Solved Twin motor & twin battery set up

[shadeyB]

Hi pilots
I have built a few twin motor jets and love them.
I am building my 1st twin EDF and looking for advice on both options below.

usually I wire up option B through a Y-harness, and have had great results and using 1 large battery

im thinking about Option A this time with twin EDF ?
reason being is due to EDF being battery hungry, I have 2 battery sections in the Bay.
Rather than one battery dedicated to its own motor I thought that if I wired up option A and a battery died before the other then I wouldn’t loose power to 1 unit ?

causing an amazing death spiral brought on by unpredictable Yaw with only 1 motor running and me jamming the sticks trying to figure out what to do 😊😜🤪😂😂

thought and advice greatly appreciates please

ill admit I don’t really know much about all that technical wizardry behind the internals of our planes.
I just have a passion for building, flying, crashing, repairing and repeat repeat repeat 😃

 

[leaded50]

by A and one battery dies, you also "ruins" the second, because it will always try draw power from the one who gives best, and push power to the battery who have less power/died.(ag, can make the died/low power battery heat up) . I found it better that use one battery at each EDF, than you have at least one motor to run/land with. Normally both EDFs is pretty close to each other anyway, and wouldnt affect a plane much, as an differential thrust.

--- another thing is if both batterys are similar, and the EDF power draw are too..... one battery shouldnt die before the other (IF both batterys are in similar conditions)

 

[shadeyB]

by A and one battery dies, you also "ruins" the second, because it will always try draw power from the one who gives best, and push power to the battery who have less power/died.(ag, can make the died/low power battery heat up) . I found it better that use one battery at each EDF, than you have at least one motor to run/land with. Normally both EDFs is pretty close to each other anyway, and wouldnt affect a plane much, as an differential thrust.

--- another thing is if both batterys are similar, and the EDF power draw are too..... one battery shouldnt die before the other (IF both batterys are in similar conditions)

Thanks 👍
I hate solder anyway
I would normally run 1 battery for both but I have 2 bays for balance

 

[quorneng]

shadeyB
If you wire up two batteries as in 'A' both batteries will become exhausted at the same time regardless. Which ever battery has the slightly higher voltage will take more of the load until both battery voltages are equal. Because of a LiPo's low internal resistance we are talking of just a tiny fraction of a volt difference.
If for some reason one battery becomes physically disconnected then the other will keep both EDFs running but you have to recognise the problem and land sharpish before the remaining battery becomes exhausted.
With 'B' it is a simple case of 'all or nothing'.

It is worth noting that in both cases a serious battery failure, as distinct from just running low, is most likely to result in a crash anyway.

From a pure risk point of view 'A' is actually better as you have a degree of redundancy that 'B' does not have.

 

[L Edge]

I look at it from a different viewpoint. First of all, I over the years have had a number of multi engine planes(electric and nitro) where if one craps out and you do nothing, you will crash. That is, even if they are close together. The reason being, having an offset thrust will set up a yaw problem which will roll the plane and spiral in. How about making the turn into the dead engine side. The only chance you may have is the use of the rudder if it is large enough area to fight the yaw. Most planes, no is the answer.

So, what to do batterywise. I look at the total weight of the electrical setup, that includes all connectors, length of flight you want, etc., to see what the which lower the wing loading. In my case, I usually end up with one battery, so I pick that B setup.
One additional point I have found is that you usually have to increase the C factor in your battery using the B setup.

There is only 1 way to save a multi in most cases, that is, as it yaws and starts to rolls over(assuming you recognise one engine out) you just kill the throttle and try to stabilize it in a fast glide back to earth and hope you have enough kinetic and potential energy to flaire and land.
That is why I go for the lowest wing loading, so I use only one battery.
I have drop a shuttle for some AMA events and have been caught once with an EDF going out on me, so it works.

 

[shadeyB]

Great input pilots thanks
the twin - multi engine set up is full of tricks and know how's to get them to operate as efficient and effective as possible.
and its great to have a post just full of tips n trick's that can help others
ie. twin esc set up and removing 1 power wire

my intention is to have voltage alarm's on the batteries until i understand the flight window. while i do know my motors individually this is 1st time with twin edf set up soooo looking forward to the maiden.

keep them coming because batteries is what gets us up there