Piano Drive Wire Snapped like a Shot

[FloatDaBoat]

HiYo Fellow Members !!! Yes, I’m a Newbie ….
I’ve visited other FE forums, but chose this one to join, because you all seem to be more knowledgeable, helpful, and friendlier than the others.
I designed & built my current boat from fiberglass. It’s a cat 30” in length with a 12” beam. Power is provided by a Novak HV Pro 7.5 System (3000Kv), using two 8.4 volt, 4500 mAh NiMH packs I made utilizing Tenergy cells. I fabricated all the running hardware myself - - Motor Mount, Prop Shaft Strut Assy, Rudder Assy, Trim Tabs, Water Pick-ups, etc.
Now, my problem: While trying to fine tune my set-up, I managed to snap the 1/16” piano drive wire, resulting in the loss of the prop shaft & prop (Octura X637). I was running the prop half-in/half-out of the water (centered on the bottom of the sponsors). I’ve provided photos in my album. One is the fractured shaft itself, the other’s the location of where the wire broke (red arrow).
Questions: Is there a higher quality .0625” wire available? I used Sig piano wire (all that was available at my local hobby shop ). Or, would I be better off using .130” flex cable?
Thanks in advance for any assistance.

[Diegoboy]

Welcome to OSE!

There's a .078 wire available here
I personally don't like the wire drives, I have seen too many props lost on them. but when they're setup properly, they're great!

[Darin Jordan]

Way, WAy, WAY too much bend!! You are leveraging that section of the drive against the ferrel at the front of the strut... You can't bend a wiredrive that far... and definitely not bending it all way back by the strut...

Should be more like the second attached pic here...

If you have to keep this stuffing tube config, I'd go with a .130 cable.... I'd actually use .150 in a boat this size, but .130 should hold up fine...

If you want to continue to run wire, then you need to flatten out that angle a LOT.... It should be a gradual bend from the motor to the strut... almost flat once you get it pointed to the strut...

That strut also looks WAY too deep... or is it just the picture... it shouldn't be much, if at all, below the ride-pads...

[HOTWATER]

Great job on the hardware fabrication!

Good info from Darin as always! Go with the .130 to .150 flex...

-Kent

[FloatDaBoat]

Thanks

WOW - - I didn’t expect multiple responses so quickly !!! Whoopie ….
I’d have to do major modifications to DaBoat in order to reduce the amount of bend to keep utilizing wire or to use .150” flex cable, so it appears the .130” cable is the easiest solution. Thank you all very much !!!
The apparent depth of the prop strut in the photo I submitted is an optical illusion. I took the attached picture to show a better perspective.

[Simon.O.]

Very nice hand made hardware and nice wood work on the stand too.

It does not matter if you run a wire or a flex, it is important to get your drive line aligned properly.
For a wire, a good rule of thumb, is to have the motor point to an area about 2-3" in front of the strut. This will give you a fair bend on the wire.
I can not say much about flex as with the exception of my OB tunnel I use wire

For 30" cat to run a wire well I would see the rear of the motor about 10" forward of the transom and the drive dog about 3"aft of that.
That is where mine will be.............roughly

It has been said before and I will reinforce it. Wires need a very relaxed drive line and will perform well when setup correctly.

Nice boat there !!

[FloatDaBoat]

Thanks for the input Simon.O.; I’ve already ordered an Octura .130” flex drive & two more Octura props from OSE. Should have DaBoat operational again within a few weeks.
Your info will be kept in mind though, as I’m planning on building a Hydro based on a 7 Litre/Gran Prix
type configuration over the winter, & I’ll be using a wire system. Thanks for the compliments on my workmanship (I actually enjoy building stuff more than running it).
All of the offered advice is appreciated.

Ignorance is relative . . . .
Stupidity’s . . . .

[FloatDaBoat]

Exsplosive Permatex

Thanks Paul.

I used Permatex High Strength/High Temperature Sleeve Retainer (Green, item # 64000) to secure the wire to the prop shaft. It seems to work very well. However, I had a potentially dangerous situation occur while using it.
I needed to replace the old wire with a longer piece in order to move the motor CG farther forward in DaBoat. I had the wire clamped in a vice & was heating it with a propane torch to break the bond, when !BANG!, the prop shaft was launched like a missile, ricocheted off the overhead light fixture, & landed on the nylon carpet below. The still VERY HOT shaft melted itself down to the carpet backing. ‘What-if’ it had gone down my shirt collar ?
Next time, I’ll attach a piece of wire to the shaft to keep it from flying off to who-knows-where.

Ignorance is relative . . . .

Stupidity’s . . . . [apt to be the result of wishful thinking as to the desired outcome]

[FloatDaBoat]

Why did my post appear above Pauls? System Glitch?

[paulwilliams]

Piano wire will snap if overheated when silver soldering. Unless you have a really good reason for wanting to silver solder, use Loctite 603 instead - it won't alter the temper of the wire.

The other guys are spot on about the installation though - too tight a radius bend will also make the wire more likely to snap, to say nothing of the side load imposed on the bearings in the strut.

Paul

[Steven Vaccaro]

Are the two 7cell nimh packs wired in series or parallel?

[paulwilliams]

I used Permatex High Strength/High Temperature Sleeve Retainer...heating it with a propane torch to break the bond

been there, done that.

Avoid breathing the fumes given off by Loctite or similar when heating to break a glue joint - I imagine it's probably quite toxic.

Paul

[FloatDaBoat]

Are the two 7cell nimh packs wired in series or parallel?

This Novak HV Pro ESC is designed with two battery connectors, providing a series connection through the ESC circuit board (max voltage 14 cells NiMH/4S LiPo). It can be run off a single pack, in which case the battery must be connected to Battery #2, & the Battery #1 inputs must be shorted together. If the single pack exceeds 8.4 volts (minimum is 7.2), the ESC’s On/Off switch is to be left Off & a RCVR battery must be utilized as the BEC doesn’t have switching capabilities.
Clear as muddy pond water?
I haven’t seen an ESC schematic, but I used-to-be an Electronic Tech; you’d have to query NOVAK to verify if my supposition is correct.

Paul's warning about toxicity is most likely dead-on!

Ignorance is relative . . . .

Stupidity’s . . . . [often confused with Genius - - especially by those who are Ignorant]