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Old 08-09-2012, 02:12 PM   #126
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Not clear to me what you are reporting.

You say the servos work find with no load. I presume you mean with nothing attached to the servo arm.

If you apply some resistance to the servos with your finger do they seem to move OK?

You say the surfaces move freely with nothing attached.

How about the push rods? Do they move smoothly or are they sticky?

Is there flex in the push rods or do you have them well supported all along the way?


Since you say the servos work OK unloaded and the surfaces are not tight, the issue must be the push rods OR something in how you have the radio set-up, but I would look to the push rods.

When you move the elevator or rudder surface by hand, look at the servo arm, is it moving or is the movement the result of a sticky push rod releasing or a flexing push rod unflexing???

Can you provide photos of your set-up?

You could have one bad servo, but 4? Seems unlikely.

Other possibilty, which I doubt, is your BEC is dropping under voltage under load but it seems you tested that.

I would look at the push rods next. Either they are binding or they are flexing.

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Old 08-09-2012, 02:51 PM   #127
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Default see if this is a better discription of what I am experiencing

I am having troubles holding Fluke VOM leads on receiver plus and minus pins to measure BEC voltage but as near as I can tell my voltage is 5.95 with no servos being moved and 5.85 while wiggling all sticks at the same time with servos connected to push rods and flight surfaces. That is close enough to 6 volts to not be causing me troubles, right? You expect some fluctuation in voltage as servos draw current and then stop drawing current, right?

Servos appear to work with no load. By this I'm saying I disconnect pushrod or pull-pull cables and they appear to work well. Yes they present resistance to my finger when I try to hold them from moving. But my finger isn't very skilled. I have never done this before so I have no idea how much resistance it takes to stall a servo of this type much less any other servo.

I agree, 4 bad servos is very unlikely but 4 fouled up flight surface hinges, linkage, etc, is also an odd thing to get my head around.

Elevator servo is right at the tail of the plane. A short purshrod to surface. No pushrod inside a sleeve or anything like that. It is all out in free space. When I disconnect push rod from servo the elivator seems to move freely.

Rudder is pull - pull cable with clevis at servo and ball link at rudder. When I take servo arm off of servo I can move rudder by hand. Yes it takes some effort but no more than any of my other pull-pull setups.

Ailerons seem to work the best but even they are questionable. There are times they stop short of 100% and don't return to the same zero point. They are mounted in wing and use similar linking and pushrod as the elivator does.

It is as if the servos doesn't have the gas with guts, doesn't have the torque. In my experience an analog servo with grunt, graon, hum, buzz, or somthing if it is trying to move and the flight surface or linkage is keeping it from moving. These are silent.

I will try to take pictures this evening and post them. First time I have ever experienced something like this. Maybe it is just a coicidence that it is also the first time I ever used digital servos.
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Old 08-09-2012, 05:54 PM   #128
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Very odd. Those are pretty strong servos.

The resistance test with the finger is not scientific just a confirmation that the servo is pushing and that you don't have any damaged gears at the start of the push.

This is a real head scratcher.

So, what do they all have in common?

Radio, reciever, BEC. I would look there but not confident that is going to be the answer.

Do you have a receiver battery you can sub for the ESC/BEC connection?

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Old 08-09-2012, 06:15 PM   #129
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I sure appreciate your help.

No I don't have a flight pack. I have gone all electric. But I am using a CC UBEC. I could remove it and use the BEC built into the CC ICE 50amp ESC that I'm using. That is a good idea, right? It would allow me to divide and conquer?

Not having spare stuff is a problem. Other than the 4 @ HS-5065MG servos all I have is one $2.87 TP 9 gram servo. So I don't have much to play with. I guess if I could find a servo arm for the TP I could see what it does but I doubt the Hitec servo arm and mounting holes are the same as the TP.

The rudder I used clevis at the servo and 3DHS supplied ball links at the other end. That should be as friction free as you can get, right?

I'll try the ESC's BEC tonight and report back with pictures.

Thanks again for your help.
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Old 08-09-2012, 08:04 PM   #130
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Originally Posted by DanWard View Post
I sure appreciate your help.

No I don't have a flight pack. I have gone all electric. But I am using a CC UBEC. I could remove it and use the BEC built into the CC ICE 50amp ESC that I'm using. That is a good idea, right? It would allow me to divide and conquer?

Not having spare stuff is a problem. Other than the 4 @ HS-5065MG servos all I have is one $2.87 TP 9 gram servo. So I don't have much to play with. I guess if I could find a servo arm for the TP I could see what it does but I doubt the Hitec servo arm and mounting holes are the same as the TP.

The rudder I used clevis at the servo and 3DHS supplied ball links at the other end. That should be as friction free as you can get, right?

I'll try the ESC's BEC tonight and report back with pictures.

Thanks again for your help.
Yes, take the UBEC out first and confirm that it is not a power problem.

Assuming nothing changes, put the UBEC back in.

Swap out one of the servos with that spare you have. Any change?

If not it has to be something with the Radio or the receiver and I would lean more toward the radio though I can't imagine how.

Are your servos and control horns aligned straight? No angles! the control horn and the servo are in line. The control rod moves freely in the servo arm and the control horn holes. No binding?

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Old 08-09-2012, 10:49 PM   #131
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Originally Posted by DanWard View Post
I sure appreciate your help.

No I don't have a flight pack. I have gone all electric. But I am using a CC UBEC. I could remove it and use the BEC built into the CC ICE 50amp ESC that I'm using. That is a good idea, right? It would allow me to divide and conquer?

Not having spare stuff is a problem. Other than the 4 @ HS-5065MG servos all I have is one $2.87 TP 9 gram servo. So I don't have much to play with. I guess if I could find a servo arm for the TP I could see what it does but I doubt the Hitec servo arm and mounting holes are the same as the TP.

The rudder I used clevis at the servo and 3DHS supplied ball links at the other end. That should be as friction free as you can get, right?

I'll try the ESC's BEC tonight and report back with pictures.

Thanks again for your help.
Some 5 years ago I ran across a bad connection inside one of my AR7000 Spektrum receivers. This bad connection killed DC power to several servos. Lucky this was found on the ground, and not in the air.

You indicate you have a $$$$ Fluke meter, so I'm assuming you know how to use it?

These digital meters can be used to measure the signal output from your receiver to your servos. Doubt if this is the cause, but its worth a try.
Take a look:
http://www.wattflyer.com/forums/showthread.php?t=54123

Also, might be a good idea to use your Fluke meter and check resistance between all the black servo pins on your receiver. They should all be a dead short to each other. Same for all the "red" servo pins, in the middle of the connector. Should all be a dead short to each other. This would be checked with all the servo plugs removed from the receiver.

As for using a digital multimeter, take a look:
http://www.wattflyer.com/forums/showthread.php?t=52821

As a very wild guess, one idiot RC'r decided to make certain none of his RC connectors would come loose. So he glued them with very thin CA (superglue). He then blamed the resulting failures on the Spektrum radio system. If you apply this stuff to a servo connector, this stuff will wick into any servo pins, and makes a very good insulator.

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Old 08-22-2012, 02:44 AM   #132
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Question Now what the heck?

OK so life dealt me some interruptions and other delays.

kyleservicetech - Nope, didn't glue the servo connectors together (actually used your heat shrink suggestion). Also, I have a Fluke 87 III and while I'd like to say I know how to use it as soon as I did...well someone would prove me wrong. But I do OK. (The capacitance scale sure came in handy when the run capacitor failed on my AC condenser fan. Fixed it myself for $35 instead of $$ that the A/C guys wanted to even show up on a Saturday much less fix it.)

Yes I checked what I believe is the BEC negative on all receiver channels and I see a dead short (use relative to cancel meter lead resistance). Did the same on receiver BEC positive and all seem good.

Group-
While I have made great progress, before I get to that let me share what Hitec tells me. I was about ready to go fly, most servo issues resolved. Last thing to do was adjust high and low rates as well as adjust travel limits so that flight surfaces move the same amount in both directions. I got my trusty flight surface deflection meter and life is good.

With the plane on my work surface elevator and aileron servos hum (analog servos never did that). Hitec says that is the weight of the flight surface trying to cause the surface to fall (gravity) and the servo working to keep it in place. Just sitting there one servo burned up. Hitec says that is quite normal and has happened to others that are new to digital. They say it could even happen to an analog servo but due to the 300 times greater update of the digital a digital works that much harder to keep the flight surface in place while fighting gravity. Good Grief

So now for some pictures and the improvements I made to get things to the point that I felt I was ready to fly as soon as I adjusted flight surface travel. (delayed again due to smoked servo)

1. Please see picture 1. This kit uses these silver post that bolt to the servos arm and then use a setscrew to secure where the push rod passes through it. If you tighten them enough in the servo arm that they don't wobble then they present rotational resistance (takes torque to turn them). A bit looser so no torque to rotate them and the result is you can watch them wobble a bit when the servo changes direction. I loosened them all up to where they wobble a bit which corrected aileron and elevator surfaces but did nothing to help rudder.

2. Rudder - please see pictures 2 and 3. My first effort was to stay with the manufactures extended arm but moved to a clevis for connecting pull pull cable. It was better but still had troubles. Then I moved to a standard Hitec length servo arm and all is 100% better. I had to adjust endpoint on my DX7s to greater than 100% to get the recommended (or close enough to it) travel but by using the shorter arm I gained mechanical advantage.

Summation of beginner lessons learned:

A. Don't leave digital servos turned on for toooo long. Unplug all but the servo you are adjusting and be quick about adjusting. This still gives me the willies as I can see a servo burning up while in flight.

B. I really don't like the silver thingys that are shown in picture 1. To keep the nut from backing off you have to use loctite blue or thin CA. And there is no happy place. A bit to tight and they require torque to rotate. A bit to loose and the wobble. In the future (and maybe before this planes flys) I will solder a threaded link to end of push rod and move to using a clevis like shown in picture 3.

C. I believe the servo torque of the recommended servo for this application is marginal, no head room, requires all the servo can deliver. (At work when I size a motor I always target 80% of what the motor is capabhle of which leaves 20% cushion). Couple that with manufactures recommendation of longer servo arms and the poor servos is overwhelmed. Hitec designed there servo arms the length they are for a reason. Maybe?

D. I wish I could find a servo with more torque that was close to the same sizes as a Hitec HS-5065MG (or HS-65MG). I'm seriously worried I'll burn another servo in flight.

E. Not sure I will use digital servos again. Same torque and speed as analog, I'm just not getting it. Maybe my skills are not keen enough to appreciate digital.


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Old 08-22-2012, 04:57 AM   #133
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Originally Posted by DanWard View Post
OK so life dealt me some interruptions and other delays.

kyleservicetech - Nope, didn't glue the servo connectors together (actually used your heat shrink suggestion). Also, I have a Fluke 87 III and while I'd like to say I know how to use it as soon as I did...well someone would prove me wrong. But I do OK. (The capacitance scale sure came in handy when the run capacitor failed on my AC condenser fan. Fixed it myself for $35 instead of $$ that the A/C guys wanted to even show up on a Saturday much less fix it.)

Yes I checked what I believe is the BEC negative on all receiver channels and I see a dead short (use relative to cancel meter lead resistance). Did the same on receiver BEC positive and all seem good.

Group-
While I have made great progress, before I get to that let me share what Hitec tells me. I was about ready to go fly, most servo issues resolved. Last thing to do was adjust high and low rates as well as adjust travel limits so that flight surfaces move the same amount in both directions. I got my trusty flight surface deflection meter and life is good.

With the plane on my work surface elevator and aileron servos hum (analog servos never did that). Hitec says that is the weight of the flight surface trying to cause the surface to fall (gravity) and the servo working to keep it in place. Just sitting there one servo burned up. Hitec says that is quite normal and has happened to others that are new to digital. They say it could even happen to an analog servo but due to the 300 times greater update of the digital a digital works that much harder to keep the flight surface in place while fighting gravity. Good Grief

So now for some pictures and the improvements I made to get things to the point that I felt I was ready to fly as soon as I adjusted flight surface travel. (delayed again due to smoked servo)

1. Please see picture 1. This kit uses these silver post that bolt to the servos arm and then use a setscrew to secure where the push rod passes through it. If you tighten them enough in the servo arm that they don't wobble then they present rotational resistance (takes torque to turn them). A bit looser so no torque to rotate them and the result is you can watch them wobble a bit when the servo changes direction. I loosened them all up to where they wobble a bit which corrected aileron and elevator surfaces but did nothing to help rudder.

2. Rudder - please see pictures 2 and 3. My first effort was to stay with the manufactures extended arm but moved to a clevis for connecting pull pull cable. It was better but still had troubles. Then I moved to a standard Hitec length servo arm and all is 100% better. I had to adjust endpoint on my DX7s to greater than 100% to get the recommended (or close enough to it) travel but by using the shorter arm I gained mechanical advantage.

Summation of beginner lessons learned:

A. Don't leave digital servos turned on for toooo long. Unplug all but the servo you are adjusting and be quick about adjusting. This still gives me the willies as I can see a servo burning up while in flight.

B. I really don't like the silver thingys that are shown in picture 1. To keep the nut from backing off you have to use loctite blue or thin CA. And there is no happy place. A bit to tight and they require torque to rotate. A bit to loose and the wobble. In the future (and maybe before this planes flys) I will solder a threaded link to end of push rod and move to using a clevis like shown in picture 3.

C. I believe the servo torque of the recommended servo for this application is marginal, no head room, requires all the servo can deliver. (At work when I size a motor I always target 80% of what the motor is capabhle of which leaves 20% cushion). Couple that with manufactures recommendation of longer servo arms and the poor servos is overwhelmed. Hitec designed there servo arms the length they are for a reason. Maybe?

D. I wish I could find a servo with more torque that was close to the same sizes as a Hitec HS-5065MG (or HS-65MG). I'm seriously worried I'll burn another servo in flight.

E. Not sure I will use digital servos again. Same torque and speed as analog, I'm just not getting it. Maybe my skills are not keen enough to appreciate digital.
H'mmm
Don't understand Hitecs position on "Leaving a servo on to long". Methinks any servo should be able to hold a control surface in neutral for long extended periods of time. After all, this is the position the servo is in during flight.

I also do not care for the type of push rod connectors you have in photo #1. These things can slip, I've seen more than a few crashes where they did slip. At the very least, put a very slight groove into the pushrod with a Dremel tool, then install the set screw into that groove with blue loctite. If you use CA, that will be permanent!

Having said that, just picked up a little foamie jet (EF-16 Phase 3) with radio/motor/ESC for a very good price. And that foamie uses these type pushrods. Will have to secure them very carefully!

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Old 08-22-2012, 02:16 PM   #134
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Could be that the extra long arms on the servo are causing a chatter feedback loop while in flight, and the poor servo is just working itself to death oscillating around the rest position (or whatever the set position is).

Ask me why your DX5e is doomed... and how to fix it.
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Old 08-22-2012, 03:24 PM   #135
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Default verification of what I tyhink I know

This is supposed to be a 3D plane so it has oversized flight surfaces. The recommended servos is an HS-65MG and the plane comes with extended servo arms.

My change to the HS-5065MG should not be causing me trouble, right? I think that has been confirmed.

But what I don't know is if the recommended HS-65MG is marginal for the application when extended servos arms are used. Extended arms are a trade off, right? I get increased travel but torque is reduced, right?

I think I am going to get rid of all extended servos arm and use the longest one provided with the servo which assumes Hitec did the math and they are the length they are for a reason.

Then I hate the &^%$#*&^ silver things shown in picture 1 that the manufacture uses to attached pushrod to the servo arm. They stand the pusrod off the servo arm by approx 3/16" so they are a lever. If they are tight enough to not wobble then they require torque to rotate them.

I am going to stop and purchase solder on pushrod thread adapters and clevises for all surfaces and convert them all to look similar to the change I made to rudder. To make the rudder work I got rid of extended arms and moved to clevises.

But I'm also going to call Hitec back. Like kyleservicetech said,"Don't understand Hitecs position on "Leaving a servo on to long". Methinks any servo should be able to hold a control surface in neutral for long extended periods of time. After all, this is the position the servo is in during flight."

I agree and if a servo burned up sitting on my work surface then they will burn up in the air. Yesterday they said the servo gets additional cooling when in flight but that is poppycock. The aileron servo is mounted down in the wing and will get very little airflow.

Do you think my plan is right? I guess I should count my blessings. At least it burned up on the bench and not in the air.
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Old 08-22-2012, 04:02 PM   #136
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Give them the what-for Dan ! I don't mind paying a premium for an upgraded servo like Hitec but when I hear this kind of news, it make me want to turn to Htx or Solar. On the light, smaller planes , no fear of the 9g Htx's. But something as active as a 3D plane, I would want the best and expect only the best from Hitec.
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Old 08-23-2012, 05:39 AM   #137
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My dad is 100% against "ez connectors" and thinks their garbage. On his planes he always uses either z bends or clevises. I haven't had any problems, but I way over tighten stuff. My dad also hates the ca and film type hinges they use on planes now. He uses nylon hinges with pins, and I can see how much better they are. If I ever build a plane instead of buying an arf, its getting nylon hinges. They move effortlessly.

Where you get torque twisting problems on the connector, have you tried to drill the hole out slightly bigger? How big are the holes now? If the holes are slightly loose and the connector can be pulled out of its straight line it could increase effort. If you drill it out too big, then the keepers on the bottom will try to pop off.
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Old 08-23-2012, 06:43 AM   #138
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I kind of like the ez connectors. Use them on all my 'prop in the slot' foamie parkjets. Easy to dial-in. Z bends are fine but there's always a little slop in them. At least in the ones I make.
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Old 09-29-2012, 05:21 PM   #139
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Can anyone offer advice regarding a UBEC re servos. I'm just beginning to read a few threads and not too sure I'm grasping the info correctly. I read in a thread that 4 or more servos being run on a 3s battery is asking for trouble. Borderline failure area. A Ubec was suggested.
Reason I ask is I had a Sensei with upgraded motor (3536-10) and ESC 40 amp running on 2200 mah 3 s batteries. 4 OEM servos. I was using an OrangeX RX with Spektrum DX6i.
Had 30-40 flights on it. One day it went dead and nosed in from 50-60 feet up.
We did an immediate autopsy on it. TX,RX batteries were up. RX ran all servos. Snapped off the shaft but motor ran. All connections were secure. As it went in nothing worked E/A/T/R but on the table later they worked.
Wasn't sure if the fail safe went on the ESC but I have been reading about the BEC portion shutting down.
Anyone point me to a thread on this info.
Thanks
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Old 09-29-2012, 07:20 PM   #140
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alot of it depends on the esc. there are linear bec's and switching bec's used inside the esc to supply power to the receiver and servos. switching is better than linear.

what esc were you running? what is the internal bec inside the esc rated for? what servos are you running?

there are tons of factors to this, but here it is in a nutshell. MOST esc's supply around 5-6 volts, and 2-3 amps from the bec. now you will notice i said MOST. not all, as in the case of my eflite 30 amp pro switchmode esc. it supplies 5.5v, but only 700ma on the bec.

if you draw more power thru the bec than it can supply it will kick off, and usually turn back on pretty quickly. now when it kicks off, you lose everything! basically it shuts down the receiver so you have no control. when the bec kicks back on (again usually pretty quickly) it's up to the receiver to reset. this sometimes is really quick, sometimes its not fast enough!

basically the biggest question is what size servo's are you using, how much power do they draw, and what kind of power does your esc put out on the bec circut?

its usually best to run an external bec. i prefer the castle creations 10 amp bec.

it doesn't matter how many servos your running, it matters how much power they draw. on our rc rockcrawlers we HAVE to run an external bec and we are running 1 servo! altho my steering servo runs at 7.4 volts and puts out way over 400oz of torque.
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Old 09-29-2012, 10:03 PM   #141
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Originally Posted by touche View Post
Can anyone offer advice regarding a UBEC re servos. I'm just beginning to read a few threads and not too sure I'm grasping the info correctly. I read in a thread that 4 or more servos being run on a 3s battery is asking for trouble. Borderline failure area. A Ubec was suggested.
Reason I ask is I had a Sensei with upgraded motor (3536-10) and ESC 40 amp running on 2200 mah 3 s batteries. 4 OEM servos. I was using an OrangeX RX with Spektrum DX6i.
Had 30-40 flights on it. One day it went dead and nosed in from 50-60 feet up.
We did an immediate autopsy on it. TX,RX batteries were up. RX ran all servos. Snapped off the shaft but motor ran. All connections were secure. As it went in nothing worked E/A/T/R but on the table later they worked.
Wasn't sure if the fail safe went on the ESC but I have been reading about the BEC portion shutting down.
Anyone point me to a thread on this info.
Thanks
There are several factors here.

*) the capacity of the BEC in your ESC.
*) Type of BEC in your ESC
*) the number of servos
*) your flying style
*) type of servos.

I use about 125 mah as my guide line for analog micro servos like HS-55s or the typcial 9 gram servo. 250 would be a standard servo. So 4 micro servos would need an ESC of about 500 mah to meet my criteria. That assumes that all 4 servos are pulling at full load all at once, which typically they don't. I bump that up 50% for digital servos as they can pull more power under extreme load.

If your ESC has recommendations about its BEC rating based on the voltage of the motor pack, you have one type of BEC, a linear BEC. This is the cheaper kind and its ouptput varies by pack voltage.

However switching BECs don't care what voltage the pack is. Most after market BECs are switching. Many built in BECs are linear but some are the better switching type.

If you are flying a glider that floats along at 15 mph your servos aren't going to draw much at all. If you are flying an F27 striker at 80 mph and yanking and banking all over the place, you are to draw a lot of power and your servos may be pulling at maximum load much of the time.

If you are flying a jet at 200 mph your servos are pulling like crazy during manauvers.


So, the comment about how many servos based on an 11.1V 3 cell pack assumes you are using a non-switching BEC and that your BEC rating is marginal for that voltage. The comment may be correct or it may not.

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Old 09-29-2012, 10:07 PM   #142
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Originally Posted by touche View Post
Can anyone offer advice regarding a UBEC re servos. I'm just beginning to read a few threads and not too sure I'm grasping the info correctly. I read in a thread that 4 or more servos being run on a 3s battery is asking for trouble. Borderline failure area. A Ubec was suggested.
Reason I ask is I had a Sensei with upgraded motor (3536-10) and ESC 40 amp running on 2200 mah 3 s batteries. 4 OEM servos. I was using an OrangeX RX with Spektrum DX6i.
Had 30-40 flights on it. One day it went dead and nosed in from 50-60 feet up.
We did an immediate autopsy on it. TX,RX batteries were up. RX ran all servos. Snapped off the shaft but motor ran. All connections were secure. As it went in nothing worked E/A/T/R but on the table later they worked.
Wasn't sure if the fail safe went on the ESC but I have been reading about the BEC portion shutting down.
Anyone point me to a thread on this info.
Thanks
Yeah, if your ESC has a "Linear" BEC, IMHO they should not be used on anything more than a two cell LiPo.

Take a look:
http://www.wattflyer.com/forums/showthread.php?t=63779

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Old 09-30-2012, 12:40 AM   #143
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Thanks for your replies,
This is a 40amp Esc ,5V-3 amp linear BEC. As for the servos. I guess they are a generic brand for the Flyzone Sensei. I had to change one out as the arm broke and the arms are specific to that brand. I used 1- SG90..All from HURC. That servo was used for the rudder/front wheel.
At the time I was flying in a light wind and just banking on a turn so A/T and possibly slight El was being used.
As the plane is now gone I am still trying to figure out what the cause was so there was no repeat.
I am also flying an Alpha 450 sport using a 40 amp ESC and 4 sg90 servos.
I run 6 minutes on these and the batteries are usually 3.85 and barley warm. So far it has held up.
I should also mention I use a satellite ant on the orange X RX
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Old 09-30-2012, 12:46 AM   #144
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Haven't used them myself but I've read about more than just a few failures with those clone Rx's.
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Old 09-30-2012, 01:25 AM   #145
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Originally Posted by touche View Post
Thanks for your replies,
This is a 40amp Esc ,5V-3 amp linear BEC. As for the servos. I guess they are a generic brand for the Flyzone Sensei. I had to change one out as the arm broke and the arms are specific to that brand. I used 1- SG90..All from HURC. That servo was used for the rudder/front wheel.
At the time I was flying in a light wind and just banking on a turn so A/T and possibly slight El was being used.
As the plane is now gone I am still trying to figure out what the cause was so there was no repeat.
I am also flying an Alpha 450 sport using a 40 amp ESC and 4 sg90 servos.
I run 6 minutes on these and the batteries are usually 3.85 and barley warm. So far it has held up.
I should also mention I use a satellite ant on the orange X RX
Linear BEC on a 3 cell LiPo battery, that linear BEC was likely running rather hot. I'd consider upgrading to a uBEC such as Castle Creations 10 Amp BEC.

Don't know about your servos, but I've measured over 2 Amp currents each on my various Hitec 645MG servos. With seven of them in my giant scale models, thats a measured peak current of over 14 Amps.

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Old 09-30-2012, 08:05 AM   #146
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I see that many modellers are posting very positive comments regarding the HXT 900 HK servos and I would have echoed their comments as I have used the white geared ones for years with no issues at all.
Until that is the first black geared ones arrived a couple of months ago and I discovered that one was DOA. One out of four dead is not good considering the number of good white geared ones I'd had before.
Due to illness I haven't modelled for a while but in anticipation I ordered some more HXT 900's from HK thinking that the issue I had previously was a one off.
This time they all worked but one of the batch jittered and wouldn't hold position.
A check on RC Groups showed that others are experiencing similar problems with the "new" black geared 900's.
Is anyone on the forum having similar problems as I would hate to have to stop using these little gems through a lack of confidence as they have served me very well in the past.
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Old 10-01-2012, 02:18 PM   #147
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Friends, I appologize for an error in post 141 that I just fixed. I was using the wrong name for the BEC.

A linear BEC is the cheaper type that is impacted by the voltage of the motor pack.
A switching BEC is not impacted by the voltage of the motor pack.

There is more information in the e-book at this link. Read the chapters on the ESC and the BEC.

EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.wattflyer.com/forums/showthread.php?t=31368


Here is an excerpt from one of the articles:
http://www.wattflyer.com/forums/show...0&postcount=23

Note that the voltage rating for the ESC may be different than the voltage
rating for the BEC. Your ESC may be rated for 14.8 volts but the BEC may have
to be disabled over 12 volts and you will have to power the receiver separately.
If you don't take note of this and pop in a four-cell lipo, your ESC may be fine
but your BEC may be heading for a failure, resulting in a crash.

According to Dimension Engineering, a maker of BECs, "Many people don't realize
that their ESC's BEC rating is misleading. With the linear BEC built into most
speed controls, the current rating decreases as pack voltage increases. For
example, several popular 25A ESCs with "3A" BECs are only capable of supplying
0.5A when running from a 3s pack".

If you are flying an RTF or "receiver ready" model, there may not be ESC/BEC
documentation included. As an example, the manufacturer of the plane may
designate that the plane takes an 8.4V pack. At that voltage the included BEC
may be fine. However, if you decide to pop in a three cell lipo, a problem may
only be a launch away. The BEC may do fine for a couple of flights, or maybe 5
minutes or may fail 100 feet out, and down you go.

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Old 10-01-2012, 10:38 PM   #148
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Thanks for all your replies.
As I'm stepping up a model or two I believe I will go to the UBEC. I'm thinking a Trojan as I will get time to fly this winter in Fla. I'll do more reading on this and as I will be near HURC I'll get an earful there as well.
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Old 10-01-2012, 10:45 PM   #149
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So having read the above info re BEC's am I correct in understanding that a separate UBEC wont be affected by a higher voltage battery. There is a disclaimer on the HURC site with regards to 3S batteries. I'd just as soon bypass the BEC if the UBEC is more reliable.
I can always dead stick her down if I can have some useful controls.
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Old 10-01-2012, 10:53 PM   #150
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Originally Posted by touche View Post
So having read the above info re BEC's am I correct in understanding that a separate UBEC wont be affected by a higher voltage battery. There is a disclaimer on the HURC site with regards to 3S batteries. I'd just as soon bypass the BEC if the UBEC is more reliable.
I can always dead stick her down if I can have some useful controls.
UBEC, to the best of my understanding, is a brand name.

You have built in BECs and External BECs.

Some are linear and some are switching.

The linear are more impacted by pack voltage than the switching. Doesn't matter if they are internal to the ESC or external.

So, in the end, read the instructions. If there are no instructions then you are flying blind.

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