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Learning how to build Lotus Seven replicas...together!
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PostPosted: March 23, 2011, 6:46 pm 
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Hi everybody, I've been a lurker on this forum for a while now but wanted to hold off on a build thread until I my design was a little more solidified. I've been into heavily modifying cars now for a while but have always wanted to build one from scratch. My last project was an 88 Fiero GT that I swapped a Cadillac Northstar and G6 6 speed trans into. When I first began the design my intention was to make a clone of the @tom with a K20a as the power plant but my plans changed, partly because of the engine choice but more so I wanted it to be my own design. I can't count the number of times I've changed something critical and had to start over but I'm pretty happy with what I've got now.

The power plant is a Honda H22A1 from a 95 Prelude SR-V. I managed to score a whole car with some frame damage for $650 and sold a bunch of parts from it so the total cost for everything i kept (engine, trans, shifter, cables, wiring, ecu, axles, etc.) was only $176. At 197hp it's not to shabby but eventually I'll build it up to 225-250whp. The motor is all aluminum but it's not exactly the lightest.

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I'll be using Miata spindles, brakes, swaybars, bushings, and steering column. After parting out the Miata that I picked up it's cost me about $1400 but I kept the engine, trans, hardtop, koni shocks, and some other bits for my turbo Miata. I went with bushings over heim joints for cost and longevity. I found it was just as cheap to buy a whole poly bushing kit for the Miata than individual bushings, and if I have anything left over (diff mounts) I can throw it on my DD. Alignment settings will be adjusted with eccentric bolts on the lower control arms just like the Miata as well. The wheels will be 15x9 6UL's from 949racing.

The steering rack is a de-powered shortened rack out of an 84 Corvette with HD suspension. It has the same travel as the miata ~4.5" except it's only 2.0 turns lock to lock.

The wheelbase is 94.5" and the track width is 62.5".I did the suspension design using Lotus Suspension Analysis (LSA) and ended up with ~120" swing arms, 1.77" and 2.62" roll center heights front and rear. The roll centers only move a few mm with respect to the CG in bump and laterally the front and rear only translate 7mm and 19mm respectively with 4.5* of roll. Front and rear motion ratios range from 1.6-1.4 from full droop to full bump and I'll be using the 14" extended length QA1 promastars. The miata rear sway bar was too narrow to attach at any respectable position on the lower control arm so I tied it into the rocker arm.

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LSA Screenshot.jpg
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I managed to get access to a 3D laser scanner at my old college and do a bit of surface scanning on the engine. It really helped for figuring out the boundaries for the suspension and also designing the engine mounts. I had to reduce the resolution of the surface model from ~3 million polygons down to 100k so I could work with it in Solidworks but if anybody is interested in the model let me know. It's a little patchy and you might need a pretty beefy computer to use it but I found it extremely useful.

The frame is mainly 2", 1.5" and 1" 16ga round tube and 2" and 1" 16ga square tube. The floor and firewall will be aluminum, probably .05". I've got pretty much everything in the model that i'd like except for body panels so that's what i'll be working on next. I originally figured I could keep the weight under 1400 lbs and it looks like I'll make it but not by much. I have sacrificed weight for durability and ease of construction in a few things but I would like to try and lighten it a little so if you have any suggestions let me know. Under 1300 lbs would be fantastic but probably unlikely.

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The next steps I guess are to do a rough model of the bodywork, and start making drawings for all these parts. I will probably have access to a waterjet cutter for all the flat pattern stuff so that will save a lot of time. Let me know what you all think.

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March 21 Front Render with Spoilers 1920x1080.JPG
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March 21 Rear Render with Spoilers 1280x1024.JPG
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Last edited by Zac88GT on July 18, 2014, 2:12 am, edited 1 time in total.

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PostPosted: March 23, 2011, 7:39 pm 
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Phenomenal looking rendering.

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PostPosted: March 23, 2011, 7:46 pm 
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I like this design alot, how long have you put into designing this beast


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PostPosted: March 23, 2011, 8:21 pm 
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Wow! What more can we say. CG looks like a real car. If the final product is half that good you'll have a winner. Russ

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PostPosted: March 23, 2011, 9:39 pm 
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I like the look of it a lot. My opinion on these type of cars is the less bodywork the better generally. Good luck with the build!
:wink:
BT


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PostPosted: March 23, 2011, 10:27 pm 
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Look through these two sites. The first used the H22A1 and the second is using a turbo K24, both mid-engine.
http://www.kimini.com/
http://www.midlana.com/

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PostPosted: March 23, 2011, 11:51 pm 
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Thanks for all the compliments guys. madblkscientist I've been working on the ideas and researching for the past 2 years or so but I just started modeling and designing 3 months ago.


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PostPosted: March 24, 2011, 12:08 pm 
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awww I can't get Imageshack, can somebody with a kind heart take pity on me and post one of the pics of this interesting sounding design pretty please?


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PostPosted: March 24, 2011, 12:16 pm 
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Hopefully this will show up.
Image


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PostPosted: March 24, 2011, 1:30 pm 
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Your a Champion Zac, cheers :cheers:


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PostPosted: March 24, 2011, 4:21 pm 
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Nice pictures. But, what I don't understand about this and similar designs is what does that big (heavy ?) tube running front to back at shoulder height do? All the heavy loads (suspension, engine, seats, fuel etc.) seem to be fed in somewhere else. Like the bottom and mid height tubes. If it is for crash protection why not a dash hoop and side bars? Just asking.


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PostPosted: March 24, 2011, 9:27 pm 
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VERY VERY COOL!!!

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PostPosted: March 25, 2011, 6:32 pm 
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vroom wrote:
Nice pictures. But, what I don't understand about this and similar designs is what does that big (heavy ?) tube running front to back at shoulder height do? All the heavy loads (suspension, engine, seats, fuel etc.) seem to be fed in somewhere else. Like the bottom and mid height tubes. If it is for crash protection why not a dash hoop and side bars? Just asking.


The top and middle tubes form the main truss that everything ties into. The structural floor was an afterthought, but if you removed that top tube the frame would loose a lot of it's rigidity, and aesthetic appeal.


I finished modeling the body panels today. I'm not super creative when it comes to this surface modeling stuff and it's probably better to keep it simple to manufacture in the long run anyway. I'm not sure how much body work the car should have so here are a few renderings with full bodywork, no scoops, and no skirts at all, and without spoilers. One scoop would be purely for looks but I plan on mounting a heater core on one side for added cooling if I do keep the scoops.

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What looks best? I'm open to changes and color schemes as well but I was leaning towards the blue panels with a gunmetal colored frame and carbon fiber or satin black highlights.


Last edited by Zac88GT on July 18, 2014, 2:21 am, edited 1 time in total.

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PostPosted: March 25, 2011, 7:01 pm 
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You've done a lot of nice work.

Some questions:
Where is: the radiator(s)? battery?
Is the fuel tank in the passenger foot well?
Will the car be highway legal? Can fuel tank be in the cockpit?
Will the engine clear the coilovers?

After you locate all of the necessary items, you may find that the A-tom packaging is very efficient. The coil overs give more space if located high and longitudinal. A forward radiator and rear steer rack are compact. Fuel tank behind the seats and rear firewall is good packaging. My wheel base is 89". Yours is 94.5" and may have to grow to fit everything.

Keep working, it looks good.


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PostPosted: March 25, 2011, 7:52 pm 
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JonW wrote:
You've done a lot of nice work.

Some questions:
Where is: the radiator(s)? battery?
Is the fuel tank in the passenger foot well?
Will the car be highway legal? Can fuel tank be in the cockpit?
Will the engine clear the coilovers?

After you locate all of the necessary items, you may find that the A-tom packaging is very efficient. The coil overs give more space if located high and longitudinal. A forward radiator and rear steer rack are compact. Fuel tank behind the seats and rear firewall is good packaging. My wheel base is 89". Yours is 94.5" and may have to grow to fit everything.

Keep working, it looks good.


The radiator is mounted just behind the front coilovers and the battery slightly behind the front swaybar in the center. The front coilovers are horizontal for several reasons, lower CG, CG further forward, simplified geometry, and the horizontal force components will partially cancel each other. The rack is a front steer since I already have the Miata uprights and the Corvette rack and also improves weight distribution.

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Front Components Together.jpg
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The car will be licensed for the street and the fuel tank is located forward of the passenger footwell instead of behind the seats to give a better weight distribution and is seperated from the passenger compartment by it's own isolating firewall. Even with the fuel tank much further forward the ballance looks like it's going to be 36/64 ish. The space behind the rear seats remains unoccupied so in the event that I must put the tank there for legal reasons the space is available.

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Fuel Tank and Firewall.jpg
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The engine clears the rear coilovers easily. They are vertical because the space would otherwise be unused, lower CG and the rear swaybar ties into the rocker arms nicely. Everything mechanical is in the model and I don't see the final dimensions needing to change much

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Engine and Rear Coilovers.jpg
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Engine and Rear Coilovers 2.jpg
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Pedals are very close to the Tilton foor mount design using wilwood dual master cylinders and balance bar for the brake and factory Prelude clutch master.

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Drivers Footwell.jpg
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**Edit: The CG in solidworks is only 13.75" above ground level.


Last edited by Zac88GT on July 18, 2014, 2:23 am, edited 1 time in total.

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