thrust bearing.....what's your take?

[tlandauer]

No to stir anything, and I believe everyone's point of view, let's say the flex doesn't shrink as much as people tend to think, with the thrust bearing at the strut end, any shrinkage however small the amount would then be 'absorbed' by the motor rotor being pulled, NO???
I am just trying to understand, please don't take this wrong.

[Cooper]

Long debate on this one! I always put the thrust on the motor. Why do flex shafts snap when they have no room to wind up? Why do we leave a gap at the strut and drive dog? Motors today are much better at taking thrust because they are built different than our old brushed motors. It still pushes hard on your motor arm against the rear bearing...you do not think that thrust pushing a 5-10# hull matters on a motor? If not why need a stuffing tube......a flex wants to wrap in a knot from thrust.

Absolutely, I've pushed a lot heavier boat over 115mph. Both bearings on the motor work with the load, taking in account quality of a motor is being used. I use to use the rule of thumb that a gap between strut and dog should be at least half the diameter of flex being used to a max of the flex diameter. But I go by trial and error, load about three Teflon washers, if one is squashed then good and remove one. I've taken accurate measurements from multiple runs and adjust accordingly. If I proped up and just rip into throttle max it is usually gonna end up with lost props and a swim. Radio throttle curves and a light finger on the throttle help. Again this is for pushing the limits on equipment. Sport is whatever is gonna hold up the best and last the longest :).

[Cooper]

Oh and to add the thrust debate,, that is why bulkhead and lots of reinforcing for the struts are necessary

[rearwheelin]

No to stir anything, and I believe everyone's point of view, let's say the flex doesn't shrink as much as people tend to think, with the thrust bearing at the strut end, any shrinkage however small the amount would then be 'absorbed' by the motor rotor being pulled, NO???
I am just trying to understand, please don't take this wrong.

Correct !

[ray schrauwen]

Some of the German flex cable I've used from H&M is far more rigid and far less prone to shrink or whip. I'm thinking of possibly changing all my spec boats to .130" H&M cable. I really liked that stuff. If Rocket City racing ever gets his order in I'll show you what I mean. I should order some 3/16 from them too. They don't even bother with ,150" cable because the .130" is good for boats up to 40" on 6S1P. I know... sounds like hooey but, I've used it before and a side by side comparison and in boat use has me sold. It actually performs more like wire drive but, bends better.

[rearwheelin]

Some of the German flex cable I've used from H&M is far more rigid and far less prone to shrink or whip. I'm thinking of possibly changing all my spec boats to .130" H&M cable. I really liked that stuff. If Rocket City racing ever gets his order in I'll show you what I mean. I should order some 3/16 from them too. They don't even bother with ,150" cable because the .130" is good for boats up to 40" on 6S1P. I know... sounds like hooey but, I've used it before and a side by side comparison and in boat use has me sold. It actually performs more like wire drive but, bends better.

I have 3 new .130 cables I need to sell ! I got them from FDM several years ago . I will never use them as they were a shipping mistake and Chris told me to keep them. Always looking to sell them :)image.jpg

[keithbradley]

Something like this [ATTACH=CONFIG]128423[/ATTACH]

Thrust bearing or no, pick your side, I don't care...BUT, you're absolutely crackers if you think people are moving heavy boats across the water by placing the load on a thin brass tube, while spinning against it at 30k RPM. That would last about 5-10 seconds.

The tube, and the motor, CONTAIN the assembly. You keep visualizing the thrust from the prop pushing up at the motor. It's not. I understand that without the motor, the flex would extend at the angle that it is at when it meets the motor. I think this is where you are getting the idea of the flex pushing something up. However, once the motor is in place to CONTAIN the flex, this action no longer happens and is not relevant. The system is now contained and the prop/strut are allowed to determine thrust vector, which ultimately is what will affect the attitude of the boat. This is something that is seen all across the mechanical world and in every day basic physics.

[rearwheelin]

Thrust bearing or no, pick your side, I don't care...BUT, you're absolutely crackers if you think people are moving heavy boats across the water by placing the load on a thin brass tube, while spinning against it at 30k RPM. That would last about 5-10 seconds.

The tube, and the motor, CONTAIN the assembly. You keep visualizing the thrust from the prop pushing up at the motor. It's not. I understand that without the motor, the flex would extend at the angle that it is at when it meets the motor. I think this is where you are getting the idea of the flex pushing something up. However, once the motor is in place to CONTAIN the flex, this action no longer happens and is not relevant. The system is now contained and the prop/strut are allowed to determine thrust vector, which ultimately is what will affect the attitude of the boat. This is something that is seen all across the mechanical world and in every day basic physics.

Yes the motor contains the thrust . There is no containment of thrust at the strut as long as the shaft "Free Floats " . Meaning no dead stop in the strut it's self . The stuffing tube is containing the flex , keeping it together other wise why would you even need a stuffing tube right ? So if the motor is the 1st dead stop then the second dead stop must be the stuffing tube ! If you are running thrust washers or bearings with no gap or enough gap that compensated for the "shrinkage" and you are certain that you are 100% smashing the drive dog into the washers then you are thrusting at the strut then the strut becomes the dead stop via thrust washers or bearings at the strut effectively eliminating the dead stop at your motor and stuffing tube. The key is finding the correct gap or no gap so as to use the brass tube more as a guide than a "stuffing tube". I can see differences in the handling of my boats when I run both types of thrust setups.

[Shooter]

I'm with Keith regarding the thrust vector and the affect on attitude. The reaction takes place where there is relative motion(the water and the prop).

However, I do believe rearwheelins drawing is accurate. The flex loads up the side of the tube.....and trying to make the tube more of a 'guide' is the right direction. That's why I'd love to see someone try a thrust bearing at the strut with a kaleidoscoping square drive (like an outboard).

[rearwheelin]

I think there are many benefits pushing on the brass hard , seen the proof on many boat vids ! They seem to run a little lighter on the back end and handle harder acceleration better.

[rearwheelin]

Some of the German flex cable I've used from H&M is far more rigid and far less prone to shrink or whip. I'm thinking of possibly changing all my spec boats to .130" H&M cable. I really liked that stuff. If Rocket City racing ever gets his order in I'll show you what I mean. I should order some 3/16 from them too. They don't even bother with ,150" cable because the .130" is good for boats up to 40" on 6S1P. I know... sounds like hooey but, I've used it before and a side by side comparison and in boat use has me sold. It actually performs more like wire drive but, bends better.

Sounds like awesome stuff !

[Lightknight]

In an ideal world all of the thrust from the prop should be taken by the strut/Stinger. The issue as many have alluded to is that the flex tube contracts. In this situation you have a negative thrust on the thrust bearing on the motor - not ideal -and if you have no thrust bearing, again not ideal as the motor is under a pull force. The real issue it seems to me is how much do you allow for the flex contracting? If you know this figure then you can obviously slacken the drive dog the right amount. I allow 1/16 (1.5mm) but I have no idea if this is the right amount and of course the "right amount" varies according to the prop you are running and the size of the shaft.
So, in an ideal world the right setup is to have just enough float in the shaft for it to come under a little tension as it tries to shorten, possibly with some light spring washers on the motor to allow a few thou in-out movement in the motor. That way all of the prop thrust is born by the stinger. It seems to me having a thrust bearing is adding something that may or may not be used...one more thing to go wrong, but the other side of this is of course that if you allow enough float the full thrust of the prop can be born by the thrust bearing. In a real ideal world the motor would have thrust bearings built in.

[rayzerdesigns]

heres my 2 cents..if a motor has fore and aft paly in it..you don't want to put a thrust washer on to the point where it takes all of the play out of it..the motor should be free to center itself in the magnetic field..yes.maybe that means a bigger gap in strut..but it should be free to at least stay at point where it rests if you pull or push on it ant it returns..

[Lightknight]

Agreed

[kfxguy]

The best way to do it is have a stub shaft in the strut with a thrust beating at the drive dog. Then have a floating square drive flex shaft.