|Jul 03, 2014, 11:27 AM|
Canada, ON, St. Catharines
Joined Jun 2014
BECs for electric soarers ? ...
I am finding out there are BECs and BECs, one type is basically just a voltage regulator, the other type being a smarter one, that actually saves you enough battery capacity to fly on for a while.
So, what does one look for in a ESC description to make sure you get the good one for anything that's not gonna glide like the shuttle as soon as the juice is used up?
Also need a bit of a mental recalibration, due to being out of things a good while, about how much juice does modern gear need? I have a sortakinda expectation that back in the day, you'd expect about half an hour out of an AA receiver nicad pack. What were they then, 500mAh 4 cell.
So what do you guys do now, use a specialist ESC, get a standalone smart BEC to be sure, or use a separate tiny LiPo that's 1000mAh or something.?
Thanks for the hints,
|Jul 03, 2014, 11:34 AM|
I just use the BEC on the ESC, in my case all Castles.. Some say don't put all your eggs in one basket and use a separate power input, but to date I've had no problems in 7 years of flying this way. There's no guarantee that a separate Nimh or a UBEC won't go wobbly on you either. A 1800 or 2000 mah main power lipo will last along time supplying power to the radio. I've had flights just a tick over 2 hours and didn't hardly put dent in the battery. Commonly I can get 5 launches from a 2000 mah lipo to 200 metres pulling about 600 watts. power consumption will vary with the number and types of servos you use. A two channel 2 analog servo setup is going to use lots less than a full house plane with 6 digitals. Others will have different ideas, there is no right or wrong way, you'll have to come up with a gig that makes you comfortable and works for you.
|Jul 03, 2014, 02:47 PM|
Joined Apr 2012
I've only been flying modern electrics for a bit more than 2 years but, like, Leadchucker, I have had good luck with the built in BECs.
What you are looking for will be called a "switching BEC", "SBEC", or a "UBEC". The simple ones will either be called a regular BEC or linear BEC. Switching BECs, as the name implies, actually feed the power to the receiver in short bursts while the linear BECs are basically just a resistor that dissipate the extra voltage as heat.
Between the different discharge curve and modern electronics you will find that the radio will run for a very long time compared to an old dinosaur with a NiCad. Last year I "landed" my stunt plane in a tree and it took a few days to get the dang thing down. About 8 hours after said landing it dawned on me that I had not tried to loosen it up by running the servos and it still had enough power to move the servos. This was running 4 analog servos with a 2200mah LiPo. We have indeed come a long way. My first radio was a Rand Galloping Ghost and it's 1 pound battery was good for about 30 minutes.
|Jul 03, 2014, 05:22 PM|
I have been using the YEP ESC's from Hobby King. They have 6 amp SBEC's and work great. They even have some larger SBEC's that do 12 amps now but I don't own any of them (yet). A 60 amp 6 amp SBEC is $28 bucks, that's a great deal and they are reliable and easy to program with their card.
|Jul 04, 2014, 03:52 AM|
Most ESCs in production now have low voltage cutoff (LVC) to protect the LiPo against overdischarge. You should not use LVC as a matter of course (timer and monitoring recharge to not exceed 80% battery capacity is better practice), but if an ESC shuts the motor down due low voltage (remember this is voltage under load), varies around 3, to 3.3V per cell, the flight battery will still, have more than enough energy to get you home, plus probably more than an hour.
|Jul 05, 2014, 05:33 AM|
LI, New York, USA
Joined Mar 2003
In simple terms:
ESC = electronics speed control - pulses power to the motor to manage the motor's speed.
BEC = battery elimination circuit - this adjusts the voltage of your motor pack to 5 volts, typically, so you can run your receiver and servos from the same battery that runs the motor which is usually too high a voltage to be used directly on the receiver. There are two different types, linear and switching.
Some built in BEC are only useable up to a stated voltage. For example the ESC in my e-Supra can accept up to a 6S LiPo pack. BUT the BEC must be disabled if I am going to run more than 3S. Then I would have to use an external BEC or a receiver pack.
LVC = Low voltage cut-off. This is a circuit in the ESC that monitors the voltage of the motor pack under load. If that voltage drops below a certain point it will cut power to the motor to preserve power for the receiver and servos. Some pulse the power to the motor which should be easily recognized so you know to get off the throttle.
As lipos became more popular this LVC also served a dual purpose of helping to protect the lipos from being run too low. You can run NiCd or NiMh packs flat without too much harm. Typically you don't want to drain Lipos below 3V per cell and they start to take damage below 2.5V as I understand. The useable capacity left between 3V and 2.5V is not a lot.
You can read more about this and a lot of other topics in this free on-line book.
EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
How much current you need to drive your servos naturally depends on the servos and how you fly. The faster you fly and the higher the surface deflection the more current the servos will pull.
For example, I believe the BEC built into the ESC of the Radian Pro is 1 amp. That drives 6 micro servos and seems to work just fine. However this is a thermal glider, not a high speed fighter plane, so the servos will typically be under light load most of the time.
My e-Supra has 6 strong digital servos. I would want at least a 6 amp BEC to feed those servos under extreme conditions, say a high speed diver followed by a pull out. Not my typical maneuver with this glider but it could happen. The BEC built into my ESC is 5 amps. Probably enough, but I am running an external 10 amp BEC just to be sure. This is an expensive aircraft and I don't want to lose it because I overloaded the BEC.
Most electric pilots use the BEC built into the ESC. And if the BEC built into the ESC is large enough then I see no problem with this at all. They have been getting larger over time.
Some prefer a separate BEC and some prefer a receiver pack. Up to you how you do it.
BTW, my pure Supra, for winch launching, has a 1500 mah receiver pack. I find I use between 300 and 400 ma per hour of flying, including several winch launches. So I would expect that pack to be good for about 2.5 hours of flying with a safe reserve. That is usually enough for me to use the glider for a 5 hour flying day as I don't have it in the air all the time.
Going back to my e-Supra, which is set up for ALES contests, I usually use a 1300 mah motor pack in this one. My motor pulls about 45 amps at full throttle, which is the only way I run it as I have it on a switch. It also has a separate 10 amp BEC that runs off the same battery. I find a 30 second launch and a 10 contest flight drains about 30% of the capacity of that pack or about 400 mah. Naturally most of that is being consumed by the launch. I would not hesitate to launch and make a 90 minute flight off that pack because the servos and receiver are not drawing near what the motor draws. And a 2 hour flight might be OK.
Naturally your mileage will vary.
|Jul 05, 2014, 09:02 AM|
Joined Oct 2005
for high performance systems, I use a separate 10 amp BEC and disable the ESC BEC by removing the red wire from the lead that plugs into the receiver...if you do this, make sure that you program the ESC before removing the red wire, as programming will not be possible while the red wire is removed.
For moderate power systems, I use the internal BEC in the ESC.
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