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PostPosted: April 25, 2020, 6:06 am 
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Joined: May 13, 2019, 9:29 am
Posts: 4
Hi people, this is my design of a mid engined chassis, building with 1.5 x 0.1 inch 4130 round tube as well as some square tube. It is a track only car, homebrew cars like these cannot get legally registered in my country.
It's my first time designing a big project like this and I'm also quite new to welding and fabrication. So my main design goals are driver safety and ease of construction. At the meantime I'll try to make it as lightweight as possible and achieve good torsional rigidity (which is guesswork for now, I don't have the access or knowledge to do fancy FEA software)

Anyhow the construction started like half a year ago but I stopped because of the covid19 and other things in life... which is also a good time to revisit the design and thought it definitely needed some changes before I get back on with construction


this is what it looks like now (or for the past 2 months)
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and here is my design, for now
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It probably looks very crude compared to many of the amazing builds I'm seeing on this forum, which is why I could really use some honest opinion from you guys

the front subframe
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and the roll hoop area/ rear subframe and engine bay
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my own thoughts:
so the first thing that comes to mind is that it needs a roll hoop in the front, along with the rear hoop, provides enough protection to the driver in case of a rollover. it looks like too much weight in the back, but at the same time the engine/rear frame sill looks flimsy... I don't like how the front subframe (the reverse trapezoid box) connects to the main frame. seems weak and also the subframe itself is unnecessarily heavy.

man this is hard :|


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PostPosted: April 25, 2020, 7:35 am 
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Joined: September 22, 2005, 8:12 am
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Location: 4AGE in S.E. Michigan
You should consider adding a 2nd loop across to the top front on the cabin area. It should be tied to the first loop. Add a short brace across the top of the X's. That should improve torsional strength. I would take a look at your lower section below the front sub-frame. You could save Wt and increase section modulus by lowering the bottom tube extending i.e. using typical control arm brackets, if your suspension design allows it. Also add a diagonal cross the front sub frame.
One hell of a nice shop :) What is your location?
Davew


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PostPosted: April 26, 2020, 8:00 am 
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Joined: September 22, 2005, 8:12 am
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Location: 4AGE in S.E. Michigan
Your front sub frame needs to attach at node points, not un-support locations to the center bay. The OPEN center bay needs additional loops for the steering column. Triangulate off the new tube and add a perimeter bulk head. Think of the design as separate bays, and the front and rear bays putting a twisting load into the center bay.
Davew


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PostPosted: April 27, 2020, 7:21 am 
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Joined: September 22, 2005, 8:12 am
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Location: 4AGE in S.E. Michigan
You need to know your front control arm attachment points before you design the front sub-frame. Looking at the front view of the sub-frame it should be a trapezoid. Consider re-designing the front sub frame. It should allow for a shorter upper control, needed for camber gain. [ outboard upper control arm attachment ] Put the frames tubes where the control arm mount are, Vs any stand-off type bracket which will just increase the leverage on the brackets.
Davew


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PostPosted: April 27, 2020, 5:57 pm 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
I'll try to sketch out some thoughts about the structure later. But in the mean time, if you haven't already, I would recommend checking the roll bar/cage rules of any and all track event organizers that you might run with. Yours has some unconventional elements, and is something you will want to be 100% compliant with all sanctioning bodies.

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-Justin

Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


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