BRUTUS MK 11

[Paul TParticipant @pault84577]

Sorry Bob but my experience with brushless is only good for aircraft and drones, but the ones that you fitted in MK1 could have used just a little more power to move the extra weight that I added.

Paul

[Bob Abell 2Participant @bobabell2]

Hi Paul

The present motors have a KV rating of 1250 RV

Prop speed = KV x Battery voltage

We`ve got 1250 x 7.5v = 9375 rpm

The next motor up has 1400 KV rating

1400 X 7.5V = 10500 rpm

No doubt somebody will jump in and put me right

Bob

[ashley needhamParticipant @ashleyneedham69188]

But….how powerful are they?? and how big are the props??

How big are the motors??? These are the things to know Bob.

You can get motors 28mm 35mm and 50mm in diameter at 1250Kv, but they are obviously different animals as far as power and torque go.

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you Ashlley

Some one will chip in with a recommendation…….Hopefully

I'm surprised that after three years, there is still no obvious choice of brushless motor

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. You have the answers to my questions to hand!!

What size props are you going to use:

What is the labeling on the motors:

How big are they (diameter)..just in case the label is not much help.

No one is going to recommend anything that will be the RIGHT thing as this is a "custom" project. Just knowing the size of prop would help!

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you, Ashley

I think that we are all in the same boat, on this question?

Since my post last night, we have had 73 views, where normally, overnight we would get 10 views

When I built the very big SloMoShun, ( Billings x 2 ) there were lots of big motors about, but far too expensive at the timeand they still are

I`m beginning to think that the old faithful MFA 850 may have to do?

Afterall. I`m only building a futuristic warship

I can see a few long faces out there now!…….For all sorts of reasons

Sorry chaps

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. If you have them, a pair of 850`s with plastic X50 props on would no doubt fit the bill!

It cuts out extra expense and even then the motors you buy may be too much, or not enough.

Go with what you have. I can see Brutus 2 going acceptably well on the 850`s despite what the detractors may say!!

Ashley

[Bob Abell 2Participant @bobabell2]

Sound advice, Ashley

Very tempting

Bob

[Bob Abell 2Participant @bobabell2]

Progress p[cture

Finally made a start on the decking, will be nice to hide all that Hardboard stuff

Bob

[Paul TParticipant @pault84577]

Bob

Here is another chance for a master class as you could explain to Kevin what that strange looking wooden tool is for.

Is that a pencil that you have in it?

I doubt that 1 in 50 people young people could even guess at what it is.

Paul

[Bob Abell 2Participant @bobabell2]

Do you know, Paul, I put that strange device on for your benefit!

i know you take delight in spotting the tools of yesteryear……Like my Spokeshave etc

I used it for marking the width of the decking around the deck edge

Well done my mate for bringing the forum down on a level keel!

Bob

[Paul TParticipant @pault84577]

Back to an age when tools were an investment and lasted a life time.

For example to buy this one today would cost £67 but it is a beautifully made piece of equipment.

How many forum members under 40 can tell us what it is?

[Bob Abell 2Participant @bobabell2]

I`ve got my hand up, Sir……..It`s for marking out Mortice and Tenon joints

The Marking gauge on my boat photo was purchased about 1949

You ask a teenager to demo it…….Most have no idea

We were tool mad in those days

Bob

[Paul TParticipant @pault84577]

We were tool mad in those days

Yes but we bought with care and looked after them, far different from the throw away attitude today

[Tim CooperParticipant @timcooper90034]

Paul

That reminds me that I saved to buy some Stanley screwdrivers before I was married, still in frequent use today. We also bought expensive Sheffield cutlery for the our use after marriage, still be used daily. Not bad for 48 years use.

Tim

[Bob Abell 2Participant @bobabell2]

Progress picture

Working on the stern section now and is working out OK

On the original Brutus, the Rudder mech was in the rear compartment, which only allowed for very short rudder shafts and water ingress was a problem

I`m thinking of fitting normal rudders in the next compartment and moving the props up too

Come in Paul

Bob

[Ray Wood 3Participant @raywood3]

Hi Bob,

Why not put the rudder behind the boat ??

Here is a concept from my sketch book, no issue with the water getting in, as it's mounted on an external platform and you can have the prop or props nearer the stern 😀

Could be closed loop or push rods or chain drive your favourite!!

Regards Ray

Edited By Ray Wood 2 on 02/07/2020 11:29:18

Edited By Ray Wood 2 on 02/07/2020 11:29:49

[Bob Abell 2Participant @bobabell2]

Hi Ray

That`s not a bad idea and could look good too

Will bear it in mind, my mate……..Thanks a lot

May be too far from the props……Could fit the props pointing in reverse?

Bob

[Paul TParticipant @pault84577]

Bob I honestly don't know how the performance dynamics will be effected by moving the props and rudders so much further forward.

As you will remember a lot of time was invested in designing the hull around the motors/props/batteries/rudders in their current positions which equated to a very finely calculated centre of gravity, moving everything forward will significantly change this critical point and it is very possible that the model will become nose heavy and 'dig in' as opposed to gliding over the water.

Extra ballast would re-trim the boat but the extra weight will only compound the problem as the hull would sit to low in the water

I'm sorry to say that I don't think that it is a good idea however this is your build and you are free to do whatever you want, I might be wrong about how the change will effect the boat but if you want to try then I am happy to re-do the calcs but this will take a couple of days.

Rays idea has certain advantages but from the original design perspective it would ruin the hydrodynamics of the stern by introducing a surface piercing element in an area intended for smooth water.

Another soloution to your problem would be to fit azipods with full 360deg rotation, this would have the advantage of lowering the C of G without moving it further forward.

Paul

 

 

Edited By Paul T on 02/07/2020 11:51:40

[Bob Abell 2Participant @bobabell2]

Thanks Paul

Will weigh up the situation when it`s come to the rudder stage

It`s just something to think about in the mean time

The build is very interesting and addictive

Bob

[Paul TParticipant @pault84577]

Bob

It was a very addictively demanding hull to design as it was neither traditional planing nor displacement but a hybrid of both with a lot of aerodynamics thrown in.

Paul

[Bob Abell 2Participant @bobabell2]

Rapid progress today

Opened the decking for access to the motors and control gear etc

The big question is…..What motors and where will the rudders go?

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. Use the 850’s if you have a pair.

What did the design specify for rudder placement?.

If not… rudders as far back as tiller operation will allow, props in front?.? You have loads of room there.

Use a “remote” servo, operate the tillers via a long aircraft control line snake so the servo can be forward.

Ashley

(awaiting ratification of suggestions by the design supremo)

[Bob Abell 2Participant @bobabell2]

Thanks Ashley

El Supremo is ominously quiet on the motor subject at the moment

You mentioned 50mm plastic props…..Sounds about right

Will be working on the super structure while I make my mind up

I like the idea of the chunky 850`s though and the plastic prop too

Bob

[Paul TParticipant @pault84577]

Bob and Ashley

The 850s sound like a good solid answer to the question of motors as for rudders you could fit moveable kort nozzles around the props.

Paul

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