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Old Oct 11, 2005, 05:22 PM
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San Francisco Bay Area
Joined May 2001
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Will 6 micro servos overload my Jeti Advance 40 Plus BEC?

I am setting up a new e-Telemaster 40 with a modified "no dihedral" full house wing

I'll end up with 6 servos. I'm using a Jeti Advance 40 plus ESC with a TP 3S2P 4200 mAh lipo, and an AXI 2826/12 motor.

Does anyone have an opinion of whether this will fry the Jeti, or will I need a UBEC, or an additional on board battery? I'd love to avoid the extra weight from an additional battery!

thanks in advance

John
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Old Oct 11, 2005, 05:33 PM
no wings any more, just dust!
Ghost 2501's Avatar
stoke on trent
Joined Oct 2004
8,052 Posts
the esc BEC should cope ok with 6 servos, for what current they would pull, it would be naff all, even if ALL 6 SERVOS WERE OPERATING AT THE SAME TIME
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Old Oct 11, 2005, 07:37 PM
I'd rather be Flying
davecee's Avatar
Nashville, NC, USA
Joined Mar 1999
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Your Jeti Advance 40 plus ESC will handle 4 servos on a 3S Lipo pack, according to information posted on the Hobby Lobby site. It also says to decrease the number of servos by one if you're using "cheap micro servos" and decrease by two if using digital servos. Make your own decision. I wouldn't do it.
Dave
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Old Oct 11, 2005, 07:54 PM
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United States, WA, Puyallup
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I'm with davecee. It might work, but too close to the edge for me.

Bill
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Old Oct 12, 2005, 10:59 AM
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Boston, MA subburb
Joined Sep 2004
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I'll third the recommendation not to try it because you will loose control at the worst time in your flight. On the ESC I was using (not a Jeti), when the BEC overheated, it removed voltage from receiver and servos but held motor speed. I was at the top of a loop, ~250feet AGL, full throttle, partial up elevator and starting a roll when everything frooze. The plane completed 2 1/2 rolls before making a 1 inch deep hole in the ground - all within the 5 second thero-overload recovery time I measured later on the bench.

At the very least, do a bench test, move all servos simultaneous for about 45 seconds and then feel the ESC for a very hot chip (most likely located opposite the heat-sink). Even if it passes on the bench, that test cannot replicate the real aerodynamic loads placed on the servos so you cannot be really sure. If the test fails, you've saved a plane.

Alan
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Old Oct 12, 2005, 11:28 AM
Dimension Engineering
Akron, Ohio
Joined Jan 2002
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What servos are they? It makes a huge difference. If its 6 HS-81s, then the answer is no chance. If they're six hs-55s then maybe.
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Old Oct 12, 2005, 11:38 AM
Mmmm.
Andy McCowan's Avatar
Selkirk, Scotland.
Joined Jun 2001
294 Posts
I would not risk it, some of those smaller servos are a bit Amp hungry.
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Old Oct 12, 2005, 12:36 PM
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East Anglia, UK
Joined Sep 2002
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Quote:
Originally Posted by Al Offt
I'll third the recommendation not to try it because you will loose control at the worst time in your flight. On the ESC I was using (not a Jeti), when the BEC overheated, it removed voltage from receiver and servos but held motor speed. I was at the top of a loop, ~250feet AGL, full throttle, partial up elevator and starting a roll when everything frooze. The plane completed 2 1/2 rolls before making a 1 inch deep hole in the ground - all within the 5 second thero-overload recovery time I measured later on the bench.

At the very least, do a bench test, move all servos simultaneous for about 45 seconds and then feel the ESC for a very hot chip (most likely located opposite the heat-sink). Even if it passes on the bench, that test cannot replicate the real aerodynamic loads placed on the servos so you cannot be really sure. If the test fails, you've saved a plane.

Alan

Not as bad as you, I had a mere 4HS55's on a 12A brushed ESC on 3s LIPO.

I was pottering around 1/2 throttle or less, 7-8 minutes in to a flight, using lots of aileron corrections in the mild turbulence.

In my case the throttle closed and all servos ran to their end stops. Thank heavens it was 'up' elevator not 'down'. Spun in from 30 feet. A lot of damage, but reparable.

She runs with a bigger ESC and more cooling these days - so far without trouble.

I am putting together a 3s/4s ship with 6 servos. NO WAY will I use a linear BEC.

But them those nice guys at SMARTBEC sent me a free unit in return for making up a silly advert line.

Weighs very little, and if it does what it says 'on the tin' it will be perfect..

Why risk the plane for a few oz of servo battery or a few dollars of switching BEC?

Would you run with potentially intermittent crystal, or a servo which has any potential to fail on you in mid air?

No, and this is potentially worse..

Don't risk it. Its not worth it.

3s LIPO and 4 servos is the limit for linear BECS.
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Old Oct 12, 2005, 12:53 PM
Flying motor mount master
fly_boy99's Avatar
San Jose, California, United States
Joined Oct 2004
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For godsake just get a BEC because the money you will spend on it will more then be made up in time NOT spent repairing your plane or keeping someone out of the hospital!!!
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Old Oct 13, 2005, 03:52 PM
Registered User
San Francisco Bay Area
Joined May 2001
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thanks all...

I think I have my answer and will use either a dedicated NIMH for the receiver/servos (HS-81's), or a UBEC.

I haven't been able to find much information about the reliability of UBEC's. Does anyone have any experience with them (good or bad) that they can share?

John


John
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Old Oct 13, 2005, 05:55 PM
I'd rather be Flying
davecee's Avatar
Nashville, NC, USA
Joined Mar 1999
2,761 Posts
I've been using a UBEC in a 20 cell NiMH plane which then was changed to 6S LiPo. I'm running 4 servos, which is no where it's full capability. It's been flawless.
Dave
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