Glow to Electric Conversions Discuss glow/gas conversion to electric here.

need some confidence(help)

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Old 08-09-2004, 07:31 PM
  #1  
clay pigeon
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Default need some confidence(help)

ok here is the set-up;
-.40 trainer, high wing, high elevator(mounted at top of rutter, instead of bottom), 5lbs plane and all the "e-stuff"
-"TP" 3s2p 11.1v 4200mah lipo
-AXI 2820/10
-jeti advance 40-3p esc
-figure on using either the 11x7 apc e-prop or 12x6 apc e-prop

---i have everything placed roughly were i want it and cg is looking good.
---my first question is do i need to worry about direction/angle of the placement of the motor?
-angle up/down/left/right measured/compared to what?
----my second question is what about the "BEC"?
-do i continue to use the rx batts or completely remove them?
-i did not get a "BEC". i think this esc has one built in, or does it not have one, and i need to purchase the "UBEC"?
-or do i just wire the lipo's to the esc, esc to the motor, and by plugging the esc to the speed "port" of the "rx" this gives the rx power.

thanks for the help, it is difficult to find any help at the LHS in/around Knoxville, tenn. they all are still scared to even carry lipo's(they fear the whole town will burn down from one faulty lipo) and none carry the brushless and esc's for them. so info is hard to find. so i drove to nashville just to talk to the guys at hobby-lobby in person to get this e-quipment.
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Old 08-09-2004, 08:10 PM
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jonnyjetprop
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Default RE: need some confidence(help)

You're on the right track. Here's some answers.

1. Placement of the motor. Put the motor at the same downthrust/right thrust as the glow engine. You will find this in the directions.

2. To "bec" or to not, that is the question. Let's start off simple. "bec" stands for battery elimator circut. If your speed control has it, (and you want to use it), then all you have to do is to wire the speed control to the motor and battery pack and the radio receiver will be powered through the speed controller's lead going to the receiver. But in this world there is no free lunch and so is the case with a bec. You can only use a bec when your cell counts are low. How low? How many servos are you using and what type are they. Check the directions (you knew this part was coming) and you will see a chart or something that will say (example only, your milage may vary) with 8 cells (2s in the dark, explosive, firey world of lipo's) you can run 4 servos. With 10 cells, you can run 3. With 12, only two. Any more and you can't use the darn thing even if it is installed.

If you exceed this limits, then you must disable the bec. Simply cut the red lead going to the receiver and the juice will no long flow. The esc still works great. A better idea is to get a short extension, plug it into the esc and then cut the red lead on the extension. Change your mind and want to restore your bec, just unplug the extension and plug the esc into the receiver.

Another reason to not use the bec is that most "non bec esc" are electrically isolated from the receiver to reduce nose and gliching.

Why use a bec? Weight is the enemy and since you have to carry a big battery to power this model arround, just tap a small amount to run the radio. This is a big deal in a small plane (smaller than yours, bye the way) and not such a big deal in larger planes. (like yours).

Not content, those seeking the absolute lightest setup but who can't use a bec because of the cell count/servo count, can call on a device sometime called a ubec and sometimes its called a sbec. This device is separate from the speed controll but acts just like a bec without the cell count/servo count limits of a bec. It uses an electrical switching simular to the way a speed control works to reduce the voltage down to a low enough value for your receiver to work without blue smoke coming from it. It can cause electrical noise just like a bec though.

Others like me just use a receiver battery like a normal, overly loud glow powered model would.

3. Does my esc have a bec? I don't have a clue. I'm not there. If your esc has a switch, then you have a bec. No switch, no bec.
This doesn't always hold ture as some bec equipt speed controls don't have a switch, but I beleive that Jeti's do.

One more peice of advice. By turning off the bec (the switch thingy), you are still drawing a small amount of current. Lipo's don't like to be discharged below 3 volts per cell. Unplug the battry right after you fly. Don't wait until you get homeand have feed the dog/cat/child/wife or you will destroy the battery. And it only takes once to do it.

Be careful and fly safe.

John
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Old 08-09-2004, 08:45 PM
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jonnyjetprop
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Default Unwanted advise

http://www.modelmotors.cz/index.php?...id_odkazy=m_ac

I know this is not what you asked for, but in the spirit of kindness, happiness, and world peace, here are some additional bits to help your entry into the world of clean, silent flight.

Above is a link to the guys who built your motor. Not the folks how sold it to you (but there nice also) and not from some faceless, wantabe, know it all guy giving you advice on an internet site. I blew my cover already You will notice that in that sea of numbers, there are a couple of pearls. Maximum effency amperage is listed, topping out at 30 amps and then there is a red line of sorts stating that the maximum current is 42 amps for 60 seconds. This means that you can run this motor at 41.9 amps all day long.

NO, IT DOESN"T

There are two types of drivers in this world. The folks who drive 55 in a 45 mph zone and those who drive 45 in the 45 mph zone. Which one are you? Do you feel lucky, punk? ( please think of Clint Eastwood pointing a gun).

IMHO

Sucess in electric flight comes from knowing the limits and not going over them.

Can you just get to the point, you ask.

1. You won't know if you are coming close to a limit unless you have the means to measure it. Get a whatt meter from Astroflight or borrow one from someone that does. (yes, I have one, but you'd have to drive to Florida)

2. I have found great happiness and satisfaction from not testing the limits of my electrical equiptment. Motors, batteries, and speed controls all seems to live long happy lives at my hangar.

3. I check the current draw of all my planes before they leave the ground, because it's too late after that.

4. Close only counts in horseshoes, hand grandes, and nuclear war. If its just slightly over the limit, then fix it.

5. But the package said it was good to 900 amps for 10 sec is not a good enough reason to run it that hard.

6. If you dispute #5, just tell yourself that you won't run it at full throttle for more than 10 sec.

7. Some great pilots can do #6 all day long. I'm just not one of them. Are you?

Have fun. After all, this is a hobby.

John
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Old 08-10-2004, 12:12 PM
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Matt Kirsch
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Default RE: need some confidence(help)

You'll be able to find out about the features of the ESC by reading the instructions, of course. IIRC, the 40-3P does have a BEC that's good to 10 cells. Otherwise, JJP has hit the nail right on the head and beat it solidly into the board underneath

The AXi setup Hobby Lobby sold you is just fine for a 5lb trainer. In fact, it doesn't even need that much power to fly well. You've got plenty of overhead with the LiPoly pack (presumably Kokam 2100 20C cells in a 3S2P config), so that'll handle anything this motor can throw at it. Stick with the smaller 11" prop, though, and you'll be happy. It'll never overload the motor. You could run as large as a 12x8, but that's pushing the motor pretty hard.
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Old 08-11-2004, 08:42 AM
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Default RE: need some confidence(help)

thanks for the quick and detailed responses matt and jonny. i have a couple more though, after your responses.
-matt, actually it is the thunderpower big 3s2p 11.1v 4200mah pack.
-the main reason i went with this batt, motor, esc combo is the lipo batt in this set-up will likely do great in the .60 hanger9 p-51 mustang i have. just add one more pack just like it in parrellel, the 4130 axi, and the jeti 70-3p.

-what does that mean that this bec is good up to 10cells?
-and i cannot grasp what that means to use only 4 servos with 8 cells, 3 servos with 10cells, etc.(actuall numbers may vary in my application). i mean, if i need four servos to fly this plain, what do i do, just decide which servo i can do without? screw that elevator, real pilots dont need that....lol.
--seriously though, how does this apply. the pack i have has 6 lipos in it 3 in series, 2 parrellel. and is there a calculation to this?
--it might come in handy when applying it to my mustang with retracts.

-matt, the instructions to the esc were pretty vaige it seemed to me, or it was too late, and i just read right over that section...lol. the "tp" lipos have a 7c discharge if i remember correctly. as far as "overhead" that is what i was hopeing for on this set-up, "go big or go home".

-jonny, great idea on the extention from the esc to the "rx". i think for this set-up i am going to try and use the esc's bec, wire it to the axi, lipo, and rx, asap or i will be sos at the lff when i am doa.
-as far as me being a driver who goes 55 in a 45. when i made that special trip to nashville(hobby lobby) i got a ticket doin 80 in a 70. so yet again proving it is cheaper to order on-line. being that, going there in person will cost me an extra 200+ dollars, and a day from work, to go to court. so i think you only shot 5 times with one left in the chamber(in reference to that movie)

thanks again for all the help. if it was not for sites like this and people like yall, we would all still be tuning our engines every 10deg change, and wiping our planes down at the end of each flight.
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Old 08-11-2004, 11:05 AM
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Matt Kirsch
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Default RE: need some confidence(help)

Okay, you don't have nearly the overhead I was presuming before. 4200mAh, or 4.2Ah, at 7C is only about 29 Amps. That means you can only draw 29 Amps continuously. Check the motor specs at www.modelmotors.cz to see how many Amps the motor will draw with an 11x6 (or as close as you can get) prop on 10 cells (comparable to 3S LiPoly). If it's more than 29 Amps, you either need to go with a smaller prop, add a third pack in parallel, or limit your full throttle bursts.

For your much larger Mustang plans, you will need to do more than just add two more packs in parallel. VOLTS are the electric equivalent of cubic inches. Your trainer normally uses a .40 engine, while the Mustang needs a .60. You need to increase the voltage, that is add more cells in SERIES, to fly the Mustang. You'll want at least 6S3P using the cells you currently have (electric "cubic inches" don't scale the same as engine cubic inches, which is why you need twice as many Volts).

I'm not sure how I can explain the BEC thing any better, but I'll try: The BEC is a voltage regulator that burns off the excess volts as heat to reduce the main battery voltage from whatever it is to 5 Volts to run the receiver and servos. As the difference between the battery voltage and 5 Volts gets larger and larger, the more heat it has to generate. This is just a tiny chip we're talking about, and it can easily overheat and burn up. The more work the BEC has to do to reduce the voltage, the less capacity it has left over to run the servos. When you hit 10 cells (12 Volts), you've hit the practical limit on the design of these BEC chips. It could regulate from a higher voltage, but it wouldn't have any excess capacity left over to run the servos, so it's useless with more than 10 cells.

You have a 3S2P LiPoly. When we talk about "cells" in general we mean NiCd or NiMh cells with 1.2 Volts per cell. LiPolys have 3.7 Volts per cell, but are equivalent to about 3.5 NiCd or NiMH cells. So, a 2S*P LiPoly is equivalent to a 7-cell NiCd, a 3S*P LiPoly is roughly equivalent to a 10-cell NiCd, and a 4S*P LiPoly is equivalent to a 14-cell NiCd. With your 3S2P LiPoly pack, you need to follow the instructions pertaining to 10 cells. Any limits in the instructions for 10-cell packs must be followed.

If your BEC can only run 3 servos, and you need to run 4, there are a few options:
1. Do it anyway and hope for the best. Not recommended
2. Try to find a speed control with a BEC that can handle more servos.
3. Disable the BEC and use a regular receiver pack like what's used on glow planes.
4. Disable the BEC and use a UBEC. A UBEC, or Ultimate BEC, is a regulator of a different design that can handle practically any number of cells and any number of servos. It's a separate product that costs about $60.
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Old 08-11-2004, 07:03 PM
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Default RE: need some confidence(help)

thanks again matt, that explains it well. i believe i will stick with the rx batteries and cut the red wire leading to the rx from the esc, because i have 11.1 volts.
-- i think the missunderstanding may be my fault. in my previous post, i had said the liposi have are a 7c discharge, but i was incorrect, going by the statement on hobby lobby. it reads;
-Thunder Power "Dynamic Power" 2100 mAh cells can withstand 10C average discharge and up to 15C in short bursts. Because these packs are two 2100 mAh packs wired in parallel, the capacity of the pack is doubled as well as the amount of current that the pack can deliver. This means that the 3S2P pack can be discharged at 42 amps with bursts to 63 amps! Use the 3S2P 4200 in place of 1700 mAh packs, in models like PIGI 3D (CEM001). Dimensions: 4 x 1-5/16 x 1-1/2", 9.2 oz. Charge as a 3 cell pack.
--so am i back in the "overhead" range?
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Old 08-12-2004, 11:36 AM
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Default RE: need some confidence(help)

You can figure the overhead pretty easily.

Take the total capacity of the pack (4200mAh) and convert it to Amps (4200/1000 = 4.2Ah). Now, multiply by the continuous discharge rating (4.2Ah * 10C = 42A or 42 Amps).

If 42 Amps is at least equal to, or preferably greater than, the peak current being drawn by your motor setup, then you have "overhead."
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