Friction w increased # of bearings on one axel

if an axle has to go through more than two bearings, should that make the friction weird? or do you have to just make sure it’s aligned really well? been getting differing opinions from ppl on my team

this should be priority… also mounting bearing flats correctly.

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Making sure your holes are properly lined up is the most important thing for friction. Definitely make sure that you axle has 2 bearings, and you should always have a bearing where a shaft goes through a hole. However, having a shaft pass through 3 or more mounting points can increase friction and I would avoid this if it isn’t too much hassle. On that note, if you line everything up, friction increase with 3 bearings vs 2 will be very small.

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Generally, you should avoid more than 2 points of contact on an axle. The reason for this is that with 2 points of contact, even if they are slightly misaligned (which they will always be because the universe is not perfect), you can still draw a perfectly straight line between them, meaning that friction of a shaft between 2 points of contact is very easy to get low. If you add a third point however, all 3 points need to be perfectly inline otherwise a shaft will be pressing on one or more points.

It is still possible to get low friction with more than 2 points of contact, but it is significantly more difficult and is more prone to misalignment. There are also almost no instances where using 3 or points of contact is advantageous in any way.

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As a corollary, you should also avoid a single point of contact on an axle as well. While 2 points is better than 3, 1 point is definitely not better than 2! In this case 2 > 3… > 1

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also worth noting that the motor counts as a contact point. When using a motor, bearing should not be used on the same side as the motor, because that would create 3 contact points.

Additionally, in most cases contact points should be placed such that they straddle the load of the shaft. Cantilevering in many instances is ok if you know what you’re doing, but should be avoided for someone who doesn’t.

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Sometimes longer axles may be necessary when constructing gearboxes. But longer axles are prone to bending and you could end up with extra friction even if your 3 bearings are perfectly aligned.

Also, it may be desirable to avoid putting additional side loads on the internal motor gears.

To help in such circumstances it is recommended to use shaft couplers to join shorter axles and allow some flexibility, while still transmitting full torque.

Here is an example of such use from a PLTW tutorial:

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I mean sometimes if you are doing something where you are transmitting a lot of torque on a shaft that can stop it from bending. I used 4 bearings, one through each channel, on a LS shaft on my lift last year, the extra bearings helped to keep it from bending. I could have used a HS shaft, but that would have been a lot more work and more friction than more bearings.

But yeah on something like a drive shaft you only want 2 points of contact.

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it probably wouldn’t have been more friction. But something like a lift isn’t quite as sensitive to friction as something like a drive or intake or flywheel, since lifts generally move very slowly with very high torque.

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thanks all, i ended up changing the design to just have two bearings. friction is much better now :+1:

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The most important things are checking it is aligned correctly and see if the axle is straight.

Having a straight axle is very important.

You can run the motor using the brain, leave the screws slightly loose, move the metal/etc to where the watt usage is least, then tighten everything up.