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dasintex 01-20-2020 09:36 PM

New to Electric Flight
 
New to Electric Flight, been reading through a lot of the threads.

Here is what I have or proposing: 7lb, 74" Wingspan Twin Otter, powered by 2 Power 25 840 to 1000 Kv motors; one battery to power both like a 4S/5000 MaH Lipo.

Questions: Would 3S work vs 4S; one battery or 2?

Thanks

Wildflyer 01-20-2020 11:42 PM

I have a E-Flite Deuces Wild, it is also powered by two Power 25 motors.
I would not even try my plane on a 3s battery, you will lose about 1/2 of your power.
You say power 25 840 to 1000 kv I hope you are thinking of the motors you might buy, as they MUST be the same kv on each side.
My plane weighs in at close to 10 lbs and flys with the 870kv motors on 4s 2200 giving me 4400mah. I think the props are 12x6
I could up grade to two power 32's if I want to.

At 7 lbs and two power 25's I think you will be fine.
Electrically the ESC's should feed from one power source, it may be one battery in the fuselage, or in my case two batteries in the pods that plug into a wire that connects the batteries in parallel.

dasintex 01-20-2020 11:55 PM

Have not got the Motors yet, 840 to 1000 KV was the range I was thinking, same for both side; I was thinking since the battery(s) have to go in the fuselage, one large battery with a Y feeding 2 separate ESC's located in each engine pod/mount

So would a single 4S 4000 to 5000 MaH Battery do the job?

Wildflyer 01-21-2020 03:49 AM

You would it would be easy.
Unfortunately there is a problem if the wires between the battery and the ESC's get to long, it is VERY hard on the ESC's.
You will need an extra bank of capacitors located at the ESC's to help prevent damage.
It is a hard thing to explain but some people compare it to a water-hammer effect.
Ron Van Sommeren on this forum can explain it much better than I can.

5000mah should give you a decent flight

dasintex 01-21-2020 10:50 AM

Wire Length from battery to ESC
 
I'm thinking the wires from the battery to the ESCs would not be any longer than 12"

Wildflyer 01-21-2020 07:27 PM

Basically if you have to make an extension, you should use a capacitor pack, at least that's my rule.
There is far more happening inside an ESC than most people understand, it is amazing that they do not cost far more than they do.
The current flowing into the ESC is not a smooth steady stream, it starts and stops extremely rapidly which cause something sort of like an electrical water hammer. As a ex-General Contractor I have seen water hammer break copper pipes.

Make a google search for ----- Capacitor pack for ESC
Here is one listing.https://www.google.com/aclk?sa=l&ai=DChcSEwjChsGatJXnAhUrHq0GHdSJCT4YABAD GgJwdg&sig=AOD64_3u2uZ8HuGTsuaz7yimz2ji2PwFMw&ctyp e=5&q=&ved=2ahUKEwiQyrmatJXnAhXVu54KHWjgCB0Q9aACeg QIDBA_&adu

ron_van_sommeren 01-22-2020 12:46 PM


Originally Posted by dasintex (Post 1022486)
New to Electric Flight ...

I would start with a dedicated single-motor beginnersplane. Otherwise you are in for a very steep, expensive, frustrating and risky learning curve.
Do you have RC flying experience? What with?


Originally Posted by dasintex (Post 1022486)
... Kv= 840 to 1000rpm/volt motors ...

Two very different motors, even though dimensions and power rating are the same. Batterycurrent drawn is proportional to Kv cubed. Both current and power drawn would differ by factor (1000/840)³=1.7!


Originally Posted by dasintex (Post 1022486)
... Would 3S work vs 4S ...

Choice of voltage does not matter much from an electric point of view.
E.g. 3s and Kv=1000rpm/volt and 6s and Kv=500rpm/volt will give same rpm, performance, power and flight time.
More in
www.rcgroups.com/forums/showpost.php?p=40233560&postcount=165

However, for a given powersystem (i.e. Kv, pitch & diameter) batterycurrent is proportional to voltage squared, differ by factor (4/3)²= 1.8!
Increase in current with one or two cells added, simple table

ron_van_sommeren 01-22-2020 01:11 PM


Originally Posted by dasintex (Post 1022486)
... Twin Otter, powered by 2 Power 25 840 to 1000 Kv motors

Don't forget to remove the red pin from one of your ESC connectors. Otherwise you get two different voltages, linear lbec and battery, or lbec and lbec, fighting each other. Or in the case of switching sbecs, two frequencies fighting each other.
No need to remove the red pin if you have a bec-less controller.

(UBEC is a propriatery brand name, a generic informationless acronym, I prefer LBEC, linear, and SBEC, switching, those two acronyms contain more info.)

But don´t cut the red wire, you may need it again in another plane.

https://static.rcgroups.net/forums/a...1338992600.jpg

https://static.rcgroups.net/forums/a...1338992600.jpg

https://static.rcgroups.net/forums/a...1338992600.jpg

dasintex 01-23-2020 01:29 AM


Originally Posted by ron_van_sommeren (Post 1022523)
I would start with a dedicated single-motor beginnersplane. Otherwise you are in for a very steep, expensive, frustrating and risky learning curve.
Do you have RC flying experience? What with?

Hey Ron;

I have over 30 yrs RC experience, mostly Glow and Big Gasser Planes including Twins; a few Small Electric single Motor RTF Planes that didn't need a lot of guesswork; Being Canadian and former Canadian Armed Forces Member, I am a big Fan of the RCAF Twin Otter, and just had to get the VQ Models Canadian Otter; would have preferred to power it with Glow Engines but the Plane is set up for Electric Only, the Otter will be the biggest Electric I have had and the only Twin Electric, looking forward to the challenge and all your help is appreciated.

You posted that I need to cut the red Lead or Pin on one of the ESC's to eliminate conflicting Voltages and/or frequencies depending on the type of BEC; Y-connecting both ESCs leads into single feed into Receiver won't accomplish this?

Again Thanks for the info.

quorneng 01-23-2020 10:46 AM

1 Attachment(s)
dasintex
The need to remove the red wire connection on one ESC depends on the type of the battery eliminator circuit (BEC) in the ESC.
If is is a linear BEC (it simply maintains a constant voltage by 'loosing' the excess power in the form of heat) then it is safe for both BECs to feed power. In fact the one that has the fractionally higher output voltage will do most of the work.
On the other hand a switching BEC chops the power on and off rapidly to give the effect of a constant voltage. It is much more efficient done like this so there is very little heat generated but it must "stand alone". The pulses of another switching BEC are likely to confuse the voltage sensing so it will not maintain a proper constant voltage which could prove expensive. ;)
Most modern and powerful ESC (above 30A) will use a switching BEC.
Of course some ESC do not have a BEC circuit at all in which case a stand alone UBEC unit is used.

As an example here is 4 x 20A ESCs (no BEC) with a 5A UBEC providing the 5V supply in this case to a servo tester to test the four motors.
Attachment 187825
So small and light it will all be buried inside the wing.

dasintex 01-23-2020 10:56 AM

quorneng;

Appreciate the reply, this E Flight stuff is coming together, I still use a Y-Connector Lead joining both ESCs, cut the Red Pin on one of the ESCs (if SBEC) going into the Y, single lead from Y feeds into Throttle Channel on Receiver.

Thanks.

quorneng 01-23-2020 12:34 PM

dasintex
Correct
It is a good idea to extract and tape off one of the red pins as shown in the earlier post. It means it is then simple to re use the ESC in a single engine job later if the worst comes to the worst with the twin Otter :(.

dasintex 01-23-2020 01:06 PM

A quick question; in Glow or Gas Twins we usually put each Engine on separate channels to help with Radio idle adjustment, top end, servo end points, etc. the alternative is making these adjustments mechanically with the pushrods; any need to put electric Motors on separate channels?

quorneng 01-23-2020 03:42 PM

dasintex
Not really, unless you want to stop one in flight on purpose! I did on my Cessna Skymaster. ;)
More likely reason is if you fit floats on your Twin Otter then individual throttle control on, say, the rudder stick for water manoeuvring is very useful. If your TX is clever enough it can be programmed to disable the individual throttle above a certain power setting. The really keen even use reversible (vehicle) type ESCs so you can go backwards at the flick of a switch.

If you use a single channel for both it may be worth 'teaching' the ESCs the throttle end points individually so you are sure they both recognise the same Tx full power point. Personally I have never found it necessary on any of my multi as most ESCs now have 'auto' throttle range detection.

ron_van_sommeren 01-23-2020 05:13 PM


Originally Posted by dasintex (Post 1022534)
... I have over 30 yrs RC experience, mostly Glow and Big Gasser Planes including Twins; a few Small Electric single Motor RTF Planes that didn't need a lot of guesswork ....

No worries then, you already have experience with e-equipment and e-routines.


Originally Posted by dasintex (Post 1022534)
... Being Canadian ...

Slightly worrisome :D


Originally Posted by dasintex (Post 1022534)
.... You posted that I need to cut the red Lead or Pin on one of the ESC's to eliminate conflicting Voltages and/or frequencies depending on the type of BEC; Y-connecting both ESCs leads into single feed into Receiver won't accomplish this? ...

No, it won't. The whole point of an Y cable is to connect the three plus pins in the three connectors, the three minus pins and the three pulse pins.

https://static.rcgroups.net/forums/a...06-servowg.gif

https://static.rcgroups.net/forums/a...o-stekkers.gif

ron_van_sommeren 01-23-2020 05:28 PM


Originally Posted by dasintex (Post 1022539)
... if SBEC ...

Four anything above 3-4s use a (controller with a) switching SBEC, not a linear LBEC.

The higher the power-pack voltage, the fewer servos a non-switching = linear LBEC can handle. Switching SBEC's hardly have this restriction.
(UBEC is a propriatery brand name, a generic informationless acronym, I prefer LBEC, linear, and SBEC, switching, those two acronyms contain more info.)

An LBEC, if it could handle the voltage at all, would have to dissipate way too much power (P = ((Vbatt -Vservos) × Iservos)) and would get very hot and/or shut down, temporarily. It will work fine again after the crash since it has had plenty of time to cool down.

The higher the battery voltage, the hotter a linear BEC will get, for a given current/load/servos.
Or, in other words ...
The higher the battery voltage, the lower the current a linear BEC can supply.

In depth:


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