Drawings of Thrust Easy Drawings of Thrust

I have never used a wire drive before and am wondering where most of you put the thrust bearing when using a wire drive? At the motor or at the strut?

jim

thrust bearings go at the motor all the time. and a thrust bearing is recommended to use no matter the drive shaft type. if there the pressure on the motor. use a thrust bearing!

All of my thrust bearings go on the motor under the coupler... However, I have seem some successful setups that used the thrust bearing down at the strut... These have almost always been larger sized boats, however... 1/8th scales, big gassers, etc...

I prefer the simplicity of using it at the motor...

Ideally the thrust of the propeller is directed up via the wire drive or any drive, so you want to reduce that force at the last spot where this thrust will cause the most damage if not redirected which is at the motor shaft.

It's thought that if a motor has bushings that a thrust bearing is a must, but if a motor had bearings in it, that a thrust bearing was not needed which is now "old shool" thinking as new motors all types brushless or not are achieving amazing RPM's.

To distribute this thrust to the frame of the can since it's a direct drive, the thrust if there is no bearing has no where to disburse. When you place the thrust bearing at the end of the wire drive then there it will much easily distribute itself to the frame of the can and not the front bearing of the motor which is NOT designed to take this force, only to address the motor's armature.

Hope that helps.

Quote Originally Posted by SweetAccord View Post

..... the front bearing of the motor which is NOT designed to take this force, only to address the motor's armature.

I must respectfully disagree. How have the airplane guys managed to log thousands of flight hours without a thrust bearing (albiet in the opposite direction)? I spin 90 mm ducted fans in a 7-pound jet at 45,000 rpm plus with no thrust bearing and no issues with the motor bearings taking the thrust loads. Look at Boca Bearings website, and you will see that modern bearings are rated for "some" thrust loads.

That said, a thrust bearing will not hurt anything, but with a modern ball-bearing armarure/rotor, it may not be entirely necessary.

I understand the primary use of the thrust bearing but I was thinking that using a wire drive there would be more flex and therefore somewhat less thrust being transferred to the motor bearings

Jim

With my open 0.030" wire drives, I have to take the thrust at the strut; for precisely those flex issues you mention. I suppose it is a function of power to wire diameter to wire length. If more of the wire is supported in a tube, it could take proportionatially more thrust for a given amount of power.

01:37 AM

Quote Originally Posted by Dr. Jet View Post

I must respectfully disagree. How have the airplane guys managed to log thousands of flight hours without a thrust bearing (albiet in the opposite direction)? I spin 90 mm ducted fans in a 7-pound jet at 45,000 rpm plus with no thrust bearing and no issues with the motor bearings taking the thrust loads. Look at Boca Bearings website, and you will see that modern bearings are rated for "some" thrust loads.

That said, a thrust bearing will not hurt anything, but with a modern ball-bearing armarure/rotor, it may not be entirely necessary.

Sorry but you can't compare an air plane system with a boat system. Lets see the comparables and logic:

1. How long is your drive from the armature to the propeller? I gurantee it's not more than a few inches, guranteed not more than 10 inches. < Different
2. The thrust on an airplane is completely horizontal and you can't compare to a angled drive which has more of a thrust load due to the angle. <Different
3. The motor is completey horizontaly driving the prop. < Different
4. Plus the resistance of air is different than of water. Lets see the login again, I can gurantee you can wave your hand a lot easier though the air than in water. < Different
5. How many amps are these plane pulling? For the same size/scale nothing close to a boat-wonder why? < Different
6. The same motor ran one without a thrust bearing vs. another that utilizes one in the same install will have a shorter life span/issues.

So that is how the airplane guys "manage". So I respectfully disagree that a thrust bearing is ideal to use as airplanes loads/amps/drive/setups are different than boats.

Peace~

I always thought of thrust bearings for cheaper motors... not that there aren't any pressure problems with expensive motors. The reason I say that is that the endbell of the cheaper motors will detach easier then it's counter part... the endbell would be my main concern...
again, I am not saying that there aren't bearing problems in the equation.

I'll fire in my 3 penny worth.
It depends on where you want the thrust vector to act upon.
At the strut = very close to the WL and beyond the transom
At the motor = above the WL and well forward of the transom.
These two thrust vectors in any given hull with the same powerplant will produce different handling characteristics.
That said there are differing issues with the thrust load up a wire, flex and solid shaft.
In my lightly loaded WD's I let the load go to the motor with no thrust washer at all.
In the heavier setups I try to get the load at the strut.

I can draw thrust-vector diagrams all day, but time on the pond tells me what I need to know.

Please bear in mind that I use Brushed motors ( sort of quick ones ) and Ni cells to achieve my experience.

Quote Originally Posted by SweetAccord View Post

Sorry but you can't compare an air plane system with a boat system. Lets see the comparables and logic:

1. How long is your drive from the armature to the propeller? I gurantee it's not more than a few inches, guranteed not more than 10 inches. < Different
2. The thrust on an airplane is completely horizontal and you can't compare to a angled drive which has more of a thrust load due to the angle. <Different
3. The motor is completey horizontaly driving the prop. < Different
4. Plus the resistance of air is different than of water. Lets see the login again, I can gurantee you can wave your hand a lot easier though the air than in water. < Different
5. How many amps are these plane pulling? For the same size/scale nothing close to a boat-wonder why? < Different
6. The same motor ran one without a thrust bearing vs. another that utilizes one in the same install will have a shorter life span/issues.

So that is how the airplane guys "manage". So I respectfully disagree that a thrust bearing is ideal to use as airplanes loads/amps/drive/setups are different than boats.

Peace~

1. Doesn't matter. It could be three miles. The thrust vector remains the same. I've built aircraft with a driveshaft like a P-39.
2. Ever seen an airplane hover? Ever heard of P-factor?
3. Your flex or wire drive BETTER be parallel to the motor shaft.
4. Try to spin a 17" propeller underwater at 15,000 rpm. The actual loads are proportional.
5. My F5B airplanes pull about 250 amps continuous (3-second motor run puts you 500 feet high) with a higher burst as the motor fires up. Try to accelerate a 4-pound boat from 30 mph to 180 mph in 2 seconds. Serious thrust loads my friend.
6. If you can find a light and simple way to put a thrust bearing on an aircraft, let me know.

Thrust is thrust. Axial loads on the motor. Doesn't matter what type of vehicle, the motor doesn't care. Pulling or pushing on the shaft still produces an axial load.

What parts and what is the install sequence? I assume the TB goes between the coupler and the face of the motor mount?? I am just getting ready to install a TB as soon as OFE delivery comes. I was installing a tran in my Titan 29 but decided to go direct drive. Thanks

01:17 PM

Sdarrt, trust me you need one, talk to Steve from OSE or any EXPERIENCED boater her and they will tell you to install one, and don't allow anyone to convince you that boats are the SAME as anythig else and that you don't need one. I have had and still have loats of RC cars and they don't need one. So I'm not going to tell you that you don't need one cause my RC car does not need one, that's silly. It's a small investment and does not hurt anything at all, if anything helps if you understand mechanics.

SDartt, there are two kinds, one piece and three piece.

The three piece are installed by order: Washer, ball ring bearing, washer. See pic below.

Or you can use:

http://www.offshoreelectrics.com/products.php?cat=49 that is one piece, simply slide onto the armature.

Note: On either one, be sure to leave a small gap to not allow the thrust bearing to bind, or you defeat the purpose/function of it.

~Peace

01:33 PM

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.

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.

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

02:22 PM

Quote Originally Posted by ghostofpf1 View Post

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~

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.

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

Peace~

04:00 PM

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?

Quote Originally Posted by Simon.O. View Post

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.

Quote Originally Posted by Dr. Jet View Post

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.

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

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.

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.

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.

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

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

Drawings of Thrust Easy Drawings of Thrust

Wire drives and Thrust bearings

Thrust loads

How about the bearing install?

Thanks SweetAccord

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