Flex or solid shaft

[knotsofast]

Ok, I am relatively new to rc boating, but I have about 20 years experience maintaining and servicing my own IO 20 to 28 foot boats, all single or double V8's. I just don't like flex drives. They are 'sloppy' and, well, flexy. Sorry, but for me, flex just seems like an easy way out from using 'proper' u-joints, solid shafts, and gears.
In my first non-production fast electric rc boat I used a solid stainless shaft in a double layer brass tube and a Dumas dogbone coupler between the motor and the shaft. That has worked fine for me so far, but the dogbone spurs are wearing down. I tried the same set up in my second boat, but with a little more angle between the motor shaft and drive shaft, and the dogbone spurs broke off first time I gave it full throttle. So I am debating whether to give in to the standard in the game, to go with flex shaft, or to try a ProBoat U-joint system between the motor and solid shaft. I have read in this very forum that a solid shaft is more efficient than a flex shaft. The downside being less ability to adjust shaft angle. I have already installed a flex shaft from OSE, but I may pull it out before next water test. Any suggestions? Comments?

[photohoward1]

You're not going to be able to find a reliable ujoint to take the power we put down. For a mono I once experimented with a solid .187" shaft knowing it would come straight out the back of the boat. You could mount the motor dead flat. The best way to get the power to the shaft was gear or belt. My big issue was balancing a shaft spinning at 25-35K. You need to have it ground and well supported.. The whole system with what I am capable of would not be as reliable as a flex shaft.
Ill still dream of it though.

[ray schrauwen]

Hydro & Marine flex cable has much less 'flexy' than most in North America. I will have some .130" cable very soon. It's either that or wire drive is a possible option for you.

[kfxguy]

Flex cable. There's quite a few people here that put down some serious numbers speed wise and most of use flex shafts. I use a flex in everything. Gears, u joints....will not hold up as well. Plus they suck up more power than a flex. If you don't have adjustability to your prop angle, you'll have a hard time dialing it in. The mono I just built, my first few passes was 41 mph. Had I not been able to adjust things, I'd likely be stuck around that speed. Now on 6s I'm around 70 (gps verified). I don't know about you, but 29mph more means a great deal to me.

[dasboata]

Go Flex & @#!& the rest LOL can't help myself ,, everyone in model boating world runs flex shaft nothing wrong with them 140 MPH model boats use them !!!

[knotsofast]

Thanks for all the responses. I just got home from work and was wondering if anyone would have responded, and I was very pleased and a little surprised by all the responses. I know that the flex shaft is the industry standard, but I didn't know if the alternatives had been fully vetted and discarded. I bought a bunch of hardened stainless steel shafts of 1/8 inch and 3/16 inches of different lengths to experiment with. I may try to dial my 23 inch mono form OSE with the flex shaft, then use the best angle and height for the solid shaft. I know I won't be able to make adjustments for changing water, but that is the trade off for an arguably more efficient drive. I will let the GPS logger be the judge of which system is more efficient. Thanks again for all the responses.

[iop65]

Go Flex & @#!& the rest LOL can't help myself ,, everyone in model boating world runs flex shaft nothing wrong with them 140 MPH model boats use them !!!

solid shafts are often used by European ,Asian racers for "smaller "boats

less maintenance , less friction....

not everyone in model boating uses flex : H&M sells solid shafts too , tenshock......

[kfxguy]

I can save you lots of trouble. Your not going to be able to get the slight positive angle that you'll need to properly air the boat out. Good luck to you tho!

[NativePaul]

solid shafts are often used by European ,Asian racers for "smaller "boats, less maintenance , less friction.... not everyone in model boating uses flex : H&M sells solid shafts too , tenshock......

As I race in Naviga I see a lot of European and Asian boats, and it has been quite a few years since I last saw a true solid shaft.

What I do see is a lot of wire drives in monos that are run straight down carbon tubes, with a centre bearing and a little bigger than the wire needs to be for the power, to reduce the whipping that comes with a straight wire, for example a 2mm wire for a 25" 2-3s Mono1 on around 500w and 2.5mm on a 4-6s Mono2 with around 1kw, whereas if it had a bend 1.6mm/.062" would be fine for either.

I am sure it has less friction, but the maintenance is pretty high, like all shafts they need taking out water dispersing and drying after a run day to avoid rust issues, but the ball races need drying and oiling too and the one in the middle of the shaft is a PITA, unlike a flex with a Teflon liner and lead/teflon bearings in the strut, which needs nothing done to the tube or strut.

European and Asian Monos are stepped and the motor is mounted just in front of the step, which keeps the motor and drive angle low, usually with the coupler barely above the floor, just a few years ago they would use brass or alloy stuffing tubes and struts or stingers to allow some flex and adjustment, but many have switched to carbon stuffing tubes and immobile stingers as the angle is workable for the hulls/setups and it saves a lot of weight.

[dasboata]

solid shafts are often used by European ,Asian racers for "smaller "boats

less maintenance , less friction....

not everyone in model boating uses flex : H&M sells solid shafts too , tenshock......

I ran solid shafts in the late 1980's on my SAW rigger they require more maintenance because they use roller bearing, they are louder and cause more vibration, because of the u joints, they limit your strut adjustments, and they are old new's so anyone looking for performance and ease of use I would use a flex shaft,, you can use what ever you want if you make it work and you are happy with it, that's all that matters

[knotsofast]

A video of my solid shaft first fast electric build. https://youtu.be/yqQvNDOmMwY I tried the link and it works on my end. This was taken last fall. The dogbone link in this boat has held up for several runs, but the angle is quite small and the shaft is not parallel to the bottom of the boat, it angles down a few degrees.

[Norwest]

The angle isn't much. Lay boat on table and the angle should be 2 or 3 mm at the front edge of prop with cg at close to 30%. You know that I found out it depends on prop size. I like to run more of an angle as I run smaller boats ( 22" or 23" ) with a P735 cut down to 733 b/s, but that's me.

[knotsofast]

I gave in

After reading your comments and suggestions and viewing kfxguy's video 'for the non believers' for a look at the state of the art, I have given in to the fact that flex is the way to go. kfxguy found a lube for the flex shaft that would seem to eliminate any significant friction difference. I converted my 'white boat' to flex. I am working this weekend, but hope to test it next Wednesday. I will try to take a video for comparison, and stick my gps logger in this time. Here are some of my before and after pics.2015-04-24-811a.jpg2015-04-24-813a.jpg

[kfxguy]

After reading your comments and suggestions and viewing kfxguy's video 'for the non believers' for a look at the state of the art, I have given in to the fact that flex is the way to go. kfxguy found a lube for the flex shaft that would seem to eliminate any significant friction difference. I converted my 'white boat' to flex. I am working this weekend, but hope to test it next Wednesday. I will try to take a video for comparison, and stick my gps logger in this time. Here are some of my before and after pics.[ATTACH=CONFIG]131163[/ATTACH][ATTACH=CONFIG]131164[/ATTACH][ATTACH=CONFIG]131166[/ATTACH]

Yea man I wasn't trying to steer you wrong. With the prop like that it will slow the boat down a lot, cause a lot more current draw...funky handling, drive bow into the water and lift the stern. All stuff you do not want. I have seen some boats with the prop angled down like that but the prop was under the boat and not at the rear. Once you get it tuned in, she should cruise pretty good. Try giving a degree or so of positive prop angle (rear of prop angled up instead of down). And most importantly, have fun!

[kfxguy]

Btw, did I tell you what I use for lube?