I would note that we are building a prototype longtail for use with a generic 6.5 horsepower gasoline pump motor. Once we have played with this I would really like to try a longtail with Craig's "Electric Hubcap" motor.
I have to agree with Robert. Any change in direction spells a loss of energy. Be it gears belts or U-Joints a straight shot is best for saving that hard earned power supply.
It should be noted that even a long shaft has a loss. Longtails have a safety issue that should be addressed. I would like to see a surface piercing longtail.
Kevin Pemberton
On 06/14/2012 01:28 AM, boblq wrote:
Why not get rid of the 90 degree joint as well? Use a Thai longtail. Works like a bomb. Here is example of home brew Philippines variation based on a 6.5 HP pump engine.
http://www.pinoyboats.org/forum/viewtopic.php?t=2295
Robert La Quey
http://www.facebook.com/TropicalBoats
--- In electricboats@yahoogroups.com, Craig Carmichael <craig@...> wrote:
>
> Of course U-joints squirm around if they're not held in position, and
> flop to angles that don't operate smoothly. So I tried a little test.
> I put a bearing race on a 1/2" square driveshaft and clamped it down
> (to a piece of "angle bracket" steel, in the corner.) Then the two
> U-joints, then a socket, then a 5/8" SS hex head bolt (somewhat too
> long) for the prop shaft. A 5/8" I.D. pulley served as a "bearing". I
> just held the pulley/prop shaft in position by hand, and turned the
> far end of the square shaft.
>
>
>
> Perhaps unintuitively, it turned pretty smoothly, even if I gripped
> the socket to put a load on the output shaft. I'm not saying there
> was no torque ripple, just that it wasn't really noticeable as I
> turned the shaft. It seems practical and that two U-joints is enough.
> Like others, I almost discarded this simple idea immediately in my
> head when I first thought of it. (KIS principle rides again) Next is
> to make a mounting assembly of some sort.
>
> With only a slightly larger pivot angle, eg 110º (or maybe even 100)
> instead of 90º, or if positioned such that one U-joint was making a
> steeper angle than the other, the torque got noticeably lumpy.
>
> (It's real easy to put a round bearing on a square shaft... get one
> just a bit too small, and grind the corners off the shaft evenly
> until it slips on.)
>
> BTW Somebody mentioned gear reduction... One of the main goals of
> doing an electric outboard from scratch is to get rid of that
> undesirable gear reduction that all the gas outboards seem to have at
> the foot. 1:1 should be pretty close to optimum with the right prop,
> and again building from scratch doesn't limit prop diameter selection.
>
> Cheers,
> Craig
>
> =====
>
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