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Old Apr 05, 2011, 03:55 PM
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USA, CA, San Diego
Joined Oct 2007
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Xtreme frame with Boca radial and thrust bearings

Today were going to talk about the proper use of thrust bearings for the Xtreme framed V120's.

In case nobody was aware nearly all larger heli's use a combination of radial bearings and thrust bearings in the head support. There are plenty of good reasons for this besides the fact that it's the mechanically correct method for reducing friction on a helicopter head.

I decided that the el cheapo chinese radial bearings that my Xtreme frame came with weren't doing the best possible job of reducing friction. This was evidenced with the fact that if I over tightend the collar just a hair it would bind the radial bearings up big time. It made no difference if the tail gear was on or not so this wasn't caused by a gear mesh problem.

This apparent binding due to side axial loading a radial bearing is what happens everytime you use pitch in either direction. Placing high axial loads on radial bearings is mechanically incorrect, IMO this can lead to premature bearing ware and lots extra friction.

This isn't something you want on a micro heli that has very limited battery and motor power. As a result of using incorrect bearings you can expect to see wasted power with reduced run times, premature motor and bearing ware, unsmooth operation, increased bogging during pitch manuvers, and higher temps of both the battery and the motor will occur.

Luckily the Xtreme frame was designed to use both radial bearings and a thrust bearing at each end of the head support. It was too expensive to impliment this design feature using the expensive bearings so they cut corners on the final production run. They originally used cheap radial and thrust bearings but they had issues, mostly just because of the lower quality.

Fortunately they had the demensions correct to allow the use of 2x5x2.3 radial bearings on the inside along with the 2x6x3 thrust bearings on the outside part of the bearing mount.

I just had to type in the required size, metric series 2x6x3, this is a link to the correct size thrust bearing.
http://www.bocabearings.com/bearing-...8523/F26-2x6x3

Page with thrust bearings in the correct size, not many here to choose from.
http://www.bocabearings.com/search.a...thOperator=%3d

Same for the inner radial bearings 2x5x2.3, I'm using the 440C ones part# SMR682-ZZC#3.
http://www.bocabearings.com/bearing-...R682ZZ3-2x5x23

List of all bearings in this size group.
http://www.bocabearings.com/search.a...thOperator=%3d


I can tell you that the difference is night and day, no comparison at all. The radial thrust bearing combo is so much smoother I can't believe it. There is also zero play in this system and obviously much less friction.

You pay for what you get here, these boca bearing are over ten bucks each.
It was well worth the money in my case. But this did bring the total for the Xtreme frame up to nearly 90 dollars.

It's no wonder they couldn't impliment this into production, it's just too expensive "to do it the right way".

These pictures show the thrust bearing and the incorrect size 2.5mm wide radial bearing. The correct size for the radial bearing width is 2.3mm. This width allowed for perfect gear mesh as well. Everything just fit right in like it was originally designed that way,...which it was.
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Last edited by chevell; Oct 21, 2011 at 12:58 PM.
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