Straight drive shaft or flex drive shaft?

[gfm1135]

What is the difference (other than the physical difference). When should one be used over the other?

[siberianhusky]

No adjustment in a solid drive once it's installed, I use solid in slow speed scale boats but anything you want performance out of I'd go with a flex so you can tune the setup properly.

[dana]

No adjustment in a solid drive once it's installed, I use solid in slow speed scale boats but anything you want performance out of I'd go with a flex so you can tune the setup properly.

[gfm1135]

The hull I purchased came with the brass tube and the straight shaft. Can I use the brass tube and just change to a flex shaft?

[dana]

Probably not. Is this your first boat?

[gfm1135]

Its my first build. How can you tell? lol

[siberianhusky]

As long as the diameter is within reason, depending on the diameter of tube and flex you could end up using a teflon liner of just the plain brass. 7/32 or 1/4" and you'll be ok. Hard part will be bending it while in the boat. Usually very easy to remove a stuffing tube, need just enough heat to soften the epoxy.
Way back in the day we all ran sub surface drives with solid shafts, but we had a couple universal joints in the setup to give some minor prop angle adjustability. That ended in the 80's though for the most part.
The other option depending on the setup is a wire drive, kinda halfway between a solid drive and a flex cable, but have to be set up very carefully or you can run into shaft breakage problems, I might be going wire drive on my new Whiplash sport hydro, motor is far enough forward that the bend in the stuffing tube isn't going to be severe.

[gfm1135]

I iust purchased from OSE a universal joint. Why did you stop using straight shafts?

[dana]

Its my first build. How can you tell? lol

Do you have any other rtr boats to go by?

[gfm1135]

My entry boat into the hobby was a Aquacraft Wildcat. But it is no longer. I have the parts but not the hull. It tangled with a dock and the dock won.

[dana]

What kind of boat and what are you powering it with?

[gfm1135]

Its a 22.5 Arowana with a 2860 3400kv, 120a esc and 3s 4000mah 45c lipo

[siberianhusky]

Far easier to set up and tune a flex shaft, also less hardware to fail under load, we ran a u/j at the engine and one under the hull to get the thrust line paralal to the keel, still couldn't adjust the depth of the prop with that kind of setup without a rebuild of the entire driveline. SHorten the primary shaft then make up a new longer secondary shaft to make up the difference.
Flex also runs much smoother and quieter, less vibration.
In scale boats it's usually a straight shot to the prop with a single U/J at the motor to compensate for minor dis-alignment. Since they run in displacement mode it doesn't make much difference with the thrust angle.
Flex shaft needs a bend in the stuffing tube so the cable doesn't thrash about inside the stuffing tube when running, in most of my boats I run a gentle S bend in the stuffing tube. I tend to run my motors farther forwards than some, Batteries aer the heaviest component and I like to get them mounted as close to the CG of the boat as possible.

[dana]

Dude, 37000 Rpm will blow that universal joint to pieces.