Sergio M

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Hi guy,

I am in need of some help, my son and I, are in the process of building a 60" lobster boat made Aeromarine out of fiberglass. we want to power this boat with an electric motor,esc and power source that can last a very long time without having to worry about recharge. another requirement would be lots of torque. i can either go with one or two motors. but prefer two just to make it more fun. hulls is very large and it would be very easy to fit almost anything inside. I would also prefer 12v power. I have some large fish in my lake and my kid and I are planning on doing some r/c fishing , plus retreival of our disabled gas rc boats. we are open to all suggestions and greatly appreciate all the help.

Thanks
Mena Racing

nick_75au

There are a few options available, brushed motor relatively small say 700 geared down about 10:1( a recycled cordless drill works well ) or large low speed motor such as a blower motor from a car.

The another option is a brushless setup, a very low Kv motor direct drive.

all of these options are going to have approximately the same runtime for X rpm of the prop, the slower the prop speed the lower the current(higher runtime).

Do you know the size of the prop you are going to use? this will help in getting a better idea of setups.

Nick

Sergio M

My Feedback: (1)

Hi Nick,

Thanks for the help, a brushless system sounds nice, as for the prop. I am not really sure, I quess the bigger the prop the better. I use flex shaft on our race boat, but I am not sure if this would be the best set up for this boat. I quess I also need a prop and shaft suggestion.

Where can I see these motors you are talking about, again all the help is appreciated as electric motors are a new thing for me.

700 geared down about 10:1
a very low Kv motor direct drive

Thanks

nick_75au

Hi,

Straight propshaft will be fine chose one with a M5 thread, this will give you a wide range of brass props to try, you may be limited in prop diameter by the hull

For a brushless setup on 12 volts a maximum of 400Kv motor I reckon.

http://www.hobbyking.com/hobbyking/s...eq:_4030AXi%29

will work on 12 volts and up 80 MM props go lower Kv if you use a larger prop.

We have a supplier here in Australia that specialises in geared 700 motors, Im not sure about US suppliers , on further reflection a 6:1 reduction is probably closer to the mark,
If you can fit a 100 mm prop a 14.4 volt cordless drill and gearbox will work well.

Nick

mfr02

A visit to an auto scrap yard might be rewarding.  Fan motors and window winder motors are a good choice and are basically 12 volt motors and tend to be very well engineered.

rye

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hey guys
ok i am starting a 50" orca ,had the plans blow up from 35" to 50" and going to use a fan motor i have now i need a esc and prop size? thanks rye

Tony Fitzpatrick

[*]The correct prop/gearing should slow the motor should turn at 80% to 50% of its unloaded rpm.At 80% rpm it is running at its efficient,at 50% rpm it is delivering maximum power.If it is outside that region then change the propor ratio to suit.[*]With a suitable prop measure the current.[*]It should be a permanent magnet type if you want it to reverse.[/list]

rye

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HUH what size do you think i should start at ?

Tony Fitzpatrick

Try all of your props.

Sergio M

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would these fan motors or window motors draw too much current, draining the battery too fast ? or is this set up good enough at least to run an hour at scale. thanks

nick_75au

Blower motors are very good on power, in a car they draw about 5-10 amps, they are usually used in boats with largish batteries will give long runtimes, in saying that its the prop and the RPM that you want to spin it at that determines the current drawn.

Nick

Tony Fitzpatrick

The ones recovered from cars will not draw much current and they have a high torque compared to those sold in the RC trade.
I take it that the unimotor one came out a car so it needs a large prop to get enough power from it.

rye

My Feedback: (10)

what you think 2 or 3 ", two or three blade?

nick_75au

3- 4 inch , a guy at our club runs two 2 inch geared up slightly on one blower. 3 blade will draw more than 2 blade but give more thrust.

Nick

Sergio M

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What kind of speeds should I see in this set up roughly, and what speed control can I use with one of these blower motors or blower motor,

THanks for all the input guys, so far you guys have been a great help in pointing me in the right direction.

Tony Fitzpatrick

If you mean the speed of the blower motor then look under the hood of your car.
They look mean because of the size but on 12 volt they are low rpm so the power and current is not that great even with a four inch prop.

The coupling,suppression and the mount is a challenge but any esc is fine but it must be electronic with no relays.

mfr02

Quote:

anyescis fine but it must be electronic with no relays.

Tony Fitzpatrick

The energy stored in one of those motors is huge.Just look at the sparks when you hook up the motor straight to a battery.

Sergio M

My Feedback: (1)

Actually I meant what speed will the boat run. Not really concerned for speed, but just curious, what I really need is lots of torque. can any body post a picture of one of these fan blower motors mounted, would be a great help.

Where can I buy the needed ESC for the fan motor.

foodstick

I don't know if your boat has the room to do it..but have you considered using a car battery for power, and cutting down an trolling motor for the propulsion?

you will probably need tons of weight for ballast..and a trolling motor can move a full size boat well.. I would think it would last a long time on an rc..

rig up a servo to run the switch..already some sort of a speed control..or on off switch in there...

Sergio M

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Actually , I have thought about it, if I could fit it, it would be really nice but I just dont see how I can cut one down to make it fit. all trolling motors are very bulky. I have room because the hull is really long but not to deep on the sides. I was planning on using jetski batteries which are 12 V yet small. I will take a picture of the boat tonight and post. that will give you guys a better idea .

rye

My Feedback: (10)

hi
i have a extra mcd sc-480 esc do you think it will hold the un-motor 12 volt motor and a 12 volt 7 amp gelcell and a three blade 3" prop" on the orca 50" this is a enlarger orca from 35" to 50" boat

Tony Fitzpatrick

mfr02

This is why its a good idea to fit suppressors, capacitors and, if need be, inductors, plus as a last measure diodes from the motor terminals direct to the power lines. This applies to both relay devices and semiconductors. The relay contact should never switch the current, the relay operates at a given point in the deadband, the transistor then starts to switch. A badly adjusted and/or designed ESC can have the relay operate at the wrong time which does nobody any favours, similarly, slamming the control from full forward to full reverse is not a good idea as it might be possible to create a situation where the relay contacts are travelling from one state to the other while current is flowing.
The real downside of relay types is that most were intended to work on 6v systems, when used on 12v the coil tends to get hotter that is really good for it, again, depending on design. Add the occasional sloppy setup, where the relay operates for forward, doing a great job of flattening the battery, if the particular ESC ran off the RX supply, if there was a separate RX battery, this could give a very short run time, culminating in the "I've only got reverse" symptom.