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Motors and Batteries

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Old 03-24-2010, 05:41 PM
  #1
79Trapper65
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Default Motors and Batteries

I am thinking about adding a ducted fan to a two meter glider I am building. I plan to use aFataba six channel radio and will have rudder, elevator, flaps and throttle control. I have aquired a ProTek RC11.1volt 3300 mah lithium polymer batterypack, I also have a 8.4v 2100 mah nicad pack which is of course heavier. I am confusedabout a number of technical issues, and could use someadvice.
1. ShouldI use a brushed or brushless motor.
2. I have an ESC which came with abrushed motor but it motor is to heavyfor myglider.The ESC hastwoheavy wires going in and out of thecard, a on/off switch and aservo connector. My question is the Lipo pack has two connectors one has two light wires and the other has four wires (three black and one red)
A. what is the four wire connector used for?
B. can I use the Lipo battery pack even though the wires are so small?
3. Will the ESC ( Spectra model GPMA2345) work with the lipo pack?
4. I wish to power the receiver, servos, ESC, and motor from the same battery pack, can this be done?
I suppose these are some dumb questions but I am just getting into this electric stuff and could use some help.
Regards
Dan
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Old 03-24-2010, 06:50 PM
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Default RE: Motors and Batteries

There are no dumb questions, 79Trapper65.

1. A brushless motor will allow you to use a lighter, more powerful flight system. You will likely get longer flight times with a brushless system due to increased efficiency as well.
2. ESCs are either brushed (2 wires to motor) or brushless (3 wires to motor). You can't use brushed and brushless together.
2A. The two wire connection from the battery is the main output wiring that goes to the ESC. The smaller 4 wires are connecting to a balancing jack for safely charging the battery.
2B. You should be able to use the LiPo battery once you match the 2 wires to the connector type on whichever ESC you choose.
3. You can use the ESC with the LiPo pack, assuming you pick out a brushed ducted fan/motor setup
4. Yes, you can power the ESC, receiver, servos, and motor all from one battery assuming there is a battery elimination circuit (BEC) on the speed controller and you're only running 3 or 4 servos max.

Feel free to post any follow up questions.
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Old 03-24-2010, 07:40 PM
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Default RE: Motors and Batteries



Thanks for your reply
I did a search on the internet for the Spectra part number and found some tech notes on the Tower hobby site which did not say anything about a BEC connection and I can not see any other connection on the ESC. So I guess I have to go shopping again. I saw a couple of ducted fans on ebay which look like they will work with this ESC they are brushed motors. I plan to use the motor to launch the glider and intermittantly during flight so I hope to extend the battery life. This is sort of my first experiment with electric power and so far it has been a learning experience.
Thanks again.
Regards
Dan

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Old 03-24-2010, 07:50 PM
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Default RE: Motors and Batteries

Almost all electronic speed controllers (ESCs) under 60 amps or so have a built-in battery elimination circuit (BEC). A battery elimination circuit cuts power to the engine while continuing to send power to the receiver and servos in order to allow the pilot to land safely once the flight battery gets low. On electric power setups of significant weight (5lbs. or more) or complexity (5 or more servos), a separate receiver battery is used so adequate current can feed the receiver and servos without overloading the built-in ESC on the speed controller. External BECs can be used for greater current delivery, but a separate receiver battery is considered for safety so control can be maintained in case of ESC failure during flight.

That's more than you probably needed to know, but talking about BECs may clarify a few things for you.
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Old 03-24-2010, 11:19 PM
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Default RE: Motors and Batteries

No this is good information. Soare yousaying that a BEC is part of the circuit of the ESC?
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Old 03-25-2010, 02:03 AM
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Default RE: Motors and Batteries

http://www3.towerhobbies.com/cgi-bin...2345&search=Go
is the page for that ESC it has a BEC but it tells you to use only a 8.4 volt battery. Why not use the motor and prop that came with it? a ducted fan will not be efficent with the stock ESC and required battery as the stock motor and prop.
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Old 03-25-2010, 07:19 AM
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Default RE: Motors and Batteries

You are correct it does say it has a BEC and the high voltage of the 11.1volt Lipo pack is to much. So I guess if I am going to do this Ihave to use the Nicads. I dont want to use the motor which came with it because is extreamly heavy and the design of the glider restricts the lenght of the prop I can use, unless the pylon gets very high above the fuselage. I wanted to use a ducted fan because I can blend it into the contour of the fuselage, if I can find one 50 mm in diameter or smaller. Which still has the thrust I need.Do you have a schematic or wiring diagram which showsthepower connections? I do thank you and anyone elseforyour help.
Regards
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Old 03-25-2010, 10:54 AM
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Default RE: Motors and Batteries

Not necessarily. If I understand your question correctly, two cell LiPo packs are commonplace and can be used on a system with a BEC. Just check the ESC/BEC to see what the voltage range is. If it includes the 7.4 volt 2 cell pack, then you're all set. Just about any brushless motor will operate at 7.4 volts, check the KV rating.. that's RPM per Volt rating.. and see the difference between operating with a 7.4 or 11.1 pack.

This is an example of a typical 10 amp (15 amp surge) ESC with BEC. Note the info that says 2 - 4 cell LiPo packs..

http://www3.towerhobbies.com/cgi-bin...?&I=LXGVR9&P=7

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Old 03-25-2010, 11:48 AM
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Default RE: Motors and Batteries

To add to the good already posted information....

On board analog BECs tend to be present on ESC that are designed to be used with 11.1v LiPo packs and BELOW.

When using 11.1v LiPo packs, the on board analog BECs can barely drive 3 servos let alone more.

Above that voltage, "Opto" ESC ( no BEC ) or ESC's with SWITCHING MODE Becs are used.

Manufacturers charge a premium for on board switching mode BECs and at higher voltages and amperage ratings it is much cheaper to simply wire in your own external Bec.

-

Brushed motors are not well suited to ( particularly larger diameter ) EDF's because of the required high RPM's the impeller must be spun at along with the high power demands.

-

As you increase the voltage using the same ESC you must be sure that you DECREASE the amperage draw accordingly.

So if you have an ESC rated for 40A and the manufacturer specifies 3S-4S LiPo's assume that the 40A rating applies ONLY when 3S LiPo's are used.... e.g. worst case!

Using a 4S pack, assume that you should push no more than say 32A through the same ESC.



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Old 03-25-2010, 12:48 PM
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Default RE: Motors and Batteries

Get a thunder Tiger .07 engine, and build a pod on the glider for it , put a 1oz tank on it, 1 more servo and be done with it....Rog
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Old 03-25-2010, 01:22 PM
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Default RE: Motors and Batteries

That was the origional plan and I could still do that but I have to deal with the drag of the engine and pylon while flying and I actually wanted to try something different and maybe learn a new trick even if I am an old dog.
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Old 03-25-2010, 01:37 PM
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Default RE: Motors and Batteries

We have a glider pilot in our club from Poland. In fact, he is a national champ over there, immigrated over here on a work visa. Very nice fellow. Anyway, he brings his gorgeous glider to the field all the time. His is powered by a small electric motor with a folding prop (folds back when the motor is shut down).

What's nice about this is he powers it up, flys it high as a powered plane, then shuts the motor down and glides around. When it comes down to low, he simply poweres it back up and climbs back up. He's often up for over an hour.

There's the advantage of electric over glow power. Once your glow runs out of fuel, well, once you get to low, that's it for that flight.

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Old 03-25-2010, 02:35 PM
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Default RE: Motors and Batteries

Well the glow engine generally is to get the glider up,, you dont generally power one down to the ground ,,,and gliders are meant to deadstick in, you try and position the prop so that it is straight up and down in line with the pod for less drag..,,but I guess if you want to go electric,,you would still need a separate battery for the motor, or a really powerful motor/battery/combo.....Rog
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Old 03-26-2010, 05:43 PM
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Default RE: Motors and Batteries

I have another question, if I have two ducted fans which are rated at 29 amps and want to run them from one ESC which is rated at 60 amps can I parallel the output leads of the ESC to accomplish this using the throttle control on my receiver to control the speed of both or do I have to be two ESC rated at 30 amps and a wye cable to connect them to my receiver output.
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Old 03-26-2010, 09:21 PM
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Default RE: Motors and Batteries

If you are REALLY gentle on the throttle it might work, if you jam on the power it will die,,seen that happen in many smaller applications...Rog
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Old 03-27-2010, 04:45 AM
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Default RE: Motors and Batteries


Quote:
ORIGINAL: 79Trapper65

I have another question, if I have two ducted fans which are rated at 29 amps and want to run them from one ESC which is rated at 60 amps can I parallel the output leads of the ESC to accomplish this using the throttle control on my receiver to control the speed of both or do I have to be two ESC rated at 30 amps and a wye cable to connect them to my receiver output.
On a glider???
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Old 03-27-2010, 04:59 AM
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Default RE: Motors and Batteries

Morning CG, Kinda early isn't it. I have a glider with the folding prop and it is really nice. No more broken props when you land.
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Old 03-27-2010, 05:42 AM
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Default RE: Motors and Batteries

G'Mornin, Irish.

Yeah, I woke up about 6 and just got up. We are going to breakfast at our favorite restaurant this morning about 9 AM.

The folding prop works great. But, unless I missed something, the suggestion is for, what.. 60 amp ESC and a pair 29 amp ducted fans? On a glider? The battery pack itself, well, this would go quickly from a glider to a flying brick, ya know?

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