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Author Topic: GT380 ground up build  (Read 4659 times)

Offline themotoworks

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GT380 ground up build
« on: May 25, 2018, 20:10:19 »
Starting a new project with a new idea, I picked up a gt380 for free with a valid registration and want to use it as a design experiment to see if I can put some ideas I've had into one single project.  The idea is really to conceive the entire bike before really building anything, my hope is that it both makes a really functional bike, speeds up the mechanical side of the build process, and makes for a really nice looking build.  I pulled the motor already and have been measuring it to put it into solidworks and integrate it with the other parts.  The front end is a gsxr-750 with custom made triples and a custom machined spoked hub, rear end is all custom fab, going to run an ohlins shock for a 900ss ducati because I'm familiar with them, planning on a large diameter tube backbone frame and machined aluminum swingarm mounts that combine the engine mount, frame to engine mounting and subframe/seat mount... came up with some sketches, and talked to jeremy lacy about him basically designing the bodywork and look of the bike, should be interesting. 




Offline farmer92

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Re: GT380 ground up build
« Reply #1 on: May 25, 2018, 20:44:32 »
This looks like a sweet project!
Just wondering how you ended up with the frame style you chose.
I presume by large diameter backbone you mean something like an Egli frame,

That one is for a tz350 i believe.
What did you plan for material?

Offline themotoworks

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Re: GT380 ground up build
« Reply #2 on: May 25, 2018, 21:05:02 »
chromoly, I'm having trouble finding large diameter thin wall tubing in that material though, I may need to have a sheet rolled. 

Offline farmer92

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Re: GT380 ground up build
« Reply #3 on: May 25, 2018, 21:18:03 »
Figured it would be chromo, was hoping maybe you would have had better luck than me at finding something in a proper size.

Did you model it yet? What sort of weight are you aiming for for the frame?

I modelled several frame designs this design seemed to give the best stiffness to weight ratio, it was about 18lbs

Online irk miller

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Re: GT380 ground up build
« Reply #4 on: May 25, 2018, 22:44:03 »
YZ frames were pretty light.  When the shock tubed into the frame, the backbone was stamped.



They later went to this in 80.   




Offline teazer

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Re: GT380 ground up build
« Reply #5 on: May 26, 2018, 00:34:01 »
How large do you want the backbone?

http://www.onlinemetals.com/merchant.cfm?pid=10434&step=4&showunits=inches&id=250&top_cat=197

That's 3.0'' but it's pretty thick.  You may have to go to rolling a sheet into tube as you suggested.

in DOM you can get up to 4.0"    http://www.onlinemetals.com/merchant.cfm?pid=12690&step=4&showunits=inches&id=283&top_cat=197



Offline themotoworks

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Re: GT380 ground up build
« Reply #6 on: May 26, 2018, 08:45:37 »
I talked to Fritz Egli and he actually told me what I had suspected for a while, he doesn't use chromoly tubing, the modulus of all steel is basically the same, and there's not going to be a difference in the stiffness from a513 to 4130 unless it's being bent to yield, which it shouldn't be.  4" .083" is available, I'll model a frame from that and see how well it does, from my experience, changing the diameter or wall thickness of the main backbone section very predictably changes the tortional stiffness of the front end

Offline Hurco550

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Re: GT380 ground up build
« Reply #7 on: May 26, 2018, 12:03:32 »
A friend of mine is working on building a tube chassis autocross truck, and we've been researching the use of docol r8 tubing vs chromoly. Similar weight, yet there are far less brittleness issues in the heat affected zone from welding. It just became available in the u.s. market fairly recently, though it's been used in Europe for a bit. Just another possible option. When i build a frame (someday) ill likely use it.


http://www.aedmotorsport.com/catalog/product/docol-tube-r8

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Offline farmer92

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Re: GT380 ground up build
« Reply #8 on: May 26, 2018, 12:29:17 »
Donít they all weigh nearly the same? Like less than 1% density difference?

I was under the impression that you have more elastic deformation from 1020 vs 4130
But that they both reach plastic deformation at nearly the same points.

Offline themotoworks

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Re: GT380 ground up build
« Reply #9 on: May 26, 2018, 12:51:11 »
yeah, the density of all steel is basically the same, the modulus is basically the same, the things that vary with different alloys and heat treatments are the tensile strength and the yield, which really only determines where they "break".  so if I were designing a roll cage, chromoly would be a good choice, because for a given weight roll cage, the chromoly one would take more of a beating before it gave way, but in a design built to be predictable under known loading, with an adequate safety factor in the design, there wouldn't be a difference in performance between 4130 and a513