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Old Mar 09, 2014, 02:14 PM
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NQD 757 High Wind sweet conversion

The NQD 757 High Wind doesn't maneuver well in stock form; It only has 4 modes: No power, full ahead both motors, full head right motor, and full ahead left motor.

This boat has been converted with dual 3530mm 1700kv outrunners, dual 30A car ESC, 4 mm prop shafts with sealed ball bearings, and large Graupner surface props. And a decent radio with channel mixing, of course.

It can run 3S LiPo with around 400watts of combined power. But the sweet thing is the maneuverbility. The boat can do soft curves and slow 360s within it's own length

NQD 757 High Wind maneuverbility, brushless / car ESCs (0 min 47 sec)
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Old Mar 10, 2014, 04:38 AM
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Double post, sry
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Old Mar 10, 2014, 04:40 AM
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On-board slow motion GoPro3 footage:

NQD HighWind 757 RC boat, twin motor conversion on black lake (1 min 17 sec)
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Old Mar 10, 2014, 04:54 AM
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Hi Mike,

Impressive!

I like the sound of the slow mo video, two growling diesels...

Could you show us some pictures of the set-up and general overview?
I'm curious as to where you put the props, as there's no roostertail in the video.

Regards, Jan.
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Old Mar 10, 2014, 06:14 PM
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Originally Posted by pompebled View Post
Hi Mike,

Impressive!

I like the sound of the slow mo video, two growling diesels...

Could you show us some pictures of the set-up and general overview?
I'm curious as to where you put the props, as there's no roostertail in the video.

Regards, Jan.
Jan,

thanks! Pictures attached. The set-up is pretty straigh forward. One or two peculiarities:

The prop shafts only have bearings in the prop end. In the opposite end, they rely on the motor bearings. This makes the alignment very simple even though the shafts need to be kept short.

I had to make the props rotate in the opposite direction of what I intended and had seen before. Otherwise the prop walk would have eliminated the diff thrust torque:


I suspect that this reduces rooster tailing, but it still has quite a lot at full power. Most of the video was shot at low power because the heavy GoPro elevated the center of gravity a lot, and made the boat rather unstable - I didn't want to flip it and go swimming
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Last edited by mike_o; Mar 10, 2014 at 06:24 PM.
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Old Mar 11, 2014, 12:36 PM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
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Hi Mike,

Thanks for the pictures!

The boat is very maneuverable at low speed, but I have my doubts about the position of the props.
They are very close to the transom and will lose efficiency when the hull gets on the plane.

Rule of thumb for a surface piercing drive, is to have the prop(s) between 10 and 13% of the hull length from the transom:



The way you've mounted the props will no doubt push the boat forward, but increasing the distance to the transom will make it run substantually faster (specially if you change the props for 'genuine' hydroprops like the Graupner 2318 series).

Regards, Jan.
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