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BEC question

Old 04-22-2011, 07:56 AM
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jap71173
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Default BEC question

Why is this statement true:

BEC: 2 amp (2 cell Lipo = 4 to 5 sub micro servos, 3 cell Lipo = 3 to 4 sub micro servos)

I would think it be the other way around where a 3 cell could handle more load distribution to the servos. What am i missing here?
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Old 04-22-2011, 08:21 AM
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CHELLIE
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Originally Posted by jap71173 View Post
Why is this statement true:

BEC: 2 amp (2 cell Lipo = 4 to 5 sub micro servos, 3 cell Lipo = 3 to 4 sub micro servos)

I would think it be the other way around where a 3 cell could handle more load distribution to the servos. What am i missing here?
AMPS, low voltage less resistance more amps, higher voltage more resistance less amps, its the amps that does the Heavy work. thats why using a switching UBEC is better. most esc/bec are Linear, they use a resistor, and are weak, and not a true Amp rating, switching becs are much better, as they use electronics to govenor the amps and volts better. some ESC have switching Becs, but they have to contend with the heat the ESC generates, thats why its better to have a seperate UBEC, Hope that helps, Chellie

Last edited by CHELLIE; 04-22-2011 at 08:44 AM.
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Old 04-22-2011, 09:10 AM
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Originally Posted by CHELLIE View Post
AMPS, low voltage less resistance more amps, higher voltage more resistance less amps, its the amps that does the Heavy work. thats why using a switching UBEC is better. most esc/bec are Linear, they use a resistor, and are weak, and not a true Amp rating, switching becs are much better, as they use electronics to govenor the amps and volts better. some ESC have switching Becs, but they have to contend with the heat the ESC generates, thats why its better to have a seperate UBEC, Hope that helps, Chellie

Ahhh, so this would explain why I got better aileron response on the last plane i built (Furious 3D) whenever I used the 2S vs. 3S battery. I thought it was doing better because there was less air being pushed over the wing surface with the 2S but i guess that had nothing to do with it?

BTW Chellie, i just replaced that monster ST .10 motor and 35A ESC with this setup from Head's Up RC: 2408-21-B Brushless Motor & 18 Amp ESC
Do you think it's ok to use a Orange 10x4.7SF prop with a 2S 1350mAh 20C batt on this setup?
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Old 04-22-2011, 09:24 AM
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Hi If Jeff at Heads up Rc says you can, then you Can use that prop with a 2 cell lipo, your 2 cell 1350mah lipo will be fine to use

http://www.headsuprc.com/servlet/the...tor-%26/Detail

The very popular 2408-21-Ais a 1.6 oz, 1400KV, 400 class direct drive outrunner brushless motor designed for medium to high speed park flyers. This version comes with a Firewall Mount and a Plastic Stick Mount.




Propeller test data using a 3 cell Lipo battery:
Rotating propellers are dangerous. Please stay clear of prop and wear eye protection.
GWS and TP props fit the 3mm shaft on this motor perfectly - no adapter is needed. APC and Master Airscrew props require a prop adapter or prop saver for a 3mm shaft.
The GWS EP8040 is the most commonly used prop with this motor. It will produce about 22 ounces of thrust at 14 amps with a pitch speed of 43 mph.
We do not recommend using any other 8 inch props with this motor when using a 3-cell Lipo battery.
The TP 7x6E produces 20 ounces of thrust at 14.5 amps with a pitch speed of 60 mph. Good choice for high speed on flying wings and profile jets.
The APC 7x5E produces 20 ounces of thrust at 14 amps with a pitch speed of 54 mph.
The GWS EP7035 produces 16 ounces of thrust at 9 ampswith a pitch speed of 47 mph.
The APC 6x5.5E produces 11 ounces of thrust at 10 ampswith a pitch speed of 65 mph.
The Master Airscrew 7x4 3-blade produces 15 ounces of thrust at 12.5 ampswith a pitch speed of 43 mph.
The Master Airscrew 6x4 3-blade produces 11 ounces of thrust at 9.5 ampswith a pitch speed of 48 mph.
Propeller test data using a 2 cell Lipo battery:
The GWS EP1060 prop produces about 15 ounces of thrust at 11.5 amps with a pitch speed of 33 mph.
The GWS EP1047 prop produces about 15 ounces of thrust at 12.5 amps with a pitch speed of 24 mph. **********
The APC 9x3.8SF prop produces about 16 ounces of thrust at 11.5 amps with a pitch speed of 24 mph.
The GWS EP9047 prop produces about 14 ounces of thrust at 10.5 amps with a pitch speed of 27 mph.
The GWS EP9050 prop produces about 14 ounces of thrust at 10 amps with a pitch speed of 32 mph.
The GWS EP9070 prop produces about 13 ounces of thrust at 12.5 amps with a pitch speed of 35 mph.
The GWS EP8040 prop produces about 12 ounces of thrust at 7.5 amps with a pitch speed of 32 mph.
The GWS EP8043 prop produces about 12.5 ounces of thrust at 8 amps with a pitch speed of 31 mph.
The GWS EP8060 prop produces about 13 ounces of thrust at 10 amps with a pitch speed of 39 mph.
The GWS HD8060 prop produces about 12 ounces of thrust at 9 amps with a pitch speed of 41 mph.

Last edited by CHELLIE; 04-22-2011 at 09:39 AM.
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Old 04-22-2011, 09:33 AM
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I love that Little 2408-21 motor its a Power house it has 2 little issues with it, and here is how you correct it, the radial or stick mount need to be epoxied to the motor, or the motor will turn in the mount and twist and break the motor wires over time, by using 5 min epoxy that will prevent that, dont get any epoxy on the rear bearing, also, the wires that come out of the motor will vibrate and break over time, here is the cure for that too cover the magnets with some masking tape on the bell on the wire side, so no epoxy gets into the magnets, add some 5 min epoxy to the wires that come out of the motor and epoxy them to the windings and motor mount to secure them better, thats all there is to it, now you have a Bullet proof bell motor, well almost on 3 cells with a 7x6 SF prop, that 2408-21 motor really comes alive, Take care and have fun, Chellie


Remove the radial mount 2 screws, clean the mount and motor with rubbing alcohol, add the epoxy to the motor, slip on the mount and replace the 2 screws, or slip on the stick mount and tighten.
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Old 04-22-2011, 09:20 PM
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I'm also putting together a Multiplex Funjet... i'm learning to test out the electronics before installing them. I just pluged everything together an ran a 1/2 throttle test for 30 sec with no prop and my motor is getting hot... the esc and batt are cool, any ideas why?

This is what i'm using:
Motor: PKZ4216 1880Kv (it's the F27C Stryker stock motor)
ESC: 35 AMP
Battery: 3S 1000mAh 30C (same result on a 3300mAh 3S 20C)

P.S. When i add the prop, both the motor and the ESC are getting hot???

Last edited by jap71173; 04-22-2011 at 09:36 PM.
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Old 04-23-2011, 02:42 AM
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Originally Posted by jap71173 View Post
I'm also putting together a Multiplex Funjet... i'm learning to test out the electronics before installing them. I just pluged everything together an ran a 1/2 throttle test for 30 sec with no prop and my motor is getting hot... the esc and batt are cool, any ideas why?

This is what i'm using:
Motor: PKZ4216 1880Kv (it's the F27C Stryker stock motor)
ESC: 35 AMP
Battery: 3S 1000mAh 30C (same result on a 3300mAh 3S 20C)

P.S. When i add the prop, both the motor and the ESC are getting hot???
you need the cooling air of the prop to help keep the motor cool, also all motors will get hot on the test bench, dont run them for very long. they need that cool crisp air Take care, Chellie
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Old 06-01-2011, 10:25 AM
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Found this esc in my pile of junk and want to use it for a lightweight 3d foamy...

Can someone please tell me what the extra 2 wires are for that are on the motor side of the esc??? Is this just a programing plug or is it something to do with the BEC?
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Old 06-01-2011, 11:14 AM
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Originally Posted by jap71173 View Post
Found this esc in my pile of junk and want to use it for a lightweight 3d foamy...

Can someone please tell me what the extra 2 wires are for that are on the motor side of the esc??? Is this just a programing plug or is it something to do with the BEC?
Dang that question came up before and I forgot whats its for, I think its for a arming switch, so the motor does not accidently take off on you, if i remember right I will try to find the post that has those 2 extra wires on the esc, Take care and have fun, Chellie

hook the esc to a receiver, mount the motor, add a lipo, and see if it works, if not the 2 extra wires might have to be connected to each other, i could be a safety item on a plane, are there any markings on the ESC
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Old 06-15-2013, 02:09 PM
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Some ESC's I've had in the past have the two wires (extra)on them, in this case they were power supply they the wires could also be the arming switch as Chellie mentioned.
Maybe put a volt meter to them and see what voltage they are putting out if anything.

Last edited by FlyingBrick50; 06-15-2013 at 02:11 PM. Reason: add
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Old 06-15-2013, 07:06 PM
  #11  
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"AMPS, low voltage less resistance more amps, higher voltage more resistance less amps, its the amps that does the Heavy work. thats why using a switching UBEC is better. most esc/bec are Linear, they use a resistor, and are weak, and not a true Amp rating, switching becs are much better, as they use electronics to govenor the amps and volts better. some ESC have switching Becs, but they have to contend with the heat the ESC generates, thats why its better to have a seperate UBEC, Hope that helps, Chellie"
--------------------------------------------------

Sorry Chellie, it doesn't quite work that way.

The BEC is putting out the same voltage to the servos, with either battery.

Lower or higher voltage, does not control resistance, that is a property of the load.

It is really watts, that do the heavy work. Thats why we use watts to predict motor proformance.

Back to the original question;

Using a 2 cell battery,
you would have an input voltage of about 8 Volts (+/- still the same math)
output to servos should be 4.8 volts
that means the regulator has 3.2 volts across it
if the load is pulling 2 amps,
the regulator is then generating 6.4 watts of heat, which it must dissipate or burn up

Using a 3 cell battery,
input voltage would be about 12 volts
output to servos is still 4.8 volts
the regulator now has 7.2 volts across it
if the load is pulling 2 amps
the regulator is then generating 14.4 watts of heat, which it must dissipate or burn up

I know it would seen you could drive more of a load with a higher voltage battery, but the problem is the extra amount of heat that a linear type BEC must get rid of.

In this example, the 14.4 watts with a 3s, is 2.25 times the 6.2 watts the 2s battery would cause.
The BEC may simply not be able to get rid of the extra heat, that will cause a failure.


Switching BEC's operate much differently inside, and do not create the heat that kills the linear type,
Basically a linear BEC operates like a resistor as Chellie says, it is really a variable resistor controlled by the BEC circuit.

In the simplest terms a switching regulator, is either on or off, this happens at a very high rate. When on it is a very good switch, with very little resistance causing heat, when off, there is no current therefore no heat. The circuitry sort of fills a capacitor to the correct voltage, then shuts off. It constantly checks the voltage output level and keeps refilling the cap as the load draws it down. This happens so fast that we see a constant voltage out, regardless of load ( within the ability of the BEC )

I know my description of a switching BEC is very basic and not exactly correct, but it is close enough for our use.
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Old 12-10-2013, 05:44 PM
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Watt is a measure of power consumption and relates directly to heat generated in the device. Amp is a measure of current. 1 Watt = 1 Volt x 1 Amp so it is the amp which does the heavy work while the watt is a measurement of the work. E=IR and P=IE From the physics text, etc. The volt is a measurement of the force pushing the amp, etc. The internets is also a fun term coined by ole Dubba.
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Old 12-10-2013, 08:11 PM
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Originally Posted by jap71173 View Post
Found this esc in my pile of junk and want to use it for a lightweight 3d foamy...

Can someone please tell me what the extra 2 wires are for that are on the motor side of the esc??? Is this just a programing plug or is it something to do with the BEC?

First of all - insulate those deans plug connections !!

The extra plug only has red and black leads - no signal wire ... and it's a plug - not a socket ... mmmmm
It cannot be for high power load as the leads are too thin. So it must be an arming or low power take of ..

I'd connect up to a lipo with servo tester and see what happens ... if no joy then I'd jump the leads on that extra and see what happens then ...

A standard radio switch could be the answer plugged onto it ... to disarm the ESC ............... but needs testing with a meter and run her up to see.

Nigel (call me Mr. Holmes !)
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Old 12-10-2013, 08:22 PM
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Nigel - this is one of those "old" threads brought back to life. That user has not posted for over 1.5 years. The old thread from the dead.

Mike
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Old 12-10-2013, 08:25 PM
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Originally Posted by rcers View Post
Nigel - this is one of those "old" threads brought back to life. That user has not posted for over 1.5 years. The old thread from the dead.

Mike
I'm bored and just saw post above mine ... and latched on !!

I've got to go have a rest !! We have Gale force winds out here - we've already busted our fenders - have 74,000 tons of cargo sitting waiting to transfer .... another ship on route ...

Should have checked dates !!

Cheers
Nigel
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Old 12-10-2013, 08:26 PM
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Originally Posted by edray999 View Post
Watt is a measure of power consumption and relates directly to heat generated in the device. Amp is a measure of current. 1 Watt = 1 Volt x 1 Amp so it is the amp which does the heavy work while the watt is a measurement of the work. E=IR and P=IE From the physics text, etc. The volt is a measurement of the force pushing the amp, etc. The internets is also a fun term coined by ole Dubba.
Sorry but you cant realistically say that amps 'do the work'. If it's true that amps 'do the work' then how much work could the system do with no volts (i.e. replace the battery with a wire)?

Previous comment was 100% correct, Watts is the measure of work rate and Watts is Volts x Amps. You need both volts AND amps (ie Watts) in order for any work to be done because without the volts there will be no amps.
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Old 12-10-2013, 08:35 PM
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Originally Posted by solentlife View Post
I'm bored and just saw post above mine ... and latched on !!
Yep it's your bedtime....



Originally Posted by solentlife View Post
We have Gale force winds out here - we've already busted our fenders - have 74,000 tons of cargo sitting waiting to transfer .... another ship on route ...

Cheers
Nigel
We have had 4 days of ice here in north Texas. Rare for us but when it hits - it is a HUGE mess as they essentially just let the weather solve the issue.

Mike
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Old 12-11-2013, 04:44 AM
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Originally Posted by rcers View Post
Nigel - this is one of those "old" threads brought back to life. That user has not posted for over 1.5 years. The old thread from the dead.

Mike
For new members, the first spot you land on is the original (old) thread and since there's a lot to this forum one does not automatically pan to the bottom. Well I didn't.

Maybe the web design could be set to jump to the bottom/latest comment of a chosen thread. I would like to suggest this to the boss.

ER
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Old 12-11-2013, 11:41 AM
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Originally Posted by JetPlaneFlyer View Post
Sorry but you cant realistically say that amps 'do the work'. If it's true that amps 'do the work' then how much work could the system do with no volts (i.e. replace the battery with a wire)?

Previous comment was 100% correct, Watts is the measure of work rate and Watts is Volts x Amps. You need both volts AND amps (ie Watts) in order for any work to be done because without the volts there will be no amps.
When I was at College and doing Electrical theory AC and DC etc. .... it was put to class as :

Imagine a water pipe with running water.

Volts is the volume at any one instant of water in the pipe.

Amps is the flow rate of the water.

Watts is the total volume x flow rate equating to the work capability.

A very rough way of describing it but fits especially when you consider the old saying :

Mills Kills
Volts Jolts

Nigel
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Old 12-11-2013, 06:21 PM
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Hate to disagree with someone with an English accent , but in your water example I thought voltage is supposed to be the water pressure. And amp hours is how much water.
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Old 12-11-2013, 07:40 PM
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+1 to Xmec2k, voltage is analogous to water pressure (how high above the outlet) regardless of the volume.
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Old 12-11-2013, 08:08 PM
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Originally Posted by xmech2k View Post
Hate to disagree with someone with an English accent , but in your water example I thought voltage is supposed to be the water pressure. And amp hours is how much water.
You could be right - was 40 odd years ago I did all that crap !!

I hate to agree with someone who cannot speaky de Queens English !!

Nigel
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