How to test servos
01-02-2002, 01:48 PM
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How to test servos
Does anyone know what tests are done to servos when you send them back to the manufacturor? I have a bunch of servos I would like to check out without having to mail them in.
Thanks,
Mark
Thanks,
Mark
01-02-2002, 02:48 PM
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SERVO TESTING
I JUST RECENTLY PURCHASED A DEVICE CALLED THE EDR SERVO-CISER FROM ELECTRO DYNAMICS GREATEST THING SINCE WHITE TOAST ITS A DEVICE ABOUT THEW SIZE OF A PACK OF BUTTS (MARLBORO) TWO LEADS COMMING OFF IT ONE FOR BATTERY AND ONE TO PLUG WHATEVER SERVO U WISH YO CHECK OUT (UNIVERSAL LEAD) IT WILL CYCLE SERVO IN A FAST MODE OR IN A SLOWER MODE ALLOWING U TO CHECK GEAR TRAIN FOR ANY BAD GEARS OR BAD CENTERING ETC. BUT THE BEAUTY OF THIS BABY IS THAT U CAN SET UP A WHOLE AIRPLANE AND GET ALL SERVOS EXACTLY DEAD CENTER AND HOOK UP LINKAGES BEFORE U EVEN FIRE UP YOUR RADIO ITS THE BEST 45.00 I EVER SPENT ON R/C EQUIP,.THEIR TELE # IS 734-422-5420 AND WEB ADDRESS IS http://www.electrodynam.com take a look u wont be sorry!!!!!!!! hope this helps you out
01-02-2002, 03:03 PM
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How to test servos
Jay,
Thanks. I already have a servo-cisor. However, I have servos that were under water and others I am just unsure of. Do you know of any more tests to validate if they are still good?
Thanks. I already have a servo-cisor. However, I have servos that were under water and others I am just unsure of. Do you know of any more tests to validate if they are still good?
01-02-2002, 06:56 PM
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How to test servos
You can tell your servos have gone bad, if they hang around the street corner with the gyro's, and receivers, smoking cigarettes, drinking beer, and telling dirty jokes...
Oh man, I just couldn't resist that one!!
Oh man, I just couldn't resist that one!!
01-06-2002, 07:28 PM
#6
How to test servos
Hmmm,
OK, now that I know how to tell if a servo is going bad
I also need a good way to test if a servo is failing.
I suspect a elevator and rudder servo may be going bad on me, but need a good way to verify it. It's a trainer, and after a few minutes of flight the trim is all out of wack....Kinda hard to teach someone like that
OK, now that I know how to tell if a servo is going bad
I also need a good way to test if a servo is failing.I suspect a elevator and rudder servo may be going bad on me, but need a good way to verify it. It's a trainer, and after a few minutes of flight the trim is all out of wack....Kinda hard to teach someone like that
01-06-2002, 07:57 PM
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How to test servos
There are many things that could cause trim to go out of whack...
1) Nyrods expanding and contracting.
2) clevises slipping on the wires, or loosening up
3) Servo horn stripped/slipping on the servo.
4) Nyrods NOT supported adequetly (a friend lost his after at least 6 flights, due to that)
5) Wrong servo horns for that brand servo, causing slippage
6) Stripped internal gears, although that usually renders the servo useless, immediately!
Do you have to re-trim with the trim pots? And do you always have to trim the same direction? That might indicate #1 and 2, possibly 3, 4
Do you have to alternate the direction of trim pots all the time? That might indicate 1, 3, and 4, 5
I find it difficult to believe 2 servos would go at once, or even "begin" to fail. Are they the same manufacturer as the radio? Are they "low end" servos? Ball bearing? Did you look over all the linkages CAREFULLY to make sure they are done well? Oftimes a beginner will not realize the finer points of radio installation, and sometimes that's hard to see (note the trainer crash above - I looked it over, as far as I could see in the fuse, supported every 3 inches, however, since he put them in later, he didn't support them in the tail of the fuse, with a push for up elevator, although it had flown quite a few times, once it got in a dive, the nyrod took the flex, NO elevator, nosed in hard!)
The easiest way to ascertain if it's a servo problem, is to replace them with a known "good" servo, and if the problem is still there, then it is something mechanical in the linkages, or servo horns, not the servos going bad.
To be honest, everyone will eventually need a few extra servos, for the next plane, etc, and they are not very expensive at all, especially standards, that would be fine for a trainer. Buy a couple extras, and try them.
If the problem is still there, look deeper...but definitely DON'T fly unless you get the problem solved!!
After all my years of flying, I haven't seen a servo give much warning IN THE AIR that wasn't obvious on the ground with a range check, etc. I am sure someone has, so no flames please, but usually they work, or they don't!
Flying a knowingly unsafe plan can void your AMA insurance!
1) Nyrods expanding and contracting.
2) clevises slipping on the wires, or loosening up
3) Servo horn stripped/slipping on the servo.
4) Nyrods NOT supported adequetly (a friend lost his after at least 6 flights, due to that)
5) Wrong servo horns for that brand servo, causing slippage
6) Stripped internal gears, although that usually renders the servo useless, immediately!
Do you have to re-trim with the trim pots? And do you always have to trim the same direction? That might indicate #1 and 2, possibly 3, 4
Do you have to alternate the direction of trim pots all the time? That might indicate 1, 3, and 4, 5
I find it difficult to believe 2 servos would go at once, or even "begin" to fail. Are they the same manufacturer as the radio? Are they "low end" servos? Ball bearing? Did you look over all the linkages CAREFULLY to make sure they are done well? Oftimes a beginner will not realize the finer points of radio installation, and sometimes that's hard to see (note the trainer crash above - I looked it over, as far as I could see in the fuse, supported every 3 inches, however, since he put them in later, he didn't support them in the tail of the fuse, with a push for up elevator, although it had flown quite a few times, once it got in a dive, the nyrod took the flex, NO elevator, nosed in hard!)
The easiest way to ascertain if it's a servo problem, is to replace them with a known "good" servo, and if the problem is still there, then it is something mechanical in the linkages, or servo horns, not the servos going bad.
To be honest, everyone will eventually need a few extra servos, for the next plane, etc, and they are not very expensive at all, especially standards, that would be fine for a trainer. Buy a couple extras, and try them.
If the problem is still there, look deeper...but definitely DON'T fly unless you get the problem solved!!
After all my years of flying, I haven't seen a servo give much warning IN THE AIR that wasn't obvious on the ground with a range check, etc. I am sure someone has, so no flames please, but usually they work, or they don't!
Flying a knowingly unsafe plan can void your AMA insurance!
01-06-2002, 08:05 PM
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Oh yeah, one more thing...
I meant to emphasize,
Expect ANYTHING from beginners...they don't know what you and I know. And there are many things that seem ok, until you learn they aren't ok.
The pre-first-flight check should be done extensively, and it's FAR better to have one done by every competent builder/pilot at the field! They may see something you haven't...i.e., E-Z connectors having a loose hold down screw, binding in a linkage, reversed throws (Don't lie to me, we have ALL been there! ), etc, etc.
You want this to be the most enjoyable experience in the "newbies" life, not the scariest, most dissappointing! It's FAR better to go home and not fly today, then to risk it, and go home with pieces. And it is the responsibilty of every person training a newbie that they have every opportunity to experience the thrill of their model taking to the air safely, and returning to the ground in one piece...
Sorry to preach, but I have seen TOO many "instructors" grab a newbies plane, do a quick check, take off, no control (or reversed, etc) and crash the plane, hand the transmitter back, and tell the newbie "build it better next time" and walk away....
Expect ANYTHING from beginners...they don't know what you and I know. And there are many things that seem ok, until you learn they aren't ok.
The pre-first-flight check should be done extensively, and it's FAR better to have one done by every competent builder/pilot at the field! They may see something you haven't...i.e., E-Z connectors having a loose hold down screw, binding in a linkage, reversed throws (Don't lie to me, we have ALL been there!
), etc, etc.You want this to be the most enjoyable experience in the "newbies" life, not the scariest, most dissappointing! It's FAR better to go home and not fly today, then to risk it, and go home with pieces. And it is the responsibilty of every person training a newbie that they have every opportunity to experience the thrill of their model taking to the air safely, and returning to the ground in one piece...
Sorry to preach, but I have seen TOO many "instructors" grab a newbies plane, do a quick check, take off, no control (or reversed, etc) and crash the plane, hand the transmitter back, and tell the newbie "build it better next time" and walk away....
01-06-2002, 09:17 PM
#9
How to test servos
rcav8or,
But it WAS MY plane! It has been flying for a long time, I am using it to train some people with. Not their plane. Don't jump the gun here.
Just as a note. The plane was grounded once it was determined that is was not just a bumping of the trim error or cold. Nothing wrong with the linkages, they are strong wood. The plane was sitting in the cold for 4 hours before the first flight of the day and trimming, so any shrinking or expanding of linkages would have already been done.
I have been in RC long enough to know a servo can fail in all kinds of ways, one way is to not return to center every time(that's one's rough in a RC car).
As for the plane, the servos are Hitec, and the radio is Futaba. Never had a problem, they are the non-BB type servos I think. And I know the different brand is not a problem, because I also use other brand hi-torque servos on my larger planes.
However, rest assured, new servos are already being installed in the plane(Futaba) and a new battery will also be installed before the next flight, just incase. (The battery is also in suspect, since it dropped voltage WAY to quickly,it's being tested now)..
But, I would still like to know like the original poster, if there is a way to test a servo. They are cheap, I know. But I hate to throw them out if they are good, and hate to re-use them if they are bad.
Sorry, I don't take anyone's plane up unless another flyer has also inspected the plane as well- like you say the more eyes the better.
In regards to the last comment, that is KNOWINGLY flying an unsafe plane, if you check everything out and find nothing, you aren't actually KNOWINGLY flying it unsafe are you?
But it WAS MY plane!
It has been flying for a long time, I am using it to train some people with. Not their plane. Don't jump the gun here.Just as a note. The plane was grounded once it was determined that is was not just a bumping of the trim error or cold. Nothing wrong with the linkages, they are strong wood. The plane was sitting in the cold for 4 hours before the first flight of the day and trimming, so any shrinking or expanding of linkages would have already been done.
I have been in RC long enough to know a servo can fail in all kinds of ways, one way is to not return to center every time(that's one's rough in a RC car).
As for the plane, the servos are Hitec, and the radio is Futaba. Never had a problem, they are the non-BB type servos I think. And I know the different brand is not a problem, because I also use other brand hi-torque servos on my larger planes.
However, rest assured, new servos are already being installed in the plane(Futaba) and a new battery will also be installed before the next flight, just incase. (The battery is also in suspect, since it dropped voltage WAY to quickly,it's being tested now)..
But, I would still like to know like the original poster, if there is a way to test a servo. They are cheap, I know. But I hate to throw them out if they are good, and hate to re-use them if they are bad.
Sorry, I don't take anyone's plane up unless another flyer has also inspected the plane as well- like you say the more eyes the better.
In regards to the last comment, that is KNOWINGLY flying an unsafe plane, if you check everything out and find nothing, you aren't actually KNOWINGLY flying it unsafe are you?
01-06-2002, 10:11 PM
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How to test servos
In response, I would harbor a strong suspicion, that servos returned to the manufacturer, for repair, would, in fact, just be replaced...it's not worth their time nor money to check out a servo that might have cost them $5.00 in parts, not to just replace it, but have a $30 an hour tech fix it.
I know, why do they cost so much, then?? Because we will pay it! A large (read that "LARGE") amount of the cost of servos goes to marketing...sponsorships, advertising, etc, etc, and they have a fairly captive consumer base...servos don't really have expensive components, it's the setup and manufacturing that might be somewhat costly...
It's also evident in the larger motors us hobbiest's are willing to buy for large amounts of money - 100cc motors costing well over a grand?? But, if the money wasn't there, no-one would put the time and effort into developing them. If it were something every home wanted, then the price would come down dramatically, I would think.
As for it being your plane, I am sorry if you felt anything was directed at you. Your first statement led me to believe you were training someone on their plane. And good advice in general, can never be bad.
As for not using servos that you even suspect of being bad, I agree. If I am ever in question about a servo, it becomes a throttle servo, or a parachute release servo, or even a camera servo. Never a control surface servo. I can fly until I run out of gas, or land deadstick, or not get the picture or drop the parachute, but couldn't live with myself if I harmed someone with a servo I suspected.
And you already said you suspected several bad servos...that, to me, is acknowledging that you would be "knowingly flying it unsafe", in my opinion...have seen some damage done by a plane, and the pilot said afterwards "Yeah, I thought things were funny the last couple of flights"!! If I EVER have any questions about the plane, I would never fly it in company of others, and not until I felt I had the suspect problems corrected. Even then, it would have to be tested, and made sure it was safe again.
No offense was meant in any of this...
Just my $.02 worth...
I know, why do they cost so much, then?? Because we will pay it! A large (read that "LARGE") amount of the cost of servos goes to marketing...sponsorships, advertising, etc, etc, and they have a fairly captive consumer base...servos don't really have expensive components, it's the setup and manufacturing that might be somewhat costly...
It's also evident in the larger motors us hobbiest's are willing to buy for large amounts of money - 100cc motors costing well over a grand?? But, if the money wasn't there, no-one would put the time and effort into developing them. If it were something every home wanted, then the price would come down dramatically, I would think.
As for it being your plane, I am sorry if you felt anything was directed at you. Your first statement led me to believe you were training someone on their plane. And good advice in general, can never be bad.
As for not using servos that you even suspect of being bad, I agree. If I am ever in question about a servo, it becomes a throttle servo, or a parachute release servo, or even a camera servo. Never a control surface servo. I can fly until I run out of gas, or land deadstick, or not get the picture or drop the parachute, but couldn't live with myself if I harmed someone with a servo I suspected.
And you already said you suspected several bad servos...that, to me, is acknowledging that you would be "knowingly flying it unsafe", in my opinion...have seen some damage done by a plane, and the pilot said afterwards "Yeah, I thought things were funny the last couple of flights"!! If I EVER have any questions about the plane, I would never fly it in company of others, and not until I felt I had the suspect problems corrected. Even then, it would have to be tested, and made sure it was safe again.
No offense was meant in any of this...
Just my $.02 worth...
01-06-2002, 10:49 PM
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How to test servos
Magnum,
The low end Hitec servos can do some strange things after they age a bit. My guess is the bushings wear some and the pot gets dirty. I love the higher end Hitecs (225, 525, 545 and all of the digitals). I, personally, don't think the 300's or 400's are as good as the Futaba 148 or the JR 507.
I am still looking for an answer to my original question. Maybe the answer is "there is no test". If they are replaced when sent in for service, why bother testing?
The low end Hitec servos can do some strange things after they age a bit. My guess is the bushings wear some and the pot gets dirty. I love the higher end Hitecs (225, 525, 545 and all of the digitals). I, personally, don't think the 300's or 400's are as good as the Futaba 148 or the JR 507.
I am still looking for an answer to my original question. Maybe the answer is "there is no test". If they are replaced when sent in for service, why bother testing?
01-06-2002, 11:02 PM
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How to test servos
Have you heard of them being tested, or seen anything that indicates that they do? I haven't, which is why I would presume they just replace them...they may test them so's they can see what's wrong, but I STILL suspect it's cheaper for them to replace them, should you send them in for repair...otherwise, the costs would be more than buying a new one!
It's pretty much done the same way in computers with "waranteed" hard drives and the such - it costs more to try and fix them, than to just replace them, that's why they don't warantee the data on them...
I personally don't know of any tests, other than the servo-ciser, and put the servo under load, and just watch it.
I have heard of VERY few problems with the higher end servos, that weren't apparent from the get-go, and the lower end ones are truly inexpensive enough to delegate a questionable one to other uses, in my opinion. And don't assume this means I have all kinds of money - I don't, but I am of the opinion, that I would rather spend good money to fly one or two planes, without ever having to worry about them, than fly 10 that were built as inexpensively as possible - I find it a LOT more enjoyable! And the added advantage is, I can always trust those servos, etc, in the next plane.
With lot's and lot's of planes (more than I like to think about!!), I have NEVER had an equipment failure in the air of any sort, construction wise, or radio/battery/etc...knock on wood!!
I have a tendency to fly "higher end servos" on everything, even my daughter's trainer, and have yet to ever have a servo failure in the air. If I stress one, in my opinion, then I replace it, and again, delegate it to other uses. I find that the costlier the plane, the costlier the servos, as a rule, and it's not worth the expense of any plane to chance a questionable servo.
It's pretty much done the same way in computers with "waranteed" hard drives and the such - it costs more to try and fix them, than to just replace them, that's why they don't warantee the data on them...
I personally don't know of any tests, other than the servo-ciser, and put the servo under load, and just watch it.
I have heard of VERY few problems with the higher end servos, that weren't apparent from the get-go, and the lower end ones are truly inexpensive enough to delegate a questionable one to other uses, in my opinion. And don't assume this means I have all kinds of money - I don't, but I am of the opinion, that I would rather spend good money to fly one or two planes, without ever having to worry about them, than fly 10 that were built as inexpensively as possible - I find it a LOT more enjoyable! And the added advantage is, I can always trust those servos, etc, in the next plane.
With lot's and lot's of planes (more than I like to think about!!), I have NEVER had an equipment failure in the air of any sort, construction wise, or radio/battery/etc...knock on wood!!
I have a tendency to fly "higher end servos" on everything, even my daughter's trainer, and have yet to ever have a servo failure in the air. If I stress one, in my opinion, then I replace it, and again, delegate it to other uses. I find that the costlier the plane, the costlier the servos, as a rule, and it's not worth the expense of any plane to chance a questionable servo.
01-06-2002, 11:04 PM
#13
How to test servos
MMallory,
I have ton's of the S148's, so I have no problem replacing them, and I do think they are better than the std Hitec.
The servos in this plane are old, my guess is they are getting worn, or dirty as you suggest. IN my case, they are way out of any warranty, so even if I sent them in I would have to pay to have them repaired - cheaper to just buy new ones...But, if I did send them in for repair and they sent me new ones I would never know if they were bad...bummer....
There is a test, I have seen suggestions before. But I can't remember how it's done. I do think you would have to test the load on the servo in both directions for the servo's max oz operating load. Then see if it fails.
But like rcav8or said, once a servo has put doubt in my mind, I will mark it and use for something else. But not on the throttle, the last thing I need is a fully fueled plane running at high speed all over the field (or that might be fun).
Good luck,
I have ton's of the S148's, so I have no problem replacing them, and I do think they are better than the std Hitec.
The servos in this plane are old, my guess is they are getting worn, or dirty as you suggest. IN my case, they are way out of any warranty, so even if I sent them in I would have to pay to have them repaired - cheaper to just buy new ones...But, if I did send them in for repair and they sent me new ones I would never know if they were bad...bummer....
There is a test, I have seen suggestions before. But I can't remember how it's done. I do think you would have to test the load on the servo in both directions for the servo's max oz operating load. Then see if it fails.
But like rcav8or said, once a servo has put doubt in my mind, I will mark it and use for something else. But not on the throttle, the last thing I need is a fully fueled plane running at high speed all over the field (or that might be fun
).Good luck,
01-06-2002, 11:42 PM
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How to test servos
Originally posted by magnum
There is a test, I have seen suggestions before. But I can't remember how it's done. I do think you would have to test the load on the servo in both directions for the servo's max oz operating load. Then see if it fails.
But like rcav8or said, once a servo has put doubt in my mind, I will mark it and use for something else. But not on the throttle, the last thing I need is a fully fueled plane running at high speed all over the field (or that might be fun).
Good luck,
There is a test, I have seen suggestions before. But I can't remember how it's done. I do think you would have to test the load on the servo in both directions for the servo's max oz operating load. Then see if it fails.
But like rcav8or said, once a servo has put doubt in my mind, I will mark it and use for something else. But not on the throttle, the last thing I need is a fully fueled plane running at high speed all over the field (or that might be fun
).Good luck,
servos
And yes, it IS fun chasing a full airplane around...never had servo failure, but had a linkage problem once! Went to Failsafe, and the servo over-ran the linkage, and bound up...wouldn't come back. Doh!!
But seriously, I would use a servo I felt was "weak" on throttle, because throttles seldom need much torque. With a "centering" problem, I probably wouldn't worry too much, either, because, throttles never "center", unless it was an obvious centering problem. Your's doesn't sound obvious, or you would have picked up on it. Any other problem that I suspected, the servo would be a "donor" for connector, etc...
Please, let us know if swapping the servos, corrects the problem or not, and if not, what you find...It's a bad day I don't learn anything!!!
01-07-2002, 12:04 AM
#15
How to test servos
rcav8or,
The test you mention in that thread is what I have heard being done. You are correct, it's not obvious, and since it showed up on the third flight and after the flight the batteries were way to low(checked before the flight - they were ok). I will make a guess here, and say that the servo is somehow overheating, binding or something causing it to draw more current than normal and running the battery down faster than normal.
That's just my guess, but I am sticking with it
I will let you know, I probably won't get to fly again till this weekend.
And also, no offense taken. I can get wound up sometimes, when I shouldn't - I should have explained the problem better.
Later
The test you mention in that thread is what I have heard being done. You are correct, it's not obvious, and since it showed up on the third flight and after the flight the batteries were way to low(checked before the flight - they were ok). I will make a guess here, and say that the servo is somehow overheating, binding or something causing it to draw more current than normal and running the battery down faster than normal.
That's just my guess, but I am sticking with it
I will let you know, I probably won't get to fly again till this weekend.
And also, no offense taken. I can get wound up sometimes, when I shouldn't - I should have explained the problem better.
Later
01-09-2002, 09:57 AM
#16
How to test servos
rcav8or,
Well I said I would let you know if I found anything. Since I couldn't sleep tonight (had surgery today) I decided to test the servo in my plane.
On all of these tests, I made a connector where my multi-meter could be connected to measure MA while I was moving the servos.
All other servos were removed from the RX except the one being tested. Just as a side note RX draws 10.1ma constant, so that needs to be subtracted out from the readings below.
Bare Servo:
First I setup one new servo, Futaba and tested with no plane linkage the MA draw was 20.5. The throttle servo in the plane (HItec)tested close to the same result, so that was my starting ref.
First The Elevator Servo:
Initially I noticed it was drawing around 70ma. So I removed the linkage and tested servo with no linkage. With radio trim centered the servo matched the ref. So I added the elev linkage and made sure the meter was around 20.5. Then I moved the elevator up and down a few times. When the servo came back to center it was reading well over 70-80ma. First I suspected binding, but after testing I realized that at center there would be no load or binding, only when the servo is moving. I then moved the servo to the max up and max down positions, I noticed the servo was drawing well over 120ma at times, and using the MAX recorder on my meter noticed it had pulled over 300ma at one time.
Second, I installed a new Futaba servo (128). Added the elev linkage and centered for 20.5ma draw as with the other servo. When I moved the servo back and forth I noticed this servo came back to 20.5ma every time at center rest. That meant there was no binding Also on full up deflection the servo draw was only 20.5 and on full down deflection the draw was just slightly higher around 30ma. The peak reading was around 180ma.
Maybe the servo pot is dirty on this servo, but there is no doubt it was pulling more ma than it should be. No telling how much it was actually pulling in the air with the load of the wind going over the surface.
The Rudder servo:
This one I noticed at rest was pulling around 120ma. OUCH! SO I started checking for binding, then I noticed the nose gear. Although I have not had a hard landing on this plane, the nose gear steering arm was shoved up higher than it should have been and was binding. Probably damaged in transport, or pushing down to hard on the plane when cranking. Bummer..
Anyway, after disconnecting the nose gear, the rudder servo did the same as the elevator. Consistently not centering back to a 20.5ma draw.
Conclusion:
Well the first thing I did before I started testing, was hookup my meter with all the original servos on and test the current draw. It was around 180ma. Now with a 600ma battery, you can tell it would not long to run the battery down, when you add in the current the servos will draw in the air. Much less the time the plane is on cranking and taxing.
So what does all this tell me. I have no idea But I do know that when I set the plane back up I will check the current draw and if it's to high I will start checking individual servos to see how much they are pulling at center. A servo at rest, should pull it's minimum current draw. (assuming the flight surfaces are balanced)
The Battery:
After cycling the battery and plotting the results, the batteries are fine. So there had to a heck of load placed on them to run them down that quick.
So, now when I cycle my plane batteries, I will also check the current draw, just to make sure my servos are behaving as well.
MMallory, hope this helps some. AS for reusing the servos on another surface. Nope. They are going in the trash. Even if I used them on something like the throttle, chances of running my battery down to quick is not worht the risk.
P.S. Sorry for the typos, I used the spell checker, but like I said I couldn't sleep and was still drugged up pretty good (legally).
Well I said I would let you know if I found anything. Since I couldn't sleep tonight (had surgery today) I decided to test the servo in my plane.
On all of these tests, I made a connector where my multi-meter could be connected to measure MA while I was moving the servos.
All other servos were removed from the RX except the one being tested. Just as a side note RX draws 10.1ma constant, so that needs to be subtracted out from the readings below.
Bare Servo:
First I setup one new servo, Futaba and tested with no plane linkage the MA draw was 20.5. The throttle servo in the plane (HItec)tested close to the same result, so that was my starting ref.
First The Elevator Servo:
Initially I noticed it was drawing around 70ma. So I removed the linkage and tested servo with no linkage. With radio trim centered the servo matched the ref. So I added the elev linkage and made sure the meter was around 20.5. Then I moved the elevator up and down a few times. When the servo came back to center it was reading well over 70-80ma. First I suspected binding, but after testing I realized that at center there would be no load or binding, only when the servo is moving. I then moved the servo to the max up and max down positions, I noticed the servo was drawing well over 120ma at times, and using the MAX recorder on my meter noticed it had pulled over 300ma at one time.
Second, I installed a new Futaba servo (128). Added the elev linkage and centered for 20.5ma draw as with the other servo. When I moved the servo back and forth I noticed this servo came back to 20.5ma every time at center rest. That meant there was no binding Also on full up deflection the servo draw was only 20.5 and on full down deflection the draw was just slightly higher around 30ma. The peak reading was around 180ma.
Maybe the servo pot is dirty on this servo, but there is no doubt it was pulling more ma than it should be. No telling how much it was actually pulling in the air with the load of the wind going over the surface.
The Rudder servo:
This one I noticed at rest was pulling around 120ma. OUCH! SO I started checking for binding, then I noticed the nose gear. Although I have not had a hard landing on this plane, the nose gear steering arm was shoved up higher than it should have been and was binding. Probably damaged in transport, or pushing down to hard on the plane when cranking. Bummer..
Anyway, after disconnecting the nose gear, the rudder servo did the same as the elevator. Consistently not centering back to a 20.5ma draw.
Conclusion:
Well the first thing I did before I started testing, was hookup my meter with all the original servos on and test the current draw. It was around 180ma. Now with a 600ma battery, you can tell it would not long to run the battery down, when you add in the current the servos will draw in the air. Much less the time the plane is on cranking and taxing.
So what does all this tell me. I have no idea
But I do know that when I set the plane back up I will check the current draw and if it's to high I will start checking individual servos to see how much they are pulling at center. A servo at rest, should pull it's minimum current draw. (assuming the flight surfaces are balanced)The Battery:
After cycling the battery and plotting the results, the batteries are fine. So there had to a heck of load placed on them to run them down that quick.
So, now when I cycle my plane batteries, I will also check the current draw, just to make sure my servos are behaving as well.
MMallory, hope this helps some. AS for reusing the servos on another surface. Nope. They are going in the trash. Even if I used them on something like the throttle, chances of running my battery down to quick is not worht the risk.
P.S. Sorry for the typos, I used the spell checker, but like I said I couldn't sleep and was still drugged up pretty good (legally).
01-09-2002, 01:05 PM
#17
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Servo testing
Magnum, just imagine the number of rc model aircraft that would still be flying today if their owners had taken the time between trips to the field for some routine servo testing and maintainance using the method you described! No doubt they would be have been glad to pay the measly cost of $20 to $30 for a new servo to prevent the loss of their plane. Thanks for sharing your results and mehods with us.
BTW, I would mark the old servos "Do Not Use" and save them for parts such as gears, motors, cases, hardware, etc., but then I always save everything for something anyway!
BTW, I would mark the old servos "Do Not Use" and save them for parts such as gears, motors, cases, hardware, etc., but then I always save everything for something anyway!
01-09-2002, 01:07 PM
#18
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servo loads
Magnum, you made a very wise test. I do the same type of current load tests as they are the only type of test I can think of that accurately tells you what is going on. For those of you who want to try this, the only caution is that the current measuring technique you use is important. It must have a very low impedance or it will adversly effect your results. You need short, large diameter (low resistance wire) conductors and a very good ammeter. Even adding as little as 1/4 ohm to the wiring will cause significant error but: even with this, the relavent readings between different servos is very enlightning and give you true comparisons. Again, very wise Magnum, we need more inputs like that you presented. Thanks, Rod
01-09-2002, 03:40 PM
#19
How to test servos
George and Rodney,
Thanks for the comments, I really expected people to shoot holes all in my theory, but if it helps people then this thread has served a good purpose.
I really don't use these type servo's, they were in the plane when I bought it. So I may disable them and give them to someone who can use the parts. This is the only small plane I will have, the others will be large scale. Which brings up the importance of doing this test on a used plane you purchase, just to make sure.
Rodney,
I am a mechanical type person, but what you are saying about the larger dia wiring is true. I used a std futaba connector and leads connected together. When I build a permanent unit, I will look into using as much larger wire as possible.
Randy
Thanks for the comments, I really expected people to shoot holes all in my theory, but if it helps people then this thread has served a good purpose.
I really don't use these type servo's, they were in the plane when I bought it. So I may disable them and give them to someone who can use the parts. This is the only small plane I will have, the others will be large scale. Which brings up the importance of doing this test on a used plane you purchase, just to make sure.
Rodney,
I am a mechanical type person, but what you are saying about the larger dia wiring is true. I used a std futaba connector and leads connected together. When I build a permanent unit, I will look into using as much larger wire as possible.
Randy
01-23-2002, 02:50 AM
#20
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Servo-ciser
I went to there site and they have some interesting things......what they are lacking is information. Very brief discriptions...........and everything is 40plus bucks a pop. If they want to sell there product they need to sell it. A picture and a brief discription is not going to get me to pull my credit card out.
There was one testimonial for the servo-ciser which was also brief.
Just my two cents.
Happy Thermaling !!!
There was one testimonial for the servo-ciser which was also brief.
Just my two cents.
Happy Thermaling !!!
