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Learning how to build Lotus Seven replicas...together!
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PostPosted: June 25, 2018, 4:22 pm 
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Joined: June 25, 2018, 3:58 pm
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Hi everyone! I just gone done with my eighth grade year. I graduated with a 3.83 gpa and I was accepted in to the International Baccalaureate program for next year. I am very technically minded and have a lot of experience with tools, building and designing things, and I know quite a bit about cars. This summer I want to build a go kart in the style of a lotus 7. I would like to use a smaller engine between 200 and 300cc (maybe a modded predator 212?), but possibly more if needed and budget allows. The full size book chassis is probably way to large for what I need to do, so I'll need some guidance on scaling the frame. I currently have a large garage workshop with tools and space, and some of the materials required already, and I even have access to a welder. I would like to spend under $200usd but I can spend more if absolutely needed. I am also interested in making this a 'shifter kart' with a manual transmission to get more speed, but that inst something necessary and is something I can do later down the road. I'd like to add that 'creature-comforts' aren't necessary so if removing them results in a cheaper and faster kar (this includes a second seat) I'm all for it. However, I really love the look the sevens have and I have dreamed of building one since I was 11, so I would like to keep the same look and styling, but changing size/scale is okay.

Thanks for any guidance or help. I can answer any questions as to what my skills and abilities are and what tools and materials I have. I live in Salem, Oregon if that helps.

tldr: I don't need anything super fancy, but I want a small, lightweight and cheap go kart in the style of a lotus 7


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PostPosted: June 25, 2018, 7:12 pm 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
For what you're talking about, I would highly recommend researching "cycle karts". They're pretty much exactly what you're looking to build. Although outside of traveling a substantial distance to one or two events a year, I'm not sure how much (or where) you'd actually be able to spend much time driving it when you're done.

If you can get the approval, guidance, and (financial) support of your parents, and think you have the drive and determination to do so, you might even be able to get a full size Locost built by the time you are getting your drivers license...Just don't tell them it was my idea. :mrgreen:

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PostPosted: June 25, 2018, 7:38 pm 
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Joined: April 22, 2010, 4:43 pm
Posts: 314
Location: Livermore, Calif.
You've taken on quite a task. I suspect your budget may be way too low. Here's an example of one that's currently for sale. Note the price.

http://www.usa7s.net/vb/showthread.php?11986-Baby-7-For-Sale

Nick, who is a member of this site is currently building an example of a scaled Lotus 7 replica, so maybe you can get some ideas.

Here’s Nick’s build log.

http://www.locostusa.com/forums/viewtopic.php?f=36&t=18660&hilit=1%2F4+scale+lotus+7

Here’s one that recently sold on the “Bring-a-Trailer” site.

https://bringatrailer.com/listing/2012-beauchamp-7-58th-scale-lotus-7-series-2-replica/

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Build log http://www.locostusa.com/forums/viewtopic.php?t=16510


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PostPosted: June 26, 2018, 12:51 am 
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Joined: July 4, 2006, 5:40 pm
Posts: 1927
Location: Novato, CA
Tom, when I was your age I wanted to build a scale XKE Jag. Your task sounds much simpler. Still a lot of work, though. As Roy mentioned, I built a half scale book frame and suspension, powered it with an electric motor and added a single caliper hydraulic disk brake on the rear axle. My wife had a lot of fun with it, I could barely fit. I learned a lot and can share a few ideas.

1) You want to go at least 5/8 scale, and that's for a rear or mid-engine single seater. Trying to duplicate a full size Locost drivetrain layout with two seats, you'd have to go at least 3/4 scale. At 5/8 scale, chassis width is about 26". Take out a few inches for a drivetrain (in my case batteries) and you're not left with a lot. And that's just width. I made the pedals adjustable on mine, and still had to move them all the way forward, ahead of the front suspension, for my 5'6" wife to be comfortable.

2) I built a mock-up frame out of 1/2" square balsa sticks. Good thing, too, because the first one I made was way too small. Balsa isn't cheap so you can skip this step if you're sure your frame is going to be big enough (my first balsa frame was way too small).

3) I used 1/2" square mild steel tubing and it worked well, although it was 16 gauge, same as a full size Locost, and therefore pretty heavy. Not a huge issue. The floor was 18 gauge, 20 gauge would probably have worked just as well. I used 3/8" round tubing where 3/4" is specified in the book, and the good thing is I could make the needed bends by hand.

4) Use go-kart components wherever possible, and get them used if you can. The hydraulic brake kit cost me somewhere around $80, so things like that will eat up your budget quickly. Wheels and tires can really add up too. They don't sound like a lot, $15 for a wheel, $20 for a tire, but then add another $15 for an inner tube. I ran a spare, so that was about $250 altogether in wheels and tires.

5) My suspension turned out to be more for looks than anything else. I couldn't find soft enough springs anywhere, and travel was minimal, half an inch at most. Mobility scooters and the like are a good source for coilovers, and they're amazingly cheap new ($7-$12 each), although they don't actually have any internal damping so they're just a perch for the springs.

6) I used a solid rear axle for simplicity, but it created a tremendous amount of understeer and a huge turning radius, particularly at low speeds. Difficult to maneuver in close quarters. I would seriously consider next time using a split axle and only drive one rear tire, or add another motor (they're pretty small) and drive each half axle separately.

The project stalled because I was unhappy with the chassis size and the handling with the solid axle. My wife didn't seem to mind as much and enjoyed drifting it flat out in large circles, but you can only do that for so long before you get bored. If I ever finish it, I'll probably build a new, bigger frame, and redo the rear transaxle for independent drive axles.


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PostPosted: June 26, 2018, 1:08 am 
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Joined: December 4, 2011, 6:19 pm
Posts: 708
Hi Thomas,

You've probably read that Locost cars were originally based on Ron Champion's book "Build Your Own Sportscar for 250 Pounds". For your project you may want to read one of his other books "Build Your Own Off-Road Buggy For As Little As 100 Pounds" as some of the ideas in it might be close to what you're looking for. Check your local library to see if they have a copy or can get a copy for you. There may be a .pdf online too.

Best of luck, Bill

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PostPosted: June 26, 2018, 9:05 pm 
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Joined: February 8, 2007, 4:20 am
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Location: British Columbia, Canada
Like others have said, a $200 budget is really tight, and might not allow you to build what you want. I'm not sure if you would be okay with a wooden bodied car, but perhaps something like a Buffy-Porson with an engine added to it?

https://www.amazon.com/Buffy-Porson-Car ... ffy-porson

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