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Old Apr 16, 2012, 02:31 AM
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Cheap fun boat?

Hi All,
I'm deciding if I should retire my old scratch built FE which is almost 25 years old. It runs well with a standard 540 motor but doesn't turn nicely at speed and has a history of flipping over. (costing me a GPS)
I'm giving it one more chance and have lowered the tiny rudder down more in to the main slip stream of the prop instead of just the upper half. I've seen the back of the boat lift when doing a modest turn at speed and believe this is the beginning of a possible flip.
When I made this boat all those years ago I was young and stupid but now I'm old and stupid and get tired of waiting 45 minutes for this to drift ashore.

I'm looking at possibly getting a cheap Chinese boat, see how it goes and perhaps adding modest upgrades. Does anyone have 1st hand experience of the NQD Mosquito RC 1/14 Large Aeroboat 757 BOAT? I think it is also referred to as the Silver Rocket.

Main attraction is the single motor and conventional servo steering (not differential drive). I'm in to electronics and write embedded software for my own PWM ESCs and would fancy using a 3S LiPo in this but is the boat and drive train up to it?
Would very much appreciate the collective wisdom of those that know better.
I should also add that I'm more in to woodies and scale boats but at times the boy racer comes to the fore.

Best regards,
David
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Old Apr 16, 2012, 05:00 AM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
5,116 Posts
Hi David,

Do a google search for the Graupner Key Biscayne and you'll know the Germans had their boats vacuum formed in China decades ago.

Most Key Biscaine's were set-up with a 700 motor by their owners and ran like this:
Graupner Key Biscayne RC Rennboot + LiPo Power (2 min 20 sec)


As it's a large hull, even for a 700 motor, you could install more power in the Chinese version, but you'd have to reinforce the hull to make it able to cope with 40 mph+.

Also the steering outdrive can't take much more than a 700 motor, it'll wear out very quick.
Quote of a wellknown German raceboater: a universal coupler doesn't belong in a fast electric.

In order to turn properly, the boat also needs a turnfin (on the right), or two, if you wish to turn left too (not the wisest thing to try at full speed...)

Other than that, it's a nice design, somewhat outdated, but who cares.

Regards, Jan.
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Old Apr 16, 2012, 05:39 AM
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Hi Jan,
Thanks for the reply.
I can now see the boat I'm looking at is a total knock-off of the Graupner but if it went half as good as the one in the video clip I'd be fairly happy. 25-30kph would be nice and I won't even expect the 30mph claimed in some ads for this modeI.

I accept I would have to stiffen the hull but will try to avoid over-powering it.
It's not a lot money involved but I thought if it was total junk I would rather make another scratch built boat off a plan.

Cheers,
David
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Old Apr 16, 2012, 08:11 AM
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If yours has a steerable outdrive, the "rudder" doesn't doesn't do anything at all except give you some steering ability with the power off.

What do you mean by "doesn't turn nicely"? Is it hopping and skipping, or does it just plow straight?
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Old Apr 16, 2012, 08:55 AM
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I have an NQD Spurt which has basically the same outdrive.................it'll work well at 35mph or less. Run lower rpms with a larger prop to keep the stress off of the outdrive u joint. I actually put a metal u-joint on mine and works well with a brushless motor.

The outdrive is also very similar to the Super Hawaii.

Oh..........the stock waterpickup barely works, if at all.
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Old Apr 16, 2012, 09:18 AM
I feel the need for speed!
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Here's my 37" Spurt on 6s lipo and a 540XL 1250kv

NQD Spurt 37" RC boat on 6s Lipo with XL brushless motor (0 min 41 sec)
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Old Apr 17, 2012, 01:22 AM
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Hi,
No steerable drive on this old boat. The motor was from an old off-raod RC car and the RC gear was salvaged from an old Tamtech car. I used the output of the Tamtech motor drive to run 3x low resistance FETs. This all works fine. The boat turns almost in its own length at very low speeds but at anything near full speed it is very reluctant to turn even slightly - virtually a straight line drag boat.
I suspect with light rudder the back of the boat is being lifted rather than turned and then the side of the boat digs in and it flips.
Given its age and its humble origins it is probably time I upgraded but it was quite fast and many of the "Happy Duck" boats look like they're dragging anchors and just frothing the water.

I'm impressed with the boat in the video but will resist going brushless just yet and will try the new boat stock standard before plotting any upgrades.
I've never used a steerable drive before and hope that the electronics are fairly standard if I want to move from 7.2V NiMH to 11.1V LiPos. This I can cope with fine but some of the differential drive boats would be hard to upgrade I suspect.
Water cooling (or lack of) well noted.

Cheers,
David
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Old Apr 17, 2012, 09:09 AM
I feel the need for speed!
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Here it was Brushed.......................700 Graupner 8.4. 4s lipo.

This is how I first modded it.....................it ran very well, cool and stable, i just wanted more speed

NQD Spurt 37" RC Boat Modification 8.4 700bb on 4s Lipo (1 min 21 sec)
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Old Apr 17, 2012, 10:34 PM
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Ok, hold on... so the NQD boat isn't the boat you're having trouble with? If the boat you're having issues with is the one in the picture and you're using tamtech gear, I bet the rudder is too small and/or the servo isn't strong enough. Are you using the old tamtech 1/24th scale parts, or the bigger ~1/16th scale tamtech parts?
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Old Apr 18, 2012, 02:19 AM
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Hi,
No the NQD "Happy Duck" boat is the intended replacement for the troublesome white scratch built boat.
I can't remember the Tamtech scale but I think the rudder is fine. It's about finger nail size and turns the boat well at low speeds. I think at high speeds it deflects the water up rather than sideways and the boat lifts it rear and digs the rather sharp side in and goes flip - bye bye GPS.
I've since lowered the rudder down as it was only catching the top half of the prop wash whereas it's now about centre on the prop.
Over the years it's been a pig of boat but it is fast for such modest running gear. It is based on the classic UK FE's of the mid '80s (2kg class??) with some running up to 20 cells - gulp!

The video shows a well behaved boat that can be easily steered. I live in fear of the slightest twitch of interference flipping my boat.
Winter's approaching - the boat has one more chance before it goes in the fire.
The NQD is on its way..... Will let you know my first impressions. Hope it's not as tragic as some I've seen on YouTube.

Cheers,
David
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Old Apr 18, 2012, 12:38 PM
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Sneek, Netherlands.
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Quote:
Originally Posted by KiwiDavid View Post
I live in fear of the slightest twitch of interference flipping my boat.
Cheers, David
Hi David,

Interference can be dealt with, what remains is the rudder being very close to the prop, resulting in a very nervous and direct steering boat...

With more distance between the prop and rudder and a mild rudder throw, the steering will be less direct and the boat won't respond so agressively to ruder input.

Regards, Jan.
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Old Apr 19, 2012, 06:38 AM
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Hi,
That's a good point. The rudder/prop geometry could well have been goofed-up all those years ago and has haunted me down the ages. It was a very simple boat and it will be little loss. I will try the modified rudder this weekend but it's still very close to the prop, just lower down.
I will also be gutted if the new plastic boat looks like it's dragging an anchor or a handful of weed. There really is a heap of tragic boats on YouTube.

Cheers,
David
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Old Apr 20, 2012, 03:07 AM
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Hi All,
NQD Silver Rocket turned up today and was stripped shortly thereafter.

The electronic is scary - no crystal for the receiver and no semiconductors bigger than a TO-92 small signal device. There is however a big relay and next to it a biggish resistor so I'm guessing that speed control is stop, medium, fast. Bit like the old mechanical speed control on RC cars. Not sure I can suffer that after full PWM.
The electronics is well sealed up to stop water ingress but I suspect it could also get warm at mid speed with the resistor putting out a bit of heat.

The servo looks like a proprietary job and is fed with power, gnd and 4 other wires. Why 4 - 3 for position pot feedback + 1 for ....?
The servo mount looks almost as if a standard servo may drop in - has anyone done this? If so I could get rid of all the electronics.

The motor looks like it has a gearbox - wasn't expecting that but given the biggish prop I guess it would need it with a 540 motor.
Great entertainment for the price - may even try it in the water one day.

Cheers,
David
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Old Apr 20, 2012, 09:14 AM
Boaters are nice people.
Sneek, Netherlands.
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Quote:
Originally Posted by KiwiDavid View Post
Hi All,
NQD Silver Rocket turned up today and was stripped shortly thereafter.
Cheers,
David
Hi David,

Pictures please.

Regards, Jan.
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