breaking flex

[walter geens]

Hello guys,

For some time now i've been running a modified K/B leg with electric motor on it. For some reason the flex cable keeps breaking and i am getting desperate here ( i am down to the very last spare cable i have) I have replaced the teflon liner to a brass liner ( upon advice from a nitro guy). At first i thought the cable was too long, so i cut it shorter at the motor end. I personaly think the problem is to be found in cable length but right now i am lost here. I know a 3.5cc K/B has more power then my 12 cell brushless motor so the power put on the cable can't be the cause of my problem. Please HELP!!!

Walter

View attachment 3520

 

[topfuel443]

what size prop are you running?

how deep are you running the prop shaft in reference to the sponson bottom?

does the boat have a tendacy to "bounce" or "hop" while at speed?

what does the boat weigh ready to run?

do the shafts break in the same spot every time?

~James

 

[chriscarbon]

walter,

what type of lube do you use?

chris

 

[Jerry Dunlap]

The bad news is you are breaking flex drive cables.

The good news is, they are available.

JD

 

[GRoth265]

Do you run the motor in reverse being a electric? Nothing will hurt them faster than going against the wind. Greg

 

[Geraghty]

Hello guys,
For some time now i've been running a modified K/B leg with electric motor on it. For some reason the flex cable keeps breaking and i am getting desperate here ( i am down to the very last spare cable i have) I have replaced the teflon liner to a brass liner ( upon advice from a nitro guy). At first i thought the cable was too long, so i cut it shorter at the motor end. I personaly think the problem is to be found in cable length but right now i am lost here. I know a 3.5cc K/B has more power then my 12 cell brushless motor so the power put on the cable can't be the cause of my problem.  Please HELP!!!

Walter

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Where are the cables breaking???That will really narrow down the required fix.

As a general rule however ,if you are running a 3.5 lower unit then you need a 7/32" O.D. brass cable liner with 1/4 O.D. spacers soldered over the 7/32'" O.D. tubing to center it in the lower unit channel.That liner I.D. doesn't allow the cable to knot up.

The 3.5 K&B does make more power on the top end but has no bottom end torque to punish the cable while spooling up to max RPM.The electric motor makes max torque from the time the trigger is pulled [from 1 rpm and up].That coupled with your prop selection and set up is what is killing your cables.

 

[walter geens]

Thanks guys, some very interresting thoughts here.

I am running an Octura X637 prop on the outboardleg because this seems to be the best combination for speed and acceleration. The prop is placed so that the centreline is about 1/8" higher then the line between the sponson bottom. Yes indeed, the cable usually breaks at about the same spot, about 1/2 inch from the propshaft. I keep the flex well lubricated at all times with fine machine oil. The strange thing is that the original cable lasted a very long time, but ever since i broke it, the cables seem to snap within minutes. The cable is running in the proper direction, otherwise i would be running backwards with the normal Octura props. The boat rides very nicely on the last inch of the hull, no tendancy to hop or bounce. Flying of the water happens, but that is when pushed at little hard i guess. It is a WOF ( yes Jerry one of your designs scaled down to 61cm length) boat very light compared to let's say the Graupner F1 tunnel

Walter

View attachment 3519

 

[Jerry Dunlap]

re: 61 cm

So, that's about 24"? I'll have to get out my metric ruler after I finish sending this.

JD

 

[duc]

Hi Walter

nice to 'meet' you here. Do you use the black foot you got from me? I got it from one of the guy's overhere.

Sorry no answer to your question, however I still have some cables left so if you want some please pm me.

Oscar