Stuffing Tube Bend/Bending Issue...

[Checkmateguy01]

If anyone has looked in the boat building section of the forum, you know that i'm in the process of building a FighterCat Daytona, the Genesis hull. So i'm trying to get the stuffing tube mounted and was worried that i did not have enough angle on the motor/mount, which turned out to be what i thought! Anyways, the only way i could get the stuffing tube to line up right with the strut and motor was to bend the tube in a slight "S" curve, not dramatic but enough (see pics). The alignment is dead on, angle is good, but i'm worried about the "S" in the bend and if it will cuase flex shaft issues?? This is a simple 40-45 mph build, not gonna be turning extreme RPM's, but before i go any farther i'd like to know if i'm gonna have issues or not! Thanks!

IMG_0385.jpg IMG_0386.jpg IMG_0383.jpg IMG_0384.jpg

[Chilli]

"S" bends are no problem. I run one in my trials rigger turning close to 40K rpm and my bend is much sharper. Many say the S bend causes less drag than a single bend in the stuffing tube.

[JimClark]

What about moving the motor further forward

[Checkmateguy01]

"S" bends are no problem. I run one in my trials rigger turning close to 40K rpm and my bend is much sharper. Many say the S bend causes less drag than a single bend in the stuffing tube.

Thanks man, you made my day!! Like i said, i'm real happy with the alignment, all looks good except for the S bend, but if it's not a problem i'm not worried about it!!

JimClark, the motor won't go any farther back, the mount is perminatly epoxied down! The location of the mount is based off a factory Genesis for measurements.

[longballlumber]

I am not sure where is mis-conception comes about "S" bends

Your S bend will be just fine. As a mattery of fact, you could bend it more with out issues. I feel it's more important to make sure your stuffing tube has been line up with the motor and collet. I use 3/16 rod and then telescope brass tubing into the stuffing tube while everything is glued.

Later,
Mike

[BHChieftain]

My toysport triton has an S-bend, works great. I have read that a single bend is not a good idea, due to the flexdrive wanting to whip inside the stuffing tube (which does not happen with a double bend).
Chief

[Checkmateguy01]

My toysport triton has an S-bend, works great. I have read that a single bend is not a good idea, due to the flexdrive wanting to whip inside the stuffing tube (which does not happen with a double bend).
Chief

Learn something new everyday i guess!! My reason for asking in the first place was i thought that the S bend may cause a "whip" inside the tube, i never thought of it that way with a single bend.

[JimClark]

you don't get more friction with a S Bend? Learning here on this one also

[siberianhusky]

When a flexible cable is loaded it tries to assume an S shape naturally, the flex will still only touch the stuffing tube at the bends in the cable and won't whip because it's in the S shape.

[m4a1usr]

you don't get more friction with a S Bend? Learning here on this one also

The answer is an "absolutely" YES its fact. The answer is the math. Bends are restrictions. Thats the simple term. Look at the various manufacturers of flex shaft assemblies, like in the Aircraft or Automotive business. Lets pick S.S. White as an example. They give you a nice chart to use for guidance when selecting a size of flex material. And as the bend radius decreases, so does the torque output of a flex shaft? Why? Simple friction. http://www.sswhite.net/unidirection_eng.htm

Or you can go to BIAX and look at their website. Same story. http://www.biax-flexwellen.de/en/all...anchor=2110001

Flex shafts, under load, look like a cork screw inside the stuffing tube. They twist around the inner ID of the tube they reside in.

John

[keithbradley]

Almost every tube I've seen fail had:
-excessive bend
-Poor mounting/support or worn struts allowing cables to whip
-Crushed tube from improper bending

^^^any of the following will cause issues.
Other than that you're probably ok. I prefer single bends like John stated but yours doesn't look concerning unless it's improperly bent, in which case it doesn't matter how many bends there are.
As for "s" versus single bends, an "s" bend will definitely net more side load on the tubing wall, unless the single bend is on a tighter radius. In large radius, slight bends you can usually get away with both though.

[longballlumber]

This cracks me up every time it comes up...

Nitro Boaters (actually Ed Hughey a pioneer in FE too) introduced the world of model boating to flex shafts. He started using flex cable out of automobile speedometers. Before that they were using harden steel straight shafts with needle bearings.

I can’t count the number of SAW records, 2 lap oval records, IMPBA US1 Championships, NAMBA National Championships, and club level heat races that have been won using an “S” bend stuffing tube. If they can break records doing 100+ or heat racing .45 powered riggers doing 80+ in heat racing trim; then it’s good enough for me. If those guys thought for a minute that a “J” bend stuffing tube was faster, better, stronger, or more efficient THEY WOULD HAVE DONE IT ALREADY.

Now, I am not saying a “J” bend won’t work. I think it becomes a preference. In my experience, the “S” bends works just fine for me assuming that it’s installed correctly. However the same caveat goes for the “J” bend too. Regardless of what bend you make it must be installed correctly for it to work efficiently.

The answer is an "absolutely" YES its fact. The answer is the math. Bends are restrictions. Thats the simple term. Look at the various manufacturers of flex shaft assemblies, like in the Aircraft or Automotive business. Lets pick S.S. White as an example. They give you a nice chart to use for guidance when selecting a size of flex material. And as the bend radius decreases, so does the torque output of a flex shaft? Why? Simple friction. http://www.sswhite.net/unidirection_eng.htm

Or you can go to BIAX and look at their website. Same story. http://www.biax-flexwellen.de/en/all...anchor=2110001

Flex shafts, under load, look like a cork screw inside the stuffing tube. They twist around the inner ID of the tube they reside in.

John

If this entire math translates directly to our use of flex shafts in FE model boating, I have to ask; Why does an “S” bend work?


Later,
Mike Ball

[Mattwarner]

I would be more worried about the gap between the stuffing tube and collet, as i understand it this needs to be kept to a minimum?

What does everyone think?

[siberianhusky]

I remember solid shaft boats far too well! I still have universal joints kicking around from those days! I should have a museum sale, some of my airplane stuff goes back to the early 70's.

[Checkmateguy01]

I would be more worried about the gap between the stuffing tube and collet, as i understand it this needs to be kept to a minimum?

What does everyone think?

Looking at pics of the factory Genesis i don't think my gap is much, if any, wider than their gap between the tube and collet. I'm interested in hearing opinions on this too now, but i think it comes down to alignment more than anything.