Wire drives and Thrust bearings

[SweetAccord]

Thrust bearings are designed to support a high axial loads. They are also known as an axial-load bearing where the load acts in the direction of the axis of rotation. In other words, a bearing that is designed to handle axial forces along the centerline of the shaft. This is the force of the water pushing back against the blades. Really, take it slow and take some time to think about it. Maybe this will help:



The bearings in this stool are subject to a thrust load.



The bearings in a car wheel are subject to both thrust and radial loads. The bearing above is like the one in the hub of your car wheel. This bearing has to support both a radial load and a thrust load. The radial load comes from the weight of the car, the thrust load comes from the cornering forces when you go around a turn.

Do search this board and other boards, and do more research on them, and you will understand their purpose and concept.

~Peace.

[Dr. Jet]

From Boca Bearings tech website:

"Single row radial ball bearings with ball separated by a cage can support radial loads, axial loads and tilting movements. All full complement V-type ball bearing can support only radial loads and some low axial loads."

I am not advocating not using thrust bearings, I am saying they may not be necessary in all cases.

[ghostofpf1]

Thanks for taking the time to post. I had not considered the load imposed back wards from the prop to the motor shaft and see now why a thrust bearing might be useful.I have a hard time believeing the loads are that high at that point but will have to bow to those with more real time experience than I have in FE boats.
As far as searching other boards I'd rather ask the questions here as opinions are like ..well you know..... and if I search I'll likely be overloaded with 100 different ways to change the time on a clock for my efforts
Did problems arise that dictated the use of thrust bearings ..were the motor cans being pushed out backwards ??
Won't they be a source of more drag.....or will their drag be offset by some lesser drag in the motor now that the rotor is ostensibly no longer in contact with any bushings or washers inside the can ??


PS...Really....thanks for the illustrations but in the future it's not necessary ...I've had engineering terms pounded into my head since 1975 so I can pretty much understand whatever it is you're trying to convey
thanks again
Ghost

[SweetAccord]

Did problems arise that dictated the use of thrust bearings ..were the motor cans being pushed out backwards ??

YES! I have seen the back of a brushless bearing pop out from not using one.

I posted the pics and provided more examples not just for you Ghost, but for everyone so that any new members may read and learn, it was not just directed to you Ghost as you did state "but understanding the concepts" and that statement did not go unoticed.

Peace~

[sdartt]

Thanks SweetAccord

Great picture, it's like worth a thousand woirds-so they say, I assumed that was how to install the TB but your picture clears up any ? a newbe has. I ordered a TB from Steve last week, part # dh-53136, I thinks it's the correct part.
Thanks again to all form members, I learn more by what other members ask as much or more than I do from my questions.

[SweetAccord]

That's the idea!! To learn from others! Why re-invent the wheel and learn by costly mistakes? Glad to help.

Peace~

[Dr. Jet]

Just to make things clear, I do use thrust bearings when I believe it is necessary. Here’s what I have:

1. MHZ Micro Shovelnose. 2.3 mm flex shaft. Chinese outrunner. No TB. All thrust on the motor.
2. MHZ Gecko (2X). 2 mm straight shaft. Chinese outrunner. No TB. All thrust on motor.
3. Campbell Hydro. 1/16" wire, SV27 motor. TB at motor. (I don't trust the endbells of these motors).
4. Campbell Hydro (old setup). 1/16" wire. Speed 700. TB at motor. Can motors with bushings need a TB.
5. JetCat 29. 0.130" flex, SS-1 (Speed 700 with one bearing). TB at motor. The bearing provides no axial support.
6. 1/16 Finlay hydro. 1/16" wire (straight). Neu 1110. No TB. All thrust on motor.
7. MHZ Miss Madison. 2.3 mm flex shaft. Neu 1107. No TB. All thrust on motor.
8. BBY Twin Micro Scat Cat. 0.030" wire drive. Chinese outrunners (2X). No TB. Thrust at prop end of stinger (flanged ball bearings).
9. BBY Micro Hydro. 2 mm straight shaft. Chinese outrunner. No TB. Thrust at prop end of stuffing tube (flanged ball bearing).
10. Graupner Key West. 0.130" flex. Hughey gearbox. No TB. Thrust at gearbox (flanged ball bearing).

Setup #9 could take the thrust at the motor if so desired.

Note: What is the difference in taking the thrust at the flanged bearing on the Hughey gearbox and a ball bearing on a motor (aside from the endbell issues)? How many of you use a TB with the Hughey 'box?

[Simon.O.]

Sorry Simon, I have to disagree.
I doesn't make any difference if the thrust bearing is down at the strut or up at the motor, the 'thrust vector' is the same.
I have proven this argument several times by taking the example of an outboard motor with a flex cable drive that takes the thrust via a bearing on the bottom of the motor and not at the dog drive.
The pressure on the motor from the shaft and bearing is vertical, but the boat does not try to go upwards like a little helicopter, because the thrust occurs down at the prop regardless of where the thrust bearing might be.
To exaggerate this example further lets construct a boat with a long flex cable that start off going forward as usual, but then curves through 180 degress so that the motor is now at the back of the boat, still with a thrust bearing on the drive end.
The thrust on the bearing is pushing towards the back of the boat but it still goes forward. Right !
I was feeling argumentative but now my brain is just tired !
Graham.

Thanks for shining the light on what should have been blindingly obvious to me.
I have an OB powered hull and forgot that one.
Graham, you have simplified the matter and made it very clear, to me at least. !!
I was doing too much maths on this one
I still do not use thrust bearings as such but try to keep the thrust at the strut to take the compressive load and therefore the whip potential off the wire.
I hope I am on the right path here

[Dr. Jet]

I still do not use thrust bearings as such but try to keep the thrust at the strut to take the compressive load and therefore the whip potential off the wire.
I hope I am on the right path here

Be careful when trying to take the thrust at the strut when using flex cable. It will shorten up slightly as it absorbs a twisting force. That is why most will take the thrust at the motor (either through the motor bearings or a dedicated thrust bearing). Wire drives and straight shafts do not experience this shaft-shortening condition, although Jim's original post relates directly to this.

If wire flex is a cause for concern, taking the thrust at the strut is a way to mitigate this concern.

[SweetAccord]

Be careful when trying to take the thrust at the strut when using flex cable. It will shorten up slightly as it absorbs a twisting force. That is why most will take the thrust at the motor (either through the motor bearings or a dedicated thrust bearing). Wire drives and straight shafts do not experience this shaft-shortening condition

I agree!! Absolutely correctly stated.

[JimClark]

Thanks Doc for the info and opinions. All my experience has been with straight shafts and taking the thrust on the motor bearing in my 1/10th scale boats.

Jim

[Jeff Wohlt]

I use them at the motor coupler. Here is what I know. This deals with thrust and torque of the motor...this can be substantial.

There are differences on the motor than the strut. For hydros we always put the thrust on the motor because that goes to the sponson areas and you have more width to absorb the thrust and torque and it can actually change your CG depending on where the motor is mounted. We mounted the motors way forward for this reason.

When you take it at the strut very small changes in angle make BIG differences because now you are pushing the strut down with contact with the strut. When you put it on the motor you are now just dealing with the prop cone trhust...much easier to make adjustments.

This goes for riggers as well. All the trhust and torque should end up at the motor and torque on the sponsons. Motors forward.

Hope that makes sense but it is late.

[Simon.O.]

Jeff, that makes a huge amount of sense.
That is what I was getting at earlier but had difficulty putting descriptions into words on paper or screen. I can do the verbal and hand gestures thing easily to describe things.
I think there is a huge difference between solid / wire / flex drives.
A solid will take the load all the way to the motor with no issue.
A wire will do so almost as well, in my experience.
A flex will do ???? I will not place an opinioon on this one as the only flex in my fleet is on an OB and the thrust is taken at the hub, same as the strut.

I will qualify my opinion with one last thing.
As a result of todays runs and another blown wire I will now run the thrust at the strut on that hull, in fact I will run the thrust at the strut on all of my wire drive hulls now.
Drive dogs and plastic props are not cheap enough for me to lose one a week.

[Jeff Wohlt]

Simmon, a few of the hardcore boys across the pond that have used wire for over 10 years also think the thrust should be on the strut. Yes, a wire will take some and can actually free up the resistance with thrust on it. I have never had one come apart on me in my boats and I leave the std gap just as I would the flex shaft but I also run the thrust on motors. You can't do that with flex very well or it can come apart as many have seen over the years.

The wire will touch the top of the stuffing tube at the bend coming in to the hull. When you apply thrust it pushes the wire and can actually make clearence for the wire to brass where you then have virtually nothing touching the walls of the stuffing tube. If I could animate it on the pc then I could show you.

A flex...well that is just a big soft noodle that will also try to straighten out as torque and thrust are applied. Cable was only really designed so it can turn as it bends in tight areas...it was the best solution years ago.

Yes the straight hard shaft IS the most efficient out there...just can't get them to work in many hulls besides hydros and monos.

[SweetAccord]

To sum it all up: the thrust bearing, basically:

If wire drive> goes on Strut
If flex drive> goes on Motor