Brushless Outboard

As I badgered the moderator to add an electric propulsion sub-section I probably should post something, so here is my brushless outboard motor.

The motor itself is a Turnigy c80-100, a large low cost motor for the model 'plane hobby; the rest of the outboard is a Evinrude 3.3hp. Pictures show the current iteration which is compact and splashproof; a previous iteration had the motor mounted higher up on pillars to avoid cutting the vertical shaft. So now the motor is mounted as low as possible, the stainless cover has an O-ring seal above the screws to keep the water out and the shaft has been cut down to suit. The adapter plate has an extension so that I can add remote steering if required. The two halves of the lower shaft (making a forward/neutral gearbox) have been fixed together inside the gearbox so that i can have reverse, and also try model 'plane propellers which are hard to find in LH rotation.

 

Hi Alan,

How is the motor cooled ? I'm surprised that you can cover it up completely.

It looks like a nice compact set up.

Regards, Hans

 

Hi Alan, very cool setup. I did a 10hp brushed outboard conversion on a Johnson 6 HP. I've since built a 25hp electric surface drive but was curious how the brushless motor performs with the conversion. What voltage are you running? How many rpm does the motor make when loaded? What is the gear reduction in the outboard leg? What batteries are you using? Have you tested in the water yet? If so what kind of speed are you seeing? With the setup pictured I was getting 9.5 mph. The same boat with surface drive does 25 mph, so I've abandoned outboard conversions but perhaps with the higher rpm of brushless motors they might perform better.

 

Zilver - I've used it at up to 800W continuous when it had a vented plastic cover with no heating issues for motor or controller (heatsink of controller contacting inside of die-cast box). I haven't tried it as shown on the water yet but the motor is mounted with heatsink compound to plenty of aluminium; the cover is very thin and I am expecting that the air whizzing around inside will give adequate cooling. I do know that there is no eddy current effect with the stainless cover; measured power is exactly the same with or without.

Irie - thanks! The motor kV is 130 and it runs on 24V lead-acid batteries 105Ah total weight 54Kg. The gear reduction is exactly 1:2 and the original prop is about 8" dia, unknown pitch. Maybe 5mph for a light skinny 16ft boat? and slower but consuming slightly more power on an 11ft fat heavy boat.

Do you have a thread for your brushed outboard? Put it in this section! And what was the power consumption for your two different motors at the mentioned speeds? It seems like a 10hp would naturally be that much slower than a 25hp.

I have also tried using a model plane prop using greatly reduced power for the same speed but not practical due to picking up too much weed.

 

That is absolutely true. I should have elaborated more. Initially I used the same motor from the outboard conversion on the surface drive which gave speeds of 20 mph, but pushed the motor harder than I was comfortable with. So I upgraded the motor for the surface drive. I've got controller data and video from both setups. I'll work on getting it together and posted.

 

Do you have any control system or panel for the brushless motor? If the motor connect directly with battery without any control, the battery and motor will be dead faster than normal using.

 

Who, me? Hobbyking 100A controller inside a diecast box, Also a wattmeter with built-in servo controller to operate the Hobbyking ESC.

 

So do the motor will be over heat if the motor run in full speed for some time?

 

Please see post 4, reply to Zilver.

 

Here is an update:
I've used the brushless outboard and controller with my newly built 14ft skiff/rowboat and have a few more numbers for you.
I have previously measured the motor/controller/outboard drawing about 135W at full speed with no load, but this seems to be proportional to speed because I found that in use, the motor will still move the boat and have steerage way at just 40W! The lowest number I saw on the wattmeter was 18W with the motor still turning reliably - it's generally considered that sensorless brushless motors won't run at very low speeds. Not much steerage and boat barely moving at that level though.
Max power for this boat/prop/24v was 650W. If you use a bigger prop/more volts/fatter boat, the power goes up.
I fitted a thermocouple deep in the motor, ran for 15 minutes or so and did not see temperature above 40 C at 650W. Unfortunately I have not been looking after my batteries properly and the voltage started sagging rapidly after that but I don't think there will be any problems with heat dissipation.
Finally, the boat is so stable (with those heavy batteries) and power required so low that I will probably make a solar canopy using flexible panels, for complete autonomy. I anticipate that four hours of sunshine will give me one hour of playtime!

 

I know this is an old thread but I'm considering building an outboard with a Turnigy 50cc equivalent and I'm curious about the long term results you had, particularly with respect to heat. Do you have an idea what the power limit would be for this motor in the sealed enclosure?

 

The motor I used is considerably derated, it is rated for up to 6kW in a model 'plane with plenty of air cooling but I've never run it at more than 800W. I suggest you do three things:
Derate the motor - run it at lower power than it is specified for.
Monitor the temperature with a digital thermometer and thermocouple, gradually increasing power level.
Experiment with changing motor timing while running at a particular rpm (fixed output power level) and monitoring input power level (to find most efficient setting).

Also, power dissipated in the windings is proportional to current so running at a higher voltage and lower current is advantageous, even if you have to add a reduction gear or belt to bring the prop speed down to a sensible level.

 

Long overdue update on my electric outboard: here is the controller for it, in a completely watertight enclosure as I have already lost two controllers due to water ingress. It is 36v 100A capable but has only ever been used with 24v batteries. The enclosure started out as being far too big but as you can probably guess it was a bit of a struggle to fit everything in. If you click on the pics you get a short description. I now have to get the solar charging cable into this box but there is nowhere to fit another cable gland except on the LH side which will be ugly, so I may remove the small white cable as I haven't yet fitted a solenoid to enable reversing (without the leg tilting up) and use that cable gland.

I should add that the speed controller is arranged with its' heat sink pressed against base of the enclosure so that excess heat is dissipated into the metal of the enclosure.