Slo mo Shun

[Paul TParticipant @pault84577]

Sorry Bob

 

Cant make anything out except black land, grey sea and sunset……is it Iceland?

 

How long will you super motor setup run for before needing a re charge…..3mins?

 

Paul (international traveller)

 

Edited By The Fat Controller on 14/10/2009 10:45:01

[Bob Abell 2Participant @bobabell2]

Come, come now,  Paul

 

On the left is Wales, Boyo …….and on the right is Mona`s Isle….now known as Paul`s Island…………..and just in front, to the right a bit is Puffin`Island….Where you come from!

 

Bob

[Paul TParticipant @pault84577]

Well that explains the photo………now what about the run time for your brushless motor?

 

[Bob Abell 2Participant @bobabell2]

….and beyond that……where the bright light is coming from is……Yes!, Your right!…It`s Iceland!

 

Bob

[PierreParticipant @pierre]

ffice:smarttags” name=”City”>ffice:smarttags” name=”place”>

Hi Bob

Congratulations on an outstanding build  –  I look forward to seeing the completed model and  a report on how it runs!

I haven’t checked in to this forum for a while so the points I’m about to mention might have been raised already  – if so excuse the repetition.

My Slo Mo Shun is much smaller, length overall 800mm. I found an old plan on the  internet and also used the Model Boat article as inspiration for the build.  I use a Graupner  Speed 700 motor with two 9.6 V Nicad packs in parallel. Propeller is a 45mm two blade Graupner. ESC is a 45A forward only, designed for model aircraft – very small and light.

Initial trials weren’t very encouraging. Using the Model Boat article I had positioned the propeller about 5 mm behind the transom. This produced a huge amount of cavitation and no forward motion (much to the amusement of my fellow club members!)  Back to the drawing board and a new longer propshaft, with the propeller projecting about 2  inches behind the transom. This produced a dramatic improvement and the boat came onto the plane almost instantly.

The boat of course is designed to go fast in a straight line and it shows in the model!  You’re going to need a large lake  – turning circle is to put it mildly, generous.  I later improved this with a larger, deeper spade rudder .  I also wondered if having the rudder in a central position, instead of offset, might not improve matters.  Also a vague thought, not acted upon yet about linking the “air rudder” with the rudder servo. Full rudder turns weren’t possible unless using reduced throttle, which resulted in the boat falling off the plane and behaving in a more stable manner.

Ballast was critical, both fore and aft and athwartships.  Too much weight aft and it didn’t rise onto the plane, too much forward and it was too sensitive to every little ripple on the water. The rotational torque of the prop produced a list running at full throttle, corrected with ballast in the higher sponson.  A better method, I think would be a small, vertical trim tab on the lower sponson.

Anyway, I had fun setting it up and the roostertail it produced when running at full bore made it all worth while!  Am now thinking of brushless motors and LiPo batteries, exchequer willing!

Hope this was constructive.

lace w:st=”on”>Pierrelace>

[Bob Abell 2Participant @bobabell2]

Hello Pierre

 

Long time , no read!

 

Thank you for your constructive comments and info on your model etc

 

I`ve read that surface piercing props don`t steer too well at low speed and this type of boat only goes round the course in one direction only…..that`s why the rudder is offset!

 

Don`t think reverse will be required either

 

I`m certainly going to connect the water rudder to the air rudder…..if only for visual effect

 

The expert friend I referred to, does recco a little protrusion down below somewhere

 

Call again Pierre……………….Bob

[Bob Abell 2Participant @bobabell2]

Paul………………..The runtime of this system…as seen at Bury was about  20 mins…which ain`t bad really

 

If my boat performs reasonably well…………..I`ll have a few spare sticks on hand

 

Cheers my M8………Bob

 

PS….What`s the basic weight of your Barrelback?

[Dave MilbournParticipant @davemilbourn48782]

Bob

(You could have sent me a message, but never mind, eh?)

I have absolutely no experience of brushless motors whatsoever!  We have chosen to avoid this technology as it is still in its infancy with regard to model boats. LiPo batteries have all sorts of issues as well and definitely are not for the “fit-and-forget” brigade. Mistreat them and they will go BANG. Most of our customers start their telephone calls with “I’m an idiot when it comes to electronics” – ’nuff said?

Having said that, brushless motors seem to be a lot more efficient than the brushed types for fast planing hulls and I can well believe Herr Graupner’s man. Your SloMo is a big beast and needs as light and powerful a drive system as you can get.

Take a deep breath and write a cheque………….or borrow a couple of quid from TFC!

Dave M

Edited By Dave Milbourn on 15/10/2009 19:19:52

[Bob Abell 2Participant @bobabell2]

Thanks Dave

 

The basic boat only weighs 7lb……..So I`m feeling confident?

 

Bob

[ashley needhamParticipant @ashleyneedham69188]

The efficiency is what you pay for in a brushless motor, and in a big boat like yours you could do with some of that to get a decent run time, Substantial gearing may be called for as well, as the more powerfull motors run to 50,000 RPM…..

 

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you, Ashley

 

But my expert friend uses brushless motors running at only 840 rpm

 

Good point though, the boats at Bury, simply scream round the lake and motors running at 840 rpm….Don`t scream!

 

You`ve got me thinking now……….Bob

[ashley needhamParticipant @ashleyneedham69188]

Conventional brushed motors vary quite a bit in size, from little 140 can-sizes, to whopping 800`s, but I have not thus far seen such a variance in brushless jobbies.

 

I agree, you can get low volt-per-rev motors for direct drive applications, but in my limited experience the much more powerfull volt-per-rev motors just seem to be much smaller, and are designed to drive  (typically aircraft) props via quite a high ratio gearbox, or am I speaking rubbish here?

 

However you look at it, your boat is going to have a biggish prop and needs to turn a bit quicker than 840 rpm…

 

Ashley

 

 

[Phil Winks 1Participant @philwinks1]

very slightly Ashley depends on what you call a high ratio box!  the small high Kv motors(Kv = revs x volts) are usually only reduced to about 5:1 however there are much larger high Kv motors that turn up to 80 or 90mm fans in EDF units (Electric ducted fans) without a gear box. and there’s a clue to the 840 figure that bob mentions I’m guessing that is the Kv figure for his proposed motor and he is I gather using an 8s1p bty (8 cells in series 1 in parralel) at 3.7volts per cell now correct me if I’m wrong but aint that 24,864 rpm  840 is quite a low Kv so if the motor is an outrunner I’m tipping it will have good tourque.  Please note that the max rpm figure is only its potential and prob off load so actuall rpm will depend on the prop size and vessel weight and drag etc etc etc

[Paul TParticipant @pault84577]

And for warp speed add the dylithium crystals at 4g p/millisecond over a period of 7.342 seconds but only if the motor is turning in the same direction as the earth if not you will meet yourself coming back.

All this changes if you use a Headron machine which you have to switch on next August to sail last week at a speed of minus 4kph upside down with your finger in your ear.

 

Paul (sticking to simple)

[Bob Abell 2Participant @bobabell2]

That`s putting the whole situation in perspective, Paul, or are we on some new medication?

 

Seriously boys…………This is getting very technical and is beginning to spill over into Colin`s thread about OTT technical complication

 

Now that Dave has confessed that he knows nowt about the brushless stuff and considering he is an expert…………..We`re in for a struggle!

 

The struggle is a struggle because the gear is so expensive and we haven`t got anything to copy

 

I`m going to have further talks with my expert friend shortly and try to understand the subject a little better!………………..Paul, got any more of those pills?….I`m going to need something psychodelic to clear my head!

 

Thanks to Ashley and Phil for your constructive thoughts

 

Bob

[Paul TParticipant @pault84577]

Bob

 

Try a different route to solving your problem and also give a thought to just how fast you want your little boat to go (does it really need to fly)

 

If you had built this model 10 years ago, and given that you don’t want to use a petrol engine what would you have used as a power plant?

 

Perhaps a pair of high speed buggy motors driving a single shaft and a couple of packs of nicads?

 

Paul (still sticking to simple)

 

As for medication I could open my own chemists shop

[Bob Abell 2Participant @bobabell2]

Perhaps you`re right there, young man

 

I could go back to the gear that Dave recc`d at Llanberis and have a peaceful life!

He recco`d  twin props…..my expert recco`d one prop for good reason….Hmmmmmm?

 

I`ve always wanted to sail the boat at Etherow anyway and run about in all directions, with the occasional burst of speed…………The brushless route may not allow stooging about?

 

The motor drive decision is a long way off at the moment, so the matter is academic

 

I`m really surprised that nobody out there has constructed a similar sized model?

 

Bob………..With head spinning like a BM!

[ashley needhamParticipant @ashleyneedham69188]

see I knew I was talking rubbish! Although you were taliking LiPo batteries I think.

 

The trouble with all this is the motors are expensive and if they dont perform, it will cost you. This is the problem with doing something different…the great unknown, and getting really great conflicting advice!

 

If I was building this I think i might try an 800 ish sized motor and NiMh packs as a starter?

 

I sense a good article for someone here, to try, say, three standard sorts of hulls (tug,cabin cruiser/pt boat and, oooooo a something else), and fit them with an appropriate  conventional brushed motor, and note speed,current consumption,duration etc, and then brushless them up and see what the difference is. Then we would have some sort of comparison to start with.

Even a comparative table would be handy, equating power/prop turning ability..

 

Ashley

[Bob Abell 2Participant @bobabell2]

A good idea, Ashley.

 

I could fit the stuff that Dave recco`s……………………If it`s a no goer…………fit the brushless option……..if that don`t work……….take up knitting and call it a day?

 

My problem is…..Do I want a car or a motor bike?………..Answer……make two boats!

 

Bob

[Bob Abell 2Participant @bobabell2]

Another thought….

 

Will a twin prop boat go faster than a single prop?

 

I was going to jump in with both feet, with……..”The Spitfire went faster than a twin engine bomber”…………………then I thought about the Moquito and Lockheed Lightning!…….They were fast!

 

So………Do I fit twin or single props?

 

Bob……..Staring into space, looking blank……and fed up!

[Phil Winks 1Participant @philwinks1]

Someone hit the nail on the head back there somewhere we do not appear to have any data easily available on power to weight requirements and suitable prop/motor combinations for either brushed or brushless motors in the model boat world. It was easy when I was building model aircraft as that sort of data was easily available most motor manufacturers recomend a prop size and give consumtion data as well and once you’d sused that a trainer plane needed 80w/lb and anareobatic model needed 100-120w/lb it all became relitively simple I have to confess to some bewilderment when it comes to choseing even a good old brushed motor/prop combo for a new model. starting to get there now though. Perhaps model aircraft atract more techno geeks and boats more technophobes. We definately need some one with deep pockets and lots of patience to develope some comparison tables.

 

Fit a single Bob! thats assuming the original only had one

 

Phil off to the shed to charge some good old NiHm and NiCd bty’s

[Bob Abell 2Participant @bobabell2]

Thanks Phil….More food for thought

 

Just looked into what the scale speed is…….and it`s quite slow

 

The speed of the full sized Slo Mo was nearly 180 mph

At 1/ 6th scale, this works out to be 30 mph…..Which is 88 feet per minute

And this works out at only 1.5 feet in one second!

 

Conventional equipment should be OK for this speed…….but would it look right?

 

Bob

[ashley needhamParticipant @ashleyneedham69188]

No, water is not scale, and I have never subscribed to the “scale speed” thing. Although its deceptive just how fast large boats are,or appear to be on the water.

 

I was disappointed with my Fantome (48″ long by 14″ wide) when i first had it out, as there was virtually no noise (the Torpedo 800s run at a miserly 5500 Rpm) and it didnt appear to be as fast as I had hoped . BUT when in company with other smaller “fast craft” or the RTR types , it was apparent that generally it was FASTER then most of them. The other one, my Seahawk, which IS a bit faster, looks to be MUCH faster, being a bit smaller (40″) and sitting higher on the plane.

 

For your project, the only advantage I can see for fitting twin props is you can up the power to each one easily, up to the practical maximum (bb820 or something), and have twice as much “go” as opposed to a single shaft, WITHOUT bothering about twin geared motors and all that mucking about.

 

Having spent all that time and effort on the thing, I would say that if the original had only a single screw, then thats what you should fit!  and after you have finished it, using a single shaft with a 90mm (or whatever!) plastic prop, you can then have a fantastic looking brass one made to finish it off nicely and garner additional pondside admiration.

 

 After all, the boat will spend most of its time OUT of the water being looked at, and in your minds eye if you had fitted non standard twin props there would be that  nagging “I should have only fitted the one prop” thing going on in the back of the old bonce. It would if I had built it!

 

Ashley

 

 

 

 

 

[Bob Abell 2Participant @bobabell2]

Thank you, Ashley

 

No matter how slow the boat appears to travel….the calculated scale speed is the correct speed. The overall appearance would benefit from extensive spray from a surface piercing prop and a large speaker with roaring engine sound……but can`t see a way of getting the noise out!

If the boat was balanced, it could give the appearance of getting on the plane?

 

I`m thinking that if I go the normal motor drive route…two props would be essential!

 

Picture above shows the business like high performance stand and some progress on the fin area

 

Bob…Still clutching at straws!

[Dave MilbournParticipant @davemilbourn48782]

Bob

I haven’t kept up with this thread so I’m not sure quite how big this model is. However, at the Llanberis do was a gent who has a 49″ Perkasa powered by ONE of the motors I showed you, running on 20 cells with a X55mm x 2 blade prop. At full chat the rearmost ten inches of the hull are in the water – just – and the rest is airborne. The model is considerably heavier than SloMo. He reckons he gets nearly an hour running time from one charge. There is a video of the model doing its stuff on YouTube somewhere.

Motor is £30; 20 x 4600mAH cells would cost around £73 and the same speed controller as he uses is £54. Just to give you some idea of what you might expect in the way of bangs for your bucks if you go down this route.

Dave M

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