Aeromarine 44" hydro

[AntronX]

Hi all, i finally decided to start building larger hydro for rougher (real world ) water conditions. This is experimental build, and will not be intended for racing. I decided to go with cheap motors / ESCs for lowest total cost possible to see if electric boat of this size can be built for same amount of money as the gas boat. Parts will be:

2 x KB45 17XL (700Kv 0.022 Ohm)
2 x Turnigy 100A 12S ESC (will be waterproofed and watercooled)
14S2P A123 pack (split in two 7S2P packs in series)
.187 cable (left and right)
45 - 47 mm props

I am hoping to get 60A per motor for total of 120A which should get me about 4400W of power. That should be between 4.7 to 5.1 total horse power.

Does anyone know where i can get 6mm to .187 hex motor couplers?

[Raydee]

Nice, I have a Stryker 44" Hydro that I plan to start over the winter. I am going to go with a Neu 2130 motor though and 10s....ouch my wallet hurts already.

As far as the couplers go I am not sure if Steve sells them here but I did see them on ebay.

[AntronX]

I've looked at 2230 and Hydra 240HV, but the total price would be $1000 more. Although i would end up with more powerful and dependable setup than what i am building now.

[Raydee]

I know, the extra money hurts! I often wonder why I spend the money that I do when I don't even race but once I am at the pond and smiling then its worth it.

[lonewolf]

Jeff Wohlt just made me that very same coupler. Perfect fit...

[AntronX]

Jeff Wohlt just made me that very same coupler. Perfect fit...

Hex one? I don't like the ones that use grub screws on the flex shaft.

[AntronX]

Got started working on motor couplers today. I decided to try and drill out Octura 5mm coupler with 6mm drill bit. Don't do it, did not work. So i decided to grind down motor's shaft to 5mm instead. I hooked up the motor to the speed control and gave it about 15% throttle. Then i carefully grinded the shaft on electric benchtop grinder. At about 5.2mm i finished by hand with sand paper while revving the motor to about 50% throttle. To get nice sharp edge i used cutting wheel on dremel tool. Did not get it perfect, but the coupling fits nice and seems well balanced. Pictures of end result below.

[AntronX]

Ordered some aluminum for motor mount and ESC water cooling plates. Interesting part about Turnigy 100A HV controllers is that transistors they use are rated at 12A at 25 degrees C. There are 8 of them in parallel per string, which equals 96 Amps. But at more real world operating temperature of 70 degrees C they are only rated at 8.7A each, or 69.6 Amps total. A far cry from advertised 100A continuous current. That's why i think its important to try and keep them as cool as possible while in operation. And i believe water can do that much better than small fan on stock heatsink. I hooked up everything together for a test, here is short video of it: http://www.youtube.com/watch?v=xPoZCF2jg8o

[AntronX]

Got some news...

I ran the boat today for the first time at the park lake with a bunch of other rc boaters. It took off like a drag car, but 2 seconds into the run i realized my steering was reversed. I let go the throttle and then tried to get the boat going again, and that's when one of the controllers blew up. There was a little flash of fire and some popping. I had both ESC's mounted away from everything on the top of the motor mount to get some air cooling for them, and i ran without cowling. So my boat got spared from the flames. I had data recorder hooked up. First run peaked at 130 amps for both motors, so that's 70 per motor. I could not get any average reading because i only ran for 2 seconds. Then i got couple peaks flat topped at 180 A indicating a short circuit. I will do some more testing and will post some pictures of the boat. I want to figure out why that ESC burned up. But there were some positive results of this experiment today. The boat easily got on plane even with heavy batteries in the front. Also, 45 mm carbon props worked great and could push this big and heavy hull no problem.

[Fluid]

There are several reasons for one ESC blowing. One is quality control - how much QC can you expect in a $100 controller? Another is wiring length - show us photos of the interior setup, too much wire stresses the ESC a lot, especially at high loads. Another is back-EMF, if the boat was near full speed and you just cut the throttle, the spining props will turn the motors into generators, feeding volts back into the ESC and packs. It is possible for this voltage to exceed the rating of the ESC caps, which often means "bang".

I'm not certain that the 180A readings were shorts at all, they could have been real amp spikes and were flattopped by the limits of the datalogger. There are other possibilities, tough to tell without more info.



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[AntronX]

Each battery pack has 12" of 10 AWG wire. There were 2 packs in series, so that's 24" total. Then controllers had 10" of 12 AWG wire on battery side and 3" on the motor side, plus 2" on the motors. Since 2 controllers were in parallel, total wire length for controller side would be 10" on the input side. Thats 34" of wire going from battery to controller, 71% 10 gauge and 29% 12 gauge. That's total wire length, not half circuit length, which is 17" (for wire loss calculations). Edit: there were 2 "Y" adapters also, that are about 1" of 10 gauge wire going to each ESC, so total 2" extra. Also, data recorder has about 2" of 12 gauge wire, that's 4" extra. Grand total is 40".

There was also vibration of the flex shafts, due to motor couplers not being centered perfectly. The motor that had highest vibration, is the one that had it's controller burn up. Other motor did not vibrate as much, and it's controller did not burn up, but it has one surface mount cap that is shot on the driver board, and one of the driver FETs is shot also. On the power board side, one of the power FETs is shot too. So i think its safe to say that the second controller is also burned up, but it did not burst into flames like the first one did. I will post some pics of the controllers after i clean them up.

Here are couple pictures of the wiring setup and the amp/volt graph at the time of the event. First spike is when i ran it, then series of small spikes was me trying to steer it, then second big one is either when i tried to get it on plane or when the controller popped, or both. Third one was the fire.

[duncanjerry]

Spinning up your motors with no load is BAD.

[Fluid]

That is just SO MUCH wire for your setup. I know that the boat is huge, but there has to be a way to reduce the wire. Most high-end ESC makers recommend less than 8" of wire between the closest pack cell and the ESC. The motor wires need to be as short as possible as well, although yours do not look as bad as the power wires do. You can reduce the jumper between packs by half. From the photos at the beginning of this thread I can't see why the wiring is so long.

All the long wiring probably had as much to do with your ESC failures as any thing else. The datalog is odd looking, where in seconds did the boat get on plane? Your voltage drops of 8 to over 10 volts are huge. Your cells will not last long with that level of abuse.

I'm not trying to be mean here, just brutally honest. I like your goal of a "cheap" big hydro, but you may have to re-think some of that goal.


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[AntronX]

Here are pictures as promised

[AntronX]

part 2