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Learning how to build Lotus Seven replicas...together!
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PostPosted: Thu Mar 03, 2011 2:27 pm 
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A little about myself first.. I know absolutely nothing about engineering and designing a chassis. Now that that's off my chest...

Would it be possible to modify a locost seven chassis and make a midi simply by making the engine compartment smaller, moving the cockpit ahead and making room for the engine behind? I made a very rough sketch below...

Image

If you think I'm being a complete idiot, please say so...

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PostPosted: Thu Mar 03, 2011 2:58 pm 
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Yes, that's what I'm doing, http://www.midlana.com/

If you're planning to use a Locost fiberglass nose, try to match the taper of the chassis to the taper of the nose, or the resulting car will look odd.

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Last edited by KB58 on Thu Mar 03, 2011 3:34 pm, edited 2 times in total.

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PostPosted: Thu Mar 03, 2011 3:24 pm 
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Sure you can do it. You don't have to change the shape much, I wouldn't change the front outside of maybe moving the front wheels back a few inches and then stretching behind the driver a bit.

Try drawing some and then maybe make a little scale model from wood from a hobby/craft store or make a full size model from wood, cardboard whatever you like.

Do check out Kurt's site too...

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PostPosted: Thu Mar 03, 2011 4:10 pm 
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I don't think you'd have to change the frame taper at all, just sit farther forward--there's no transmission crowding your feet on a middy.

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PostPosted: Thu Mar 03, 2011 10:57 pm 
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Right... I tinkered about with it a bit and made some small changes... Once I'm sure how to do the floor, then I'll go ahead and edit the entire plan... This time I used the +442E design.

Image

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PostPosted: Fri Mar 04, 2011 10:06 am 
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Welcome to the club.

Well, I don't know about midis. What you have shown is the basic floor frame and some derivatives. The top rail takes a bit of a different angle as shown in red in my markups. If your goal is to reduce the engine compartment, then you have not met that target. I have approximated the upper rail and then transferred it to your other sketches. Maybe I'm misunderstanding something here.

Nothing is sacred in chassis design. You could, for instance, keep the lower frame identical to the upper frame and then deal with the front suspension geometries.

As Jack said, with no transmission to accommodate, there is no pedal/foot size issue. But as you move the driver forward, then the ever-narrowing chassis will, at some point, become an issue. Where that point is, is up to you. You may decide that the trans tunnel may still be desirable to keep. It does add a lot of strength to the space frame chassis. Less important of you decide for a full roll cage.

You haven't stated your intended drive train. BEC Midi? CEC (FWD) relocated? Or its intended use such as Track car? Street car? Do you ant it to "look" seven(ish)? Each may require a different amount of room depending on your implementation. So there is where I would suggest you start. Decide what your drive train will be, then figure how much room you need to fit things.

Changing the side rail angle at the front will require new pickup points for the front suspension. Not a problem but just be aware. I'd really think that IF you are planning the midi approach, take a look at some of the Midi builds here on the site. Perhaps you would be better off starting the frame design from scratch rather than pushing and pulling a Locost chassis into what you need to fit a midi. You will be changing virtually every cut piece of tube either way.

So, your question is simple but cannot be answered with any one answer. Keep refining your goals and keep moving forward in your design.


Chuck


Attachments:
chassis compare.JPG
chassis compare.JPG [ 79.78 KiB | Viewed 3131 times ]

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PostPosted: Sat Mar 05, 2011 12:50 am 
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Hi Chuck,

Thanks for the welcome. The reason I want to make a midi is for lack of availability of a decent rwd donor. Any donor I choose will most likely have a 1.6-2.0ltr 4-cylinder petrol engine with 75-105hp. Styling isn't that important, but I would like to be able to use the lotus cone and other parts, just to make life that much simpler. I would consider building from scratch, but with zero engineering knowledge, I don't think I'll get very far. I think I will keep the transmission tunnel, but make it smaller than the book design... I'll work on the frame design today and post what I come up with. Thanks for your input :)

Quote:
But as you move the driver forward, then the ever-narrowing chassis will, at some point, become an issue.

This was a very big concern for me, which is why I didn't make the engine compartment too small... Also if I intend to use the lotus cone, I will have to keep the taper as close to the book chassis as possible.

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PostPosted: Sat Mar 05, 2011 6:20 am 
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My Progress so far... Its not much and I'm borrowing heavily from the original 7 and bits from the geko build, by Mr. Dominic. So don't be surprised if I land up with a Seko Or a Geven :shock: :BH:


Attachments:
Chassis Mods3.jpg
Chassis Mods3.jpg [ 160.91 KiB | Viewed 3070 times ]
Chassis Mods2.jpg
Chassis Mods2.jpg [ 79.17 KiB | Viewed 3070 times ]
Chassis Mods1.jpg
Chassis Mods1.jpg [ 86.02 KiB | Viewed 3070 times ]

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PostPosted: Sat Mar 05, 2011 10:04 am 
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[quote="psych0hans"]Styling isn't that important, but I would like to be able to use the lotus cone and other parts, just to make life that much simpler.

Use of the nose cone is not is not a large savings.

I would consider building from scratch, but with zero engineering knowledge, I don't think I'll get very far. I think I will keep the transmission tunnel, but make it smaller than the book design...

Get rid of the tunnel. Space is at a premiun. A midi doesn't need a tunnel.

As Cheapracer mentioned on another post, if you don't want to build a Locost 7, don't use the 7 frame. As soon as you decide to go midi, you have abandoned 90% of the 7 dimensions, body panels, geometry, component locations.


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PostPosted: Sat Mar 05, 2011 10:24 am 
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One of the advantages of going rear mid-engine is to eliminate the hump and give you more leg/foot room. The outside ladder frames will supply all the strength you need with appropriate top/bottom cross bracing. And, without the weight of engine/trans up front, stresses are reduced in that area. Now, if you are running a front radiator, you will need a means of routing cooling pipes, which could be done in a very small hump, maybe just made of sheet metal and screwed or bolted to the floor. It does not need to be a structural member. Mine was originally designed for rear radiator for simplicity, but that might well change. One thought is how light the front end is going to be. To help reduce understeer, some race cars move things like radiator, battery, even fuel tank to the nose to help even out weight distribution, even if only slightly. My 3.0L Ford/Yamaha SHO might end up extremely nose light if I'm not careful. Eliminating or drastically reducing the hump will let you keep a more narrow front chasis which will look better.


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PostPosted: Sat Mar 05, 2011 12:53 pm 
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It seems like you're doing this backwards... The drivetrain (and suspension, and seats, and pedals, etc) have to be known and measured before drawing the frame. How can the chassis be layed out when the suspension pick-up points aren't known?

I highly recommend this book before the chassis is drawn (and yes, I wrote it, so I'm biased): http://www.amazon.com/Kimini-design-mid-engine-sports-scratch/dp/B004J4E1VW/ref=sr_1_1?ie=UTF8&s=books&qid=1299343311&sr=1-1

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PostPosted: Tue Mar 08, 2011 6:44 am 
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I'm getting an opel astra F 199x model for around 700$. It has a 1.6l 75hp Engine with about 125Nm of torque. I've seen in several other posts of people using and recommending using 2 front ends of the same vehicle as the front and rear end... Is that something I should seek to do with the astra?

http://www.indiacar.com/maintain/astra.htm

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PostPosted: Tue Mar 08, 2011 8:40 am 
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psych0hans wrote:
I'm getting an opel astra F 199x model for around 700$. It has a 1.6l 75hp Engine with about 125Nm of torque. I've seen in several other posts of people using and recommending using 2 front ends of the same vehicle as the front and rear end... Is that something I should seek to do with the astra?

http://www.indiacar.com/maintain/astra.htm


If your doing a locost type chassis I would say no. With whatever donor you get you'll nevery everything to build it. The only stock parts you need for the front end is hubs,rotors and calipers. Everything else is custom. The rack will be of your choice and you can use the donor steering column. Two cars and you'll have a lot of spare parts. Just try to get the front and rear to have the same bolt pattern so you only need one set of tires.

evo

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PostPosted: Tue Mar 08, 2011 9:54 am 
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KB58 wrote:
It seems like you're doing this backwards... The drivetrain (and suspension, and seats, and pedals, etc) have to be known and measured before drawing the frame. How can the chassis be layed out when the suspension pick-up points aren't known?

I highly recommend this book before the chassis is drawn (and yes, I wrote it, so I'm biased): http://www.amazon.com/Kimini-design-mid-engine-sports-scratch/dp/B004J4E1VW/ref=sr_1_1?ie=UTF8&s=books&qid=1299343311&sr=1-1


Absolutely! I would strongly suggest that you not only know what drivetrain you will be using, but actually have the parts in hand. All the measurements in the world won't give you as much information as actually laying the parts out in their intended positions moving them around, especially if you're a new builder. If this is a street car, the driving position becomes very very important. Nothing worse than having a nice car with good handling but is no fun to drive. It's amazing how just a small change (say an inch) of control position can affect things.


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PostPosted: Tue Mar 08, 2011 10:45 am 
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photoman wrote:
... It's amazing how just a small change (say an inch) of control position can affect things.

That was a real revelation to me, which seemed perfectly logical and reasonable in hindsight. That is, say you have zero room for your knees, and free up one inch more space. That one inch makes a world of difference!

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