Flex cable whip at high rpm?

[kfxguy]

Last night I bored my strut for ball bearings, and I decided to run the bearings To break them in. Well I used the flex and my drill at first. Not enough Rpm. So I hooked up a 1515 2200kv motor on 4s to it. Then I noticed some things which made me experiment further. Out in the open of course the cable would whip and oscillate. If supported it got better. Put in a tube it got better and put a curve in it helped alot too. But it could still be seen whipping in the tube and you could feel some Vibration. What if I put a few short pieces of brass tubing inside of the stuffing tube to help support the flex more? Seems like it would help, no?

[Fluid]

Unless you positioned the pieces at the cable's vibrational nodes, they would just makes things worse. The vibration nodes will change with load and rpm - you would be chasing your tail. And really, who cares about cable whip on the bench? Once loaded in the water everything changes. To eliminate this kind of vibrations would require a solid shaft. That was tried forty years ago - fail.




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[grsboats]

I also wouldn't care with the bench experiment and add brass pieces will increase the drag!

[properchopper]

Just two days ago I was looking for that fraction of a mph to up my P-Ltd Cat record. SAW record time trials are like that I pulled the teflon from my .250 stuffing tube to free the .150 flex just a tiny bit. Picked up less than I needed but there was some rather noisy harmonics coming from the boat during the passes. The law of conservation of energy states that energy cannot be created or destroyed, only converted. In this case, the energy from the motor was being converted to the normal amount of heat (helped by icing down the cooling circuit prior to the passes) and NOISE from the driveline harmonics. Put the teflon back in, eliminated the noise/harmonics/energy loss. Finally got the new record btw

Jay is correct (as always) ; when underway the flex has linear force exerted on it that differs from unloaded bench trials - keep that in mind.

[kfxguy]

thanks for the replies fellas. Let me be more specific. When i wrote the first post earlier, I got busy and had to cut it short. Heres my thoughts...I could be way off, over thinking it...who knows... but I'll lay it out there...

Does the cable under load, make like a SPIRAL? My reasoning for this: the cable shrinks or pulls (or is pushed by the prop?) inward under load, correct? So what happens??? the cable spirals against the tube and creates drag at each contact point? maybe it whips too...causing power robbing vibration and/or harmonics? maybe I dont know what i'm talking about...or maybe i'm on to something...but it wont hurt to try it.

What i was going to do is put 3 or 4 short (about 1/4") pieces of 3/16 i.d. brass in the stuffing tube, to more or less help support the flex and help it from whipping, twisting...whatever it is it does.... and see if things smooth out. I drill a couple small holes at each collar and solder them in place so the dont move. Has anyone tried something like this? I cant help but think that it would help... maybe not..... but it wont cost me anything but a little time.

[kevinpratt823]

Maybe you already realize it, but the brass tube is measured by outside diameter, not inside, you would use the 7/32" to fit inside 1/4". You may have to modify the way you grease the cables also, as much less would pass by the smaller sleeves.

[kfxguy]

Maybe you already realize it, but the brass tube is measured by outside diameter, not inside, you would use the 7/32" to fit inside 1/4". You may have to modify the way you grease the cables also, as much less would pass by the smaller sleeves.

Yes, i have all those size brass tubes and some carbon tubes too :)

i can make slits (with a file) for the grease to pass through. i was also going to chamfer each sleeve...I grease my cable with one of those pro boat grease guns so it should force it in there.

[flraptor07]

I usually put a flaired bushing at the motor end of my flexes, seems to help with whipDSC02850.jpg http://www.offshoreelectrics.com/pro...=ros-spdsd-187

[kfxguy]

I usually put a flaired bushing at the motor end of my flexes, seems to help with whipDSC02850.jpg

I solder a piece in the end to take up the slack and help with water going up the shaft, but now I have the aeromarine flex shaft seal which now has a sealed Ceramic bearing in it. I don't get a drop of water in now. I'm gonna make another stuffing tube and try out what I'm talking about. I'll Baseline the boat on 5s. Make some passes. Then recharge batteries and run it with the new tube. Might help. Might not. Don't know till I try.

[srislash]

You could mount a AIR prop on the flex and bench test Travis, More controlled environment. It would load the flex.

[kfxguy]

You could mount a AIR prop on the flex and bench test Travis, More controlled environment. It would load the flex.

Scared I might cut my hand off or something. I got hit with the flex last night lol. I had it in a bend where it was running smooth right to the very edge of top rpm...then it started whipping. Ripped the motor out of my hand and the cable hit me in the finger so hard I it's swollen a little and can't move it much. Lmao. Yea, I'm a dummy sometimes

[srislash]

Scared I might cut my hand off or something. I got hit with the flex last night lol. I had it in a bend where it was running smooth right to the very edge of top rpm...then it started whipping. Ripped the motor out of my hand and the cable hit me in the finger so hard I it's swollen a little and can't move it much. Lmao. Yea, I'm a dummy sometimes

Too much time at the lake. Is there green algae there?LOL

[Shooter]

Scared I might cut my hand off or something. I got hit with the flex last night lol. I had it in a bend where it was running smooth right to the very edge of top rpm...then it started whipping. Ripped the motor out of my hand and the cable hit me in the finger so hard I it's swollen a little and can't move it much. Lmao. Yea, I'm a dummy sometimes

Man, I'd pay good $$ to see a video of that. Here is an epic boat test failure: https://www.youtube.com/watch?v=fqVLmB2KlcA

I have no idea who those guys are, but my brother and I laugh every time we watch the vid. Enjoy.

[kfxguy]

Too much time at the lake. Is there green algae there?LOL

No algae...

[jim82]

Why would you do that....lmao

Sorry that was to shooters post.

[ray schrauwen]

Could you explain a bit more? A free bushing like a speedmaster in the strut?

I usually put a flaired bushing at the motor end of my flexes, seems to help with whipDSC02850.jpg

[kfxguy]

Man, I'd pay good $$ to see a video of that. Here is an epic boat test failure: https://www.youtube.com/watch?v=fqVLmB2KlcA

I have no idea who those guys are, but my brother and I laugh every time we watch the vid. Enjoy.

All I got for you is what the flex looks like after it hit me.....

[flraptor07]

This is the Flaired Bushing I use at the motor end of the stuff tube on most of my builds. http://www.offshoreelectrics.com/pro...=ros-spdsd-187 If it's a little long and gets into your first bend just cut a little off and solder it in so it doesn't spin in the stuff tube.

[ray schrauwen]

I was going to try that. Thanks!

This is the Flaired Bushing I use at the motor end of the stuff tube on most of my builds. http://www.offshoreelectrics.com/pro...=ros-spdsd-187 If it's a little long and gets into your first bend just cut a little off and solder it in so it doesn't spin in the stuff tube.

[siberianhusky]

I've gotten away from a single bend in the stuffing tube, I use an "S" bend now, no real solid evidence other than sound but I think it has cut down on cable noise that had to be whip or vibration. One mono went from having a definate resonance to water hitting the hull being the loudest noise.
My JAE was the first one I did this on, couldn't believe how quiet it ran, done it on every build since then.

[flraptor07]

I was going to try that. Thanks!

Ray, I can't tell you one way or the other weather it makes any difference. But the boats that I have done this on are quieter and have more free spinning drivelines.