• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

number of servos??

#1
I am building a pretty large plane with canards and rudder and stearable nose wheel which will use a total of 7 and maybe 9 if i use flaps, is this too many to try to power off my esc?????
 

colorex

Rotor Riot!
Mentor
#2
Yes, I would use a separate BEC instead of relying only on the ESC. I read somewhere that 2A is just enough to pull 4 9g servos simultaneously...
 

pgerts

Old age member
Mentor
#5
I have a lot of servos - not as many as you. All is depending on the type of servos and the type of bec on the esc.

There is a smart little gizmo often used on glow planes.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=2038

C
onnect this to one servo port on your receiver (with Y-cable if there are no free connectors - battery connector is fine).
Move all your sticks simultaneously or better apply some weight on the moving surfaces (rudders). If you can se red indicators then there is a problem.
 
#6
Just let the magic smoke come out of my 20a esc on a plane with 5g servos and 2 3.7g servos last week. Normally I would trust that but they were under a lot of load and there was no airflow over the esc. I was testing control surfaces on the ground when it happened :(

It sucks when it happens to you and you don't expect it.
 
#8
I always use separate UBEC's to avoid ESC damages. OK if I give full throttle and kill it due to that but giving lots of inputs at the same time....naah

//UndCon
 

ananas1301

Crazy flyer/crasher :D
#9
Same here!

If using a little more servos, more then 4 small one (bigger then 10g servos) then I normally go for a External bec.

Just to be on the safe side!
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#10
Another thing to think of, is running a separate battery pack for just the rx and servos, like they do on nitro powered planes.

If you're running a battery under load, and you drop the voltage below LVC for a moment because of the multiple servos, you could lose your connection to the rx.
 

pgerts

Old age member
Mentor
#11
Same here!
If using a little more servos, more then 4 small one (bigger then 10g servos) then I normally go for a External bec.
Just to be on the safe side!
I am a little curious, how many of your planes have more than 4 servos bigger than 10 gram?

Bigger planes normally have bigger esc with more amps to the bec.
I have one plane with 7 servos - 70A (opto) esc and separate bec but also two planes with 6 servos (one with digital servos) flying fine with the built in bec. The separate bec on the plane with opto esc does not give any more amps than a 70A esc with built in bec woud have done.

The first question does not say what a "pretty large" is - is it a plane of 3,5 - 5 kg / 7-10 lbs then most flyers would say it is normal size. Canards however might indicate a "jet plane" with speed of 200 km/h / 125 mph or more and then even a smaller plane needs more power to the servos and probably separated power to the receiver from the power to the servos.
 
Last edited:

ananas1301

Crazy flyer/crasher :D
#13
It would depend on how much Amperage you wanna get out of. Most UBECS are set to one current output to reduce as much weight as possible so that adding the UBEC into plane won´t ruin your balance.

But I would say for all planes bigger then 1,5m with more speed then 100 mph something around 5-10A. It really depends on the weight if plane as well so it is really hard to say actually.
 
Last edited:

pgerts

Old age member
Mentor
#14
I am obviously into much smaller planes than our friend ananas ;-)
My ubecs are only 3 and 5 amps.
Not long ago people were competing in F3A class with fast .60-engine pattern planes and used small NiCd batteries like in the picture. 600 mAh would last more than one 10 minute flight. The new 2000 mAh NiMh batteries last "forever" before any need of charging. We are naturally talking different when coming up to big scale models with engines of 100 cc and up.
I had to check the amp draw from a few of my servos:
20 gram servo – stalled 0,5A
50 gram digital servo 1,0 A
I guess that the more normal 10 gram servos used many of in the modern planes will stall at about 0,25 A.
The “normal” draw from the servos are obviously a lot less than the stalled sevo.
servo.JPG
 
#15
not sure about the weight yet but its 5' by 5', Im building a slow flying multi camera plane, and when i say multi i mean like 4 key
chain cams and 4 Go Pro cams
 

ananas1301

Crazy flyer/crasher :D
#16
@pgerts:

I am 16 and have been flying for 1,5 years now. I have not had a single flight with something over 1,5m and more then 100mph but this is just my feel for the amperage the servos draw and as I like to rather be on the safe side with for example ESC´s for motors and rather have 10A too much then 1A to less (and fry that ESC) I got to the conclusion that I WOULD take a little bigger UBEC´s the more valuable the planes get, which they tend to be the bigger they get :D
 

pgerts

Old age member
Mentor
#17
I would compare your plane with a 1/5 scale CUB in size, weight and speed.
Your key cameras will not add any weight to notice. The GoPro are 150-200 grams each depending on accessories - a total of approx 1 kg (2 lbs). I think 4 std servos are more than adequate for flight. Add smaller tilt servos to the gopros?
The plane will run fine with the built in bec in the esc if you choose a better esc with 4A bec. Your servos will not draw more than 250 mA each on normal flying, probably a lot less in average.
If assume that you or a helper are controlling the cameras tilt functions with a separate radio and together with FPV?

I have built a CargoTwin with a span like yours but a lot shorter. Allservos are HXT900.
It is amazing how much load something like that can carry.
http://www.rcgroups.com/forums/showthread.php?t=1265273

Check out the video of rctestflight
 
Last edited:

Ak Flyer

Fly the wings off
Mentor
#20
I am building a pretty large plane with canards and rudder and stearable nose wheel which will use a total of 7 and maybe 9 if i use flaps, is this too many to try to power off my esc?????
What type of radio system do you have? How many channels do you have available? You may be able to do this just fine if you have enough channels. I bought an 8 channel receiver so I wouldn't have to use Y-harnesses for everything. I can run most servos on their own channel and mix them together in the radio. This cuts down on the draw per circuit. I believe this eliminates most of the problem unless maybe you are using high draw servos. Of course, until you put it together and check your voltage and amp draw you won't really know. Things like retracts and flaps aren't going to be drawing all the time though so you can probably get away with a bit more. Things like multiple ailerons and multiple elevator servos are the big concern.
I use spektrum products and they have what they call powersafe recievers where you plug one or more batteries into the receiver for high draw applications. I'm sure whichever system you use may have something similar.

http://www.horizonhobby.com/browse/...Spektrum/:kw=/:st=/:ct=34/:sp=0/:cp=1/:ip=9/: