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Old Aug 18, 2007, 01:30 PM
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Rural Westchester, NY
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Won't you help me learn my ESC/BEC abc's? Servos and ESC limits.

So last week I'm on vacation flying in Sydney, Maine with my nephew and showing him how great I can harrier my new 3DHobbyshop.com Extra 300 SHP when all of a sudden it stalls and mushes into the ground breaking the gear. Much chagrined I wander out to the field pick up the pieces and begin trying to make excuses to my nephew and sister-in-law. Gee, that never happened before. Hey maybe it was windshear. Ya know I've heard about this thing called the "cone of silence". Anyways I strap on the new landing gear and get right back on that pony without much further thought. Then yesterday back at my home field there I am performing a "wall" and pulling up into my meager attempt at hovering when -BAM- she quits and falls over wing first into the ground cracking some internal framing. Home I go where first I order a replacement airframe (even though I ultimately repaired the damage with no trouble) and then set about complaining on the Spektrum thread that I was hit by the dreaded "cone of silence" twice. Along comes a nice helpful RCer who suggests testing my unit at home to see if the BEC was up to snuff. So I placed the Extra's tail between my feet ran her up to 1/3 throttle and started cylcing the aileron and elevator back and forth to their limits at about 1 sec intervals.

Wouldn't ya know it - after 3 minutes and 8 secs my ESC/BEC shut down due to overheating. Mystery solved. But . . .



Questions:

1) Will my Castle Creations 54 behave any differently since it too has dual linear BECs rated for 3 amps?
2) How can I test the BECs on my E-Flite to see if one is failed?
3) Should I really be concerned about noise if I decide to buy a switching BEC?
4) The E-Flite ESC directions list 2 servos max for "high torque" but are the HS-65HB's really "high torque"?
5) Once one leaves the small feather servo world and moves up to larger models are they doomed to forever build using a separate BEC and battery?


The setup:

Torque 2818/900
13x6 APC prop
TP Extreme 3s2070mAh LiPo
4 HiTec HS-65HB's
E-Flite V.2 40 amp ESC w/ dual BECs
Spektrum AR700 rx

notes - I put a Whattmeter on the setup and it shows a resting amp draw of .15 and a draw between .98 and 1.22 with multiple full servo deflection, and the ESC does get hot to the touch if I simply let it sit, not so hot that I can't touch it but hot enough to be very uncomfortable on my fingers.



To any and all who decide to take time and educate the village idiot (that would be me) "thanks a bunch" in advance, and for those that have been through this topic a dozen times already, my many apologies, but I didn't find any threads that answered all my questions.


Joe
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Old Aug 18, 2007, 02:06 PM
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Letchworth, Great Britain (UK)
Joined Jul 2004
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I see that E-flite advertise that the ESC can be used with "up to 4** servos" with a 3S LiPo. The sceptic in me says that, to justify that statement, they've chosen the smallest servos they can find, and that with larger servos the limit should be 3 or less

Maybe other E-flite users will report that theirs can handle 4 HS-65s or equivalent without overheating. Have you got good cooling for yours?
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Old Aug 18, 2007, 02:23 PM
And You're Not
Timbuktu, Mali (Happy?)
Joined Oct 2002
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The Spektrum radios don't like a low voltage situation, either. If your ESC was having any trouble supplying voltage to the servos, it could have been low enough to cause the Spektrum RX to re-boot. Lots of posts/threads about this in the radio forums. Just something else to think about.
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Old Aug 18, 2007, 04:20 PM
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Dickinson, Tx.
Joined Sep 2004
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I use a add on BEC such as (http://www.dimensionengineering.com/ParkBEC.htm) even when I am only using 3S size packs on my nicer planes. I think it is cheap insurance to prevent issues that you have stated.

I have read too many posts about the onboard BEC on E-Flite ESC tripping out. I only use CC ESC, but still use the "Park BEC". At 2S levels I just use the CC ESC without an add-on BEC.

Are you giving the E-Flite ESC excellent airflow as this helps out tremendously????

Challenger413
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Old Aug 18, 2007, 04:39 PM
I need a bigger hangar
Phoenix, AZ
Joined Jan 2007
195 Posts
I'm using one of the cheapie switching BEC's on my 3DHS Extra equipped with Spektrum AR6100 (v2.1). Using it with a 3s1p Lipo. I have no problems with it and have noticed no noise whatsoever...I did test the BEC by loading it with a resistor to make it produce 3 amps for about 5 minutes before putting it in the plane. But that's one of the nice things about 2.4ghz...Not much noise gets up that high in frequency.

Here's where I got my BEC... www.donsrc.com Ask for the 2 for $25 shipped RCG price.

http://www.rcgroups.com/forums/showthread.php?t=692599

Cole
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Old Aug 18, 2007, 04:50 PM
Been There! Done That!
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Eugene, Oregon, United States
Joined Sep 2001
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I have never had a issue with Phoenix ESC with the 3A BEC however if I am over 3S or more than 3 Standard size servos or 4 micro servos on any plane I use the Hyperion BEC. I like the 4A continuous and 5A burst rating. Not cheap but compared to a $400 or more plane it's cheap!!!
boomer!
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Old Aug 18, 2007, 05:51 PM
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Rural Westchester, NY
Joined Oct 2005
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Ignorance is bliss.

The Extra 300 was my first "real" plane. Prior to this model everything I owned was 20 ozs or less and ran 2 or 3 submicro servos so I don't believe I ever experienced this problem before. As a result I didn't pay much attention to cooling the ESC so . . . the ESC on my plane gets little if any cooling.

Quote:
if I am over 3S or more than 3 Standard size servos or 4 micro servos on any plane I use the Hyperion BEC.
Based on this comment, I'm thinkin' my CCTB 54 is not a viable alternative. I really hate to put a UBEC in not because of cost but rather weight so I'm leanin' towards buying an Airboss 45. It has a switching BEC which I understand is truer to its 3 amp rating versus a linear BEC pair.

What do you guys think?


Joe
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Old Aug 18, 2007, 06:09 PM
Been There! Done That!
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Eugene, Oregon, United States
Joined Sep 2001
19,187 Posts
Quote:
Originally Posted by 2Sunny
The Extra 300 was my first "real" plane. Prior to this model everything I owned was 20 ozs or less and ran 2 or 3 submicro servos so I don't believe I ever experienced this problem before. As a result I didn't pay much attention to cooling the ESC so . . . the ESC on my plane gets little if any cooling.



Based on this comment, I'm thinkin' my CCTB 54 is not a viable alternative. I really hate to put a UBEC in not because of cost but rather weight so I'm leanin' towards buying an Airboss 45. It has a switching BEC which I understand is truer to its 3 amp rating versus a linear BEC pair.

What do you guys think?


Joe
Joe,
I read the specs and it is only 2A and nothing says it is a switching BEC! It's your plane but the minor weight added by a Separate BEC the plane won't even notice. The 4A continuous gives that warm fuzzy feeling of confidence that you will have zero problems with control!
boomer
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Old Aug 18, 2007, 06:38 PM
It should fly at least once
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Australia, NSW, Grenfell
Joined Mar 2006
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For those interested.
A beginner’s guide to switching regulators

What is wrong with a linear regulator?
Linear regulators are great for powering very low powered devices. They are easy to use and cheap, and therefore are very popular. However, due to the way they work, they are extremely inefficient.

A linear regulator works by taking the difference between the input and output voltages, and just burning it up as waste heat. The larger the difference between the input and output voltage, the more heat is produced. In most cases, a linear regulator wastes more power stepping down the voltage than it actually ends up delivering to the target device!

With typical efficiencies of 40%, and reaching as low as 14%, linear voltage regulation generates a lot of waste heat which must be dissipated with bulky and expensive heatsinks. This also means reduced battery life for your projects.

Even the new LDO (low drop-out) regulators are still inefficient linear regulators; They just give you more flexibility with input voltage drops.

How is a switching regulator better?
A switching regulator works by taking small chunks of energy, bit by bit, from the input voltage source, and moving them to the output. This is accomplished with the help of an electrical switch and a controller which regulates the rate at which energy is transferred to the output (hence the term “switching regulator”).

The energy losses involved in moving chunks of energy around in this way are relatively small, and the result is that a switching regulator can typically have 85% efficiency. Since their efficiency is less dependent on input voltage, they can power useful loads from higher voltage sources.

Switch-mode regulators are used in devices like portable phones, video game platforms, robots, digital cameras, and your computer.

Switching regulators are complex circuits to design, and as a result they aren’t very popular with hobbyists. However Dimension Engineering creates switching regulators that are even easier to use than linear regulators, because they use the same 3 pin form factor, but don’t require any external capacitors.

What can switching regulators do that linear regulators can't?
With high input voltages, driving loads over 200mA with a linear regulator becomes extremely impractical. Most people use a separate battery pack in these situations, so they have one battery pack for high voltage devices and one for low voltage devices. This means you have twice as many batteries to remember to charge, and twice the hassle! A switching regulator can easily power heavy loads from a high voltage, and save you from splurging on an additional battery pack.

Certain kinds of switching regulators can also step up voltage. Linear regulators cannot do this. Ever.

How do I tell if I need a switching regulator?
As a general rule of thumb, if your linear voltage regulation solution is wasting less than 0.5 watts of power, a switching regulator would be overkill for your project. If your linear regulator is wasting several watts of power, you most certainly want to replace it with a switcher! Here is how to calculate power losses:

The equation for wasted power in a linear regulator is:

Power wasted = (Input voltage – output voltage) * load current

For example, let’s say you have a 12V lead-acid battery and you want to power a microcontroller that draws 5mA, and an ultrasonic rangefinder that draws 50mA. Both the microcontroller and the ultrasonic rangefinder run off of 5V. You use an LM7805 (a very common linear regulator) to get the voltage down to 5V from 12V.

Power wasted = (12V – 5V) * (0.050A + 0.005A) = 0.385W

0.385W is not too bad for power losses. The LM7805 can handle this without a big heatsink. You could get more battery life if you used a switching regulator, but in this case the power consumption is so low that the battery life will be very long anyway.

Now let’s expand on this example, and add two servos that draw an average of 0.375A each, and also run off of the 5V supply. How much power is wasted in a linear regulator now?

Power wasted = (12V – 5V) * (0.050A + 0.005A + 0.375A + 0.375A) = 5.635W

5.6 Watts is a lot of waste heat! Without a large heatsink the LM7805 would get so hot it would desolder itself or melt your breadboard or defeat Iceman. Even with the heatsink, 5.6W is also a lot of life to suck out of your battery for no reason. A switching regulator such as a DE-SW050 would be very useful in this case, and would reduce power losses to around 0.5W.

Is a switching regulator really worth 10+ bucks?
The final thing to consider is of course, cost. If your project is cheap and simple enough that a switching regulator would triple the cost of the entire project, then a switching regulator may be hard to justify. However if you are building a more advanced robot, airplane etc. and a switching regulator adds 15% to your cost, but gives you 35% more battery life, then it is a good deal right?
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Old Aug 18, 2007, 09:06 PM
Check my blog-updated
Mayday!Mayday!'s Avatar
Columbus,Ohio
Joined Nov 2005
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Clive- good post
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Old Aug 18, 2007, 09:16 PM
It should fly at least once
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Australia, NSW, Grenfell
Joined Mar 2006
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Thankyou

I cannot take the credit as I got it from a supplier website
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Old Aug 19, 2007, 02:50 AM
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Letchworth, Great Britain (UK)
Joined Jul 2004
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Quote:
Originally Posted by 2Sunny
... I really hate to put a UBEC in not because of cost but rather weight so I'm leanin' towards buying an Airboss 45. It has a switching BEC which I understand is truer to its 3 amp rating versus a linear BEC pair. ..
boomerace has advised that the ESC in your link probably doesn't use a switching BEC.

If you want to be sure you're getting a switching BEC you could try a Jeti Spin http://www.jetimodel.cz/eng/hlavnien.htm . But they're pricey ...
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Old Aug 19, 2007, 03:02 AM
It should fly at least once
clive45's Avatar
Australia, NSW, Grenfell
Joined Mar 2006
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//

Just buy a seperate switching BEC and disconnect the the red wire from the ESC to RX, much better.
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Old Aug 19, 2007, 11:12 AM
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Rural Westchester, NY
Joined Oct 2005
667 Posts
You guys rock!

God I just love the internet . . .

Thanks for all the great input, and education. I think the energy loss story says it all. Why even bother with linear BECs once you move past tiny foamies. Anyways, I decided to try a ParkBEC 6v only because I am obsessed with minimizing weight. I think I can spare 6.5g , and I promise from now on to use ParkBECs everytime I go for more than 3 servos

Thanks again,

Joe
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Old Sep 20, 2007, 04:36 PM
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New Orlenans, La.
Joined Mar 2003
135 Posts
Park BEC

You all need to check out Dimensionengineering.com. They sell the ParkBEC and SportBEC. The ParkBED is good up to 1.5 amps. I have been using the SportBEC, good up to 3.5 amps, in my trex and have had absolutly no problems. It is more expensive than others but what is $10.00 compared to $50 to $70 to repair this heli. Dont short change yourself, chek out Dimensionengineering.com. Their web site also has FAQ section that explains the difference between linear regulators and switching regulators. This complany is a professional company that makes electronics for other purposes.
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