superfli

My Feedback: (42)

I have a Great Planes Giant Supersportster which has Hi-Tec 645mg servos on all surfaces and a standard Futaba servo on the throttle. It is powered with a Life battery. The reciever is a Hi-Tec Opti 7. The throttle servo keeps burning out. I kept thinking it was just the servo. I just burned out the third servo. It goes out after 3-4 flights. It locks up and you can't move it. Could the reciever be allowing to much voltage to the thottle servo?
Thanks,

Superfli

Charlie P.

The receiver does not step down the voltage. It passes along whatever you feed it - provided nothing burns out. You would have to add a voltage regulator between the battery and the receiver. Sounds like you SHOULD add a voltage regulator.

PS - The GSS is a great ARF.

BarracudaHockey

My Feedback: (11)

You sure you dont have binding? Any servo that is rated for 6v should run fine on a LiFe battery and the 645 is rated as such.

ahicks

My Feedback: (2)

Most newer servos handle 6.0 volts well and should live on unregulated 6.6v LiFe voltage just like your 645mg's do (I've been flying that exact same setup on 5 cell NiMH since summer '08 and have had no trouble). Older 4.8 volt servos may not be happy on 6.6 though? Rather than messing around adding stuff/complexity trying to drop the receiver buss voltage down so you could use an old servo, I'd just update to a 6 volt servo. That's me though...

Have you had one of the failed servos apart to check the gears? What are you using for a pushrod between the carb and the servo? Is it possible it's heavy enough or there's enough strain on it to be wiping out the servo gears?

superfli

My Feedback: (42)

The rod rod is 4/40. It is heavy but there does'nt seem to be any binding. You can open the throttle by hand and the throttle spring returns it when you let go. I've opened the other two servos to see if there was any gear dammage and there wasn't. It seems like the servo motor itself is getting cooked. You cant budge the servo arm. I guess since the Hi-Tec 645's are holding up I could replace it with one of those. How imprtant is it to balance the Life battery when charging it.

Thanks,

Superfli

Charlie P.

Throttle spring? Toss it. It does nothing but battle the servo and drain your battery. Might as well remove the idle stop screw as well. You have a throttle servo to do these adjustments.

ahicks

My Feedback: (2)

I'm not a fan of the return springs either. Suggest you don't remove it from the shaft, just pop the end that's engaged in the arm out and release it so it's loose, no longer able to return.

What Futaba servo are you using?

To get 6v compatibility, you wouldn't necessarily need to go with another 645mg. Just something newer than what you're using? This one might be one option?

http://www3.towerhobbies.com/cgi-bin...6&I=LXTRE2&P=K

If you haven't seen it yet, there's a great bunch of guys with a huge Giant Sportster dedicated string here on RCU. Starts way back in '06. There are several issues related to the airframe you should be aware of? You might want to pop in there for some reading, or just ask about them? Taking the trouble to do that could save your plane....

http://www.rcuniverse.com/forum/m_42..._1/key_/tm.htm

BarracudaHockey

My Feedback: (11)

Like I said, the 645 is rated for 6v operation.

Disconnect, but don't remove the throttle return spring, and as someone said, remove the idle stop screw.

tomfiorentino

Three servos, all rated for 6 volts and all three cooked. It's got to be binding.

A short, stiff, 4-40 pushrod is what you want. With a control surface other than a throttle, there is usually some resistance that helps you see when you are approaching max deflection (if you are even going to maz deflection in the first place). But when a carb bottoms out it bottoms out. It absolutely stops against idle (unless you remove the screw) and it stops against full throttle. No slop.

I'm fairly certain that the servo is banging against stops at idle, full throttle or both and it could be in a very small amount.

You could try disconnecting the purshrod, manually push the throttle to full and then check to see what kind of alignment you get when the receiver pushes the pushrod to full throttle. The travel can be too long or short by the diameter of the pin in the clevis...it doesn't take much. Check at idle too the same way. Also make sure you have the necessary wiggle room when you move the throttle trim tab as well.

Hope that helps some and please let us know how you make out!

Tom

BarracudaHockey

My Feedback: (11)

The best way to troubleshoot issues like this is with an inline current meter such as this...
http://www.horizonhobby.com/products...t-meter-HAN172

Its also the best way to set your plane up in the first place if you're looking for max throws w/o binding.

STUKA BARRY

Fly it for one day with a 4.8 pack and see what happens.

ahicks

My Feedback: (2)

Did I miss something? How is it that we know that the Futaba throttle servos were/were not rated for 6v? I don't see where we even know what he's using there? He's not having a problem with the HT 645MGs.

I do agree with the potential for binding at each end of the throttle servo's throw as the evil causing burn outs.

tomfiorentino

True...he only says "standard Futaba Servo"....I just went back to the original post.

Could be a servo not rated for 6 volt that he keeps smoking.

Tom

BarracudaHockey

My Feedback: (11)

LOL ooops I did the same thing! He never named the throttle servo. Foot + Mouth

superfli

My Feedback: (42)

To let you know the servo is a Futaba 3010 which is a nylon gear high torque servo. I took it out of the plane. The gears were fine. The motor and cirut board were fried. What I plan to do is remove replace the Life battery with a NiMh 5cell or 6 volt 2000 ma battery. If I still have issues after this then I'll suspect the reciever. I do think though that this may take care of the issue. I'll let you all know the outcome.

Superfli

Charlie P.

I do not think there is anything a receiver can do that will fry a servo.  Has to be binding or excessive voltage/current. 

BarracudaHockey

My Feedback: (11)

Ok well, that one is rated for 6V too.

dignlivn

Agree, +1

Bob

tomfiorentino

OK so we used handgrenades instead of preceision bombing to get to THAT answer...

In summary: If you cook three servos that are all rated for 6 volts, on the exact same throttle set-up...the servo is binding and I really think you should focus on the pushrod assembly.

You wouldn't happen to have the engine soft mounted would you? Or does the engine have excessive vibration and/or motion when it is running? Loose mount?

Tom

tomfiorentino

'Cuda,

I looked at the meter. From a practical standpoint, at what current reading do you determine the surface is binding? It might be a stupid question, but I would guess the extreme is obvious (ie. the current shoots up very high). Maybe the way digitals resolve, it's either binding or not. Is there any inbetween?

Please let me know how you interpret the readings on the meter to determine something is binding. I think I would like to get one of these.

Thanks,
Tom

BarracudaHockey

My Feedback: (11)

When you install the meter you will see an idle current, as you cycle the surface you will see the current go up but as you move the (for example) elevator to a new position thats not binding it will drop back to idle current or very nearly. When you hit the binding point you will see it rise significantly like .02 or .03 amps at idle, then it will rise near the end and shoot up to nearly or over an amp stalled depending on the servo you're using or worse if its stalled. Its pretty obvious. You can then use that meter to set max deflection w/o binding based on these readings.


I discuss it here including pictures http://www.rcuniverse.com/magazine/a...article_id=836 scroll down starting at Photo 34

tomfiorentino

Most excellent! I'll have to order one up!

Very well written too, nice job.

Thanks.

Truckracer

My Feedback: (19)

Using the meter is certainly a useful method for adjusting endpoints on a throttle but geee.... you could do the same thing with your eyes and just look to see if the throttle is hitting the stops and adjust accordingly. This is really just radio setup 101.

superfli

My Feedback: (42)

And the winner is Binding. That was the problem. I didn't realize that slight binding could heat up a servo so quick. I disconnected the throttle spring and the idle screw and replaced the throttle rod. I used end point adjustments to make sure there was no resistence on the servo at both ends. Thanks everyone for your imput. You learn alot on these forums.

Superfli

BarracudaHockey

My Feedback: (11)

Awesome!