Speedmaster Sport 20 hydro strut

[785boats]

You won't need the 7/32" tubing inside the 1/4". The tolerance is too tight & will bind on the flex when you adjust the angle of the strut.

[Old School]

Many thanks.

[CraigP]

You won't need the 7/32" tubing inside the 1/4". The tolerance is too tight & will bind on the flex when you adjust the angle of the strut.

I think he’s saying short 7/32” at the motor coupling end of stuffing tube. I do that on all my boats so I can leave the distance of the exposed flex shaft a bit longer to the coupler, in order to clean it before it’s inserted into the coupling.
It just keeps it from starting to whip around. You have to keep the distance to a minimum on a 0.150” flex though...

[IRON-PAWW]

Great topic. Exactly the discussion I need at the moment. I've fitted 1/4 brass tubing on a gsx380 on advice I got at ose. I have that going going all the way into a sport 20 strut - leaving the 1/4 inch gap at rear of the strut for the bushing head as described above. 3/16 ose flex with no teflon. Problem I'm getting though is terrible vibration in the flex when I bench test. Brass tube even begins getting hot. On a the gsx380 it results in a fairly long flex cable..... is 3/16 really ok on this hull? Can't figure why it vibrates like it does beyond an alignment issue....

[rol243]

1/4 inch brass logs are fine for 3/16 inch shafts so your problem must be either the motor collet is out of true or the flex shaft join to stub shaft is out of true. where does the brass log get hot ? strut end or motor end ??

[IRON-PAWW]

Closer to strut end but near as I could tell maybe 3/4 of the way from motor to strut. So mid way is getting hot. Motor end is ok. Can't see any wobble in the flex at motor end when I spin it by hand with collet done up. But I have another so I'll try it. I have another flex too so I'll try that as well. Gentle bend as I could make it. Frustrating.

[Old School]

I went with a 9/32" tube with teflon liner. At the strut end of the stuffing tube I soldered a short length of 1/4" tube protruding about 3/16", with the end chamfered to allow a degree of strut angle adjustment. It will be sometime before I can test my install but I did spend some time getting the alignment correct. The flex rotates very easily by hand.

I wonder if the weld alignment on the flexshaft is accurate as mentioned in previous post. If not then the flex will tend to whip inside the stuffing tube at the strut end of the tube causing vibration.

[rol243]

I have had some pretty badly made collets and flex shafts that had to be tossed so you should try another collet and or flex shaft as it does sound like one of these parts is your vibration issue. just one other thing, is the motor lined up well with the shaft log ? if the motor is out of alignment you will also get a bad vibe in the drive line.

[IRON-PAWW]

Thanks guys. Really appreciate the assistance. I did spend the time getting the motor alignment as true as I could get it. But I did note that after I nipped up a slightly loose motor rail mounting bolt the motor alignment did shift a shade. I've corrected that - so I'll try another bench test first. Then I'll swap collet and flex. I too have suffered bad parts in that department before. It's an OSE flex and those have been good to me so far. Octura coupler though.... I think its got to be some sort of cable whip or wobble I've got going on right now. Cheers muchly again.

[rol243]

There was some mention about the Octura Collets being not so good. you shouldn,t get any whip in the 1/4 inch tube , more likely its the collet or shaft. easy fixed.

[Old School]

I use TFL collets and these flexshafts. I have purchased quite a few of these with no issues at all. They seem to welded very well with no misalignment. Seller is excellent to deal with.

https://www.ebay.com.au/itm/3-16-X-21-520mm-flex-cable-shaft-for-rc-boat-3pcs-p1761/272821255029?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[MarkF]

It's normal to get some rattle when you don't use teflon. That is why I always use teflon in all my boats that run 6s or less. I also use 3/16 in my 380 and it's butter smooth even with the long length. Using teflon offers a better seal and more adjustment and is just as fast as boats that don't use teflon.

Mark

[IRON-PAWW]

Well. I've still got some type of issue going on. Swapped out the Octura Collet for an MBP. Tried a different Flex. Problem remains. It's a type of knocking mid-flex. To me it seems to be about where the brass tube goes through the hull. If I gently jiggle the prop back and forth I can hear the flex knocking on the brass tube at around that point. No matter how I align things - that happens. Bench testing gets up one hell of a vibration at faster revs. I just don't know how to solve it. A different curve maybe?









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[rol243]

seems very unusual as you have a very good quality collet and the brass tube log has a very even and slight bend which is perfect so what else could it be. ??? are the bearing / bushings in the strut good ? are you sure the flex shaft is perfect at the welded join with no out of trueing ? is there anything inside the brass stuffing tube at the top end area ? also are you leaving a good 3/16 inch gap at the strut to drive dog ? plenty of oil or grease on the shaft ?

[IRON-PAWW]

Hey Rol243. Thanks for helping mate.

I can't detect any defects in either of the flex shafts I tried. They both appear wonk/bend free at the join. Both roll evenly across a flat bench top etc. Bushing is not loose or worn - they are brand new. Yes - even though there's no gap at the drive dog in the pics I *am* leaving one when I run it. I packed as much grease as I could get into the tube - and that helped. That did quell the vibrations out a reasonable bit - maybe it just needed more grease for testing. But the whole tube starts getting warm with a few high speed blips on the bench - with the hottest part being mid-way. Is that expected? I might try a few very small runs (20 - 30 sec) with it tomorrow and see what transpires. My first build like this so I'm not sure how things should behave. I might try some speedmaster flexes perhaps if I can't get any breakthroughs.