The longtail type motor has little appeal for me. I might try doing a
submerged motor straight to the prop but the 'pancake' motor shape is
about the worst possible for that. (But any typical 5KW BLDC direct
prop drive motor would be too fat.) That leaves installing as an
inboard, and that's not my vision either.
For an outboard there seems to be no avoiding a 90º turn at the foot,
and I'm guessing that the double U-joint will prove to be the least
lossy way (and quietest) to make that turn.
I was refining the U-join assembly today (ditched one link; instead
using the end of the prop shaft itself as the final 45º turn element)
when the 90º bevel gears in my angle grinder broke up - teeth
everywhere inside. Not the first time either. This does little to
give me confidence that gears is a better way to turn 90º. (But
they're pretty cheap angle grinders. Maybe I'll splurge this time.)
Cheers,
Craig
>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>http://www.facebook.com/TropicalBoats
>>
>>--- In electricboats@yahoogroups.com, Craig Carmichael
>><mailto:craig@...><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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