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Electric Twin Model set up

Old 09-17-2020, 08:58 AM
  #1  
bigvern
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Default Electric Twin Model set up

Morning, I have purchased a twin electric powered model (used) form a fellow flyer, its the first twin I have owned

I have a question with regard to connecting the two speed controllers to the receiver. The previous owner had the speed controllers into separate channels on the receiver and then mixed them to the throttle channel, both speed controllers have the red wire active in the lead. The previous owner assures me that this did not fry his receiver as they work in parallel

Before I connect this up to my receiver I have a question 'connecting two speed controllers to receiver will not fry my receiver' ???

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Old 09-17-2020, 09:05 PM
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pmullen503
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Generally, if you have ESC with BEC circuits you should remove one red lead if they are switching type BECs. Smaller (up to 3s) ESCs can have linear BECs which are less problematic. A linear BEC is just a glorified resistor to drop the voltage and parallel circuits like these are common. It doesn't hurt to remove one red wire even if they are linear BECs.
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Old 09-18-2020, 07:12 AM
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bigvern
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Thanks for the reply, removing a red wire from one of the ECS removes a redundancy leg does it not ??? Having both red wires active does in the event of loosing one ECS continue to provide power to the receiver and servos.
This is how the original owner had it set up, going back to my original question though , ECS outputs say 5Volts for instance, this voltage powers the receiver and servos via throttle channel. Now introduce a second ECS via another channel on the receiver (not via a Y lead), does this mean 10 volts is going into the receiver ???
The previous owner says not as it is a parallel situation, thats what I am trying to clarify. My Futaba receiver is not rated for 10 volts I know that.
I get that by doing it via a Y lead is a parallel schematic but seperate channels

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Old 09-18-2020, 11:38 AM
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ron_van_sommeren
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Don't forget to remove the red pin from one of your ESC connectors. Otherwise you get two (slightly) 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, or if you have an optocoupled controller.
Also no need to remove linear LBEC red wire if manufacturer says so, but you must remove it when using switching SBECs.

(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.





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Old 09-18-2020, 11:39 AM
  #5  
ron_van_sommeren
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(UBEC is just a propriatery brand name, zero information in it, I prefer LBEC (linear) and switching SBEC (switching), gives more info.)

Don't use a linear LBEC above 3s.
The higher the power-pack voltage, the fewer servos a non-switching = linear BEC can handle. Switching BEC's hardly have this restriction.
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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Old 09-18-2020, 01:35 PM
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solentlife
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There is no problem to have both red leads connected and in fact will provide 'redundancy' if one fails.

All my twin motor models have both reds connected ..... linear and switched BEC's.

Yes I know that Switched BEC's are supposed to not like this but - none of mine seem have any ill effect at all.

Personally - if the previous guy flew it with both connected - why change it ??

If the ESC's are separate channels - you have an added function if you want it ... differential throttle. You can set the mix so rudder action alters the motors to have different thrusts and create a turning moment ... (I do this with my models to help turns ... )

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Old 09-21-2020, 04:02 PM
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pmullen503
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Originally Posted by solentlife View Post
There is no problem to have both red leads connected and in fact will provide 'redundancy' if one fails.
It will if the failure mode doesn't result in a short. It that case, it can take out both. If you isolate the two BECs with diodes you can get redundancy albeit with some voltage drop from the diodes.
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Old 09-21-2020, 05:47 PM
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solentlife
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Originally Posted by pmullen503 View Post
It will if the failure mode doesn't result in a short. It that case, it can take out both. If you isolate the two BECs with diodes you can get redundancy albeit with some voltage drop from the diodes.
True ..... but lets be honest - if we all worried about a short - we would never fly a single engine model.
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Old 09-21-2020, 07:42 PM
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To answer the original question,
You will NOT get 10 volts
Two power sources (batteries) in parallel give you greater current capacity, at the same voltage. However if one battery is lower voltage than the other, it will suck power from the higher voltage battery.
Example, you can not wire a 2s and a 3s battery in parallel.

BUT listen to Ron, if the two ESCs are not operating EXACTLY the same, they may sort of get in a fight with each other.
Some ESCs can handle this without burning up, but you don't know just what is going on internally without doing some very careful testing with electronic instruments.
One of the ESCs is going to be slightly higher voltage than the other because of the manufacturing tolerances of electronic components. That one is probably the one carrying the load.

My rule is simple, if the aircraft is big enough to carry 4oz of battery weight without problem, then I put a good battery in it so I don't have to worry about overloading the BEC output of the ESCs. Then I disconnect both red leads or use OPTO ESCs.
Unless the ESCs are high amperage units the BEC output is 5 amps at best. I want enough power to snap all servos at the same time. ( I love doing snap rolls )
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