Is what we have the best we can come up with?

What's wrong with them? Where you coming from?

I have 11 + gallons of gas use on my flex shaft just this year and I don't know how many gallons were used before I got it.
I do lube it after each DAY at the pond (6-8 runs 12-14 oz fuel each run) after I first give it a light spray of WD_40 and a wipe .
I use Alice's , "Witches Brew Shaft Grease" , She mixes a small pot of the brew only during a full moon and is considering putting it on the market.
Gallons Used is the way I figure time on a boat / motor .This is on a Hurricane hull with CC pro mod eng peaking 18 K rpm. Couldn't ask for anything more troublefree.

We used straight shafts and universals at either end in the early years, when I first saw the flex shafts and the grease in the tube, I thought major drag but that isnt really the case, I think that at high rpm the flex makes a hole in the greased shaft tube and the friction is reduced to some degree, at least I hope thats the case. I know what happens when you grease die grinder bearings, they get hot and the motor rpm is cut by half and it gets very hot instantly as the balls in the bearings tend to slide instead of rolling in the races.
I guess a way to test this is to grease the shaft and connect it to a 20,000 rpm die grinder and note the rpm drop to get an idea of what is going on.

mike sr

If you set up your stuffing tubes to have some degree of an "S" bend along there length, you ELIMINATE cable whip that is the greatest drag a flex system generates.

Think tank? Come on!!! Interesting to see what everyone got out of that question.

Where I am coming from... from this one point, Rotating mass. I was cutting some cable for my hydros and they are the longest I have. There's a lot of weight there is all I'm saying basically. I would love to see some high speed photography of the inside of the stuffing tube under load and unload conditions to see what happens, I'm sure it's chaos.
Yes I agree they are pretty much a flawless design and thousands of miles of wrapped cables power the fastest rc boats on the planet without issue.
I was not thinking about straight shafts and univers- those would never work with our RPM range. But, what about composite materials? High tech fibers? Could you make one with CF and Kevlar? rayon and Aramid? Ti propshafts? Hell, I don't know, that's what this forum is for... OUTSIDE THE BOX!
I know some electrics have been tested with solid wire, I don't know... just thinking outloud.
Think about this, a woven core of carbon/Kevlar and Flexible Titanium bi-directionally wrapped by small diameter wire. I think it's possible I really do.
I am talking about re-inventing the wheel so to speak. What I'm talking about is not available! This is where I'm coming from.
GO BUCKS!!!

Nice to have you back around Len!!!! ;D

I get where you're coming from now!

I am sure some other configuration of a semi flexible drive shaft could be engineered : .... But if it is for reason of mass or weight savings ? don't see the why ?

What comes to mind right off the bat is how a 2/3/4 blade prop causes loading then un-loading wind up or torque on a drive cable/shaft.

Most if not all composites while having SUPER HIGH structural strength are limited to a maximum point were they finally yield to the stress and fracture.

With the high pulsing rotational torque of a prop beating the water, it would seem to me that you have very little control over just how much stress is applied, and when a maximum is reached, catastrophic failure is ensured.

Flex cables because of design absorb the torque loading by winding up the strands of the wound cabling, Vibration caused by the pounding blades is absorbed into the struture of the cable because being strands of wire, will not really harmonize like a solid or hollow drive shaft does.

** I absolutely agree however that a semi rigid small diameter drive shaft of some sort could have far less rotational drag than a cable does while offering an installation free of a stuffing tube.

Another thing one must address is how to connect the engine to this drive without having engine vibration and motor mount flex adding to the fatigue. Along with connection to a prop shaft, or have it part of the assembly ?

:-\ At some point tho, one must weight out gains by frictional loses with reliability and simplicity .... and find a happy medium that does both at low cost.

Yup, flex cables are as K.I.S.S. at it gets ( Keep It Simple Stupid )

JMHO,
Scott

There needs to be development in a full ballbearing setup including strut bearings. I bet there would be atleast 3mph gain? from fricyional losses. Might be a little tough getting a small enough bearing inclosed in a strut assembly? I believe the trimax assembly from mh$ is a full ballbearing assembly though

A fellow in our club in the early days tried ball bearings in the strut, there was no way to keep them lubed and the grit and water did them in after a few runs, usually the balls fell out. the roller bearings lasted longer but ate the stub shafts up, due to the lube problem again.
The flex shafts arent perfect but they work for a long time and are cheap, and the strut bushings last indefinitely if it is kept greased.
Maybe some sort of electromagnetic induction system?? I think what we have works very well at least in the short term. I do think eventually someone will come up with something that could possibly work better. I wondered about the losses in the flexing of the cable due to the uneven load of the prop as one blade comes out of the water and the other starts in to it, all this takes power and results in losses.......
Someone will come up with something eventually though, its just a matter of time!!

mike sr