opinion, hope it adds some insight.
blabree
You left off number 3 and perhaps the most important.
The smaller the physical size of the servo requires proportionately sized gears. If you are using smaller servos to save weight or because it just looks cool to see tiny servos in a big wing then you are kidding yourself, because that big wing has a correspondingly large control surface to move and keep in place at speed in manuvers. The small servos are designed for small planes with small control surfaces. The purpose of high torque small servos in not that it will move a huge control surface, but rather, that it will move the small control surface it was designed for in a COMMANDING way, and keep it where you tell it to be. A large surface requires a servo not only with the torque needed, but also the more robust gear traine needed to stand up to the load imposed by the control surface size, speed of the plane(wind resistance/drag), and the amount of control surface deflection which has been commanded. There is a lot of math and physics to support this, but the math is way too involved for this forum and not really needed to understand the principles.
The reason we used standard servos 10 years ago for large scale planes is because that is what we had. Most of the really big planes back then were designs like the Piper Cub, or Taylor Craft, or something similar. These were relatively slow flying aircraft. If it was a warbird, it was flown in a scale manner and the standard servos were okay there also.
Three D flying and Extra 300s and the like werent an option. Only the guys on the raw edge were even thinking about building planes like the three D jobs that are so prevelant now. They learned the hard way about standard servos with nylon gears on high performance aircraft through plane losses and servo gear replacements etc. They are the ones who demanded of the radio manufacterers the metal geared, high torque, high speed digital servos we use today. The reason they still cost so much is due to the radio builders need to recoup their R&D bucks and it is a relatively new technology and a sellers market. The technology is soon to change again. Any time you see a flyer ganging three or four digital 8411's or such together to get the command needed to do the manuvers he wants the plane to do safely, you can bet that he wishes there was a single, 450 oz in digital servo available. There are some coming on line now but are way pricey for all but the flyers who are a pro level or wanting to go there.
My opinion, hope it adds some insight.
blabree
Sounds to me like alot more than opinion...everything you said is what I've found to be true. About the 450 oz/in job...are you talking about the that linear actuator servo by any chance?
04-27-2003, 06:24 PM
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blabree
THNX for your input, however i am still searching for the logic behind the size of the gear and its relashionship to the size of the control surface (NOT that size does not matter ) but in this case i have to question some of your basic assumptions:
1- the force (torque) required to operate a control surface is determined by two factors: the AREA of the surface and the (top)SPEED of the plane itself
THUS a small control surface on a jet might require a stronger servo than a much larger surface on a park-flyer...
in anycase if a sevo is CAPABLE of certain torque rate, its physical size has no bearing on its capabilities AND it's geartrain should be built to match it's (potential) strenth ; stronger plastic or metal gears
i don't feel the need to explain the WEAKEST-LINK theory, because it was well documented on the famous TV series (LMAO)
however, i would love to hear the basis for the gear SIZE matters theory! (other than the teeth are bigger)
with all do respect
cheers, Vasek
) but in this case i have to question some of your basic assumptions:1- the force (torque) required to operate a control surface is determined by two factors: the AREA of the surface and the (top)SPEED of the plane itself
THUS a small control surface on a jet might require a stronger servo than a much larger surface on a park-flyer...
in anycase if a sevo is CAPABLE of certain torque rate, its physical size has no bearing on its capabilities AND it's geartrain should be built to match it's (potential) strenth ; stronger plastic or metal gears
i don't feel the need to explain the WEAKEST-LINK theory, because it was well documented on the famous TV series (LMAO)
however, i would love to hear the basis for the gear SIZE matters theory! (other than the teeth are bigger)
with all do respect
cheers, Vasek
04-27-2003, 06:41 PM
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No Theories but...
Hi Vasek,
This is not a theory, but it may answer your question...the greater surface area provided by a larger geartrain ditributes the load over a greater surface area thereby putting less stress on the gears.
This is not a theory, but it may answer your question...the greater surface area provided by a larger geartrain ditributes the load over a greater surface area thereby putting less stress on the gears.
04-27-2003, 07:06 PM
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AERO
hi,
we speek the same language, as i said, if the gears were made out of a stronger plastic , there would be no problem using smaller servos... that WAS my initial point for this forum!
we speek the same language, as i said, if the gears were made out of a stronger plastic , there would be no problem using smaller servos... that WAS my initial point for this forum!
04-27-2003, 10:41 PM
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servo torque rating?
I think a lot of this makes sense about the gear sizes. Most of the re-gearing I have to do seems to be on the smaller micro, and mini sized servos, rarely a standard or giant size.
I ran a patriot with good ol futaba s148s and had no problems.
Many flights, many degrees of quality on landing, mostly on grass runways.
I think the torque rating tests must not take in the gear train as part of the test
Dan
I ran a patriot with good ol futaba s148s and had no problems.
Many flights, many degrees of quality on landing, mostly on grass runways.
I think the torque rating tests must not take in the gear train as part of the test
Dan
04-28-2003, 12:16 AM
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servo torque rating?
Vasek,
You are correct. Theoretically speaking the servo size should not matter. if it is designed to put out 55 oz in of torque, then it should do just that. I am not a mechanical engineer. I am however a high capacity digital circuit design engineer working for a national company. Many of the engineering precepts are the same though. It is not a perfect world. Best design intentions are a melding of suspected end use, material availability, material workability, finished unit cost, labor, etc. If I were on the design team that conjured up a micro/minerature servo that was rated at 55 oz in, then I would make sure the servo would perform as advertized. That is, when the prototypes were tested, if they didnt do it, back to design until it did. Now enters the Marketing side of the house and the budget managment team who want to know what the problem is (most however cant understand if you showed them) and how soon it is going to be corrected because the ads went to print and the mail order houses are screaming about back orders etc, etc!! Now everyone knows that no jet pilot in his right mind would use one of these puppies in a jet?? Right?? (well, maybe a small jet). Soooo marketing says to production, "Build them the way they are, well just fix the ones that go bad. It will be cheaper in the long run than holding up production". So much for a caring engineer who wants to see his work go out the door and do what it is designed to do....
Sorry, the soap box was just sitting there waiting, I couldnt resist.
Now, I wonder how flutter vs holding power works out in a big plane vs a park flyer????
Respectfully,
blabree
You are correct. Theoretically speaking the servo size should not matter. if it is designed to put out 55 oz in of torque, then it should do just that. I am not a mechanical engineer. I am however a high capacity digital circuit design engineer working for a national company. Many of the engineering precepts are the same though. It is not a perfect world. Best design intentions are a melding of suspected end use, material availability, material workability, finished unit cost, labor, etc. If I were on the design team that conjured up a micro/minerature servo that was rated at 55 oz in, then I would make sure the servo would perform as advertized. That is, when the prototypes were tested, if they didnt do it, back to design until it did. Now enters the Marketing side of the house and the budget managment team who want to know what the problem is (most however cant understand if you showed them) and how soon it is going to be corrected because the ads went to print and the mail order houses are screaming about back orders etc, etc!! Now everyone knows that no jet pilot in his right mind would use one of these puppies in a jet?? Right?? (well, maybe a small jet). Soooo marketing says to production, "Build them the way they are, well just fix the ones that go bad. It will be cheaper in the long run than holding up production". So much for a caring engineer who wants to see his work go out the door and do what it is designed to do....
Sorry, the soap box was just sitting there waiting, I couldnt resist.
Now, I wonder how flutter vs holding power works out in a big plane vs a park flyer????
Respectfully,
blabree
04-28-2003, 12:52 AM
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servo torque rating?
Why do you assume the gear-train is the culprit. It's certainly possible the loads induced are greater than the torque rating of a given servo. Most likely the case is just this, especially with 3D loads. You know like over sized control surfaces and extreme throws.
I believe blabree first post offers a very good argument for he failures associated with gear-trains.
There is also another consideration I'll call it, #4. Commonly known as mechanical advantage. If this exists and hopefully it does you effectively can either increase or decrease the available force realized by the control surface. It's pretty common to see modelers shorten the control arms or horns to achieve greater travel and or increase the servo arm length, which conversely effects FORCE and mechanical advantage
TORQUE ratings will never change but realized FORCE will with every change of servo arm and or control arm change...
TORQUE is the sum of FORCE x LENGTH.
I doubt that the servos/gear-sets are unable to withstand the specified torque ratings. I suspect it has more to do with application than anything else. Torque ratings don't take into consideration the shock and the extreme forces realized by todays aerobats.
Using a Hitec 225 on a 40 size fun fly with huge control surfaces is most definitely a mis-matched application. It be like using a standard servo for aileron on a 33% 3D model. NO WAY...
I believe blabree first post offers a very good argument for he failures associated with gear-trains.
There is also another consideration I'll call it, #4. Commonly known as mechanical advantage. If this exists and hopefully it does you effectively can either increase or decrease the available force realized by the control surface. It's pretty common to see modelers shorten the control arms or horns to achieve greater travel and or increase the servo arm length, which conversely effects FORCE and mechanical advantage
TORQUE ratings will never change but realized FORCE will with every change of servo arm and or control arm change...
TORQUE is the sum of FORCE x LENGTH.
I doubt that the servos/gear-sets are unable to withstand the specified torque ratings. I suspect it has more to do with application than anything else. Torque ratings don't take into consideration the shock and the extreme forces realized by todays aerobats.
Using a Hitec 225 on a 40 size fun fly with huge control surfaces is most definitely a mis-matched application. It be like using a standard servo for aileron on a 33% 3D model. NO WAY...
