Diy Brushless outboard? I have some questions.

Hi,

I want to put turnigy 80-100 130kv motor on Johnson/Evinrude 4hp outboard (2.15:1 gear ratio).
Something like this: http://endless-sphere.com/forums/viewtopic.php?f=2&t=49846&p=736675&hilit=outboard#p736675

I read form rcgroups that this motor connected DIRECTLY to a 7.25" x 7" prop draws 80A on 6s lipos. With the gear reduction it should draw about 40A(i guess).

The real question is: That I don't know what controller/esc should I use? (RC or E-bike one and how much amps it must withstand)

Infinity

Having followed a similar path to the one you are proposing, I can help with some of your questions. I gather you are planning to use a standard outboard leg, if so, you will find the gearing is a little too high and the space for a prop below the anti ventilation plate will limit the prop diameter such that the efficiency will be low!

May I recommend you read the wonderful thread initiated by JH.

http://www.boatdesign.net/forums/boat-design/efficient-electric-boat-27996.html

I am currently using two 125Ah SLA's in series and drawing typically 12A (300w) which propels my Cat at 4kts, with a 13" x 13" APC or the SS folding version I constructed, at which I see a motor speed of 1500rpm when driven through a 3:1 reduction.

If you read the afore mentioned thread, I would advise downloading Javaprop, this gives a very good insight into the advantages of a large diameter slow revving prop.

Good luck with the project.

GeoffV

Geoff

Thanks for that link. I will try to read through that(32 pages).

I could make the output shaft longer, so I could fit bigger prop after that plate. I can experiment with that later, but now I need to buy esc for my application. Do you think rc 120a water-cooled esc would be enough?

Infinity

I'm not the best person to advise on ESC's, hopefully one of the Guru's will step up to the plate.

FWIW, I'm currently using a Turnigy 150 opto ESC which is linked to a servo tester for throttle control, so far so good, but I'm drawing very little current compared to model RC applications. My understanding is, RC ESC's are designed for high current short duration applications and may not tolerate the continuous operation required by a marine installation.

The other aspect you must consider, is the much reduced capacity from lead acid batteries due to Peukerts Law.

http://en.wikipedia.org/wiki/Peukert's_law

By using an efficient propeller and there by minimising the current draw I am operating at the 10hour rate (from 125Ah cells) which permits about 8hours duration from a full charge. If you plan for the same, at 80A you would require 800Ah cells which would weigh about 220Kg each!!!!!! that, or tolerate a very much reduced duration.

GeoffV

Infinity,
I've done exactly what you want to do, with a Turnigy 80-100 130Kv and an Evinrude 3hp leg, details here:
http://uk-hbbr-forum.967333.n3.nabble.com/electric-outboard-tp4025171.html
I had no problems at all using a Turnigy Pentium 100A controller (apart from water damage). It starts fine, runs at low speed and power levels and nothing gets hot even after an hour at full power, about 30A or 800w from 24v lead batteries. The ESC is mounted with its heatsink against the surface of a diecast box. You can reverse the motor easily just with a double pole changeover switch (not while running) but my particular motor has a one way clutch in the gear case for neutral and this will not transmit torque in reverse. I just do without. Motor is direct drive to the vertical shaft. I used a Neodym wattmeter for control as this has a built in servo tester; I think they are no longer available.

Alan

Thanks. That info I was looking for! Now I can buy all the electronics and materials and start building.

What speeds are you getting with your setup?

Infinity,
as a complete guess, 4 1/2 kt on a heavy grp 11.5 ft dinghy and 5 1/2 to 6 kt on a slim and light 16ft wooden skiff. But way better than a trolling motor which was the objective, not silent like a trolling motor though.

The only build problem was connecting the motor to the shaft; I used a straight coupler with grub screws. I've read of someone sawing the female spline off the engine and using that to make a coupling. If you want to make a really neat job by mounting the motor directly to a plate on top of the leg you will need to cut down the vertical shaft, but then you don't have access to it to tighten grub screws. I found that I could not attach a coupler to the shaft and then insert the shaft into the leg from the top - I could never get the gears to mesh this way. One solution might be to cut a slot in the top of the shortened shaft and drive it with a pin in the coupling, which would only be grub-screwed to the motor.

One more thing; my little Evinrude has a left turning propeller and if you want to experiment with model plane propellers it's worth getting a right turning (clockwise viewed from aft) o/b as there is a far greater choice of props to play with.

Alan,

Do you need motor cooling? How warm does the motor get? What differences would 180kv version of this motor make (in speed/amp draw/heat...)

Sorry, just got back to this thread. Just passive cooling under a ventilated cover. ESC/diecast box never gets uncomfortably warm. I think a 180kv would take quite a lot more current as the power absorbed by a propeller goes up at the cube of speed. I make that about 78 amps.But I reckon you could just try it, keeping an eye on temperatures and just limit max throttle if things get too hot. As these motors have an extension shaft from the rotating part it would be quite easy to add a fan on top of the motor, inside a cylindrical shroud to guide the air past the motor. In theory the 100 amp ESC should still be within it's rating.

Alan-C, you mentioned reversing your bldc with a doublepole switchover switch. Have you done that with your setup? I'm thinking you place the switch between any two of the three wires from the esc to the motor. Doesn't that mess up the esc signals to the motor--extra length, etc. I'm intent on two-prop power to a small 15 foot boat. I'd like to run the two Hydra esc's off of servo testers but definitely want reverse. Is there a weapon is out there that I can plug in to the Hydra esc and have speed control as well as direction control??? Other than a receiver and a transmitter, that is... Thanks for any advice here...

1. Yes, you put the changeover switch between any two motor phase wires, but you must never operate it while current is being supplied to the motor - I think this would kill the esc. I did try it but as I said, the one way clutch doesn't allow to transmit torque in reverse. Best solution would be mechanical - get an o/b with a F-N-R gearbox.

2. Generally, it's better to extend the motor wires rather than the battery wires; long battery wires can damage the esc. Having said that my battery wires are about 8 ft long! Maybe there is no problem when my esc is rated much higher than my max. current.

3. You could probably use car esc's as they have reverse, if you want electronic reversing. In that case a cheap 2.4Ghz radio might be a good idea especially if you have two outboards - you may be able to set up each stick as a throttle for each motor (might have to buy an extra throttle ratchet).

4. It might be good to consider what can go wrong; my very first brushless esc failed at full throttle when I was holding the motor and prop it was driving!

Thanks Alan-C. Most practicable for my setup would probably be a pair of transmitters and receivers, now that you mention it. That's a lot of extra gear, but it might be easiest. Especially as I'm contemplating an aboveground pool to do much r&d on prop shaping and tuning, etc etc, Xmitters seem the way to go at this point. Anyone: what's the most compact Xmiter out there that could activate an ESC's motor speed AND direction control??? Preferable not a spring-loaded throttle, just a dial up or down, and a toggle for fwd-off-rev that an esc would recognize.

Controlling a reversing ESC:
My understanding is that some ESC's that have the reversing capability, can be actuated without a radio. The AstroFlight servo tester is calibrated in milliseconds and if you plug it in to the esc with the pot at 1.5, dialing back to 1 will give you one direction, dialing up to 2 will give you the opposite rotation. I'm guessing speed increases as you get further from the 1.5 setting. Don't know if it applies to other servo testers. I'm not yet equipped to try this. Strap down your equipment, handle with care, etc etc etc