Thrust management

[morewattsnow]

What is the best way to manage the thrust from our props? As far as I know there are 3 ways.

Let the shaft push on the rear motor bearing

Use thrust washers at the strut and space it accordingly for twist

Use a thrust bearing at the motor mount (not quite sure myself how this works- any explanation would be helpful.)

[martin]

Getting a flex shaft set exactally right to allow for wind up whilst having the dog pushing against a thrust bearing on the strut in my opinion is virtually impossible, Simply because you going to get different wind up depending on how much throttle your using. If you use the thrust bearing at the motor end, The thrust bearing sits against either the motor end cap or the motor mount depending on your motor & mount system. The flex shaft then pushes against the thrust bearing which is pushing against the motor end cap or mount & not putting any load on the motor bearings.

[morewattsnow]

So you clamp a collar onto the shaft to transfer the load to the thrust bearing?

[egneg]

Ideally the collet is used to transfer the load to the thrust bearing at the motor.

[martin]

As stated you adjust the collet against the thrust bearing.

[morewattsnow]

So the outer race of the thrust bearing will bear on the mount or motor can and the collet bears on the inner race of the thrust bearing, correct?

[egneg]

So the outer race of the thrust bearing will bear on the mount or motor can and the collet bears on the inner race of the thrust bearing, correct?

You got it.

[Steven Vaccaro]

I have another question, I've always wondered if handling is effected when taking the thrust at the motor. In my head I'm thinking the force is then placed inside the hull rather then on the back. Can Any of you engeneering types help out?

[martin]

Im convinced that with a flex drive(unless you have the 2 part design with the square end which is a good design but not that popular because of extra maintainance re when greasing) is not taking the load with the dog against the strut. But putting the load on the motor bearings, How do you get the gap spot on that you need for cable wind up which is going to vary at different rpm or with different prop loads whilst still not having to small a gap where you can snap the flex. I know from looking at the drive dogs that have run a lot & theirs no rub marks on the face of the dog or strut bearing. Martin.

[Fluid]

If all the thrust which moves a boat is taken at the motor, than when running an outboard that way the transom should jump out of the water without the boat moving forward. Since this doesn't happen - even when thrust is taken on the motor, much of the thrust must be transferred by the flex cable/stuffing tube.

Even if thrust was all taken by the motor, the thrust vectors are so similar that the end result will be about the same. On my wire drive boats I can take the thrust on the motor or on the strut, and I cannot tell the difference when running in back-to-back tests.



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[srislash]

Ok,here's my silly question as for some reason I have never considered the wind up.How much space should I leave for wind up?I am just re-entering the hobby with a MG,CC 1515&Ice 240.I am assuming if it's too tight I could get the opposite effect on the motor.Thanks guys.

[properchopper]

I've frequently pondered this issue, often to the point of giving myself a headache without reaching any conclusion. I know ( and have unfortunately experienced-don't ask :doh:) the difference in handling characteristics between front-wheel and rear-wheel drive vehicles and there is a substantial difference in high speed cornering parameters. I'm of the opinion, like Jay observed, that in the scale of our model boats that there is no meaningfull difference where the forward motion vector is located. Still, I wonder......:closedeyes:

[Fluid]

Ok, here's my silly question as for some reason I have never considered the wind up. How much space should I leave for wind up?

Are you certain you want to ask me? :laugh: The default answer is to leave a gap the same size as the diameter of the cable. If you do this you will not have a problem with 95% of setups because it has a safety factor. The amount of wind-up depends on a lot of things - the diameter, length and quality of the cable, the ID of the stuffing tube, whether you use a Teflon liner or not, and how much thrust the prop gives. It is not just wind-up but also includes the thrust that is delivered from the prop.


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