Luggage racks, aluminium vs steel and tube diameter calculations

[DaBit]

Some progress on the right side rack:

Steel part of the top mount. I did drill some holes in it later to improve composite adhesion and save a few grams:


Steel inserts to be used at the passenger footpegs mount.


Another piece of PVC sheet formed. Easy stuff to shape using a little heat.


If you can't Duck it, f.... it



Current, raw state:



It is 35 degrees centigrade in the shed, which reduced the pot life of the epoxy to slightly less than I would have liked. Other than that, the improved construction method worked flawless. Passenger peg 'flap' was still compressed using stiff foam and C-clamps, but compressing the laminate on the tubing was done using 1/2" wide pieces of thick PE foil with holes punched in. Exert as much pressure with your thumb as possible, and spiral the foil tightly around the tubing, removing (a lot) of excess resin and pushing possible air bubbles out to the side as well.

Laminate thickness on the tubing is 1,36mm for 5 layers of 188g/m2 hybrid carbon/aramid cloth. You can do the math on fiber density . It's not the 50% I got with the other rack, but I did not run bundles of parallel fibers (which compress a lot tighter than woven cloth) along the tubing this time. I'm curious about the difference.

The 'flap' to the passenger footpeg mounting points is a little less dense; the pressing did not work out well everywhere. But still no pockets full of epoxy or air so I suppose it's OK. The (rectangular) cross-section of that part is fairly huge: 18x62mm. With 5-11 layers of 160g/m2 carbon cloth (more at the bends, less and the end) I suppose this will be strong enough also.

[ThumperStorm]

Any updates?

[DaBit]

Oops, missed this thread. Of course there was progress; I also made a pair of composite cases to go with the racks :)



The luggage rack (and cases) are holding up fine. Hot weather, cold weather, light load, heavy load, smooth surface, rough surface. I even loaded the racks up to 50kg (110lbs) each side once. My headlight was lighting up the trees, but the racks didn't complain.

The only thing I did not do yet is crash with them.

[GSWayne]

Originally Posted by DaBit

The luggage rack (and cases) are holding up fine.

The only thing I did not do yet is crash with them.

What are you waiting for, remember this thread started out with how strong you needed to make this rack, only one way to tell if it is strong enough.

PS nice looking cases, is there a thread showing how you made them?

[DaBit]

Sooner or later I'll find out if these resist a minor crash.
I am not too worried about the left side. All members there are loaded in 'bending' and extension during a crash, which is something that CF and aramid is very capable of.

On the right side however, there is a member that goes straight to the subframe in an almost 90 degree angle to the driving direction. That results in almost pure loading in compression when the bike is parked horizontally, and compression is composites weakest spot.

Not that easy to see, but this is the best picture. See how the pillion-footpegs-member goes almost straight to the loop?


I should have done that differently. I am a fan of the 'make it bend, that prevents breaking'-school.



Build report for the cases is here: http://www.advrider.com/forums/showthread.php?t=834082

[JimVonBaden]

Made for me by Kirk! Beautiful work from steel. He also made the panniers.








Jim

[DaBit]

Definitely more beautiful. Kirk is one of those guys that stand out above the rest.

I could have used steel. Did that on my LC4, and it certainly makes life easier. But i wanted to fool around with something different, and structurally loaded composite parts did fit the bill nicely.

Cases+rack are a LOT lighter than steel frame+alu panniers. I could have made the panniers even lighter, but since I don't use them that often an easy construction method was higher on the priority list.

All in all the total cost of materials used was not bad either. I sold the Zega's, built the rack+cases, and still had money (and the OEM/TT rack) left.

[jestragon]

Mooi werk!