Wire drives and Thrust bearings

[JimClark]

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

[Eyekandyboats]

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!

[Darin Jordan]

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...

[SweetAccord]

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.

[Dr. Jet]

Thrust loads

..... 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.

[JimClark]

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

[Dr. Jet]

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.

[SweetAccord]

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~

[Ub Hauled]

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.

[Simon.O.]

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.

[G Doggett]

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.

[Dr. Jet]

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.

[sdartt]

How about the bearing install?

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

[SweetAccord]

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

[ghostofpf1]

Not having seen a thrust bearing in place (but understanding the concepts) I fail to see how the loads are being transferred to it ??
thanks
Ghost
edit: SWeet accord posted his pic as I was posting but I see something that would disallow any rearward movement but isn't pulling on the front of the shaft towards the transom the real problem or does the shaft want to push the back of the can out of place for some reason ??