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Old 23-05-2022, 01:09 PM   #16
Bitza
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FCF Prop stand, to replace the extended ali SS one used previously, saving 168gms (145gms) god knows how much compared to the standard OEM steel version.
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Old 12-06-2022, 10:39 AM   #17
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OK hands up, "Pride" does come before a fall. My FCF side stand gave way, actually in quite a graceful kind of a way all in front of a collection of fellow bikers at the Monyash cafe. In so doing breaking the FCF gearshift, the P/tank catch, and the clutch lever all meaning a ride home stuck in first not a great day out. Anyway I guess this is a word of warning for anyone else who fancies a go at FCF. I'm still not really clear what the failure was down to, the design or my manufacture.
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Old 12-06-2022, 10:50 AM   #18
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Oh Bu99er, that's a real shame, I'm sorry to hear it took out some other parts.
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Old 12-06-2022, 11:04 AM   #19
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A little tweaking?
Fatten the main shaft over the last third or so on the rear side of the stand, and have it flow tangential to the mount. Not a huge ammount more material but at the fracture site you'd have maybe 50% more material.
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Old 12-06-2022, 06:31 PM   #20
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Ouch! pushing the envelope to extremes is always going to carry risks. Would longer chopped fibre strands increase tensile strength of the overall part?
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Old 18-06-2022, 05:22 PM   #21
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Colin Chapman was reputed to say that if it doesn't break it's too heavy.

Not sure that's any consolation in this case and it's certainly a great shame that the stand failed, more so that it trashed the other parts that clearly were strong enough for their purpose.

Sorry to be late to the party with this as it were. I've been swotting on the Easy Composites videos and find them extremely interesting.. I'm on the verge of embarking on some projects that they have inspired.. Thanks for the heads up Bitza.

So re-watching this one on stress testing (read destruction testing).
https://www.youtube.com/watch?v=eewl...yCompositesLtd

It does show that the "optimised forged carbon fibre" does the best in the various tests.
Optimised in this case, means adding continuous ribbons of fibre tows in the direction of the part and round pivot points, rather than the short, chopped, multi directional fibres of "standard" forged parts.
I reckon a small re-design with more material round the pivot, blending it with the shaft better and eliminating the sharpish internal corners, (In other word, where it broke.)
Then the addition of continuous tows round the pivot and going some length down the shaft, (As Slob alluded to.) would probably make the stand strong enough?

Of course as the weight is gradually pared off the bike, the stand will have less to do.

One thing that does appear to happen in some of the tests, is that the optimised forged parts tend to fail more progressively rather than catastrophically. That could be an improvement in itself if you were close enough to notice the stand gradually buckling?

I hope you persevere with this and manage to produce a more successful Mk2 stand.
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Old 19-06-2022, 08:42 AM   #22
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Quote:
Originally Posted by slob View Post
Ouch! pushing the envelope to extremes is always going to carry risks. Would longer chopped fibre strands increase tensile strength of the overall part?
Well I was thinking that I had made a reasonable job of manufacturing the p/stand. I lined the mould with chop tow, followed by about 4meters of continuous fiber wrapping around the pivot and traveling the length of the stand to the foot, this was then covered with more chopped tow. This is why (I think) the stand didn't actually snap but gave way gradually (giving the rather elegant collapse of the bike on to the tarmac).
One possibility is that the stands "stop" couldn't take the pressure and disintegrated, meaning that the stand went too far forward so extending the angle until the force ceased to be predominately up the stem in compression and became increasingly across the section introducing more tension & shear force. I'm just guessing, anyway I'll have to do some thinking before a Mk II version. My next project is a FCF "pivot block " for the rear of the petrol tank.
As always thanks for the thoughts and suggestions.
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Old 19-06-2022, 01:00 PM   #23
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Got to agree with NickJ (#19) plus chopped strand does not have anywhere near the strength of cloth so you are reliant on the shear strength of the resin at the point of breakage which is not very high,
35-41 N/mm˛ / 5100– 6000 psi / 41.3 Mpa, so extra material in that area combined with better angle on the stand so that all the weight of the bike is held by compression of the stand shaft, have a look at the MotoCorse carbon stands they are really quite chunky in that pivot area
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Old 19-06-2022, 07:52 PM   #24
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Could you use some titanium wire too as stronger in the pulling strength around the pivot and down
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Old 23-06-2022, 05:17 PM   #25
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Petrol tank rear pivot block saving 53gms. (original built up as pattern for mould).
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Old 27-06-2022, 10:46 AM   #26
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So these pics show the pattern I've made for the MkII propstand, with the aluminium one that the MkI version was taken from for comparison. I am also going to weld a bit more onto the bracket to increase the size/bearing surface of the stop, and have increased the stop on the stand too (the bottom stop on the pics) as this appears to have been where the failure started.
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Old 27-06-2022, 12:38 PM   #27
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That looks nice and organic now, like a femur.
I would be tempted to add a radius into the sharp corner where the stop meets the pivot boss. It looks like the next weakest spot to me?
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Old 27-06-2022, 04:55 PM   #28
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Quote:
Originally Posted by Mr Gazza View Post
That looks nice and organic now, like a femur.
I would be tempted to add a radius into the sharp corner where the stop meets the pivot boss. It looks like the next weakest spot to me?
Sharp edged internal corners usually are a little more stressed.

On the thought that it looks a bit like a femur, the mechanics of the top where there is a cranked ange into the hip joint are that the stresses are mostly derived from your body mass and they act vertically. So if you look at the structure the lattice of bone flows up in a very gentle curve from the inside bone edge up to a little above the centre of the joint, the mid point of this is usually where you see fractures.
The mechanics of your fracture are a bit similar.
?? If you (or someone) made a model of this in autocad you could do a stress analysis to look at potential points of failure and use that to guide where you put the material to transfer that load.
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