4 or 5 motors

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4 or 5 motors

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8 July 2018 at 20:12 #78006
Queequeg Quint
Participant
@queequegquint38270
Perhaps I could use a bit of education on this matter.

My Ambassador is a 36" long Novi-style lobster boat. It's motor is the MFA 850 with 2:1 belt reduction, turning a 5-blade 70mm brass Rivabo propellor. Often, I use a heavy 12-volt 10AH SLA battery. With this setup, the Ambassador takes off like a rocket, stops on a dime, and can run for almost 1 hour.

So, now I consider my next Big Boat. Let's say it's about 55" long, and respectively wider and deeper. I think that my Ambassador's propulsion setup would move even this boat just fine, but the hooligan-in-me wants to over-power the Big Boat. So, I figure that I could install TWO motors just like Ambassador, with 2 props (perhaps even slightly larger diameter), and this would power the Big Boat more than fine. I could use a higher capacity SLA, or I could use the same size that Ambassador has (with shorter run-time).

But then my hooligan-mind goes the next step. "Why not FOUR motors just like Ambassador, with 4 props?" Obviously I would need higher capacity battery and thus heavier. Even with the Big Boat and heavy battery and motor weight, it seems that the motors should not be overworked, since they are all sharing the load (Can I say that each motor would only be pushing one-fourth of the boat?).

Now, if I put the brakes on my concept and consider just THREE motors, it seems that the P102 would simplify the equation.

What am I missing?
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8 July 2018 at 20:26 #78007
Colin Bishop
Moderator
@colinbishop34627
What am I missing?

An internal explosion hopefully….

Colin
8 July 2018 at 21:50 #78010
ashley needham
Participant
@ashleyneedham69188
Q. You must go with what you would like to do. However, an SLA, unless of a fairly LARGE capacity would not likely supply the necessary current.

4 x 850s, geared are likely to consume well over 40A, a figure an SLA is not likely to deliver. However, if you sere making a very large boat, consider a small car battery (just as a for instance).

You will end up chasing your own tail a bit…the bigger battery/motor setup, the bigger the boat will need to be and so on.

I like the idea of 4 motors for the look, but it may be that you could downsize the power requirement by downsizing on motors? This would mean a smaller vessel, and if I may make so bold, some Nimh batteries? these would deliver sufficient current to a more modest 4-prop setup.

Ashley
9 July 2018 at 11:32 #78014
Paul T
Participant
@pault84577
Q

I think that you are trying to compare two different types of hull, to the best of my knowledge a Novi style lobster boat has a semi-displacement hull which can accelerate quite fast, your proposed 55inch tug hull would be a full displacement hull which is intended to sit deep in the water.

Perhaps you should decide upon which type of hull you wish to use then we might be able to give you more detailed answers.

Paul
10 July 2018 at 01:46 #78016
Queequeg Quint
Participant
@queequegquint38270
Posted by Paul T on 09/07/2018 11:32:50:

Q

I think that you are trying to compare two different types of hull, to the best of my knowledge a Novi style lobster boat has a semi-displacement hull which can accelerate quite fast, your proposed 55inch tug hull would be a full displacement hull which is intended to sit deep in the water.

Perhaps you should decide upon which type of hull you wish to use then we might be able to give you more detailed answers.

Paul

I think you are right. I'm leaning toward the Novi style hull at this point…. which I and a boat-builder-friend will start working on in the winter.. this project will take a year, I reckon. What do you think?
10 July 2018 at 04:28 #78017
Queequeg Quint
Participant
@queequegquint38270
Posted by Queequeg Quint on 10/07/2018 01:46:36:

Posted by Paul T on 09/07/2018 11:32:50:

Q

I think that you are trying to compare two different types of hull, to the best of my knowledge a Novi style lobster boat has a semi-displacement hull which can accelerate quite fast, your proposed 55inch tug hull would be a full displacement hull which is intended to sit deep in the water.

Perhaps you should decide upon which type of hull you wish to use then we might be able to give you more detailed answers.

Paul

I think you are right. I'm leaning toward the Novi style hull at this point…. which I and a boat-builder-friend will start working on in the winter.. this project will take a year, I reckon. What do you think?

I like the Novi hulls, but I also want the ability to pull a tree up from its roots.
10 July 2018 at 15:36 #78019
Paul T
Participant
@pault84577
Q

If you want to pull a tree out by its roots then you will need a big, heavy and powerful displacement hull (tug) that sits deep in the water.

Paul
6 August 2020 at 02:58 #90646
Queequeg Quint
Participant
@queequegquint38270
OK. I'm still in the idea stage. I had a "crisis" so this boat project was put on hold… .Anyway.. I've decided to go down to three motors. Either: three MFA 800s, or three MFA 850s with gear reduction.

I have found an ESC that can handle huge loads by a company called Team Tekin. Their technician told me their ESC can work in a boat application. So, I will run all three motors on a single ESC!

The question now is: what kind of battery can handle the current draw? I'm leaning toward NiMH. Probably more simple to just use three MFA 800s…… But oh, just imagine the sound and the sight of three 850s turning those big pulley gear reduction units! It's the hooligan in me!
6 August 2020 at 13:05 #90657
Malcolm Frary
Participant
@malcolmfrary95515
The ESC in the link is brushless, so not a lot of use for any 8xx series motors.

There comes a time when you might consider that one ESC per motor and a collection of Y leads might be a better solution than putting all the eggs in one basket.
6 August 2020 at 13:44 #90663
Paul T
Participant
@pault84577
Q

We still don't know the size / shape / displacement of your hull.

Starting a design with 3 MFA motors is like 'putting the cart before the horse' and leaves you open to lots of problems further down the line.

I strongly suggest that you decide upon the type and size of model that you want to build, reading back through this thread you mention wishing to pull up trees, that will require a substantial hull and motors with far more power than the MFAs can supply.

Paul
6 August 2020 at 14:03 #90666
Queequeg Quint
Participant
@queequegquint38270
Posted by Malcolm Frary on 06/08/2020 13:05:32:

The ESC in the link is brushless, so not a lot of use for any 8xx series motors.

There comes a time when you might consider that one ESC per motor and a collection of Y leads might be a better solution than putting all the eggs in one basket.

Alas, if you look closely, it can run brushed motors too. I use one of these to run a 6WD truck that has three brushed motors and it works fine.
6 August 2020 at 15:04 #90668
Queequeg Quint
Participant
@queequegquint38270
Posted by Paul T on 06/08/2020 13:44:57:

Q

We still don't know the size / shape / displacement of your hull.

Starting a design with 3 MFA motors is like 'putting the cart before the horse' and leaves you open to lots of problems further down the line.

I strongly suggest that you decide upon the type and size of model that you want to build, reading back through this thread you mention wishing to pull up trees, that will require a substantial hull and motors with far more power than the MFAs can supply.

Paul

I'm thinking this: http://loyalhannadockyard.com/DYNUSCG40.htm

As for pulling up trees by the root, well I'm not actually going to do that. But I just want the boat to be ready, just in case I happen to get Jaws hooked on a line!
6 August 2020 at 20:36 #90675
Paul T
Participant
@pault84577
Q

A five foot boat is right up my street and normally I would be pointing you towards a couple of 30cc petrol engines but for deep down grunt I would suggest a pair of 12v DC electric motors (motorbike starter motors etc) or even a pair of powerful outrunner brushless.

Paul
9 August 2020 at 13:53 #90739
ashley needham
Participant
@ashleyneedham69188
We were talking about the round Russian battleship a few days ago…that had SIX motors on it…..??

Ashley
9 August 2020 at 14:29 #90740
Queequeg Quint
Participant
@queequegquint38270
Posted by Paul T on 06/08/2020 20:36:23:

Q

A five foot boat is right up my street and normally I would be pointing you towards a couple of 30cc petrol engines but for deep down grunt I would suggest a pair of 12v DC electric motors (motorbike starter motors etc) or even a pair of powerful outrunner brushless.

Paul

I get the distinct impression you think three motors is a bad idea. Can you explain? I know three is totally unnecessary, but the hooligan in me wants to make a video of the propwash of three 65mm 5-blade propellers!
9 August 2020 at 14:49 #90741
Paul T
Participant
@pault84577
Q

Let the hooligan have his way, if you want to see the prop wash from three chunky propellers then go ahead and make it happen.

Life is to short to miss these opportunities.

In your position with a five foot boat I would be looking at 3 Outrunners but this is where my knowledge lets me down as I know next to nothing about using brushless motors in boats so I stand to be corrected by those with knowledge but as a guess I would start at 3 x Turnigy2836 Brushless Outrunner 1000kv.

Paul
9 August 2020 at 15:00 #90742
Dave Milbourn
Participant
@davemilbourn48782
A bit small, Doc. I'd be more inclined towards something like three of these Leopard motor

I think my opinion of MFA 800 motors is well-known by now.

Dave M
9 August 2020 at 15:04 #90744
Paul T
Participant
@pault84577
Hi Dave

As you are the nearest thing to a god where motors are concerned I bow to your superior knowledge.

Paul
9 August 2020 at 15:16 #90745
Charles Oates
Participant
@charlesoates31738
Hi Q, over five and a half years and seven pages of ideas. Isn't it time to build something and make your dream come true? I've made the mistake of putting off a dream build too long, so I urge you to start building, just get on with it. Once you have started, and know the hoped for performance, and the number and size of the props, speculation about what to put in it will make a lot more sense.

Chas.
9 August 2020 at 15:21 #90746
Queequeg Quint
Participant
@queequegquint38270
Posted by Paul T on 09/08/2020 14:49:53:

Q

Let the hooligan have his way, if you want to see the prop wash from three chunky propellers then go ahead and make it happen.

Life is to short to miss these opportunities.

In your position with a five foot boat I would be looking at 3 Outrunners but this is where my knowledge lets me down as I know next to nothing about using brushless motors in boats so I stand to be corrected by those with knowledge but as a guess I would start at 3 x Turnigy2836 Brushless Outrunner 1000kv.

Paul

Aha! The hooligan shall have his way! But I prefer brushed motors — I heartell that if you use brushless motors, you must use a separate speed control for each motor. My mind is set on three MFA 800s run by one ESC. There's something about those motors that I like.

But I am stuck on what kind of battery to use. With three MFA 800 motors, the current draw is 15.6 amps when they are happy. More when they are not happy. What kind of battery can handle such a current draw and let me run for a looooong time?

I was initially thinking of three MFA 850s, with belt-drive gear reduction. But that current draw is about 33 amps when happy. I think the 800s would be a wiser choice.
9 August 2020 at 15:35 #90747
Paul T
Participant
@pault84577
Q

Three 800s with 65mm props pushing a 5ft boat might draw more amps than you think, I would be looking at an Action Electronics P98 but I would certainly take advice from Dave M.

Paul
9 August 2020 at 17:12 #90751
Malcolm Frary
Participant
@malcolmfrary95515
If it is for some reason vital that all of your eggs are placed in one expensive basket, fusing the individual motors is a must. You get exactly the same problems of equal or otherwise starting and responce caused by manufacturing variations between individual examples of motors whether using one big expensive ESC or three lower cost ones. Three correctly set up ESCs on one channel are no more liable to give uneven performance than three motors on one ESC.

If the 800 motors are 50mm diameter, 65mm props will be overdoing it and pushing the motors into their unhappy zone.

There have been cases where two sensorless brushless motors have been run off one ESC, but the guy who did it and videoed the result knew how to bend the rules. Anybody else is best advised to stick with the proven formula of one ESC per motor. Any problems are likely to involve less smoke release and be more easily solved.

What kind of battery supplies high current over a long time? A LiPo. More accurately, a really big LiPo. Probably as much as will physically fit, with a C rating that gives a comfortable safety margin.
9 August 2020 at 17:33 #90752
Queequeg Quint
Participant
@queequegquint38270
Posted by Malcolm Frary on 09/08/2020 17:12:27:

If it is for some reason vital that all of your eggs are placed in one expensive basket, fusing the individual motors is a must. You get exactly the same problems of equal or otherwise starting and responce caused by manufacturing variations between individual examples of motors whether using one big expensive ESC or three lower cost ones. Three correctly set up ESCs on one channel are no more liable to give uneven performance than three motors on one ESC.

If the 800 motors are 50mm diameter, 65mm props will be overdoing it and pushing the motors into their unhappy zone.

There have been cases where two sensorless brushless motors have been run off one ESC, but the guy who did it and videoed the result knew how to bend the rules. Anybody else is best advised to stick with the proven formula of one ESC per motor. Any problems are likely to involve less smoke release and be more easily solved.

What kind of battery supplies high current over a long time? A LiPo. More accurately, a really big LiPo. Probably as much as will physically fit, with a C rating that gives a comfortable safety margin.

I guess there's lots I don't understand. On my 38-inch Ambassador Novi boat, I have the MFA 850, with the belt drive gear-reduction turning a 75mm 5-blade brass prop. It runs off a 12 volt Sealed Lead Acid Battery with 10AH, and it runs happy for one hour, using a simple MTroniks ESC. The 850, when happy, draws over 10amps. But I have NO problems whatsoever.

My 38-inch Illusion Novi Boat uses the MFA 800, turning a 55mm 4-blade brass prop, with identical electric setup as the Ambassador. As you know, the 800 draws about 6 amps when happy. It, too, runs happy for one hour.

So, according to my mind, three MFA 800s should also be happy. As for the ESC, a company called Team Tekin makes an ESC that can handle enough current to power the starship Enterprise. As for using a LIPo, I am opposed to using LiPOs for a number of reasons, so that is off the table. Alas, I am "old school" on everything.

Edited By Queequeg Quint on 09/08/2020 17:34:48
9 August 2020 at 18:22 #90754
ashley needham
Participant
@ashleyneedham69188
Q. A flat transommed rear end I reckon would be best for three motors as I said before.

If you like the 800`s then go with it. I have an MFA Fantome with two 800`s and it goes very nicely on 14v (ganged up 6 cell Nimh) on X50 props. It also sounds nice, the motors take full throttle instantly and emit a nice deep hummmmmm sound.

I would only go to perhaps X55 on these units.

Take the plunge and build. From experience, you can overdo the thinking part.

Ashley
9 August 2020 at 18:31 #90757
Dave Milbourn
Participant
@davemilbourn48782
Posted by Paul T on 09/08/2020 15:35:34:

Q

Three 800s with 65mm props pushing a 5ft boat might draw more amps than you think, I would be looking at an Action Electronics P98 but I would certainly take advice from Dave M.

Paul

Sorry, Paul, but there comes a point when one suspects that it's not advice that's being sought – merely agreement or, in this case, submission?

Dave M
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