pritchett4

My Feedback: (1)

i was out flying my tower hobbies vista ep which i had just converted to brushless....i am also new to electric flight in general lol

heres the problem...took off and flew around for a little bit, landed, went to take off again full power, about a 70 degree climb and lost all power from the esc because the lipo reached its limit, and my plane went into a vertical dive from about 50 feet...

so here is the question lol

if i run a ubec at the battery connection and disabled the on-board bec...would the ubec still cut out after the bec loses power? does the ubec have a low limit shut off? or is that on a per ubec basis?

Walt Thyng

My Feedback: (9)

First off, you shouldn't have lost all power from the ESC just because you hit the LVC (low voltage cut-off). Are you sure the plane didn't just stall too low to recover? Did you check your controls afterward?

The LVC applies to the speed control side of your ESC which powers the motor, not the BEC which powers the servos.

If you lost all power to the rx something is very wrong.
Walt

cyclops2

Are you positive you did NOT run out of battery power for the engine while doing a second flight ? Did / do all the servos still work ? Did the RC stuff work at home during a check out ? after a recharge. What still works ?
I go for a tired battery or a connection coming apart between motor & ESC.
Stalls are stalls no mater what causes them.

pritchett4

My Feedback: (1)

havent had the chance to test anything yet...broke the plane in half haha

ill check the servos to see if they work with the battery that was crashed, and see if it is actually dead...but the motor took the blunt of the crash and is now full of dirt and doesnt turn very well.

look4one

The simple answer to your ariginal question is NO. The UBEC will work until the battery drops below it's functional limit which is about 6 volts.

The other simple answer is that using a switching UBEC will cure all your ESC BEC problems and probably save several airplanes. You will also get less heat generated in your ESC.

The ugly truth that no one tells is that the linear BEC built into all the ESC's are worse than worthless. If you use more than two servos, the linear BEC will make so much heat that (1) the ESC will go into overload and shut down. (2) and even worse is that all the linear regulator chips self-protect after about 150 C and drop the voltage from 5 to whatever. So when the receiver sees that 3 volt glitch in his power the radio will lock-out. Fun, no?

My tests show that the greatest heat production is the BEC ande not the motor driving ESC.

mehrshad

Low Voltage Cutoff is only for the motor output stage and not for the BEC.
But the Bec may be overheated if it is linear type.
go with an external Switching BEC if it overheats.

look4one

You may have confused the two cut-off terms. True, Low Voltage Cut-Off (LVCO) is the nomal and expected drop in MOTOR power with falling battery voltage. The LVCO is a seperate issue with the BEC. A linear BEC uses a low drop out (LDO) IC. These chips give 5 volts out as long as there is more than 6 volts coming in and they are NOT too hot.

When the chips temperature exceeds about 140~165 C then the output voltage (5 volts) will drop to relieve the temperature stress. There is no warning signs of this event and it will happen when the ESC/BEC is uncomfortably hot or about 50~75C. The heat sink ability of these ESCs inside a heat shrink sleeve is notoriously poor. This I say as a professional in the pwoer supply industry.

The ONLY time a linear BEC is safe is withy only 2S Li-Po packs and the BEC/ESC has a finned heat sink. If the supply is ever 3S or more then the switching UBEC is essential. You can go the cheap route with 3S battery and the stock ESC/BEC but plan to buy lots of airframes.

lorih

Okay, I've got to respond here. I have literly over a thousand flights with linier BEC's and no problems to date. Almost all my planes have 3 cell lipos and 25 amp esc's. Most have 4 servos of the 9 gram size. Most of my bec's have a 2 amp limit and this is within their limit.

If the limit of the bec is not exceeded, you should have no problems.

HOWEVER, if you are using STANDARD size servos.....yep, an external UBEC is a great, if not required, idea. There is a huge difference in the current draw between the micro, standard and high torque servos. Know what you are using.

It all goes back to knowing your system and current draw. Stay within your limits and all will be okay.

Cliff

cyclops2

I fly plane below & never have loss of servos. Motor power cut backs ? yes.

Most of my planes are all 2, LIFEPO4 cell powered............light load with only 2 Hitec -55 servos.

IF you had a servo that was just a TINY bit jammed on full travel limits. Now you are out of control due to a overloaded BEC.

Electrics are a bunch of wiggly worms you are trying to control........ Experience & experienced friends are needed.

cactusflyr

I have had four brownouts recently. Recovered from three of them, the fourth resulted in a vertical dive straight into the ground with me fighting it all the way. Mind you, this is four using microservos in a multiplex gemini. They all scare the &^$%& out of me

Buy this plane............it only broke a strut and was flying the next day when the fourth and last brownout occurred.

The esc is a new 40a e-flite (V2), power 10 motor, 1500mah lipo. I am going to switch speed controllers back to the old one......an eflite40a (V2) also as it never had this problem and was the only thing that changed in the setup.

As i am getting into bigger electrics, a ubec seems reasonable and i have but one question. Does using a ubec disable the low voltage warning that is get from my esc. I use scorpion esc's in my bigger planes that pulse when they get low,and i love them. If it does, do they have their own low voltage warning?

look4one

The linear ESC BEC and UBEC (switcher) debate centers around HEAT. If the little ESC and linear gets enough cooling, it will work okay no matter what is the servo count or amperage. BUT if the tempearture goes too high, even for a short time, your receiver might get a lock-out. You decide what you feel comfortable with.

Other response to this post shows that some BEC and servo combinations work better than others. Most of this is controlled by your flying style. A hard-core 3D pilot will use a lot more servo power than a scale flyer or a trainer. The other variable to the equation is how much air flow gets to the ESC.

The UBEC or any BEC has nothing to do with the low voltage warning techniques used by the moter driving ESC. All the ESC have their own separate linear regulator for the internal circuit and voltage detection. The BEC is by design required to regulate power right down to the end of life for the battery. There is no reason to de-power the control system as a way to fail-safe the battery.

For my own use, I remove ALL linear regulation components from the ESC, then attach a 3-lead JST connector to the appropriate power pads. then I mount the masting connector to the UBEC. This allows the stock and simple one-plug connection from the ESC to the receiver. I can also swap UBEC and ESC as required if one or the other malfunctions.

pilotpete2

70dg. climb and loss of thrust at 50' AGL = crash
Pete