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Old 04-21-2012, 11:06 PM   #1
soniczen
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Default Jesus bolt snapped

On the 7th flight after initial build, I saw that the bolt holding the main gear to the shaft was broken, causing the main gear to spin free on the shaft. Broken bolt on both sides of the shaft, the nut was missing. I'm surprised that the heli didn't crash, I guess the tightness of the normal fit without bolt was enough to provide movement. Kudos on that design I guess. But why would it snap? Full stock setup, except for the fiberglass throw away blades. The shaft did need a little encouragement to fit into the bottom bearing block, so I suppose that could cause some extra wear/vibration.

Found a 14mm bolt and ny lock nut in the spares, so I'm still in the air, but checking it now before each pack.

Any suggestions on finding a stronger bolt? Or explanation on why this happened?
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Old 04-21-2012, 11:10 PM   #2
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over tourqing could have stressed it. The heli never had contact with terrara firma before you noticed this?
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Old 04-21-2012, 11:25 PM   #3
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Quote:
Originally Posted by soniczen View Post
The shaft did need a little encouragement to fit into the bottom bearing block, so I suppose that could cause some extra wear/vibration.
When building any heli do not tighten the bolts securing the bearing blocks and frame supports to the frame until you have installed the mainshaft. By waiting to have the mainshaft in place when you tighten those bolts you ensure proper alignment of everything. A mainshaft should slide in and out of blocks under it's own weight. Nothing on a heli should ever have to be forced into place

I am not all that familiar with the protos design but any bolt that is secured with a nylock (99% of jesus bolts in this hobby) shouldn't be cranked down on, you will damage the nylock bolt.
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Old 04-21-2012, 11:35 PM   #4
soniczen
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Quote:
Originally Posted by DominicD View Post
When building any heli do not tighten the bolts securing the bearing blocks and frame supports to the frame until you have installed the mainshaft. By waiting to have the mainshaft in place when you tighten those bolts you ensure proper alignment of everything. A mainshaft should slide in and out of blocks under it's own weight. Nothing on a heli should ever have to be forced into place

I am not all that familiar with the protos design but any bolt that is secured with a nylock (99% of jesus bolts in this hobby) shouldn't be cranked down on, you will damage the nylock bolt.
I will back off the bolt a bit and see how it goes.

I disassembled the initial frame build twice to try to get the shaft smooth through all the blocks, and never got it smooth through the bottom block. Tightening in a star fashion with shaft in place. Servo blocks were silky smooth, but ended up with about 1/64th inch offset on the bottom block. Aluminum servo frames and bottom block are in the mail...
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Old 04-22-2012, 08:53 AM   #5
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Alum servo blocks should do the trick.. I just finished my build.. I put the plastic servo blocks in, and was able to get it pretty smooth after messing around with it a bit, but not near as smooth as it was with the alum servo blocks. Now the alignment is absolutely perfect. The main shaft drops right in with zero resistance.
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