New Hydro

[AlanN]

t : the brass tube is almost straight.

This is most likely the problem. Long straight sections of the stuffing tube usually allow the cable to whip. On lower RPM gas boats it usually is not an issue (besides you cant hear it whipping in a gasser but you can measure the temp of the stuffing tube). But on higher RPM motors the .250 cables want to whip. You can get smaller ID brass tubing if you want to keep the straightness in your stuffing tube. Or if you want to keep the same diameter brass tubing an s bend will work. I also highly reccomend an oiler.

 

[pda75]

New test with a another flex cable; there are less vibrations.

Here are some pics of dead prop. A K57 and a CMDI 52-80.

Andy Brown told me that large CNC prop may not resist to high power; Well that's true !

regards

Pierre

 

[jayt]

Aluminum props have no business on high-power FE boats. As for the vibration, did you notice it on the water or on the bench? If on the bench forget it as the vibration will be far different when the boat is on the water. A slight bend in the stuffing tube is preferred, but then I have seen straight flex cables run just fine. The water dampens the "bench" vibrations significantly - worry about what happens on the pond, not on the bench.

.

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[pda75]

Thanks

The vibrations were on the bench not on water.

Pierre

 

[pda75]

hi

some videos here :

The start : http://www.dailymotion.com/video/xes4j1_demarrage-epr_sport

first run, whaouh what are the swans doing here. By the way the strut angle is to high http://www.dailymotion.com/video/xes4t3_run-epr-2_sport

Another run (still too much angle) : http://www.dailymotion.com/video/xes4q8_run-epr_sport

Back to the bench : http://www.dailymotion.com/video/xes4ec_arrivee-erp_sport

New winter fashion clothes

regards

Pierre

 

[Jim Caldwell]

Perhaps not enough weight on the prop?? Thats a looong after body. What is the weight on the prop?

 

[pda75]

Yes Jim I agree, there is not enough weight with this sturt angle. On the video it is 2°. With 1°, the back of the rigger does not bump any more

Weight on the prop can be adjusted between 0.8 to 1.2 kg (eg between 28 and 42 oz) depending on the lipo position.

Regards

Pierre

 

[Jim Caldwell]

That should do it Pierre.

 

[pda75]

Jim

How do you calculate the weight needed on the strut ?

Based on my experience,I have make a calculator based on rpm and prop diameter but I am not sure it is accurate : Strut weight should be equal to prop lift. This calculator does not take into account the real prop shape, eg a 1450 would have the same lift than a x450 (if they have the same rotation speed) though I know there are different.

Regards

Pierre

 

[Jim Caldwell]

Same problem here, testing at the pond is how I do it. I take along some 1 and 2 ounce weights and tape to the top rear of the tub to see where it need to be with each of the 2 or 3 props I run on a boat, ony take seconds to change. I run all my struts at 0 degrees and adjust weight from there.

Jim

 

[pda75]

Some videos



The pound was a bit too small.

Regards

Pierre

 

[pda75]

Some videos

http://www.youtube.com/user/jfp2p#p/a/u/1/yCv1GHzCqHA

 

[pda75]

Latest wideo

http://www.youtube.com/user/scyllias91?feature=mhum#p/a/u/2/C32EwV5K4a0

Pierre

 

[MrHammerHead]

Ahhhh, I love the sound of water slapping carbon in the morning!

Chris

 

[MitjaJ]

Really nice boat !

For shaft vibrations - a custom made wire drive usually runs vibration free.

For the power I would use a 2.5 mm wire drive, best would be to use ball bearings in the strut.

The shaft and clutch must be made very precisely machined by a skilled man on a lathe (+grinding/EDM machining).

If you know somebody in a tool/die shop this in not a big problem.

The preferred way to assemble the shaft to the wire drive is to use Loctite 638, single part epoxy or shrink fit (if the

hole in the shaft is made on the EDM (2.47-2.48 hole for 2.50 mm wire diam)) - brazing is not recommended since you

almost always end with a bent wire.

You can run the wire drive in a 3 mm ID teflon tube - 40000 rpm present no problem by my experience.

 

[pda75]

MitjaJ

do you have any pictures ? 2,5 mm for 5 kW : did you experiment it ?

regards

Pierre

 

[MitjaJ]

No I have no actual experience using 2.5 mm wire drive. I use 2 mm on my hydros with no problems (1.8 kW peaks from logger), and

guys here had no problems using 2mm wire drives on 8S1P saw setups.

I made some calculations (see attached file) and I believe that a 2.5 mm wire would be enough for your power.

The only thing - the drive has to be made very precise otherwise you will still have problems with vibrations. You can use the brass & teflon tubing over the entire wire length since you have a very long shaft.

See the attached file how we make our struts (I usually use teflon bushings instead of bearings).

View attachment torsion-of-round-cross-section.zip

 

[pda75]

Thanks !

Pierre

 

[pda75]

Some navigation pictures and video

http://www.youtube.com/user/scyllias.../2/C32EwV5K4a0

http://www.youtube.com/user/scyllias.../0/ey-ZoP7gC6M

Pierre

 

[pda75]

A new motor mount

Regards

Pierre