“Tinkering” experience, need advice on 1/32 electric PT Boat project?

[Charles MiddletonParticipant @charlesmiddleton91027]

[Charles MiddletonParticipant @charlesmiddleton91027]

Evening all,

New to the forum – so hi and thanks for letting me join!

K – bit about my background in this area.

Basically, have rebuilt / renovated a couple of old mamods, done a bit of soldering (on the mamod pipework), like to learn and challenge myself on new projects like this.

So…

Bought myself what I think is a scratch built 1/32 PT style boat (on fleaBay).

Unfortunately, I know nowt about RC equipment – but always eager to learn new skills from experts like yourselves!

Will try and post some pics with this thread, but basically I'm wanting to fit full electric RC gear into this model.

She has waterscoop and "outlet", rudder, prop etc – all waiting for the rc gear.

Now – took her to a certain shop specialising in RC gear, to get all the gear I needed.

First thing they tell me, is that the prop shaft is in the wrong place, at the wrong angle – and basically needs the shaft moving and the hull redoing to allow for the move.

Kinda got the idea they couldnt be bothered, but lets see what you guys think…

The prop shaft has a "flexible rubber" section attached to the end, which I believe is supposed to act like a UJ between the motor and the shaft?

Kit I have so far / on order:

1x boat (pics and dims to follow)

1x 8-chann transmitter (presumably ex-rc aircraft)

1x motor with water cooling

(http://www.hobbyking.com/hobbyking/store/__8595__2040SL_4800kv_Brushless_Inrunner_WaterCooled_.html?strSearch=2040)

1 x ESC with water cooling

(http://www.hobbyking.com/hobbyking/store/__24567__HobbyKing_30A_Boat_ESC_3A_UBEC.html?strSearch=30A%20boat)

Basically, the shop I took her to said with the angle of the prop shaft as it is, I wouldnt get a motor in?

I've spent so long "guessing" how / if I can fit the motor (let alone anything else) that I just got some advice on which motor from HK, then will try it and see!

AFAIK, the UJ is meant to allow for any difference "in-line" between the motor and the prop?

So, in addition to the "flexible shaft" on the end of the prop-shaft, I've also ordered a couple of 4mm->3mm UJ's to allow for even more "discrepancy" in the shaft>Motor.

Dont know if I'll need them, but only cost a few £!

QUESTION: Can I mount the motor itself at an angle (to take up more of the angle between the motor and the prop shaft), or should it be mounted horizontally?

QUESTION: Quite like the idea of a small gearbox between the motor and the shaft – to both take up the angle and increase speed / reduce torque on the motor. Good idea?

QUESTION: The motor as above has the water cooled jacket, with I believe 4mm barbs on to connect the hose (which im assuming is like aquarium air hose, which I have).

The scoop / outlet already on the boat look a bit like these…

http://www.modelshopleeds.co.uk/catalog/popup_image.php?pID=7245

Unlike these however, the outlet on mine looks more like the fixing on the back of the scoop shown – looks like 6mm bore with thread on the outside?How does one attach the hose to them?

So, apologies for all the dumb "noob" questions – I've spent so long "thinking about" this project, I think it's best to make a start (hence the motor) and see what I can work out from there.

Any help or advice much appreciated!

(If you need any more info, dims, pics etc to be able to advise, please let me know and I'll post).

Pics (These are shared from my G+ album, not sure if you'll be able to see them – will work out something else if not).

https://plus.google.com/116563859822186576309/posts/TMLByumo6Lr?pid=6047880751969958450&oid=116563859822186576309

https://plus.google.com/116563859822186576309/posts/TMLByumo6Lr?pid=6047880752203589122&oid=116563859822186576309

https://plus.google.com/116563859822186576309/posts/TMLByumo6Lr?pid=6047880753105534994&oid=116563859822186576309

https://plus.google.com/116563859822186576309/posts/TMLByumo6Lr?pid=6047880753419072002&oid=116563859822186576309

https://plus.google.com/116563859822186576309/posts/TMLByumo6Lr?pid=6047880752236817378&oid=116563859822186576309

[lnvisiblemanParticipant @lnvisibleman]

Hi and welcome

having had a look at your pictures, I would suggest that you mount your motor as low in the boat as possible and then use a belt drive to connect with the shaft. By varying the size of the pulleys, you have the ability to change engine speed and torque that is transferred to the prop. The motor will need to be at the same angle as the shaft to keep the belt on the pulleys.

I am no expert on propshaft angles but even though yours may not be at the perfect angle, it will work ! I only know coz I have the same teeshirt.

Mike

[Charles MiddletonParticipant @charlesmiddleton91027]

Thanks MIke,

Like the idea… that was one of the thoughts I had too!

Will see how things look when the motor arrives, and go from there.

Charles

[Malcolm FraryParticipant @malcolmfrary95515]

Motors do no care which way up they are, so can be mounted at any angle, but preferably parallel to the shaft they are driving if using gears or pulleys. If driving in-line, the angle can be taken up by a double universal or a CV joint, but straight alignment is best. Going a bit radical, and someone else will need to answer the questions raised, a brushless motor with a solid coupler might be a good answer.

The steep angle was not uncommon in full size launches – http://albatrossmarine.co.uk/boat-types – and scroll down a bit for a side drawing, and your model was probably following this practice. With an adequate motor, water cooling should not be needed so the water cooling arrangements could be dispensed with. I think that the fewer chances of getting water inside the boat, the better.

[Charles MiddletonParticipant @charlesmiddleton91027]

Thanks for your responce, Malcolm.

Yes, I think I may well end up doing it that way, with the motor mounted at an angle in line with the propshaft.

Re the watercooling, the scoop and outlet (two outlets – one either side) were already in place when I got her. That, and the motor has the watercooled jacket – and should be here in a couple of weeks.

Certainly take your point about least-points-of-ingress – let's see how I get on with the motor, then I'll see what I can do on that front.

Thanks again for your advice!

ATB,

Charles

[Dave MilbournParticipant @davemilbourn48782]

Charles

On 2S LiPos that motor will want to rev at something like 35,000RPM. This is way too fast for anything other than perhaps a surface drive i.e. a semi-submerged prop. You will not be able to fit such a drive to a scale PT boat. Even if you could find a suitable fully-submerged prop it's certainly well into "fast electric" territory. You haven't said how big the boat actually is; 1/32 scale would be around 36" long? That being the case then I would suggest an outrunner type of much less kv (<1400) like one of the Turnigy 2822 series.

Malcolm is right when he says that motors must be mounted in line with the prop shaft – especially if the motor is running at lunatic speeds. You can't take up large differences in angles and drive lines with the use of multiple UJ's – certainly not at the rotational speeds we use in electrically-powered model boats.

There is a lot of rot talked about shaft angles (sorry, Paul). For example, the Fairey Huntsman has twin shafts which are at 15 degrees to the horizontal datum – I'm sure Alan Burnard wasn't castigated for not knowing what he was doing when he designed it! The three shafts on the full-size KD Perkasa are similarly angled, and V-T aren't noted for getting that sort of detail wrong. Any slight tendency for full power to lift the bow can be countered by using trim tabs on the bottom edge of the transom. None of my model Fairey boats has ever needed these.

I would advise settling on the right motor for the job and then fitting it in line with the shaft; if that entails moving the shaft to a steeper angle in the hull then that's what it means – you'll only have to do it once. I'd also suggest upping the spec of the speed controller to what the manufacturers claim to be 50A (it isn't, but these are inscrutable Chinese amps….).

Dave M

[Charles MiddletonParticipant @charlesmiddleton91027]

Thanks for the feedback Dave…

What do you think to a Turnigy D2822/17 1100k, as here… ?

**LINK**

or the 1450 kv as here?

http://www.ebay.co.uk/itm/D2822-14-Turnigy-1450kv-38g-Brushless-Motor-Outrunner-Small-Plane-UK-Seller-/131193918362?pt=UK_ToysGames_RadioControlled_JN&hash=item1e8bc4539a

and ESC as here…?

http://www.ebay.co.uk/itm/Mystery-Cloud-50A-Brushless-Motor-ESC-RC-Speed-Controller-2A-BEC-for-Helicopter-/300902108764?pt=UK_ToysGames_RadioControlled_JN&hash=item460f29ce5c

In most cases (barring hybrids) outrunners like this dont / cant have water cooling, which goes to Malcolms point of not needing the watercooling. If / when I get this new motor fitted inline, I'll block off the existing scoop / outlet ports.

How much heat do we think this will generate? Perhaps air cooling / heatsink cooling for a future idea? (Functional deck vents perhaps?)

But – one step at a time!

Re over all length… 32" long x 8.25" at the beam.

If you agree that new motor / ESC is apropriate, I'll get on and order them.

With HK's "up to 45 days" postage – these new ones will probably turn up before those!

BTW – any one here Yorkshire based?

THX,

Charles

[Charles MiddletonParticipant @charlesmiddleton91027]

If my newly learnt calculation is right, the 1450 on 3s @ 11.1v would 16,095 rpm – and the 1100 would give 12, 210 rpm. Of course, the prop has no markings, so I dont know what the pitch etc is on that for full speed calc.

Would the 12,210 be enough to get her on-plane?

Must say im leaning towards the 1450 @ 16095 rpm….

[Dave MilbournParticipant @davemilbourn48782]

Charles

I am also new to brushless motors so I've taken advice from those who aren't quite so green. I have bought the 2822/17 1100kv to run from a 2S LiPo in a model approx 24" long. I've also been put onto Hawk ESCs – specifically the 18A one here **LINK** and I've bought a programming card, as recommended. Haven't tried any of it out yet – the model is far from ready. You might well need a little more power but, as I've said, these things are still a mystery to me.

Trying to calculate model speed from no-load RPM and pitch is a minefield. You have to allow for slippage, loading up of the motor (less any unloading effect due to forward speed) and all manner of other variables. It's easier to suck it and see. Props are not expensive and you could probably justify both a 2S and a 3S LiPo to see which one suits best.

Dave M

[Paul TParticipant @pault84577]

Hello Charles

Sorry to invade your thread.

Hello Dave

Ha!

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