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Learning how to build Lotus Seven replicas...together!
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PostPosted: Sun Oct 25, 2009 7:31 pm 
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I've been toying with the idea of building a custom car for quite a while, and I finally decided to take some steps forward toward planning my frame and suspension. I like the Lotus 7, but to be quite honest, it's hideous, and has the aerodynamics of a barn door. I am a big fan of British cars, and I really want to create my own chassis that mounts to a Bugeye Sprite body (fiberglass replica). The planned powerplant is a turbocharged 13b rotary, tuned to around 400hp. The car is tiny enough to where it would weigh little over 1000lbs, so it would be appropriately terrifying to drive. :D

Anyway, I've read through Chassis Engineering by Herb Adams, and I've been playing around with the suspension design in Wishbone. I drew up a complete chassis, using a backbone frame design, so it can be torsionally rigid without a roof, and the weight can be kept as low as possible. I'd like to use chrome moly for the chassis, and use composites for most of the flat panels on the car along with the body. Carbon fiber would be optimal, but it may end up as fiberglass due to cost. It will have a flat undertray that'll bolt to the bottom of the car for aerodynamics primarily, but it should help with rigidity as well.

Issues I'm working on: I want to mount the engine completely behind the front suspension, but due to the extremely short wheelbase (80"), the gearshift would be uncomfortably far back using an RX-7 transmission. I am compensating for this by mounting the seats as far back as physically possible in the chassis, to the point where clearance from the rear tires will have to be carefully measured. The added benefit of everything being so far back is the weight balance will be at least 50% rearward, helping with traction considering the independent rear suspension won't be able to have much anti-squat.

Suspension design is quite complicated, as I'm finding out, but the basic design will be unequal-length wishbones front and rear, with pushrods leading to some motorcycle shocks/springs. I've worked things out to where I can adjust the length of the A-arms without considerably altering the frame design, and I'm starting to get some fairly decent numbers in Wishbone.

Considering I have no clue how to use the CAD software out there for FEA analysis, I've gone ahead and built a scale model out of balsa to test rigidity and get a good 3D idea of what the chassis will look like. I won't be able to start construction for probably a good 6-months to a year (I'm in an apartment now, and moving out of the state next year... so it'll be a while 'til I have a garage), but I want to get all the planning I can do finished by then.

Bottom of the chassis:
Image

Top of the chassis:
Image

Side view:
Image

1/12 scale model:
http://i26.photobucket.com/albums/c145/ ... G_4411.jpg
http://i26.photobucket.com/albums/c145/ ... G_4422.jpg
http://i26.photobucket.com/albums/c145/ ... G_4419.jpg
http://i26.photobucket.com/albums/c145/ ... G_4419.jpg
http://i26.photobucket.com/albums/c145/ ... G_4417.jpg
http://i26.photobucket.com/albums/c145/ ... G_4416.jpg
http://i26.photobucket.com/albums/c145/ ... G_4415.jpg
http://i26.photobucket.com/albums/c145/ ... G_4414.jpg

End concept:
(For those of you who don't know what a Bugeye Sprite looks like)

Image

So, basically what I'm looking for here is some feedback on the chassis and where you think the weak points are. Keep in mind the balsa used in the model is thicker than the scale equivalent of the chrome moly chassis would be, and in the drawings I've left just enough room for the engine to fit inside the chassis (with mounts). I can adjust this slightly once I actually buy the engine and I can get precise measurements, but for now it's pretty close.


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PostPosted: Mon Oct 26, 2009 5:38 am 
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In future posts please resize your pictures correctly before posting you can do this by using the "preview" button to the left of the submit button.

Welcome aboard....good luck with your project.

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PostPosted: Mon Oct 26, 2009 9:06 am 
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Egad that thing is hideous. You call a Lotus 7 ugly and then post a picture of that abomination?!? :lol: :P I guess that's why they say "to each his own."

If you are stuck on that plan that's fine and I wish you luck, but just to play the devils advocate what's more important to you, looks or performance? For what it will cost you to build a fiberglass or carbon body you can buy a aerodynamic fiberglass body from the UK that doesn't look half bad. More importanty it will drop right over a locost frame that will better achieve your weight distribution goals and still leave room for a driver. Not to mention it will knock a couple years off your build since you won't be doing so much of a one off wheel reinvention.

Check out AGM's WLR body. http://www.agmsportscars.co.uk/agm_spor ... _2_009.htm

Image
Image
Image
Image
Image

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PostPosted: Mon Oct 26, 2009 9:50 pm 
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I love the idea. That said I could see the photobucket pictures.

Have you seen this car?

http://s33.photobucket.com/albums/d51/Nocones/midget/


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PostPosted: Tue Oct 27, 2009 2:37 am 
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Oooohhh, Those are sexy bodies Chet. :lol:


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PostPosted: Tue Oct 27, 2009 12:19 pm 
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Is it bad that I want to remove the bodies off the cars, instead of removing the skirts?

I mean, those skirts aren't much of an impediment, but the car bodies are obscuring the interesting stuff in the car. :?

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PostPosted: Tue Oct 27, 2009 12:24 pm 
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JSullivan wrote:
Is it bad that I want to remove the bodies off the cars, instead of removing the skirts?

I mean, those skirts aren't much of an impediment, but the car bodies are obscuring the interesting stuff in the car. :?

Here's a pic of the purple and white one without its clothes on. You can see it's just a modified locost frame.
Image

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PostPosted: Tue Oct 27, 2009 8:13 pm 
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I'm afraid I can't see the pics. The links don't appear to work. Could you post them as attachments, or email or PM them to me direct?
Thnx, Mike


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PostPosted: Wed Oct 28, 2009 11:05 pm 
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Apparently this forum decided to break all my links as I posted them. hmm.

Anyway, chet, you're crazy for not liking the little bugeye :P Those bodies you posted do look great, however, and I'd definitely consider making a car like that in the future- perhaps a trackday car. If this project goes well, I'll probably build a fuel economy vehicle next- see if I can hit 300mpg with a 3-wheel super-aerodynamic hybrid, similar to the Aptera but powered by a tiny diesel engine and more solar panels. Just a thought.

As for the Bugeye, the balsa frame I built is incredibly stiff, so I think I'm doin' it right. Applying a twisting force to the front and rear suspension areas results in no visible deflection, with as much force as I dare apply to a wooden model. It was fun to feel it getting more and more stiff as I completed the thing.

Here's a link to my photobucket album for this project:

http://s26.photobucket.com/albums/c145/ ... R6/Sprite/

Let me know if you still have problems seeing the files. The model looks better in person- my camera sucks.


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PostPosted: Wed Oct 28, 2009 11:10 pm 
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Oh, and here's kinda what I'm shooting for. This is an actual Bugeye with a 370rwhp turbo rotary (it's the green one with the ridiculous spoiler I pictured earlier), that weighs 1800lbs with driver. It has Formula Atlantic tires on it, and it's just properly terrifying. It dominates pro solo autocross :D

http://www.youtube.com/watch?v=nBVVssJwx2Y


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PostPosted: Thu Oct 29, 2009 1:22 am 
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Well I have to say I agree with Chet...Calling a seven hideous, and promoting bug eyes...is like living in a glass house and throwing stones.

:|

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PostPosted: Thu Oct 29, 2009 11:16 am 
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Obviously I like your plan (tube framed Spridget with rotary power), however I think your going to have problems getting the engine as far back as you are indicating. You probably will have to shift the engine significantly toward the passenger side and do away wit a passenger to get it to fit. Take a look at my chassis and consider how you are going to move the engine back 4-5" compared to mine. Keep us up to date as progress goes on. I really like seeing crazy stuff done with these tiny cars. You've also posted some pictures of that Green car I've not seen so I appreciate it, as I've been aware of it's existence but not been able to see it in person.

Daniel

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PostPosted: Thu Oct 29, 2009 6:52 pm 
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nocones wrote:
Obviously I like your plan (tube framed Spridget with rotary power), however I think your going to have problems getting the engine as far back as you are indicating. You probably will have to shift the engine significantly toward the passenger side and do away wit a passenger to get it to fit. Take a look at my chassis and consider how you are going to move the engine back 4-5" compared to mine. Keep us up to date as progress goes on. I really like seeing crazy stuff done with these tiny cars. You've also posted some pictures of that Green car I've not seen so I appreciate it, as I've been aware of it's existence but not been able to see it in person.

Daniel

Oooh, your project is very interesting! I didn't expect to find someone doing almost the same thing. This is only an initial design concept, built off pictures and dimensions other people measured, so I fully expect to have to alter many things once I get started. I'll have to pick up a trashy old bugeye for dimensions and to make molds for the body, along with an engine + transmission off an FD RX-7. Once I actually have those present it'll be much easier to figure out what I'm dealing with. I just wanted to throw this up here to get some initial feedback and talk with people about some basic design concepts.

I really hope I can get the engine entirely behind the front suspension, even if it must be a couple inches forward of where I have it in the drawings. That much is important, because I don't intend to make the car much, if any wider, so I'll need the suspension to mount as far inward as possible to have proper travel, which I can't do with an engine in the way

Regardless, it'll be a good year before I can actually start construction, but I'll be sure to document everything when that day comes.


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PostPosted: Sun Jan 24, 2010 11:04 pm 
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I believe an early 80's b2000 tailhousing will shorten the shift lever/bellhousing distance by 4-6 inches depending on what trans you start with. My 4age fits in my Midget well behind the front axle line, so I don't think it should be hard to do the same or much better with a 13b. Good luck.

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PostPosted: Sat Jan 30, 2010 2:45 pm 
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Regarding Gearsshift lever, there are several ways to achieve this, from the veri simple (KISS) approach to very elaborate, I found this and saved this picture.
Attachment:
remoteshifterlink.jpg
remoteshifterlink.jpg [ 42.23 KiB | Viewed 7656 times ]

This has the advantage that you may change the travel adjusting the position of the articulation pins.
HTH.


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