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[Martin (Admin)]

 
or .... https://www.ebay.com/itm/355588326442 
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[1967Brutus]

That is one of the great questions of life...

And unfortunately, the "why" will never be explained. All we can do is walk along ALL hopeful wrong paths until we have the one that is not wrong...

I know about these telescopic shafts. There is one downside, they are to the best of my knowledge not availlable in the length that I need... Otherwise I would have ordered one long ago.

What I need is one that has a safe extendable length under load of 24 cm.
I have not yet seen them longer than 22 cm...
They are usually intended for Crawlers, so probably not that suitable for heavy loads.
Which is a real shame, since these splines look like they would slide excellently under load...

[1967Brutus]

A friend of mine made a copy of the coupling=cup out of hardened tool steel.


This evening I took the boat out for nearly to the minute exact 1 hour of sailing (I believe the runhour counter said 1 hr 1 minute). Where the brass cup severely worn away in less than 2 hours, the new cup did not show ANY detectable wear or wallowing-out after this hour.

Of course, pitch, now not being hindered by those horrible notches, responded quite a bit better (but still needs some work to improve controllability, because there's quite a bit of hysteresis) and all in all, I just had a nice evening of absolutely troublefree operation.
Engine started immediately, kept running, and seems to run better every outing...
The warm weather of the last few days was noticable in that in general the entire system consistently ran 2~3 degrees hotter than 2 weeks ago. It means that probably I need to increase cooling capacity a bit/ Most likely I will simply replace the existing 3 mm ID tubes for 4 mm ID. That will increase effective surface by about 30%, and dwell time (time the water spends in those cooling tubes, dissipating heat) by about 75%.

The cooling fan works wonders, and all in all, I am happy with the set-up.

https://www.youtube.com/watch?v=apmv7IJsEKM


https://www.youtube.com/watch?v=_6-f_VWYC54

[1967Brutus]

The engine by now has about 4 hr 20 minutes of "in-water" runtime.
I kept myself busy with tryihg to get the governor to work, but 3 things stood in the way. ome down, 2 to go.
One issue was that the throttle servo mount was rather flexible. this hs severe impact on precision of control. THat has been fixed.
Did not solve the governor issues.
on the to-do list are stil the issue of carburation, on this scale and for this purpose and fuel type, there simply are NO suitable carbs availlable. That is going to be a real chore.
The last thing is that this governor is very fast, and difficult to "tame".
The idea is, that I will fit a servo-slowdown in order to make it move so slow that the engine will follow without overshooting.

BUT...
In the meantime I got myself a digital dynamometer, and with that I managed to measure bollard pull.
She pulls in current shape and form about 1,9 kilo, and that is by all standards quite impressive...

[1967Brutus]

After some consideration, I have decided to try a reduction gear for the following reason:
The more RPM the prop turns, the more difficult the pitch adjusting mechanism moves, due to the centrifugal forces acting on the blade roots.
The engine won't run below approx 1500 RPM, and this RPM allready makes the pitch mechanism move "notchy".
Now if I could reduce that prop RPM, pitch will move more freely and controllability of the boat improves.'


Since I have basically 100% freedom of programming in the Taranis, my thought was as follows: I can utilize the centre half of the stick movement for pitch control at minimum RPM, from neutral to max in both directions. This should allow for fine control of thrust, and thus a good manouverability.
At stickdeflection above half, I can hold pitch as fixed in max position, and start adding RPM.

The downside is a higher engine RPM when towing, taking away a bit of the sound and "feel" of the boat, but that is going to be used only when actually towing so probably less important.

I ordered a planetary gear, as that does not change the alignment of the shaftline.

The only suitable gearbox I could find (5 mm in, 5 mm out) has a reduction ratio of 1:3.7, meaning at idling engine (appr 1500 RPM) prop RPM will be appr 400 RPM.

I have no idea what kind of engine RPM will still be acceptable WRT sound, but probably 3000~3500 and that should result in around 800~950 on the prop.
With a bit of luck, I can use a higher max pitch value, so I should not loose too much static pull.

It's a long road, but slowly I'll be getting there...