Depends on the motors... a lot of 380-size brushless motors that run $10-12 apiece are 300-400W motors, more than enough for anything short of a Vangod/Iowa/Yammer/Bis... As far as a fair comparison... my challenge is this: Easy to waterproof (yes, Mtronics comes waterproofed, I know), runs for years without drama, programs easily with a card. Dollar-for-operating hour, the Mtronics is far behind the cheap HK controllers in my experience. Others have not had a good experience with brushless, and that's okay, but certainly not my experience. I know that Lou got a bad pair that wouldn't see the programming card. But for me, they've been pretty much flawless, and the only one I killed was due to a short in the motor wiring where I had been moving it a lot and dislodged the insulation. Edit: The motors I'm using in the I-boat are in fact $20 motors, but they are complete overkill and are being used because I'm being cheap and using a pair of 700W motors that I already had in the shop... If I was buying new motors to use for the I-boat, they'd be much smaller motors.
I dare you to wire them up so that they draw that 1.4 KW. It should take about 5 seconds to hit the opposite bank.
Why do people (let alone two engineers who know better) think that one must use motors at their max rated power? Besides, to get the max rated power I would need to be running 4S LiPO, with more than double the voltage that I am running in the Invincible. But for the sake of argument... if I series-connected two of the 8AH LiPOs that I typically run in a cruiser, I get 14.4V. 1400W/14.4V = 97.77A. My 8AH LiPOs, being fairly middle-of the road LiPOs, can only discharge at a 30C rate... 30C on my batteries gives: 8AH x 30C = 240A max sustained discharge without damaging the cells. So, I'm pulling at a 97.77A rate from my LiPOs, about 40% of their max rated discharge rate. That gives me about 4.91 minutes of run time before I exhaust their capacity. If I really wanted more safety margin, I can easily buy LiPOs that handle a 45C discharge rate. But as you can see from the math, why would I? I can run at full speed (God only knows what that would be at 1400W) for almost 5 minutes, pull in the ship and quick charge the batteries at a 40A rate (charging on these batteries is at up to a 5C rate), and have the ship ready for another sortie before I've got the ship patched. Assuming that the balsa would withstand the water pressure at whatever speed the ship could achieve (doubtful), or that the driveline could handle 1400W applied (also highly doubtful). So, Jeff owes me a celebratory beverage for getting schooled by a dink nub electrician (me) Hard cider, please Jeff.
10 gauge high quality noodle wire might make it to the far side hot but intact. It's thicker than the power wire on the 100A ESCs, so I expect it would do the job. The connectors are only rated at 60A but I have read reports of people routinely carrying 100+ through them. Note for people who are new to boats and wiring: We are only talking hypothetically, and Nick, Jeff, Mark, and I are NOT in favor of anyone doing theory to practice on this with their boat. Do not wire your first boat with any of this in your mind. You'll set it on fire and people will think you're me. Or Lou. We are all smiling and hypothesizing and would not do any of this in an actual ship. Except Jeff. He's an ex-Navy submarine nuke electrician and they're batsh** crazy.
I've run up to 100amps in my 33% Extra airplane fairly regularly....at wee bit higher voltage It does have a somewhat larger motor (Hacker A60-18L turning a 24x12 prop on 12s lipos).
I have a horse and a half in my brushless powered SMS Nassau, isn't red china a great place to buy hobby stuff?
I do sometimes resemble that remark.. but I'll have you know I haven't smoke-tested any boat parts in Years Months Weeks Days
Just to put 1400W into perspective, 1200W (from 4S batteries) is enough to lift a 8-lb, 6-ft wingspan B-17 bomber at a 45-degree angle to an altitude of 4500 ft in under 5 minutes.
And now, back to our regularly scheduled programming... Don't have the wiring harness done yet, but I was able to test the drive system by hooking up a battery to each ESC. The drive sings nicely along. You can also see where some major components go inside. Where'd all the room go in there??? *you can also see my little servo stuff box with pretty labels. Also got some work done on the rudders, all that's left is connecting the arms to the servo horn... This is a closeup of the HobbyKing waterproof servo... The joints in the case have rubber seals, and it even has little o-rings on the screws! The board has a conformal coating, too. Brian K is on the way over to work on guns, so I'll be posting more awesomeness in a few hours!
I have to take issue with using a 40A ESC for two 550 series motors that can top 80A apiece when stalled. One patch of weeds = smoke, unless the esc thermally shuts down fast enough. Sure it can be done in a clean pond in normal conditions, I just prefer to have overly capable components. I have seen several ESCs smoked in this manner.
A problem easily solved. I fuse my 550s to 15A each. Or you could fuse the pair of them to <= 40A. Its not an obstacle. You don't pull that much out of two 550s in our ships unless you bind them up. I have issue with buying an ESC rated for 180+ amps just because a pair of 550s can draw that much at stall - is the rest of your wiring system capable of handling a 180amp draw?
With the traxxas 'waterproof' servos, the part I found to be my usual failure was the potentiometer, not the circuit board (though those certainly get nasty once the gasket fails) - have they done anything to address that point of failure as far as you can tell?
I don't believe so. Still, MUCH more waterproof than the standard servos,a nd at $8.62 apiece, I'm happy.
