YPC

Hi Indatube!

I have seen your seal at the coupler end - l - I have a similar seal on my solid shaft set up - the best seal on the prop end should be the fit between the bearings ( bushes) and the actual shaft.

another set up over sight in this area can be if the thrust washer and dog drive is bigger in diameter than the stuffing tube end/drive shaft housing face. If this is the case, water will flow against the thrust washer/dog drive and be deflected back up the drive shaft housing. Its important to ensure that the water is able to flow freely from the drive shaft housing 'over' the appendages that trail it, avoiding any deflection.

In the photo I have introduced a taper to flow the water over the bigger diameter of the dog drive and prop hub. Without that taper, the water flowing from the drive shaft housing would deflect off the face of the dog drive and be pressured 'up' the stuffing tube.

No amount of grease will resist the water pressure that is driven back up the drive shaft caused by forward speed deflection. Obviously, this deflection also adds to the overall drag as well as effects the efficiency of the prop, even causing tail lift and possible cavitation at certain speeds.

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RC Surfer

Hmmm, As I look at my flex shaft (witchI get from Offshore Electrics)I would say it has a left hand wind opposite that of a drill bit witch I would say has a right hand twist, If your looking at the drill bit pointend and prop end. Both drill and surfer motor looking at the prop end and drill point end they spin in a counter clockwise direction, so that means that my flex shaft would be pushing grease and water away from the inside of the board not pulling it in. As far as the thrust bearing, my bearing is up against the motor can and the flex shaftcoupler against the thrust bearing. I do leave enough play at the dog drive and stuffin box tube but maybe only 1mm or so since the force of the prop pushing foreward and the on off action of the throttleacting like a hammer is the maijor culprite of any binding problems i've ever had.
Hope this helps, Later BB

InDaTube

Very interesting thoughts..........

If there is a 2-3 mm gap between the dog and the housing, what good is a thrust washer?

With this gap, the thrust from the prop is transfered to the board via the flex cable, thru the coupler to the motor shaft and finally to the motor mount to move the board forward.

I would think that the ideal transfer point should be the housing.

With a gap, the flex cable is doing double duty. Transfering power back to the prop and transfering the thrust forward to the motor shaft/motor mounts.

By the way, today's go out was with the gap..... only leaked several drops of water and WOW, lot's more power and speed.

InDaTube

RC Surfer

You are right the flex shaft has a double duty, the fact that the drive shaft is floating and at witch point does the foreward thrust actually carrys the load? If you had too mch of a gap at the Dog ear thrust washerat the stuffing tube then the motor would carry the load and theflex shaft would arch or bow until the dog ear comes in contact with the stuffing tube and puts all the load on the motor.The stuffing box,I would like to think this is where the thrust of the propis powering the board, and as the dog ear washer wears the stuffing box down if you had no gap, as it wears downthen the motor thrust bearing would start taking on the load, so yes dual perpose.I not speeking litteraly about 1mm of gap but probly only a few thousands of an inch.When I reset the gapevery time I grease the shaftthe amountofmaterial worn off the stuffing box tube the drive shaft endthen would go in the motor coupler further.If you never had to take out the drive shaft to grease it then it wouldware the stuffig box tube end enough that thedrive shaft would bow andwhere ever it would come in contact, it would cause more drag,in your case if I'm hearing you right it would ware through the teflon tube then throughthe stuffing box tube. On the motor end of the stuffing boxI only use a 3/4 inch of piece ofteflonto act like a bearing. I like how Dom has tapered the drive dog keeping the water flow around the shaft, I'm using a .130 flexwith a 3/16 drive shaft, in my case the dog ear isn't too much bigger than the stuffing box so I haven't noticed water leaks with out the full legnth teflon tube I'm getting alot more grease in my stuffing box maybe this is the difference. As far as the motor thrust bearing, this keeps the load off the motor bearings and onto the can and helps with caring the load.
Hope this helps Later BB

surfcurls

I don't like The Teflon, Doing a step down in brass is the ticket like YPC says.
I decided to make the step down bushings for the .150 flex just at the ends to allow maximum marine grease
surrounding the exposed flex within the stuff tube.

On The Offshore Elec site, They had mentioned the
Contraction & Expansion of the flex, and to allow space for it.

As for water traveling up the shaft tube, it's inevitable since it is spinning counter clockwise.
Even with the straight shaft from Kyosho, it has the same issue. I'm Sure BB would agree ...

YPC

Hi BB..........all the best for 2013

If your Flex shaft winding is in the opposite direction to a standard drillbit, you have a counter rotating flex shaft. A standard flex shaft rotates in the same direction as a drill bit.
If you are using a counter rotating flex shaft you may run the risk of 'unwinding' the flex shaft if the load is great enough.

The gap at the drive dog end depends on the overall length of the flrx shaft - 2-3 mm is a standard.
The flex shaft when under load should be as solid as a solid shaft - so their is very little 'bowing' if any.

The ideal would be a square end coupler at the motor end which would allow the flex shaft to float within the coupler rather than push and pull.

BB - if you are running a thrust washer on the motor side AND you say your stuffing tube is wearing down on the drive shaft end, then it may be that the flex shaft is pulling in under load ( not enough gap) - otherwise you should not have ware at the drive shaft end)

Indatube - you will be amazed how much a flex shaft 'shortens' under load - 2 -3 mm may seem like allot - but chances are that it is taken up when you stab the power.
Happy to hear it made a difference.

Curls - rather contraction than expansion

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surfcurls

YCP,

Point well taken, It's actually both that need the gap. Expand and contract

InDaTube

Why then, if you have a gap between the rear stuffing tube housing and the dog do you need a thrust washer between the two?

bearcave

Real inboard engine boats spend much time working out where the thrust point is wether motor or V drive setup for the best piont inside the hull (not outboards).... drag cars use rear end links attached to the chassis in various configurations to acheive the correct weight transfer when launching.

As aflex shaft only transmits tourque i guess the thrust point has to be at the end of the prop tube.... mechanicaly speaking would imagine it would be a wind-up (spinning water in) rather than wind-out situation (water out)....
Running thrust at the motor or end of prop tube, will this changethe performance of anrc surfer hull..... very interested in anythoughts.

I like the different ways many try to seal the shafthave tried a few myself. YPC and Karl seem tohaveit sorted bestbuthave noticedthatwhen moving the water flow from large to smallworks like a venturiand not much gets in..... when stopped water goes up anything anyway.

Btwmaui surfers........ Hotdoggin short boardin green flashlookin good!

YPC

Hi Indatube

When the flex shaft is under torque (at its shortest) and you have the gap width just right, the thrust washer should just be touching against the drive shaft housing face.
Try spraying you thrust washer a color and check it for ware after a surf session. If it is not showing signs of ware then you can reduce the Gap.
This may all sound anal - because it is - however - it all adds up to having an efficient set up with the least load.

Personally - I reckon the flex shaft and thrust washers are overkill......perhaps a band aid for poor alignment at best.

I run a very simple solid spring steel shaft 'without' any thrust washers either end. To date, the bearings within the motor have handled the load of the forward thrust without any issue or sign of ware.Surface drive props may warrant a thrust washer due to the single blade of the prop hitting the water and causing a hammering effect forward -BUT -Think about this - all the electric brushless plane motors, dragging some big planes around the sky without any thrust washers - a fully submerged marine prop will act much the same as a plane prop.

Bearcave -About the thrust point !...........Thrust from the prop is effectively a driving force through a straight line. The position of the prop will effect the trim of the vessel - BUT- the THRUST is not delivered at a particular point. In the case of inboards and V drives, the consideration is where the thrust line is in relation to the CG of the craft. You could have a prop at various positions along the length of the keel yet still maintain the same thrust line.

The pictures below are of an awesome coupler I have sourced to run with my solid shaft - it will smooth the slightest misalignment out perfectly and absorb any forward thrust through the center rubber housing. 20mm L X 16mm diameter. A miniature coupler like one would find in a Jet ski set up.

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bearcave

YPC

Thanks for that info I get the thrust line thing much better now but adding another thought...... In a theoretical world, if the prop was way up the front of the hull compared to way out the back, on the same thrust line, would the only real difference be the board reactingmorelikea front wheel drivethan a rear wheel drive car?

btw Isee youliked stand up jet-skiing and was wonderingif you have contemplated doinga jet board.... or is that away different journey for another time.. lol

Liked the thoughtabout the aero engine bearings...... and could you please tell where those awesome flex couplers can be found...

bearcave

YPC

Howzit Bearcave................The year is kicking off with some great discussion........sometimes its mind boggling just how much goes into just about anything to get it to work properly, even a Yo -Yo has certain criteria........LOL

As long as the prop can be positioned within the projected thrust line 'theoretically' it should be the same - however ! - practically the CG and Lift will move therefore all things will change.

In your example it would only be possible if the thrust was paralleled or negative- otherwise the forward positioned prop would more than likely be set out of the water.

In Gas Inboard racing - some racers run a thrust washer on the drive shaft face - some eliminate the load of a thrust washer and run the dog drive well clear of the drive shaft face, placing the forward drive thrust directly on the bearings of the motor - there is NO Noticeable difference between the boats thrust line performance.
Both run Flex shafts to overcome the angle of the mounted motor in relation to the surface drive unit.
The thought that the 'flex shaft' will bow in the stuffing tube if the dog drive does not push up against the drive shaft housing face is understandable - BUT - in reality with most instillations being relatively straight ( less than 15 degrees) it is not a problem. A flex shaft develops serious rigidity ( stiffness) under torque.

As for the COUPLING - Its one of those "I have a Friend ' who works with them..............LOL - let me know if you would like one or two.......I'll get some prices.

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RC HAWAIIAN STYLE

flex shafters



the reason we use flex shafts on the maui rc surf boards is because we have twice the power and twice the size and weight, i used a straight shaft when i was using 2 and 3 cell lipos ,, when we went to 4 and 5 cell lipo and a bigger prop the 3/16 th shaft bent right at the end , to much power for a straight shaft ,, plus the teflon keeps the noise down, ( a noisy rc surfer is annoying and the real surfers dont like the noise, ) i grease every time i go out, and never get water thru the stuffing tube, i agree for the smaller lighter boards with half thepower and weight the straight shaft is great, but if you want to go big in hawaii our california you better have equipment that can handle ,



maui john

YPC

Hey Maui John........LOL

Looks like you went on a marine 4 X 4 excursion over a reef with that prop and shaft..........LOL

Seeing that prop nut you are using, having a bigger OD than the props hub will also effect the performance of the prop. Its always best to purchase an actual prop nut by Octura or Prather or who ever......one that matches the hub OD.

I reckon the carbon fiber props are 'the better way to go'.......no sharpening and balancing required........they break before anything else........... work very well.......much safer around bathers/surfers. Their are great CF props available in 3/16 size on the web.

I reckon I should spend some time in the future sharing 'how to' better shape the stock prop's down for greater performance. That prop in the picture could shed quite a bit of face area which would make it far more efficient, as well as do with some sharpening and balancing.
Balancing a beryllium copper or stainless prop is 'crucial' - at 20 000 plus rpm if it is out of balance ( which is the case with all) it can generate serious vibrations that could even damage the electronics in the esc /RX or servo.

When I step up to 4s or bigger I would use a 1/4" shaft which would run the standard lead teflon bushes well - then turn it down to 3/16 at the end for the prop to fit.

With my current 1/8 shafts I now use 'Spring Steel' rather than Stainless, as the Stainless bends quite easy at the end, if the prop is badly fowled by debris in the water

I am not a fan of 'to much grease' in the stuffing tube - even with our gas boats - packed grease in the stuffing tube sucks the power out of a motor. A thin film of grease in the bushing area should be suffice to seal the set up.

My solid shaft runs free within the actual stuffing tube from the bushing point - only at the very end of the stuffing tube, on the motor side, does the ID step down to 3/16 to center the shaft.
I use the bigger size ID stuffing tube as a type of sump and inject a thick gearbox oil into it which works well to continually lube the bushing.

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K-H2o

Yo- Prop Heads
Maui johnactually uses a coat-hanger that he streightened out, Then hewelded on alug nut hefound at thebeach. Get that in asoda stray from McDonalds (used). If you put enough greese in it it will work on 3cells, but yu can see it can't handle 5

I'm all about streightshafts on Bronze bushings. but I use Hardend Stainless shafts.In stainless tubes,Lots of Greeseand eventhough they are hardened you can still cut um.I don't know about rusty spring steel.

Aloha, Karlsharks

RC HAWAIIAN STYLE

ypc i totally agree if i was racing in a pond, but the guys you have my rc surfers are not pro racers like you, they want to use them every day an not do any work on them, the flex shaft works like a culcth, when it hits a rocks sand kelp what ever it well absorb the blow, i agree it is not the most efficient, but it is very durable



maui john

surfcurls

Some great ideas to go green.

I'm thinking of duct taping some seaweed and plastic bags together for my new figure and using some sea grass
epoxied to sea shells so it can have The look of hair flowing. Looking to use crab claws for hands.

The deck will be secured by ocean tar found in the gulf after the BP oil spill
The new board will be shaped from foam bouys that washed up from the Japan Tsunami

Still looking for an Am radio washed up from Gilligans Island, and an old payphone
to make the Tx / Rx.

Looking into solder wire for a Shaft, The coat hangers seem like overkill, I can easily solder a lug nut to it.
Gonna cut up an old hub cap I found and sharpen it for props .
Heck I can even use the Mercedes Emblem that was on it, for a new logo !

It's fun to have a laugh in here now and then.
Heck I'm Curly.

YPC

Hey Guys...........

Its really a case of 'what floats your boat'.........I just enjoy sharing info /experience and hearing what others prefer and have experienced.

Karl.....- Spring steel has memory (flex) which is great and it is no worse than maintaining a flex shaft........they both need preventative corrosive measures.......not hard to add some oil. Plus - very easy and inexpensive to replace.........scale of economics.

I added some pics of the spring steel drive shaft from Board #3........looking pretty good for the use it has had.

Muai....I have raced with flex shafts most of my life........understand them like the back of my hand......they to have their shortcomings ( excuse the pun) and weakness's.

IMO
The thing is with the ******** that does not require the drive shaft to travel through a varied angle....its so much simpler/cheaper to use a solid shaft than having to bother sourcing/purchasing a flex shaft with a drive shaft end. A well fitted solid shaft can also run more efficiently with less load. I have never known a flex shaft to save any of my props when impacting an obstacle, once a flex shaft is under load, it is as rigid as a solid shaft .I reckon a correct solid shaft set up will outlast a flex shaft set up- as well as operate more efficiently.

THOUGHTS AND PRAYERS TO ALL IN OZ BATTLING THE HEAT AND BLAZE......................HOPE IT ALL COMES UNDER CONTROL SOON AND THAT ALL WHO ARE MISSING ARE FOUND.

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bearcave

I think its safe to say everyone has their own ideas on how they prefer to paddle their own canoes..... as it should be and probably will always be.... lol
Well done guys the knowledge and practical experiences getting thrown around is great.

YPC.... Thanks for the thoughts about our fire season... the usual heat this time of year in Oz has got some fires going early... especially in Tasy (the little island hangin of the bottom of mainland) but so far not too many dead just major property loss.... there will be more fires butjust likeeskimo's are always aware of polar bears eating themnowand then itsanother one of them things humans all over the world live with withinthe forces of nature,or other nasty humans doing bad things to them.....anyway nice thoughts mate....

btw its 9.30pm here in my fibro house and still 95 degrees F (35C)... got to 105F while workin today, think its time to go back to the cave lol but would realy like to get some of those couplings but understand if they are slightly in house....what ihave worksok at moment and have spare's but the steel ones are noisy and with both motors needing new bearings my boards sound like buzz saws haha!....always lookin for a better way of doing it but, hence why i watch this forum!

On a more humerous note....Hey Curly, I still use Gilligans AM radio and haha, I think i know what happened to Slash's head.... LOL

bearcave

Ispent ages doing the above on an Octura prop (i could have spent $30 getting a prop guy to do it but had to have a go myself) and it came up ok...... was so keen to give it a run i just put a normal nut on the end and, well, it didn't go any better than the plastic one but........it fell off!

Yes i am a dickhead hahabut maybe it was a blessing in disguise. The plastic/carbon prop being the weak link and breaking before bending/breaking the other bits is bearable for meatm.

Regards bear in unbearable heat.... lol

YPC

Hi Bearcave....as you say - working a prop is 'hard work'......... yet if done correctly, can be worth the time spent.

Some may not know this - BUT - the Beryllium Copper most Octura props are made of is very dangerous and can lead to cancer.
ALWAYS wear a dust mask when shaping metal props.

Modifying a prop may sound a tad overkill for rcsurfing - BUT - for starters if a 'metal' prop is run unbalanced ( which they all are standard out of the pack) it will sure do some sort of damage over time, especially to the electronics and bushing.

Sharpening the prop is also a must, or it will simply load up the motor and generate 'prop walk' which is a pulling of the tail to one side due to the rotation ( to the the left) - often tail lift can also become an issue due to a blunt prop, as well as premature cavitation.

The trailing edges of each prop blade should also be squared of neatly to ensure that the water breaks away from the blade rather than flow around to the back of the blade.

Besides the above MUST's........there is quite a bit one can do to a prop blade, be it Nylon or Metal to enhance the acceleration - reduce forward drag - torque roll - bite........etc.

This is an area I will spend more time on this year, now having the basic ******** construction behind myself.

For the ********....plastic PP / carbon fiber props are great. For starters the Cost and Safety is tops. I have raced carbon props up to 70mm in diameter on my Gas outboards.....they are great props and have their own off the shelf advantages. Being lighter props they allow for much quicker acceleration and having thinner prop blades presents far less drag through the water. The blade itself is very easy to reshape to experiment with various shapes and cut a ways - being inexspesive allows for free'r poetic licence.......LOL

BEST OF ALL - as you say, when ever you hit something - it's simply a quick replacement of the prop - without the risk of damage to the drive train , mounts - even perhaps the motor shaft.

IMO
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billybongo63

Aloha all!
MJ, Green Flash looks killer, so short and wide it looks like a skimboard I used to ride!
I love reading and re-reading all the tech stuff, so thank you all for creating a 240+ page manual!

Servo questions?
1) does anyone use tape? I noticed a little wiggle under load.
2) how strong should it be? I know thinking has progressed over the life of this thread.
3) name brand or knock off? I found these on e-bay
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