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BEC 5amp enoguh for 6 servos - 9/12/2012 11:24 AM   
gosk8ing


 

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Status: offline 		Hi,

Quick question. I've just purchased an E-Flite 25 Ultra Stick. I was planning on using the quad flap feature. After cutting the ailerons in half I read the radio installation section and it noted that a receiver battery and switch harness must be used if using quad flap option. If I knew this was a must, I wouldn't have bothered with the extra parts and weight to the plane. So here is my question. Do I need a receiver battery or how do I check if I do?

I'm running a e-flite 25 brushless, 4s lipo (not sure what capacity yet), castle creations ice 50 amp ESC (has 5 amp BEC and will program ESC to 6 volts BEC so the servos have more torque), 6x HS225MG servos, and a Hitec Optima 9 2.4ghz receiver.

Thanks

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RE: BEC 5amp enoguh for 6 servos - 9/12/2012 12:57 PM   
Sherv


 

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quote:

ORIGINAL: gosk8ing

Hi,

Quick question. I've just purchased an E-Flite 25 Ultra Stick. I was planning on using the quad flap feature. After cutting the ailerons in half I read the radio installation section and it noted that a receiver battery and switch harness must be used if using quad flap option. If I knew this was a must, I wouldn't have bothered with the extra parts and weight to the plane. So here is my question. Do I need a receiver battery or how do I check if I do?

I'm running a e-flite 25 brushless, 4s lipo (not sure what capacity yet), castle creations ice 50 amp ESC (has 5 amp BEC and will program ESC to 6 volts BEC so the servos have more torque), 6x HS225MG servos, and a Hitec Optima 9 2.4ghz receiver.

Thanks


Not sure if the castle escs come with a switching bec, if so then it may work. Best thing to do is to test it and let us know.

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RE: BEC 5amp enoguh for 6 servos - 9/12/2012 1:33 PM   
KW_Counter


 

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Status: offline 		Remember, the higher the voltage the higher the current draw.
If you lower the output to 5 volts the better chance the
5 amp BEC will work.

Good Luck,
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RE: BEC 5amp enoguh for 6 servos - 9/12/2012 2:02 PM   
CGRetired



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Status: offline 		Hm.. adjustable BEC voltage. What is this world coming to?

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RE: BEC 5amp enoguh for 6 servos - 9/12/2012 3:30 PM   
jester_s1


 

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Status: online 		If you have a voltwatch or voltmagic device you can see if the BEC is up to the task. If you have the last issue of Model Aviation, the helicopter column tackles this very subject. It says that in some applications the peak demand of the servos could overtax the BEC, but normal operation and average current draw doesn't. In those cases, adding a capacitor to an unused channel will fix it by storing some extra current for when the servos need it. Personally I think you're fine since you're using analog servos, but testing with a voltwatch will let you know for sure. You just hook it up and stir the sticks.

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RE: BEC 5amp enoguh for 6 servos - 9/12/2012 5:08 PM   
opjose



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Yes you should be fine.

The "Mighty Mini" draws around 1A at full stall, and that is something you'll NEVER see if you've set up your plane properly.

Typical current draw is around 300-400 under normal flight loads and much less during no loads. That 300-400 tends to be only momentary too.

The Castle DOES have a switching BEC, and you can use the logging feature to double check everything if you so desire.

6v is no problem with your setup.




< Message edited by opjose -- 9/12/2012 7:26 PM >

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RE: BEC 5amp enoguh for 6 servos - 9/12/2012 5:29 PM   
Gray Beard


 

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quote:

ORIGINAL: CGRetired

Hm.. adjustable BEC voltage. What is this world coming to?

I do read these posts and pretty much all of it goes sailing over my head. I ask someone what to get for this or that plane and so far it has worked for me. I have motors and ESCs on my wall and know what weight of the plane it will work with. These electric people amaze me!! I can't keep it in my head at all.

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RE: BEC 5amp enoguh for 6 servos - 9/13/2012 4:52 PM   
gosk8ing


 

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Status: offline 		What will happen if the BEC is overloaded? Does it burnout because you're drawing too much current or does it reduce the voltage?

I've noticed that the ICE series of ESCs have onboard data logging. If I hook up all the servos and battery but leave the motor disconnected, could I use this to check how much the servos are pulling?

I know under no load, these servos will not overload the BEC (6 x 340 = 2.04 amps). From searching on the net, I found that at 4.8v and 6v, they consume 300mAh and 340mAh respectively. My only concern is how much do they consume when loaded/stalled? Also, I found it hard to find out how much the receiver consumes. Somewhere stated 190mAh. Does that sound right?

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RE: BEC 5amp enoguh for 6 servos - 9/13/2012 6:19 PM   
opjose



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quote:

ORIGINAL: gosk8ing

What will happen if the BEC is overloaded? Does it burnout because you're drawing too much current or does it reduce the voltage?



The voltage drops if the servos are drawing too much.

If you notice that the servos are behaving strangely ( e.g. sticking ) or that you had a brownout on your RX, after swirling the sticks hard this is most likely the cause.

It's super easy to verify that things are fine however.

Set up your plane and get everything adjusted.

Then put a "load" or resistive force on your control surfaces as you move the controls.

You can put weights on the TE surface, say four ounces or so, or you can merely hold them. But don't go crazy resisting the force.

Observe the behaviour of the other servos and/or if your RX reboots.

You can take it further and hook up a volt meter to a "Y" cable and look for voltage drops that might endager the RX, but this is overkill for that size of a plane.

( BTW: I regularly do this with my Giant Scale planes just to make sure that my power sources are up to the task... )

I've used NINE of those servos on a .25 Bobcat pusher "jet" plane with a 4A bec w/o problems so you're good.

quote:

ORIGINAL: gosk8ing


I've noticed that the ICE series of ESCs have onboard data logging. If I hook up all the servos and battery but leave the motor disconnected, could I use this to check how much the servos are pulling?



NO!!!!

NEVER EVER power up the ESC with the motor disconnected as you are indicating. You may burn out the ESC or ruin the transistors.

Nor is there a need to. Just don't run up the throttle as you move the servos.

quote:

ORIGINAL: gosk8ing

I know under no load, these servos will not overload the BEC (6 x 340 = 2.04 amps). From searching on the net, I found that at 4.8v and 6v, they consume 300mAh and 340mAh respectively. My only concern is how much do they consume when loaded/stalled? Also, I found it hard to find out how much the receiver consumes. Somewhere stated 190mAh. Does that sound right?


"Stall" current is a WORST CASE situation where the servo is PREVENTED from moving, due to the horns, arms or control surface hitting an extreme or binding.
You should ALWAYS set your end points on your computer controlled TX so this NEVER EVER happens. Novices rarely know about doing that....

The Hitecs will consume about 950mA of current on full stall. You'll NEVER see that in flight unless you are using undersized servos for your plane... which you are not.

The 340mAh is a more normal operating rate, and is the average they consume in use. In practice they MOMENTARILY will consume more, but it is rare to have more than two servos of this size consume even 400mA at the same time. In normal flight they actually consume far less.

Your RX figure is about right, some consume less, some a bit more.



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RE: BEC 5amp enoguh for 6 servos - 9/13/2012 9:37 PM   
gosk8ing


 

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Status: offline 		Thanks for a great post opjose!!! I'll test the setup and then go from there! It got me worried when the manual said a separate receiver battery was needed. I guess that's because a lot of other ESCs only have 3 amp BEC and also at the end of the day, e-flite have to cover their arse!

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RE: BEC 5amp enoguh for 6 servos - 9/14/2012 3:14 AM   
opjose



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quote:

ORIGINAL: gosk8ing

Thanks for a great post opjose!!! I'll test the setup and then go from there! It got me worried when the manual said a separate receiver battery was needed. I guess that's because a lot of other ESCs only have 3 amp BEC and also at the end of the day, e-flite have to cover their arse!


Actually the reason you see that in the manual is because many of the E-Flite ESC's, particularly the older ones, do NOT have "switching" BECs.

Older analog BECs shunted the excess current as heat. As you increased the voltage, the fewer servos the BEC could deal with. Typically the ESC's were rated for only THREE servos at 11.1v if that.

Look for ESC's with "SBEC". SBEC denotes a switching BEC, which uses a different technique to lower and regulate the voltage. These can handle more servos with ease within limits.

I believe all of the Castle ESC's feature SBECs.



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RE: BEC 5amp enoguh for 6 servos - 9/18/2012 9:36 AM   
gosk8ing


 

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Status: offline 		Alright, so I was finally able to test the BEC tonight.... Not so good. At 5 volts and moving all the sticks around (under no load), after about 2 seconds they would pause for about a second and then move again, suggesting the BEC wasn't up to the job. Doing the same at 5.8 volts  had the same results but more often. I guess that leaves me with one option - install a 10amp BEC.

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RE: BEC 5amp enoguh for 6 servos - 9/18/2012 12:24 PM   
Sherv


 

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Status: offline 		I'm actually surprised it cant handle it. Bummer.
I have a similar setup I'm putting in a cessna, 6 servos same size, with an 80amp ESC that has a 5.5v 6AMP SBEC on it. Hope it is enough.

Take a look at this, I've used one and had no problems with it

http://www.hobbyking.com/hobbyking/store/__6233__TURNIGY_8_15A_UBEC_for_Lipoly.html


Also I've read this one is good but I have not tested it, some like that redundancy
http://www.hobbyking.com/hobbyking/store/__14464__Turnigy_Redundant_Dual_8A_UBEC_Rx_Power_System.html

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RE: BEC 5amp enoguh for 6 servos - 9/18/2012 5:25 PM   
opjose



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quote:

ORIGINAL: gosk8ing

Alright, so I was finally able to test the BEC tonight.... Not so good. At 5 volts and moving all the sticks around (under no load), after about 2 seconds they would pause for about a second and then move again, suggesting the BEC wasn't up to the job. Doing the same at 5.8 volts  had the same results but more often. I guess that leaves me with one option - install a 10amp BEC.


Yup, that's a classic example of what happens with a momentary spike on the BEC.

I'm glad you ran the test....

Been there, solved that...

The problem with many BECs is that while they operate great if the demands are within specs, even a momentary spike will screw up the switching circuitry.

NiCD's and NiMH packs don't mind these spikes and they will rebound instantly so the servos and RX's do not see the voltage drop long enough to affect them.

Try the same test with a lowly 800mAh NiCD or NiMH pack and you'll have no problem.

Strange eh?

The problem is with those small capacitors used on the BEC. Consider them to be small "reserve" batteries with insufficient output to handle all of your servos.
In the case of directly powering the electronics with NiCD/NiMH packs, the batteries themselves act as that reserve, handling the large momentary draw easily.


BTW: I'm running five of those servos on a Addiction-X using a Quantum 45A ESC 5A SBEC with no problems. That sixth servo must put you over the top.

Yes you could try running a higher capacity BEC, or a different power source.




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RE: BEC 5amp enoguh for 6 servos - 9/18/2012 6:38 PM   
gosk8ing


 

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Status: offline 		Like I said, I was moving the sticks around the whole time which is something you wouldn't normally be doing in the air. But in saying that, I don't want to be the guinea pig. I was thinking about running a flight pack, but that would mean more weight, another battery to charge and monitor and I'm now pushing for room in the fuselage. I

Thanks for your help guys.

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