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
=====
__._,_.___
.
__,_._,___
No comments:
Post a Comment