Engineering-ish Question

"sony1492" (sony1492) 03/09/2020 at 20:04 • Filed to: locost

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Heres the issue; Ive got a huge transmission in a small space, specifically the footwell. On the LH side there are 2 designs, one follows the contour of the transmission netting about 1" of foot space along with 1" of thigh/ seat space, the other is simpler and I’m assuming stronger. Is the leftmost design viable or at least workable? If so, how?

Here is a rough idea of what I’m thinking sans the cross supports, it looks fairly weak and unnecessarily heavy. Currently there is 9.5" of foot space and at most 16.5" of seat space, going with the simpler design could push seat space down an inch.

Any ideas appreciated.

AestheticsInMotion > sony1492 03/09/2020 at 20:12

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Move the transmission off center. Like, 8 inches to the right. If you want a passenger seat, just put it behind you.

Boom, problem solved. 

sony1492 > AestheticsInMotion 03/09/2020 at 20:15

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Yes, but, no

AestheticsInMotion > sony1492 03/09/2020 at 20:18

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Okay Mr. P icky, how about you flip it around so the small end is facing forward.

Oooooh. Or mount your seats waaaaaay back.

Doge_Supreme drives a BRZ > sony1492 03/09/2020 at 20:21

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Anything is possible, But I would definitely go the simpler route. I’m not an engineer but I feel like the more bends/welds will lead to a weaker structure, requiring more bracing and there fore more weight.  I always believe in following the K.I.S.S. method.

Spanfeller is a twat > sony1492 03/09/2020 at 20:23

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How about a transversal beam in-between the two other beams rather than those cross braces? 

ItalianJobR53 - now with added 'MERICA and unreliability > sony1492 03/09/2020 at 20:23

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I would go with the simple design just because it will be lighter. Also, it may end up being stiffer.

Snuze: Needs another Swede > AestheticsInMotion 03/09/2020 at 20:29

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As an engineer I can confirm, these are the best suggestions. 

sony1492 > ItalianJobR53 - now with added 'MERICA and unreliability 03/09/2020 at 20:33

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It's just that it will kill my foot space along with seat space, I'd add any amount of weight if it can be made safe

AestheticsInMotion > Snuze: Needs another Swede 03/09/2020 at 20:33

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We should team up and take over this project.

Also, is that Repsol yours?? So pretty

punkgoose17 > sony1492 03/09/2020 at 20:33

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This should work fine to give you more space. You can not include the 1, I did not tr ase in red. I am not familiar with the plan but you can box the whole transmission tunnel to increase stiffness.

sony1492 > Doge_Supreme drives a BRZ 03/09/2020 at 20:34

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Weight isn’t a huge issue since its 1x1" 16ga tube and/or 3/4"

sony1492 > AestheticsInMotion 03/09/2020 at 20:35

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The seat will be all the way back, which puts my feet just behind the first bend behind the firewall

sony1492 > Spanfeller is a twat 03/09/2020 at 20:38

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AestheticsInMotion > sony1492 03/09/2020 at 20:40

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Oh. Yeah, guess that makes sense, given the gear shift’s location. Cut holes in the floor for more foot room?

But seriously, I’d definitely go simple as everyone else is saying. Could you not just widen the overall frame a bit?

sony1492 > punkgoose17 03/09/2020 at 20:51

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This is very helpful.

The intention is to weld sheetmetal to all the floor and trans tunnel surfaces. Would it make since to attempt triangulation of the trans tunnel using 1x1" for the frame and 3/4" for the bracing?

sony1492 > AestheticsInMotion 03/09/2020 at 20:54

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This is already 2" wider at 46" total, the  tires still need to fit outside of the frame dimensions so it cant go much wider while fitting wide wheels and 4link suspension 

MM54 > sony1492 03/09/2020 at 20:57

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I am not a chassis engineer, but to me the single straight piece is probably a better call from a rigidity standpoint. A single triangulated section has less points to flex about than the complex ‘left option’ (which very well may still be viable).

At this point you’re still early enough that you might be able to just add that inch back on in width?

sony1492 > MM54 03/09/2020 at 21:05

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I guess intuitively we all know the straight piece is better, but I should be asking: Can the other design be made to work or is there any other designs that will keep an increased amount of foot clearance over the straight design?

Wideing the front is basically a no go, it's already 38", the rear width is 46" so the angle on each side is already fairly shallow, pushing the sides out would make that worse

MM54 > sony1492 03/09/2020 at 21:14

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As long as the two new joints have vertical stays on them to tie them into the vertical structure (to keep them from trying to flex in and out of the page as-drawn) I suspect it’d be fine. Everything can move in 6 axes (three linear and three rotational) so as long as it’s braced properly it should be fine .

In terms of not-straight-line designs, I don’t think you’re going to get much more space than you have now with the 3 segments following the shape of the trans.

punkgoose17 > sony1492 03/09/2020 at 21:54

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I am glad I can help. It makes sense to triangulate the sides; it will increase front to back rigidity. The section where the transmission connects to the frame could use extra support due to torsional forces from the engine an transmission: like triangles at the joints, I don’t know if there is room. The blue lines are your moment arms with the rest of the frame.

Snuze: Needs another Swede > AestheticsInMotion 03/09/2020 at 22:16

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I agree! Ive always wanted to build a Locost. I even have the book!

It used to be, I miss it a lot. 

sony1492 > punkgoose17 03/09/2020 at 22:34

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R einforcing that spot could definitely be done, it seems on the Donkervoort chassis the opposing side already is.

Spanfeller is a twat > sony1492 03/10/2020 at 04:01

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Can you pass braces under the gear box?

NYankee1927 > sony1492 03/10/2020 at 13:18

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Creating more nodes like your left drawing is not great front a rigidity standpoint. You arnt picking up anything on those nodes, so they will hurt. The straight bar is fine, contour your interior panels around the trans, there is no reason the chassis needs to fully encapsulate the trans if you arnt picking up mounting points.   

sony1492 > NYankee1927 03/10/2020 at 16:18

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It's a spaceframe though once room has been cut out by the frame it will be forever lost through steel sheeting.