Larger engine setup, esc lipo, Help!

[Rosena]

Hello.

Im about to finish my first build of a bit larger boat.
The hull is a delta force, a bit small for the engine setup i guess, but it was samething i already had... maybe i Will swap hull later.

I have only experienced building smaller boats cars etc.
But its a bit more money in this one, so i dont want to blow everything up 😄

The setup i have is.
SsS 56104 790kv engine. Max amp 220, max V 65, 14kw.
Flier esc 320a 22s,
Planning running 4?4s lipo.
What do u guys think about that?
Start with a small prop ofcourse.
If I go down on lipo, say 12s the amps Will go up.
I dont know how to think really, in theory it Will work i guess.
Anyone who can say any weak spots?

Sry about bad english...

// Rasmus, Sweden.

[RaceMechaniX]

Rasmus, which Delta Force hull? They have many sizes.

[Bande1]

depends on what you want to do with it in terms of voltage. if you you're doing speed runs 12s should be ok up to about 10kw for brief periods. especially with decent batteries. I dont have a whole lot of experience so take what I say with a grain of salt, but I have ran 12s at 8kw.

[Rosena]

Its 42"
Im afraid its i bit small, drivetrain and rudderinstallation is old parts i have saved, that i have rebuild and put together, i have been taken a small break from RC for about 15yrs (kids) 😄so the plan is to get the boat together so all basics work then uppgrade with more modern parts.

[Rosena]

Ok! Thanks for answer,
Basic theory says high voltage = low amps under load,
So my plan was to go with 16s, to keep amps down, and be on the safe side.
The otherside is that i Will add extra Weight, maybe I should start with 12s,

[Bande1]

Ok! Thanks for answer,
Basic theory says high voltage = low amps under load,
So my plan was to go with 16s, to keep amps down, and be on the safe side.
The otherside is that i Will add extra Weight, maybe I should start with 12s,

Im dealing with a situation where Ive gone from 8s to 12s and from a 4kw motor to a 6.5kw motor, same RPM different KV, and the amps didnt come down one bit. the torque went up wildly and the boat is uncontrollable. amps almost identical @ 200A. So I dont know what to say.

[RaceMechaniX]

16S is waaaaay too high for a 790kv motor in that can size unless you like fireworks shows inside your hull. 12S is more than enough and even 10S would be fine for sport running. If you had lower kv motor options, then you would be correct in higher voltage equals lower current for the same power output. To make that happen you need lower kv.

The 42" hull can handle the 56104 motor. You will want to keep the hull on the lighter side so a 12S1P setup would work well. Target a 50-60mm prop and you be in the 60-70's fairly easily.

For comparison, I run a 40" DF mono on 6S2P with a 1200kv motor and a 55mm prop. Speeds are in the mid 60's, but it is a bit wild in race water.

[Rosena]

Ok, thanks for input, i have just done the theoretical, and I don really know how it Will work irl.
12s 1p? 1 prop?
12s = about 50V
Max output 14000/50 is about 280A
Max amp for the engine 220A, and then ofcourse its dips a bit over esc.
But in short periods, no problem?
How should i think? 😄

[Bande1]

Ok, thanks for input, i have just done the theoretical, and I don really know how it Will work irl.
12s 1p? 1 prop?
12s = about 50V
Max output 14000/50 is about 280A
Max amp for the engine 220A, and then ofcourse its dips a bit over esc.
But in short periods, no problem?
How should i think? 

that motor is 6kw. look at the continuous wattage unless you're doing 10 second drag races. real voltage under load will be around ~3.45v per cell with average batteries. Get a emeter system to go with your flier esc and you can see the what the boat is pulling. I got a very similar setup and it should take around a 70mm total pitch prop. give or take.

https://hyperion-world.com/en/p1016154-hp-em2

[Xrayted]

Amps will only be lower on higher voltage setup IF the power/work being done by the boat is exactly the same as the lower voltage setup was. This is basic Ohm's Law, but most people ignore that last part of the equation when talking about voltage.

Thats easy to sort out on things like RC helicopters or cars where you can simply double the voltage to 12S, then swap the motor out for exactly half the KV and end up with a geared head speed of exactly the same RPM as before, but with half the amps as a 6S setup. But that's not what is happening on our boats.

We aren't running geared setups or governed RPMs to hit the exact same prop RPM between setups like we do with other RC models, so rarely is the work the same. We are typically using higher voltage for less voltage sag and better maintained RPM under load, higher peak power and more speed with a bigger prop, and in this case current goes up with the increased sustained RPM and speed.

The difference in motor stator size, copper fill and host of other things will also influence the end result between one motor to another, so you cant just assume that "higher voltage automatically = less current" based on that change alone. In many cases its just the opposite because we are taking advantage of the higher voltage setup peak power by running the model even harder than before

[Rosena]

Great, thanks!

[Rosena]

Ok! Perfect, exatly this kind of things i wanna hear, thanks for a good answer!
So glad there is forums online that is still alive!

[Rosena]

Thanks for the tips guys!
First tryout today, everything works very well.
Esc set to 80% max Power.
12s setup.
Did a few top speed runs, and total runtime about 8 min.
Esc and engine has a temp of 30c, which is very good.
Octura 3 blade z457/3
I have have ordered more props.
Only problem was that one of the batteries came loose and were lying on the drive shaft... could have been fireworks inside. 😁
Is there someone who can recommand any props?

// Rasmus

[Bande1]

ABC 2216-10-50 (17-45 out of stock) thats +10mm total pitch

[TonyM995]

That?s awesome Rasmus! Do you have a video of it running? I?d like to see it if you do