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Author Topic: First post/First RC Boat build - Advice needed.  (Read 7434 times)

Riley_NZL

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First post/First RC Boat build - Advice needed.
« on: August 03, 2013, 06:42:36 pm »


First off, hello. I'm from the deep south of New Zealand and was pointed here by a member of another forum.

I've built a couple boats before but nothing RC. I've started building a new hull, similar to this sail one I built several years ago, but minus the sail/mast and with a cabin on top:






I've started looking at parts and would like some advice on what I should go with, I'm not looking to race just yet, just get around at a decent click and have some fun. I may end up using this as a camera platform. Below is my shipping list so far:


I'm also a bit stuck on on a RC unit, I was looking at either the Spectrum DX6i , or the 5 channel one. Or would I be better getting one of the surface ones (Spectrum DX4S).

Any advice would be appreciated. Also a couple photos of the non RC boats I've built:








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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #1 on: August 03, 2013, 08:03:59 pm »

Sorry, forgot to actally link the shopping list:


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hopeitfloats

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Re: First post/First RC Boat build - Advice needed.
« Reply #2 on: August 03, 2013, 11:04:03 pm »

hi riley from a fellow mainlander and welcome to the forums.  where are you sourcing your parts from. that's a reasonable list you have there.
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #3 on: August 04, 2013, 02:17:24 am »

Thats all from hoobyking.com, I've played it on the safe side so that I don't forget something and have to pay for a second lot of shipping.
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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #4 on: August 13, 2013, 12:48:23 pm »

Hi Riley,

What size is the new build?
Will the sponsons be flat bottomed like your sailboat?

Reason I ask, is the fact that with two 2000Kv motors on 3S, you'll have close to 20.000 rpm under load, which is in fact (small) speedboat material, aka a 50 - 60 cm hull that will get on the plane, running 50 km/h.
Combined with the relative small Ø28 mm motors, you'll be only able to turn a small prop, something like Ø 30 mm.

To me, this combination sounds like a complete mismatch, if you're planning on pottering around, running at partial throttle a lot, which will cause both motor and ESC to overheat.
I doubt if the 35A ESC's will have the headroom to cope with long time partial throttle, watercooling or not.

Please let us know what size and speed you are looking for.

I'm missing two cooling jackets for the motors in your shopping list.

Regards, Jan.
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #5 on: August 13, 2013, 01:26:29 pm »

Thanks for the reply pompebled.


I've already bought the parts and they are (slowly) on the way. The boat is 60cm long, It had occurred to me to try make a V shaped bottom (it's flat at the moment). At this point I've only made the top/bottom and bulkheads so it may be possible for me to make a V shaped bottom still.


Not having had an RC boat before it's kinda hard to judge the speed I'd want, 20-30km/h maybe? In my mind when buying the parts I thought not using full throttle on them would be easier on them, but I guess when I think about it, it means the ESC has to drop the voltage for partial throttle. I think the Props I ordered are 35mm. Would I be better getting a couple low KV outboards and a bigger props?


As for the cooling jackets, there wasn't anything in that motor size so I'm planning on just making my own from some copper or AL pipe.
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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #6 on: August 13, 2013, 03:36:31 pm »

Hi Riley,

Watercooling jackets for Ø28 mm motors are easy to find on eBay:
http://www.ebay.de/itm/DE-Leopard-Boat-Motor-Water-Cooling-Jacket-LB28WCJ-40MM-/271100127773?pt=RC_Modellbau&hash=item3f1ed3aa1d
Although the motors you ordered are four pole motors which run relatively cool, compared to two pole motors, an aluminium coil won't cut it, due to the small contactsurface of the pipe on the can, you really need a jacket where the water runs directly on the can.

Some pictures of your build would be nice to get some idea of the available space inside the hulls.

Will you go for fully submerged props, or surface piercing drive (= roostertail)?

Keep in mind, that with a submerged drive, the angle of the propshaft needs to be as shallow as possible, to avoid pushing the bow down, reeking havoc with the riding attitude and handling.
A shallow Vee at the bow will help getting the cat on the plane, assuming you're not building a scale catamaran with a tunnel section on which the boat will 'float' when at speed (hence me asking for pictures...).

Regarding running partial throttle; a brushless ESC doesn't lower the Voltage to the motor, it chops the full Voltage up in small pulses, the slower you go the smaller the pulses.
This 'chopping' is done by the Fets which do the switching, on and off, the more switching occurs, the more heat builds up.
That's the reason you can't run a brushless setup in partial throttle for longer periods of time, unless you take ESC's that are way too large for the motors and won't heat up, because the load is just too low.

I tried running a brushless setup without watercooling some time ago; a 40-50A outrunner, turning a 60 mm two blade prop on 4S Lipo, controlled by a 150A ESC.
It was a very hot day and the sun warmed up the interior (and the motor and ESC) to 40°C, so I was curious how long things would run before the overheating protection of the ESC would shut the propulsion down.
You can read all about it here:
http://www.modelboatmayhem.co.uk/forum/index.php/topic,34033.0.html

I just returned from a ten day vacation on the river Weser in Germany and I ran that setup for over an hour every day without any trouble, no overheating (after watercooling was added) of the components, nothing warmed up beyond 45°C.
As you can read in the topic I linked to, I went slightly overboard on the power installed; over a 1000W in a 110 cm long stepped hull with an ESC the can handle three times the max Ampdraw of the motor, but that's what it takes apparently to enable me to run partial throttle for such a long time...

The shallow Vee of my build is something you could copy on yours.

Regards, Jan.
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Richardjm

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Re: First post/First RC Boat build - Advice needed.
« Reply #7 on: August 13, 2013, 05:24:34 pm »

Hi There


I have a Spectrum DX6i which works well. Best feature is that you can adjust servo travels in the software. In my case that was essential for sail winches and you may find it useful if you build RC yachts in the future.


Richardjm
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #8 on: August 13, 2013, 07:21:47 pm »

I'm building it at my parents and I won't be back up there for a couple weeks, so I'll post some pictures then. I just bought two of those motor jackets, thanks for the tip. I might try and build a temp guage into the motors and esc that creates a loud noise or something if they get above a comfortable temp. I think I will be going for a submerged prop, from what I've been reading surface piercing props are good on high rpm boats due to cavitation etc, is 20,000 rpm consider high enough to look at surface piercing?


If it turns out these motors are no good for this setup I'll just buy some new ones and use these ones in one of the other boats I'd like to build at some stage.


As for the transmitter, the more I look at the higher spec ones, Dx7 etc, the more I want to get one of those for telemetry etc, although realistically, even a Dx6i is pushing my budget.
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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #9 on: August 13, 2013, 08:41:23 pm »

Hi Riley,

Yes, surface piercing drive works from about 15.000 rpm(large prop) into the 42.000  rpm (smaller prop).

For a subsurface drive 10.000 rpm is the limit and requires a well dialed in setup regarding the prop type and -shape in order to avoid cavitation.
Somewhat lower rpm works more comfortably and still give sufficient boatspeed, depending on the setup.

Regards, Jan.
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #10 on: August 16, 2013, 08:45:38 am »

Kinda wish I hadn't spent the extra $50 on the fast (5-7 day) shipping, it's been two weeks and hasn't even arrived in my country yet.
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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #11 on: August 16, 2013, 01:38:45 pm »

Relax,

Modelboat building shouldn't cause stress...

HK orders take three weeks (or more) to reach the Netherlands too.

Regards, Jan.
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #12 on: August 17, 2013, 09:01:34 am »

On the bright side, the motor cooling cases already arrived only 4 days after I bought them! Pretty good for international shipping.
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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #13 on: August 17, 2013, 09:30:22 am »

As for the transmitter, the more I look at the higher spec ones, Dx7 etc, the more I want to get one of those for telemetry etc, although realistically, even a Dx6i is pushing my budget.
Hi Riley,

For a theater project I purchased 15 sets from this seller:
http://www.ebay.de/itm/150864289440?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

The FlySky Tx/Rx sets are sold under different brand names and are widely used, I have programmed the 15 sets without a single hick up, for their price they work excellent.

This seller includes the USB cable, while at HK, the (orange) set is cheaper, you'll have to order the cable separately.

This transmitter can only be programmed via PC and the software that comes with it is very 'Chinglish' and confusing to work with (due to the wrong names for some functions).
I'm using this manual to work with the software, for a first time it's a steep learning curve, but even I have managed to get it working right, so you should be OK...
http://helihelp.rabbitsvc.com/Default.aspx

Regards, Jan.
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #14 on: August 17, 2013, 09:47:33 am »

Thanks, I was looking at a similar set from HK which I believe is also a rebranded FlySky product. The only complaint I've seen about them is they have a  high rate of not working straight out of the box, but at the price I could buy two or three for less then a Spektrum set and have a couple spares in case they do break.
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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #15 on: August 17, 2013, 12:34:07 pm »

Hi Riley,

This is the HK equivalent:
http://www.hobbyking.com/hobbyking/store/__9042__Hobby_King_2_4Ghz_6Ch_Tx_Rx_V2_Mode_2_.html
(comes without USB cable)

This is the receiver which you'll need if you want to run more than one model with the same transmitter:
http://www.hobbyking.com/hobbyking/store/__12901__Hobby_King_2_4Ghz_Receiver_6Ch_V2.html

You can save the setting for each model and upload them to the transmitter when you want to run that specific model.
Not the most user friendly way when you're at the pond without a computer, but you can always take a portable computer with you...

Regards, Jan.
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #16 on: August 19, 2013, 03:31:53 am »

All arrived today:








Going up to my parent this weekend so hoping to get some building done on the boat. Also still need to decide on which R/C set to by.
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vnkiwi

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Re: First post/First RC Boat build - Advice needed.
« Reply #17 on: August 19, 2013, 04:49:27 am »

Hi Riley,
I have been using the transmitter and receivers that Ian (pompebled) recommendsfor the past year, before that I had the 4channel transmitter with same receivers.
No problems ever.
I have 8 receivers in various boats, all bound and setup the same as I only run one at a time.
Will be buying more from Hobby King soon as well.
Cheap and cheerful, but works for me.
Only brought the 6-channel, as I need the extra channels for my amphibian aircraft.
cheers
vnkiwi
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #18 on: August 19, 2013, 06:45:32 am »

Did you buy it from hobbyking/ebay, or did you find one for sale here in New Zealand?
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vnkiwi

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Re: First post/First RC Boat build - Advice needed.
« Reply #19 on: August 19, 2013, 07:01:25 am »

I buy direct from hobbyking for these items, direct from other chinese electronic manufacturers for other items.
Items I can not get here in Hamilton. Items I can get here I buy local, as long as the price is not a real silly one
cheers
vnkiwi

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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #20 on: August 19, 2013, 08:23:38 am »

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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #21 on: August 19, 2013, 08:47:02 am »

Would this battery pack be suitable for the Tx you linked?
http://www.hobbyking.com/hobbyking/store/__17955__HobbyKing_1500mAH_LiFe_3S_9_9v_Transmitter_pack_.html
Hi Riley,

No, the FlySky Tx works on 8 penlight batteries, so if you want to get a lipo pack, it'll have to fit in the battey compartment.

I recently replaced my batteries with a Lipo receiverpack, I'll look up which one it is and get back to you.

Regards, Jan.
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pompebled

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Re: First post/First RC Boat build - Advice needed.
« Reply #22 on: August 19, 2013, 05:59:01 pm »

Hi Riley,

This is a (size wise) fitting Lipo receiverpack:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=23814

None of the connectors that come with this battery will fit in the FlySky, as there simply is no connector inside the casing.

I solved it by soldering the wires loose from the battery tray and solder a male and a female Ø2 mm goldplated connector onto the wires.
I cut off one pair of connectors from the battery and replaced them with the Ø2 mm goldplated counterpart.

As the battery is a tight fit, I bent back the penlight clips to avoid damage to the Lipo.
I connected the battery to the connectors on the transmitter and pushed the connectors in the casing, to have more room for the Lipo in the battery tray, it fits like a glove.

It has been three weeks since I charged the Lipo and I have been running my boat for an hour almost every day since...

Regards, Jan.
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Riley_NZL

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Re: First post/First RC Boat build - Advice needed.
« Reply #23 on: August 27, 2013, 04:48:27 am »

Ok so here is where I left off:












And this is what I got done this weekend at my parents place:






















The last photo the deck isn't glued on yet, the beams between them are only glued to one hull. I've got the second side for each hull bent and ready to go. Below is the wood bender my father made, it's just an old LPG burner under a 20mm piece of steel plate, with the bar welded to it. Also made some prop shafts with some piece of 4mm brass welding rod:

















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Circlip

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Re: First post/First RC Boat build - Advice needed.
« Reply #24 on: August 27, 2013, 10:36:19 am »

Wonder if the prop or coupling is going too rattle on that shaft? Not a good idea to grip a split die in moleys.
 
 
   Regards  Ian.
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