Brutus with Ghostly features

[Bob Abell 2Participant @bobabell2]

The feasibility of the Ghost craft that Paul is currently designing, is fascinating and novel, but the fruits of his labour are a long way off, before we can see it on the water

I was looking at the Brutus model the other day, looking all forlorn and neglected and realised that we could add the pivoting wings and sponson features without too much difficulty!

I also realised that the craft need not elevate so high, we only need to clear the water

Looking for the easy way out, the prop drives could stay unaltered and simply just add the pivoting wing things!

So in between building the VGC, I could get involved

The model is probably ideal, since it is quite fast and very light, we`ve got the Brushless motors in stock and the job knowledge too

Sounds a very exciting prospect?

Just to refresh our memories, here`s Brutus at speed on the water…..

Capt Bob

[Bob Abell 2Participant @bobabell2]

Mod to Brutus

[Bob Abell 2Participant @bobabell2]

Just like to add, that Paul is not being left out of this project

Paul designed Brutus and is a fine model and feel sure that Paul will welcome the project with open arms and get involved with the technical issues

Am I correct there, Maestro?

First thought……Could the arms be weighted and simply flop down into the water and as the speed builds up, the hull should rise up?

It would be a nice feature, though, to have the ability to raise and lower the sponsons, remotely

More good thoughts to follow

Bob

[Bob Abell 2Participant @bobabell2]

What about the rudders, I hear you say!

Simple…..Make them deeper…….Sorted

Paul…..What have you got, up your sleeve for making the sponsons?

Hollow tube or solid wood?…..Solid wood is not a bad idea…..It can float and is quite heavy, especially for the flop down version

Food for thought

Bob

[ashley needhamParticipant @ashleyneedham69188]

Food as you say. This would be a diffcult balancing act to get right with flopping arms, it may be easier to convert brutus into a Hydrofoil !! No THERES food for thought!!

Ashley

[Colin BishopModerator @colinbishop34627]

Wheels! It needs wheels!

Colin

[Paul TParticipant @pault84577]

Bob

Oddly enough I did do a set of drawings for adding hydrofoils to Brutus. I think that adding some Ghost style sponsons would be feasible but I would need to think about the practicalities.

However just thinking out loud….. I don't think the drop down units would work but I do believe that some method of mechanical device to deploy and recover the sponsons would be feasible.

I would use a lightweight but strong material to construct the sponsons, which I think should be hollow to keep the weight down.

Paul

[Bob Abell 2Participant @bobabell2]

Paul

The pivoting mechanism is proving more difficult than first imagined, due to the forces involved and the power required to lift the hull

Say the model weighed 20 lb

Each wing would need to exert 10 lb each downwards in order to raise the hull off the water

The radius arm inside the hull is about half the wing radius……..Internal force will be 20 lb

20 lb is a hell of a load for a model boat mechanism!

Ghost will require at least twice this figure…..That`s 40 lb on the internal arm

Can`t see any way round it!

Are you aware of this?

Bob

[Paul TParticipant @pault84577]

Hello Bob

Thank you for the very helpful input and I am glad to see that someone is questioning my work.

In relation to Ghost the constantly changing position of the mass in the sponsons was the first problem that I considered when I started looking at the feasibility of building this model.

The mechanism that you are worried about will actually be resisting far more forces than the obvious radial/vertical and is one of the reasons why the mass (motors/batteries) need to be in the sponsons.

In relation to Brutus I would propose that instead of using a swinging arm to deploy the sponsons it might be better to utilise legs set at 30deg to the hull sides.

I agree that, in both cases, traditional model boat machinery would be unable to operate against these forces. I do have a solution to both problems (involving simple mechanics) but I would be interested in hearing other ideas.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

The obvious solution to the surprising forces involved is to use screw thread mechanisms and geared motors

In which case, the loads can be handled with confidence

Will have to give the matter some careful attention

In the meantime……The timing belts have just arrived for the VGC

Bob

[Bob Abell 2Participant @bobabell2]

We seem to have found a solution to the Wing mechanism afterall

Using a motorised worm gearbox and vertical screw

The vertical load on the hull floor will be about 40lb! Due to the mechanical disadvantage of the mechanism

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. Like that. something similar could do for the other one eh???

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you Ashley…..I knew it would meet with your approval

Paul

Using one of the Motionco worm boxes and a 10mm screw, the wings on Brutus would take 20 secs to travel from level to 45 degrees down

Could we live with that?

It seems awfully slow?………We could cut the movement down, from just skimming the water to raising the superstructure just clear of the water

The sponsons need to have enough buoyancy to support the weight of Brutus in fresh air!

Bob

[Bob Abell 2Participant @bobabell2]

Paul

Brutus with two batteries weighs 16 lb

We could strip out the cooling fans and battery and save nearly two pounds, making it 14 lb

The wings and jack mechanism may increase the weight to 20lb

You propose the sponsons of 50 dia x 700 long

They look very small compared to the bulk of the hull?

I can imagine the finished model to be great fun on the water…..As the hull rises and the props start breaking the surface!

It should sound exciting too

If you adopted the same prop drive in your Ghost……It would make life much easier?

Don`t pooh pooh the idea straight away………Think of the simplicity of the drive…

One Abell drive and one violent 80mm prop!………I like this idea myself

Bob

Bob

[Bob Abell 2Participant @bobabell2]

Paul

What is to be gained by having moving sponsons in the first place?

Why not have fixed sponsons at any height we choose?…………Especially, if it is only a test?

Bob

[Paul TParticipant @pault84577]

Hello Bob

Before I answer your questions it might be a good time to remind everyone that we are discussing two different boats and two different systems.

Back to the Q & A

Brutus with two batteries weighs 16 lb

We could strip out the cooling fans and battery and save nearly two pounds, making it 14 lb

The wings and jack mechanism may increase the weight to 20lb

I think that you have been a little over enthusiastic with your weight estimate of the wings and operating system at 6lbs (that's 3 bags of sugar) I doubt that the new system weighs much more than 450g (1 lb) but I could be wrong.

I have been calculating the all up weight of Brutus including the new system as 7.5kg (16.5 lb)

You propose the sponsons of 50 dia x 700 long

They look very small compared to the bulk of the hull?

We must be careful not to confuse mass with bulk, Brutus does look bulky but it is really an empty thin walled box and therefore has little mass. The sponsons are sufficient to lift the boat.

I can imagine the finished model to be great fun on the water…..As the hull rises and the props start breaking the surface!

It should sound exciting too

It would both look and sound amazing although it might require a nice long stretch of water to test it on.

If you adopted the same prop drive in your Ghost……It would make life much easier?

Don`t pooh pooh the idea straight away………Think of the simplicity of the drive…

One Abell drive and one violent 80mm prop!………I like this idea myself

The Ghost is a totally different type of boat, it already exists and the propellers can be clearly seen on the front of the sponsons. I am not looking for simplicity…..if I was I would stick to designing house boats.

What is to be gained by having moving sponsons in the first place?

We have discussed this before………moving the sponsons adds speed and manoeuvrability to the boat.

Why not have fixed sponsons at any height we choose?…………Especially, if it is only a test?

If we have fixed sponsons we wont be able to properly test the boat……..unless you want to build several boats to test the sponsons at different angles.

Paul

[Paul TParticipant @pault84577]

Bob

I have been doing some work on the Brutus sponsons and whilst the 50mm dia tube works well, however they do benefit from having angled fins running the length of the outer edge of each sponson.

The fins need only be 15mm wide but the do provide an amazing amount of lift.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

Is this wing lift bonus…….. From the aerofoil shape or the kite effect?

I will use your sponson size as recommended and see how it goes…..They can easily be extended if necessary, anyway

The three bags of sugar weight, for the lifting mech is made up of…..Wormbox…..12mm Screw and nut……Coupling……Heavy duty 12v battery…..ESC……Four inner links and pivot pins……main block

I always look on the dark side

We can do it without too much aggro

Bob

[Paul TParticipant @pault84577]

Bob

The fins provide hydrofoil lift

Is your heavy duty 12v battery from a truck lol

This is how I see the sponsons working,

Paul

[Bob Abell 2Participant @bobabell2]

Paul

Just had a good idea!

With a 10mm screw, it would take 20 secs to lower the wings

With a special screw made on the lathe, we can now do it in 5 secs…..Or even faster, if we have the Jack motor power

Like it!……You bet!

Bob

[Paul TParticipant @pault84577]

Bob

How will you stop the motor overrunning when it gets to the maximum / minimum reaches of the worm drive?

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul…..Tough question….You have earned a pen just for enquiring….lol

We could use limit switches with the help of the Etherow electronic expert, the chap you met at Ellesmere last year

Or we could use a slipping clutch?……..A coupling with a spring loaded ball type of thing

We could counter balance the wings, to cut the load down?

The calc variables…..0.68 Nm ( 0.5 ft lb ) torque at the gearbox, 10mm screw with 1,5mm pitch…..Load on vertical nut is 40 lb

Brutus weighs 20 lb……Inner arm radius about 5"….Outer arm radius about 10"….ie, a mechanical disadvantage

Screw speed 156rpm = 10" per min = 3" in 20 sec

That's about it

Bob

[Paul TParticipant @pault84577]

Bob

Upper and lower limit switches will easily solve the over run problem.

By variables I also meant the effect that the increasing buoyancy load would have on your system.

There is one downside to the coarse pitch thread and that's compensating for the rapid shock load that the buoyancy from the sponsons places upon the worm drive.

Paul

Edited By Paul T on 11/01/2015 18:42:44

[Bob Abell 2Participant @bobabell2]

Paul

I would have thought that the sponsons meeting the water, would be a gentle loading?

If necessary, we could fit a compression spring under the nut, to act as a shock absorber?

Bob

[Bob Abell 2Participant @bobabell2]

Paul

Due to the amplified lever mechanism, we`ve got about 25mm spare thread, top and bottom, which is equivalent to about 20 degrees visual wing movement

We`ll use that as a reference to start with………If we have an overrun……The ball slipping clutch will trip out

Bob

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