Misuse of HS225BB?
07-31-2003, 03:12 PM
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Misuse of HS225BB?
Last nite I crashed my scratch-built Tsunami .40 sized sport/pattern plane. It's got a Rossi .40 w/pipe on it. Fairly fast plane. I'd rebuilt it over the winter after a crash last year, due to a dumb-thumb incident.
The wing servos on this plane were originally (5 years ago or so) Futaba S-133s, which I replaced with Hitec HS101s. After several years of use, they were getting sloppy, (high speed passes would cause a small amount of flutter-scary) since they are Oilite bearing servos, and I decided to replace them. Anyway, looking for a replacement, I couldn't find a Hitec servo that exactly matched the case size of the HS101's, which they don't sell anymore, so I bought 2 HS225BBs.
No more than 2 minutes into the flight, I dove from altitude, leveled out, and heard the disappointing sound of flutter again. With one major difference, that is. The plane was headed toward the ground at about 25 degrees, and no amount of up-elevator would change that. I crashed, obviously, after having pulled back on the throttle. It was a total loss.
Post-crash:
BOTH aileron servos gave no resistance at all to movement, and upon opening the servo, at least 2 teeth are missing on the 2nd to last gear.
These servos are rated at 54 oz-in of torque. That's more than some of the full-sized servos I have installed in some planes.
Was I being unreasonable to assume these servos would handle one aileron on a .40 sized plane?
I should've known better, I wasn't exactly blown away by the holding torque on these, anybody else notice this?
Why would these have failed, after using smaller (physically) and lower torque servos for years in the same application?
Man, I'm upset about this!
Joe Myers
The wing servos on this plane were originally (5 years ago or so) Futaba S-133s, which I replaced with Hitec HS101s. After several years of use, they were getting sloppy, (high speed passes would cause a small amount of flutter-scary) since they are Oilite bearing servos, and I decided to replace them. Anyway, looking for a replacement, I couldn't find a Hitec servo that exactly matched the case size of the HS101's, which they don't sell anymore, so I bought 2 HS225BBs.
No more than 2 minutes into the flight, I dove from altitude, leveled out, and heard the disappointing sound of flutter again. With one major difference, that is. The plane was headed toward the ground at about 25 degrees, and no amount of up-elevator would change that. I crashed, obviously, after having pulled back on the throttle. It was a total loss.
Post-crash:
BOTH aileron servos gave no resistance at all to movement, and upon opening the servo, at least 2 teeth are missing on the 2nd to last gear.
These servos are rated at 54 oz-in of torque. That's more than some of the full-sized servos I have installed in some planes.
Was I being unreasonable to assume these servos would handle one aileron on a .40 sized plane?
I should've known better, I wasn't exactly blown away by the holding torque on these, anybody else notice this?
Why would these have failed, after using smaller (physically) and lower torque servos for years in the same application?
Man, I'm upset about this!
Joe Myers
07-31-2003, 07:31 PM
#2
Misuse of HS225BB?
Your stripped gears are the result of the flutter, that buzzing sound and its very unlikely that the cause of the accident was the servos particularly since you indicate there was flutter with the old servos.
Yes things like tight sealed surface joints, tight hinges and powerful sevos can minimize flutter somewhat but the only sure fire cure with an aircraft that has demonstrated this tendency is to simply balance the surface and it will work every time. by the way strip ailerons are quite succeptable. A simple 4-40 rod bent ninety degrees incerted through the aileron and double nutted with the arm extending forward ahead of the hinge line and some lead crimped on will tame any fluttering surface.
John
Yes things like tight sealed surface joints, tight hinges and powerful sevos can minimize flutter somewhat but the only sure fire cure with an aircraft that has demonstrated this tendency is to simply balance the surface and it will work every time. by the way strip ailerons are quite succeptable. A simple 4-40 rod bent ninety degrees incerted through the aileron and double nutted with the arm extending forward ahead of the hinge line and some lead crimped on will tame any fluttering surface.
John
07-31-2003, 07:44 PM
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Misuse of HS225BB?
John,
I realize that the flutter was the source of the failure. As I pointed out, I'd replaced the servos because the old ones were sloppy, and flutter had developed where none had been before.
Thanks for your reply though.
Joe Myers
I realize that the flutter was the source of the failure. As I pointed out, I'd replaced the servos because the old ones were sloppy, and flutter had developed where none had been before.
Thanks for your reply though.
Joe Myers
07-31-2003, 09:45 PM
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Misuse of HS225BB?
Fair enough Joe, lets talk a bit about the HS-225. This is strickly my opinon about that servo and its applications. Even though it has excellent thrust numbers for its size it is still what would be called a twenty five size servo. The gears are so tiny that it is unrealistic to expect it to hold up well under the beating of operating large surfaces such as piped .40 size pattern ship and most particularly the folks that are putting them in 3D and fun fly types are courting disaster.
having said that I have around forty of them that I use them almost exclusively in AMA rulebook pylon racers some of which reach speeds of around 175 mph with tremendous G loads on the poles. The differance here is the control surfaces are absolutely tiny on this type aircraft and deflections rarely exceed 1/8 inch and that is why this servo is able to perform so very well in that environment. Other than this somewhat unique application I personally would not use them for anything in over a 25 powered ship.
I would look else where for solutions. Now I do not know what type ailerons are on your ship but if they are strips and made of wood that is slightly to soft that is flutter waiting to happen. The original Bridi Kaos versions for example had very light aileron material (wonderfully light kits) many would flutter and some not. Balancing the surface as above cures the problem every time when moves to high power servos, pushrods and surface sealing etc. would not. For any of my sport airplanes that even remotely hint at a flutter I alway add baleances and never worry agine.
Best of wishes
John
having said that I have around forty of them that I use them almost exclusively in AMA rulebook pylon racers some of which reach speeds of around 175 mph with tremendous G loads on the poles. The differance here is the control surfaces are absolutely tiny on this type aircraft and deflections rarely exceed 1/8 inch and that is why this servo is able to perform so very well in that environment. Other than this somewhat unique application I personally would not use them for anything in over a 25 powered ship.
I would look else where for solutions. Now I do not know what type ailerons are on your ship but if they are strips and made of wood that is slightly to soft that is flutter waiting to happen. The original Bridi Kaos versions for example had very light aileron material (wonderfully light kits) many would flutter and some not. Balancing the surface as above cures the problem every time when moves to high power servos, pushrods and surface sealing etc. would not. For any of my sport airplanes that even remotely hint at a flutter I alway add baleances and never worry agine.
Best of wishes
John
08-01-2003, 12:25 AM
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Misuse of HS225BB?
Dear John,
(no, it's not one of those letters. hehe, sorry couldn't resist)
I am putting together an old birdi kaos. What exactly do you mean by balancing and how?? Also, do you have a way to post a pic of the 4-40 rod cure you spoke of? I'd like this plane to come out as best as I'm able and I will build these ideas into it from the start once I know what it means.
Thanks!
Joe, sorry to hear your plane was destroyed. I tend to over-servo to avoid that very problem. The extra weight can be made up somewhere most of the time, if not, it's worth the sacrifice. Crashing a plane is one thing, loosing one to equipment failure is another entirely.
(no, it's not one of those letters. hehe, sorry couldn't resist)
I am putting together an old birdi kaos. What exactly do you mean by balancing and how?? Also, do you have a way to post a pic of the 4-40 rod cure you spoke of? I'd like this plane to come out as best as I'm able and I will build these ideas into it from the start once I know what it means.
Thanks!
Joe, sorry to hear your plane was destroyed. I tend to over-servo to avoid that very problem. The extra weight can be made up somewhere most of the time, if not, it's worth the sacrifice. Crashing a plane is one thing, loosing one to equipment failure is another entirely.
08-01-2003, 01:55 AM
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Misuse of HS225BB?
There have been many threads on RCU about misues of HS225 servos. They produce decent numbers but are not built to stand any abuse. I have a couple which I'm not sure what I'll do with now that I know more about them. They center very poorly, too. For a 40 size ship they need a small surface which doesn't move much, just as John says. Say, John, do you think they would work OK in a Patriot - say ailerons or elevator? Throttle, for sure.
08-01-2003, 03:15 AM
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Misuse of HS225BB?
bgi
No I don,t think I would use them in that application Its a heavy airplane and the surfaces while not like a fun fly of course are still rather large combined with a good turn of speed. The typical pylon ships that have a minimum weight of 3.5 lbs. that they are popular for, use surfaces that are only around eight inchs long by 3/4 inch wide with 1/8 inch throws each way. If you look at the airplane in my Avitar there are four of them on throttles with a four way 'Y' cord, nothing fancy and centering to match throttles is not a problem. Its also no problem at all on the pylon ships but of course we use very little mechanical advantage in the linkage geometry and there fore lose very little resolution like the fun fly types using extreme throws.
crashlessons
You gotta love them airplanes, and they make delightful sport pattern ships.
I don,t currently have the ability to post pictures but is very simple to do in about an hour:
For ailerons use two 4-40 threaded rods and obtain two nuts and washers for each. Put about an eighty degree bent in each just below the threads forming an 'L' shape with the threads on the short leg. Now half way out on the ailerons not near the ends make a small hole just behind the hinge and insert the threaded rod with one nut and washer from the bottom and install the other washer/ nut on it above the aileron this will allow you to lock it off and make adjustment. The long leg on the bottom of the aileron will extend forward around three quarter to one inch in front of the hinge line. Obtain two lead fish weights the oblong type with a line hole through the middle three eights inchs long is fine and slip one on each forward extension and crimp it tight an inch forward, then wick a bit of CA in. Last just snip off the excess rod sticking out of the lead forward and adjust the bend and nuts so that the weight will clear the bottom of the wing and allow full aileron movement.
I use to be involved in the old SWRA warbird pylon racing and I alway kept a spare set of these in the gear but usually ended up giving them away to somebody whose airplane had developed a case of the ailerons shakes at an event.
Hope that description helps
John
No I don,t think I would use them in that application Its a heavy airplane and the surfaces while not like a fun fly of course are still rather large combined with a good turn of speed. The typical pylon ships that have a minimum weight of 3.5 lbs. that they are popular for, use surfaces that are only around eight inchs long by 3/4 inch wide with 1/8 inch throws each way. If you look at the airplane in my Avitar there are four of them on throttles with a four way 'Y' cord, nothing fancy and centering to match throttles is not a problem. Its also no problem at all on the pylon ships but of course we use very little mechanical advantage in the linkage geometry and there fore lose very little resolution like the fun fly types using extreme throws.
crashlessons
You gotta love them airplanes, and they make delightful sport pattern ships.
I don,t currently have the ability to post pictures but is very simple to do in about an hour:
For ailerons use two 4-40 threaded rods and obtain two nuts and washers for each. Put about an eighty degree bent in each just below the threads forming an 'L' shape with the threads on the short leg. Now half way out on the ailerons not near the ends make a small hole just behind the hinge and insert the threaded rod with one nut and washer from the bottom and install the other washer/ nut on it above the aileron this will allow you to lock it off and make adjustment. The long leg on the bottom of the aileron will extend forward around three quarter to one inch in front of the hinge line. Obtain two lead fish weights the oblong type with a line hole through the middle three eights inchs long is fine and slip one on each forward extension and crimp it tight an inch forward, then wick a bit of CA in. Last just snip off the excess rod sticking out of the lead forward and adjust the bend and nuts so that the weight will clear the bottom of the wing and allow full aileron movement.
I use to be involved in the old SWRA warbird pylon racing and I alway kept a spare set of these in the gear but usually ended up giving them away to somebody whose airplane had developed a case of the ailerons shakes at an event.
Hope that description helps
John
08-01-2003, 04:13 AM
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Misuse of HS225BB?
OK John, I got it.
Many many thanks! Very easy once I can visualize it. Between my parts box for airplanes and my fishing gear, I already have everyting needed.
Many many thanks! Very easy once I can visualize it. Between my parts box for airplanes and my fishing gear, I already have everyting needed.
08-01-2003, 12:09 PM
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Misuse of HS225BB?
John, (and others)
Many thanks for your reply. I have heard of counter-balancing surfaces before. Unfortunately, I was never afforded the opportunity to install a suitable system.
I still wonder at why the HS101s, and the Futaba S133/S33, which are both physically smaller (about 1/3rd smaller, I'd guess) than the HS225BB survived identical treatment, holding firm enough to discourage flutter. I did have the gear trains on the S133s strip in a crash, but understandably.
Ironically, when I went looking for replacement servos, I picked a smaller unit because I didn't want to ugly up my plane by cutting larger holes for the servos. THAT'S not a problem now!
Joe Myers
Many thanks for your reply. I have heard of counter-balancing surfaces before. Unfortunately, I was never afforded the opportunity to install a suitable system.
I still wonder at why the HS101s, and the Futaba S133/S33, which are both physically smaller (about 1/3rd smaller, I'd guess) than the HS225BB survived identical treatment, holding firm enough to discourage flutter. I did have the gear trains on the S133s strip in a crash, but understandably.
Ironically, when I went looking for replacement servos, I picked a smaller unit because I didn't want to ugly up my plane by cutting larger holes for the servos. THAT'S not a problem now!
Joe Myers
