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Old Feb 02, 2006, 09:00 AM
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USA, CA, Red Bluff
Joined Jun 2000
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Esc and separate battery for rcvr/servo

I am setting up my Chrysalis 2m for e-power and read I should use a separate battery for the rcvr and servos in addition to the motor power battery/ESC. I would like to use a Himax 2015-4100 with 6:1 gears, TP1320 lipo, and CC ESC.
How do I connect these components? On my other e-powered planes I plug the small plug from the ESC to the rcvr throttle channel, the power connectors to the lipo aand motor and everything works. The BEC cuts power to the motor while there is still enough voltage to run the servos. If I have a separate battery for the servos, do I plug it into any other slot on the rcvr and everything will be ok?
I don't understand how the ESC powers the servos but guess it taps off the appropriate voltage from the motor power battery , cuts power to the motor when the lipo battery voltage drops below a selected value, continuing to provide power to the servos. How does it work when the plane has a separate battery for the servos?
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Old Feb 02, 2006, 09:27 AM
Turn down for what?
rdwoebke's Avatar
United States, IN, Indianapolis
Joined Feb 2004
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Quote:
Originally Posted by Jack Hyde
How do I connect these components? On my other e-powered planes I plug the small plug from the ESC to the rcvr throttle channel, the power connectors to the lipo aand motor and everything works. The BEC cuts power to the motor while there is still enough voltage to run the servos. If I have a separate battery for the servos, do I plug it into any other slot on the rcvr and everything will be ok?
Yes, but that is just half the answer. If you were flying a regular glider (no motor), you could plug your 4 cell battery pack into any slot on the RX. So you can do that on your Crysalis with your setup.

In the case of your electric setup, you *also* need to remove the positive (+) wire from the ESC servo plug connection. You can snip this, or, if you are careful you could pop the little plastic holder and pull out the little connector and then wrap it in electrical tape to isolate it so that you could switch back at a later time.

Quote:
Originally Posted by Jack Hyde



I don't understand how the ESC powers the servos but guess it taps off the appropriate voltage from the motor power battery , cuts power to the motor when the lipo battery voltage drops below a selected value, continuing to provide power to the servos. How does it work when the plane has a separate battery for the servos?
That is in a nutshel how the ESC powers the servos.

In a plane with a seperate battery for the servos the battery powers them and then the ESC has no power effect to the servos or receiver.

Why don't you give us a bit more details on your Crys. What is motor, ESC, battery, type and number of servos?

Ryan
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Old Feb 02, 2006, 01:07 PM
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I have Himax 2015-4100 with 6:1 gears. It draws about 15 amps and produces 25 ozs thrust with a 12x6 prop. Battery is TP1320 3s . Esc is a CC that is good for 30 amps if I remember right. I have 3 of these mtor gearbox sets, 4 batteries and 2 controllers on hand and have used this combo for more than a year on 3d foamies with no problems. The plane has 2 Hitec 80s in it - 3 if I hook up the spoiler. I am an experienced sailplane guy but haven't done the e-powered sailplane thing since lipo and brushless became pretty common.
I am not thrilled with cutting wires etc on my ESC. What if I just fly with the lipo pack and forget the 4cell nimh battery to run the servos? I would have to not fly long enough to run down the pack to the point of losing power to the servos.
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Old Feb 02, 2006, 01:35 PM
Turn down for what?
rdwoebke's Avatar
United States, IN, Indianapolis
Joined Feb 2004
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Quote:
Originally Posted by Jack Hyde
I have Himax 2015-4100 with 6:1 gears. It draws about 15 amps and produces 25 ozs thrust with a 12x6 prop. Battery is TP1320 3s . Esc is a CC that is good for 30 amps if I remember right. I have 3 of these mtor gearbox sets, 4 batteries and 2 controllers on hand and have used this combo for more than a year on 3d foamies with no problems. The plane has 2 Hitec 80s in it - 3 if I hook up the spoiler. I am an experienced sailplane guy but haven't done the e-powered sailplane thing since lipo and brushless became pretty common.
I am not thrilled with cutting wires etc on my ESC. What if I just fly with the lipo pack and forget the 4cell nimh battery to run the servos? I would have to not fly long enough to run down the pack to the point of losing power to the servos.
I don't have that setup. So take this with a grain of salt.

I use the BEC from the ESC to operate the rx and servos on 3 channel gliders or less. Anything more and I use a seperate battery. OR, if for whatever reason I feel the setup pulls enough current that it would heat up the ESC.

I don't think you have to worry about the lipo pack running down. Really, in my experience you have a pretty good idea anyway the battery is getting low when the last climb is pretty weak. That, and with lipos you don't want to run them low anyways to risk damaging them, so you tend to be even more careful.

The worry is that somehow the circuit that drops the voltage down from 10 volts to 5 volts will get overheated and crap out on you.

I think you should be OK on the 2 servos (or possibly even 3) and using the BEC. Especially if you have experience running those servos in a "power plane" with this same ESC/battery/motor (probably not same prop). I have 3 servos in my Allegro Lite and run it off the Jeti brushed ESC's BEC. Of course, I have never ran a 3S setup, so that makes it a bit worse (a bigger voltage to have to drop).

Ryan
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Old Feb 02, 2006, 03:04 PM
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I will make some short flights using the BEC and check betwenn flights to see if I can detect anything going south. Thanks for the info.
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Old Feb 02, 2006, 04:19 PM
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AndreyT's Avatar
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You can also go the UBEC way, i.e use a standalone powerful BEC instead of the weak one built into the ESC. In this case you'll also have to remove a wire from the ESC-to-receiver cable.
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Old Feb 02, 2006, 06:27 PM
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Vienna, VA, USA
Joined Dec 2005
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With that setup I don't think you need a separate RX pack. If you set the low voltage cutoff right on the ESC, you should have plenty of battery left to circle down and land, even if you run it right to cutoff. Generally, people seem to use separate RX packs either when they are using several servos (>4 or 5), or they are drawing extreme currents (and are seriously worried about frying the ESC ).
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Old Feb 02, 2006, 09:14 PM
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Wilkes-Barre/Scranton, Pennsylvania, United States
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Jack
Unless you are planning multi hour flights a second battery would just be extra weight. I have had several flights that have approached an hour and more using a standard BEC system using NiCd and NiMh batteries. You should have even more duration using LiPo. Just be certain you use low drain servos. Some draw more current than others. With three servos you should have no trouble with the system you describe.

BM
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Old Feb 02, 2006, 09:31 PM
Deletedfor proving Nauga wrong
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Rather than modifying the ESC by clipping the red wire... I clipped the red wire in a 4 inch servo extension. does the same thing... but leaves the ESC's BEC available in other installations without having to solder.

You could also modify my short extension idea, by putting a switch in the red lead. Then its useful as a power switch between a battery and RX ( when the ESC no longer needs the BEC disabled... not a great idea to turn off BEC power if the ESC normally powers the RX)

***********

Depending on the application... sometimes a separate RX battery is a good idea. Most BEC's get limited in how many servos you can drive as you increase the voltage of the motor battery pack. All ESC's have a max number of cells (maximum voltage) you can use and still use the BEC.

Do what is best for your model and the way you operate it.

Note that if you go with a separate RX battery, the low voltage cut-off of the motor will NOT be a valid indication of remaining RX power.... you can still have motor power and no RX power. (though the motor should die when the RX quits sending a valid output to the ESC, so it should crash with the motor off)
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Old Feb 03, 2006, 12:27 PM
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We've had some discussions on other threads about why you should use a separate battery for the radio on an electric sailplane. In a nutshell, when you start feeding the motor and the radio from the same battery, it becomes very difficult to predict how long it is safe to fly, before the battery runs out of power. Since the motor can generally drain the battery in only a few minutes, even 30 seconds of extra motor run equates to a big reduction in safe flight time.

You can try to keep track of it, and run both on the same battery. It may work. However, a number of planes have been crashed by this setup.

As far as how to change the wiring, it's fairly easy, and does not require cutting any wires.

If you could look at the underside of the pc board for your receiver, you'd see that all of the "+" leads for the servo connectors arre connected in one long strip, and all of the "-" leads are also connected to a strip of their own. Any voltage source plugged in anywhere on both of those two strips can supply voltage to the whole radio.

The BEC is a circuit in the speed controller that steps down the voltage from the battery to the 4.8 volts that the radio needs. It then applies this to the two power leads (the red "+" and the black "-" leads) that run back to the receiver. Power goes through these leads, through the connector on the receiver and into the positive and negative strips (or "busses") on the receiver pc board, and from there into the receiver and any servos that need power.

To disconnect the BEC from the receiver, leave the black wire connected, and disconnect JUST the red wire (typically the one in the middle, with the only exception being the older Airtronics radios).

Don't clip the red wire. Instead, use the tip of a #11 X-acto or a small jeweler's screwdriver to lift up the tiny plastic tab in the connector body that holds the red wire's brass connector fitting in the connector body. With that plastic retainer tab lifted, you can now gently pull the red wire and connector sleeve out of the connector body. Note, to do this, you may need to peel the three wires in the lead apart from each other for an inch or two back from the connector.

Fold the red wire back on itself so the brass socket is pointed away from the connector, then tape over it with electrical tape. If at some time in the future you need to use the BEC function on another plane, just remove the tape, remove any gummy residue from the wire, and slip the brass socket back into the connector till the plastic retainer tab snaps into place on the brass socket.

It obviously takes longer to describe than it takes to do it.

To power the radio from a separate battery, just plug the battery directly into any unused socket in the receiver. If you don't have any unused sockets, use a "Y" connector to couple both the radio battery and one of the servos to the same receiver socket.

A switch in the battery cable is optional. Generally I avoid switches where possible, it's more weight and complexity, and one more failure point. The failure rate on switches is not very good. However, if you plug the battery directly into the receiver, occasionally inspect the pins in the receiver where they solder into the pc board. I know of one case where someone plugged a battery directly into the receiver, and somehow managed to flex those solder joints enough with all the plugging and unplugging that the solder joints eventually failed.

Because you left the black wire from the speed controller connected, the radio and the motor battery will share a common "-" ground, so their voltages won't be floating around relative to each other, causing problems. However, only the radio battery has both its red and its black wires connected to the receiver, so that's the battery which the radio will use for its power.

On my Chrysalis, I use a 270 mah 4-cell NiMH square pack to power the radio. It only adds about 1.8 ounces, not enough to make any measurable difference in flying characteristics or performance.
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Old Feb 03, 2006, 12:57 PM
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I prefer to modify a 6" servo extension to clip the red wire.. the original cable from the ESC is then unmodified.
I've had poor results when plugging a removed pin back into one of those connectors, when the need arises to use the ESC normally.
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Old Feb 03, 2006, 01:23 PM
Deletedfor proving Nauga wrong
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Besides... the BEC section of the ESC is often the part that gets hot first. Less heat generated by not having the BEC active means less cooling needed for the ESC. Cooler ESC's "live longer."

And you are adding more on board energy to the aircraft with a second battery. While its probably a marginal increase in motor run time... its an increase.

there are arguments in favor of the single battery to power everything... and arguments against it. What it comes down to is flying style and personal preference. (if you aren't forced to the second battery by RX+servo current requirements or main battery voltage)
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Old Feb 03, 2006, 02:50 PM
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Quote:
Originally Posted by fhhuber506771
...What it comes down to is flying style and personal preference. (if you aren't forced to the second battery by RX+servo current requirements or main battery voltage)
That raises a good point.

The other issues that can mandate a separate radio battery are too many servos, and/or too much voltage in the motor battery.

The typical power supply in the BEC is a loss-type, not a switching type like in a computer power suply, or even the switching regulation used for controlling the current to the propulsion motor.

That means that the BEC steps the battery voltage down to the radio's required voltage by basically throwing away all the energy represented by any voltage above the radio's required 4.8 volts. That discarded energy shows up as extra heat in the speed controller, particularly the BEC portion of its circuits.

Volts times amps is watts, so if you have too many servos, their collective amps can get too high. This means that the volts in excess of 4.8, times that number of amps, results in too much heat, and the BEC cooks itself. This of course kills power to the radio, which will then generally finish off everything else.

For example, if you had a 2-cell Li-poly motor battery, and enough servos to collectively draw 6 amps, then the power discarded by the BEC is 6 amps x (8.2 volts - 4.8 volts), or 20.4 watts, all concentrated in a tiny segment of the speed controller's pc board.

Likewise, if you have too many cells, then the voltage gets too high. For example, if you had a 3 cell motor battery, but not as many servos (so the radio's peak current draw was only 3 amps), then 3 amps times (12.3-4.8) is 22.5 watts. That's about the same power as three night-light bulbs, all concentrated into a spot about the size of the nail of your little finger.

Look at the bright side: if you bring some eggs to the flying field, you might be able to use your BEC to cook your lunch!
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Old Feb 03, 2006, 08:07 PM
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When I get more than 3 servos working... my latest AP plane has 5, I always go to the seperate battery for the radio stuff.
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