Multi-motor wiring question

[MadMonkey]

Hi all.

I'm in the early stages of planning a 6-motor aircraft.

I've built/owned plenty of twins over the years but no 4 or 6, so I'm wondering how to go about this.

Each motor will be pulling about 30-35 amps at max power.

I'm not concerned with the mixing, likely all of the ESCs will run separately to a receiver. What I AM concerned with is power wiring. I'd prefer to run a single large high-discharge battery (likely 4S, but can go 6S).

But, drawing that many amps concerns me, as far as what connectors to use. 105 amps per wing is well over what an XT60 can handle, and even an XT90... just per wing. Even an EC5 would be on the edge. Y-ing those into a single lead to the battery doubles the capacity needed.

I'm not the most well-versed in this type of electronics so I'm looking for input. I want to make sure I don't roast anything or start a fire on takeoff.

I can probably get away with running smaller, less powerful motors, but I'd prefer not to if I don't have to.

Secondly, running 3 motors per wing makes wiring a bit of a pain. Has anyone used something like an old-school multirotor power distribution board? I.e. run a single battery lead to the board and branch the three ESCs off of it?

Thanks for any help. If this goes well you might see it at Flite Fest... no promises 🙃

 

[LitterBug]

Most race quads use XT60 connectors and routinely pull in excess of 100 AMPs. The connectors are rated at 60A "CONTINUOUS" power. Burst power is a whole other thing that is usually not speced. If you are not planning on cruising at full power, an XT60 or XT90 should be fine for short bursts/takeoff.

 

[MadMonkey]

Thanks. I'm wondering if I should run 6S since I use 5000s with EC5s for my other jets already. Their burst rating should be well above what I need.

Still debating on the wiring itself...

 

[quorneng]

You will also have to consider where to put the speed controllers.
Really need to be near to the battery and then how to keep them cool.
On my four engine AN124 the low amps involved (10A per motor) allowed the use of polyurethane insulated magnet wire. About half the weight of conventional silicone insulated wire for the same amps.

 

[MadMonkey]

You will also have to consider where to put the speed controllers.
Really need to be near to the battery and then how to keep them cool.
On my four engine AN124 the low amps involved (10A per motor) allowed the use of polyurethane insulated magnet wire. About half the weight of conventional silicone insulated wire for the same amps.

Well, that brought up an issue. Years ago I read about the problems with extending the battery-side wiring on an ESC, but since I never really needed to do so, over time my brain twisted it into thinking that it was the MOTOR side wiring that shouldn't be extended. So I had it backwards. I'd prefer not to have 3-4 feet of motor wiring 🤦‍♂️

This adds some more complexity.

 

[quorneng]

This is a picture of the four 20A OPTO ESCs and a UBEC mounted at the centre of the AN124's wing.

Each ESC is mounted vertically in a small printed frame to ensure some cooling air flow around them.
The triple magnet wires are visible leading from each ESC to its respective motor.
In this layout the inboard and out board motor pair are connected to separate 4s batteries which are also housed in the wing leading edge.
This gives an idea of the motor wire length required hence my use of magnet wire to save weight.

Almost surprisingly the motor/ESC/battery layout has not given a moment trouble. The airframe however did have a couple of issues although it now flies very nicely and at virtually a true scale speed making it an 'easy' hand launch.

 

[MadMonkey]

That's impressive and looks like a great solution! Don't know if it'll work for mine but I like it.

I'll have to brainstorm some more I guess.

 

[kilroy07]

This might be a good read (depending on how geeky you want to get)

https://www.rcgroups.com/forums/showthread.php?952523-too-long-battery-wires-will-kill-ESC-over-time-precautions-solutions-workarounds