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Author Topic: Remember how a few arm-chair engineers called this out? Well who'd a thunk it..  (Read 13161 times)

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Offline streetStreet

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Offline montymitch

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When I switched from HollowBites to Twombolts, my ankles thought they died and went to heaven. No more ankle bite!

Offline Louis

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How much heavier are current Thunderbolts than v1 Wombolts? They were beefed up in comparison?

I still have the original Wombolts and can remember thinking they were scary light taking them out of the box, they're also to this day not broken.

Offline streetStreet

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Offline got bike?

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Yeah, I was trying to figure out exactly what problem those slits would cause.... and I'm guessing "torsion." The force of cranks on a spindle is to twist the spindle in opposite directions. . . . .   
https://en.wikipedia.org/wiki/Torsion_(mechanics)



Or maybe axial load on the pedal boss area, especially if many spacers are used in crank spindle. I think this issue could simply be avoided if those slits were 90 degrees rotated (i don't know if i explained that properly)

I truely think that's a fine concept to get more tightness and get rid of wobbling, at least for the half of spindle boss of the crank.

Offline dude...

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for anyone who bought these cranks, email eclat or your local distro and they should send you a replacement non slotted axle
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Offline got bike?

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I didn't buy them or anything, I still have my old Powerbites, I just had a discussion with someone and wanted to check what exactly was the problem of those complete bikes.

I just checked other photos of those cranks and noticed they have three slits, not two as i thought, so rotating the slits 90 degrees won't really solve the issue. That photo above didn't show them clearly.

Offline dude...

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yeah its a silly design, doesnt even make removing the cranks any easier either, still had to belt them with a mallet to get em off
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Offline got bike?

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Thats the case with all cranks when they are still new. Those arms look nice with that transparent green though.

Offline dude...

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yeah but the whole point of the design was to make it easier to get the arms off as soon as the spindle bolt is loosened
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Offline got bike?

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It seems that it is the case, but only for half the splines lenght. Isn't the goal to push the spindle and spindle boss splines against each others to increase grip using some sort of conic stuff inside? I might be quick to conclude.

Offline dude...

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yeah pretty much

i drew a paint diagram to show it just cos paint



instead of screwing into the spindle itself, the end bolt (blue) screws into the wedge shaped bit (pink). the inside of teh axle is hollow, and tapers in slightly towards the end where the bolt lives. cos of the slots, when you tighten the end bolt the wedge is pulled towards it which splays the ends of the spindle out slightly ensuring a tighter fit on the arm, eliminating any wobble.

im sure i read back when they first promoed the design on like the merged or somewhere that the whole point of this was so the arm could slide on and off easily when the wedge was loose but would stay tight when done up.


found the article
http://themerged.com/eclat-aeon-crank/

Quote
These are a 2pc 22mm crank using our new ESS (Expanding Spline System) making them incredibly strong, yet super easy to install and remove. No more taking a hammer to your cranks ever again.


if the tolerances are small enough for the arm to be a really tight fit in the first place, then the wedge is pointless anyway, and just puts additional stress on the inside of the spindle. additionally, over time i reckon the constant pressure being applied to the inside of the axle would cause it to deform slightly so that it wouldnt "spring" back as easily so youd still probs need to give it a bit of clout. who knows cos it seems the cranks didnt last long enough to put that to the test
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Offline got bike?

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Yeah that paint shows it clearly now.

So to increase gripping, the bolt needs to be tight enough, and to avoid the end of spindle to expand (wich theorically may result the spindle boss to deform too, but this need to be revised considering if the materials used can withstand the tolerences to spring back or not) it desnt need to be overtightened. plus the pressure on the bolt must be constantly in check.

Looks like a new concept that needs maintenance

Bikeguide.org - Bike maintenance for BMX'ers


 

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