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Author Topic: Snapped flexishaft  (Read 3433 times)

frogking

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Snapped flexishaft
« on: April 09, 2012, 07:10:52 AM »

Hi all, yesterday while out with my Apache 57 I snapped the flexishaft just by the engine coupling. What I was wondering is, do they snap with age and general ware or have I got it set up wrong ?
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Bill D203

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Re: Snapped flexishaft
« Reply #1 on: April 09, 2012, 09:39:58 AM »

Hi all, yesterday while out with my Apache 57 I snapped the flexishaft just by the engine coupling. What I was wondering is, do they snap with age and general ware or have I got it set up wrong ?

Any photo's of your boats set up ??
How old is the flexi, where did you get it from , there are many resons why flexi give up . More detail ands i may be able to offer some help.
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scoop

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Re: Snapped flexishaft
« Reply #2 on: April 09, 2012, 10:04:56 AM »

Hi all, yesterday while out with my Apache 57 I snapped the flexishaft just by the engine coupling. What I was wondering is, do they snap with age and general ware or have I got it set up wrong ?
Funnily enough I had one go in exactly the same place during last weekends BMPRS race at Branston, engine alignment was spot on, it snapped between the shaft saver and coupling so I didn't lose the rest of the shaft or prop, looked like it had been cut in half with a grinder, dead clean break, never seen one go like that before, really weird.
Check your engine mountings are tightened up and your engine has not moved out of alignment, are you using a hex flex coupling or one of the rubber couplings ?

Cheers
Scoop
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frogking

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Re: Snapped flexishaft
« Reply #3 on: April 09, 2012, 10:11:53 AM »

The flexi I bought second hand so I don't know how old. One thing I have read is that the tube should be close to the engine but I have a good two inches from the coupling to the start of the tube. Also the end of the tube is not supported. I think it might have something to do with that. I'm reading a lot of set up pages and I think it was due to that, What do you think ? Thanks
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scoop

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Re: Snapped flexishaft
« Reply #4 on: April 09, 2012, 10:23:38 AM »

The flexi I bought second hand so I don't know how old. One thing I have read is that the tube should be close to the engine but I have a good two inches from the coupling to the start of the tube. Also the end of the tube is not supported. I think it might have something to do with that. I'm reading a lot of set up pages and I think it was due to that, What do you think ? Thanks
Yes the stuffing tube definately needs support near the engine. If you look in this months (May 2012) Model Boats mag on page 75 there is a photo of my Apache, it shows the 'T' bar supporting the stuffing tube, enough space needs to be left to fit a propshaft saver and to enable you to undo the coupling.
Cheers
Scoop
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bj

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Re: Snapped flexishaft
« Reply #5 on: April 09, 2012, 10:39:27 AM »

snapped the flexishaft just by the engine coupling. What I was wondering is, do they snap with age and general ware or have I got it set up wrong ?

Sounds as if your shaft is whirling (or trying to) which means you have a shaft running at critical revs and the shear occurred at one of the node points.
One reason why flexishafts run encased is to help restrain that effect and another being to prevent something being caught up on the rotating shaft
See http://www.freestudy.co.uk/dynamics/forced%20vibrations.pdf if you want to read more about it.
Normally the flexishafts shear at the spring/solid section braze point.
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frogking

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Re: Snapped flexishaft
« Reply #6 on: April 09, 2012, 10:49:46 AM »

Yes the stuffing tube definately needs support near the engine. If you look in this months (May 2012) Model Boats mag on page 75 there is a photo of my Apache, it shows the 'T' bar supporting the stuffing tube, enough space needs to be left to fit a propshaft saver and to enable you to undo the coupling.
Cheers
Scoop
Thanks a lot :) That will be my next "add to cart" along with the new flexi-shaft.
I don't know if you can help me on another matter, I run 2 large turn fins and out of curiosity I took them off to see how it ran without them. The difference was unbelievable, It ran so much faster. Do they really cause that much drag ? Thanks
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scoop

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Re: Snapped flexishaft
« Reply #7 on: April 09, 2012, 04:52:19 PM »

Thanks a lot :) That will be my next "add to cart" along with the new flexi-shaft.
I don't know if you can help me on another matter, I run 2 large turn fins and out of curiosity I took them off to see how it ran without them. The difference was unbelievable, It ran so much faster. Do they really cause that much drag ? Thanks
You really only need turn fins if you are racing to stop the boat sliding in a tight turn O0.  At BMPRS we race in a clockwise direction so most of the race we are turning right handed therefor a turn fin on the starboard side of the boat is all that is required. Positioning is important as well.

Regards
Scoop
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frogking

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Re: Snapped flexishaft
« Reply #8 on: April 09, 2012, 06:23:17 PM »

You really only need turn fins if you are racing to stop the boat sliding in a tight turn O0.  At BMPRS we race in a clockwise direction so most of the race we are turning right handed therefor a turn fin on the starboard side of the boat is all that is required. Positioning is important as well.

Regards
Scoop
I did read that the turn fin should only be in the water during the turn ? If this is the case then should they be set higher up the transom so they are out or nearly out of the water whilst running strait ?
I raced 1/5 scale cars for many years and this is so much harder  :embarrassed:
Many thanks, Frogking
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Andyn

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Re: Snapped flexishaft
« Reply #9 on: April 09, 2012, 08:18:44 PM »

Would be interesting to see a radio mixed turnfin that drops / raises according to rudder position, I know some muti guys mix their rudders and under hull trim tabs...
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frogking

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Re: Snapped flexishaft
« Reply #10 on: April 09, 2012, 09:58:49 PM »

Would be interesting to see a radio mixed turnfin that drops / raises according to rudder position, I know some muti guys mix their rudders and under hull trim tabs...
With a good radio like a Futaba 4PL it wouldn't be that hard. Setting up the servo's and links would be more of a problem. Makes you wonder why its not been done yet (maybe it has)  :-)
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Andyn

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Re: Snapped flexishaft
« Reply #11 on: April 09, 2012, 10:01:05 PM »

All you'd need in reality would be a Y lead and two servos, but it'd be nice to have exponential on the slave channel...
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martno1fan

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Re: Snapped flexishaft
« Reply #12 on: April 13, 2012, 08:15:18 AM »

Turn fins need to go as far to the outer edge as possible and at 90% to the bottom like in this pic.They should then only touch water when the boat leans into a turn.Heres the clearest pic i can find,this is a friends easy vee.
Mart
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gazncaz

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Re: Snapped flexishaft
« Reply #13 on: October 21, 2013, 05:42:49 PM »

Nice looking boat there, never fitted Turn fins on mine seems to be ok but might be tempted :)
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