Failure testing Clevis' and ball joints. - RCCanada - Canada Radio Controlled Hobby Forum
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Old 11-21-2020, 11:14 AM   #1
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Failure testing Clevis' and ball joints.


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Someone asked the question of why Clevis' vs Ball Joints on my Aviation Design Diamond Build so I figured some testing was in order.

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Old 11-21-2020, 11:32 AM   #2
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Re: Failure testing Clevis' and ball joints.

Cool test, thanks. The ball links could have been tested between 2 carbon plates as that is a more typical installation and would have removed the slight rotational moment in your test but I doubt it would have made a huge difference. The question this brings up is how much pulling force do we really see on our control surfaces?
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Old 11-21-2020, 11:36 AM   #3
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Re: Failure testing Clevis' and ball joints.

Very interesting video on linkages , thanks. On straight line control linkages I too use clevises but if any angular change , I use the Dubro HD ball linkages. Wonder if there would be any change if the threaded portion was only screwed in 3/4 of the way on the 4-40 ball links ? In other words would the rod pull out of the linkage ?
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Old 11-21-2020, 12:18 PM   #4
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Re: Failure testing Clevis' and ball joints.

Interesting and provocative torture test. Thanks to Johnathan and Ward.

Stronger is better, of course.

But I wonder how strong does a clevis have to be before another part of the control system, such as the servo, fails. And what are the real world force requirements of the control surfaces of our models (with different sizes/types requiring varying force requirements).

btw, I've only used clevises but that probably because that was what was available when started this hobby and they have worked for me.
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Old 11-21-2020, 05:44 PM   #5
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Re: Failure testing Clevis' and ball joints.

Interesting, has given me something to think about on my next plane. But in truth I have never lost a plane due to a clevis or ball link.
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Old 11-21-2020, 06:18 PM   #6
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Re: Failure testing Clevis' and ball joints.

I would like to see some testing on the wear resistance over time of both systems . Both systems far exceed any application they were intended for . I believe the ball system was designed to sacrifice some of that unneeded strength for increased bearing surface to increase service life .. On a jet with little vibration a clevis may be good enough, but on a gasser my guess is the ball link is far superior . I've had the clevis systems wear loose on surface before and that was 30 years ago with my super chipmunk ..
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Old 11-21-2020, 06:35 PM   #7
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Re: Failure testing Clevis' and ball joints.

Now we just need something to calculate just how much pressure our flight surfaces are putting on these joints.
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Old 11-21-2020, 07:48 PM   #8
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Re: Failure testing Clevis' and ball joints.

I'm pretty sure 50lbs would be more then enough to pull the horn from most balsa surfaces anyway , if you doubt this have a 50lb kid step on your elevator LOL. I think premature wear and linkage slop is of greater concern then strength , that's the reason they went to ball links in the first place .I've never even hear of a ball link or clevis fail. well ok I have seen a couple of nylon ones break in a crash and one guy that only put a ball link on with 2 threads . Is there some rash of ball link failures I've not heard of ???
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Old 11-21-2020, 08:14 PM   #9
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Re: Failure testing Clevis' and ball joints.

To put things in perspective, a 250in-oz servo on a 1” arm will theoretically put out 250 oz of force or roughly 15.6lbs when the arm is at 90 degrees to linkage. So even the plastic ball joints failed at many multiples of this.

Ie - don’t think linkages are the issue if applied properly.

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Old 11-21-2020, 09:10 PM   #10
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Re: Failure testing Clevis' and ball joints.

Good point Paul . One advantage to the ball link is the wear surface of the link can be replaced . When using a clevis directly in a horn not only is the pin smaller causing greater PSI on the bearing surface but once you have worn out the hole in the horn ,it's not a easy fix on most planes to replace the control horn ..
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