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Learning how to build Lotus Seven replicas...together!
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PostPosted: June 3, 2016, 11:56 am 
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Joined: October 13, 2011, 9:19 am
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Location: Denver Co
well.....

https://www.youtube.com/watch?v=R7yfISlGLNU

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You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.


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PostPosted: June 3, 2016, 2:06 pm 
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Seriously though, what are good impact factors to use? I’ve been using 4 for unsprung items and 3 for sprung items. I may be light but I expect things to break if I push them. This is on top of a 1.5 material strength safety factor. Some people use a 1.25 for material safety factor. Buildings are typically designed for a 1.67

I talked to some off-road guys and I believe their cars actually see less impact than ours with their extreme suspension travel and flexible limit stops.

I’ve got a spreadsheet on g forces if I can figure out how to post it.


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PostPosted: June 3, 2016, 7:37 pm 
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I seem to remember Carroll Smith saying 5Gs in one of the books. If its good enough for him, its good enough for me. Remember to do it under maximum weight transfer since the force from 5Gs at static weight may only be 2.5Gs at maximum weight transfer.

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PostPosted: June 3, 2016, 10:58 pm 
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Thanks for the reminder on the adding for weight transfer. And that all comes down to the height of the center of gravity.

I thought of trying to simplify things by just looking at the loads from the shock. The spring loads are easy to figure and the shock loads are proportional to their speed. But what is their speed? I'm still searching for typical shock speeds in use.

By simplifying the complicated, I am making the simple more complicated.


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PostPosted: June 4, 2016, 7:51 am 
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Bobber wrote:
Thanks for the reminder on the adding for weight transfer. And that all comes down to the height of the center of gravity.

I thought of trying to simplify things by just looking at the loads from the shock. The spring loads are easy to figure and the shock loads are proportional to their speed. But what is their speed? I'm still searching for typical shock speeds in use.

By simplifying the complicated, I am making the simple more complicated.


I ran into the same issues when doing mine. I could never accuratly find the cg without completly modeling everything.

I assume by shock speed you mean compression speed? Every single shock in the world is different and you would need their dynos to know. The best advise i can give is to pick a shock then email the mfg for a typical graph. Personally, i think you may be over complicating the design. Generally you would determine weight transfer with just the spring rate and tune the shock to th driver peference. No? I also caculated everything front and rear and then ended up completely changing the front spring rate in the front after building the car. Rear hasnt changed.

Good discussion here
http://www.fsae.com/forums/showthread.p ... t-Transfer

Also very good
https://www.google.com/url?sa=t&source= ... _ZUc0rcpeg

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You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.


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