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Learning how to build Lotus Seven replicas...together!
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PostPosted: October 14, 2018, 12:33 am 
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Hello,
A quick bit of back ground. We bought a 2 bay garage with 16' ceilings (OK- there's a house attached to keep my wife happy!) in another town five hours away with the intention of moving there for Fall 2018. Finally i could start my long burning desire for a Locost. Well....life always seems to have a way of changing your plans and that move has been put on hold for three years.
I do not currently have the room to weld up a complete Locost chassis but i can handle smaller sections. I also have multiple small storage sheds that could house all the parts needed to complete the car. From what i have learned on the forum over the years is that the construction of frame is the quickest part of the build. Figuring out suspension geometry, brackets and tabs, etc is what takes all the time. I thought that if i could completely build the front suspension (based on my donor parts), engine bay and rear end assembly i could have a relatively quick build when i move as i would have already worked out everything before hand. I was planning to make mock ups of each section recording the data then disassembling and starting on next the section. While surfing the other night i came across this:

https://grassrootsmotorsports.com/artic ... ng-room-l/

Which brings me to my question. Why make make a mock up only to take it apart if i could make it in 3 modules and assemble into a complete frame when the time came?! I tried to find any posts of someone already doing this on the forum but this is the best i could find:

viewtopic.php?f=39&t=16007

Some good info on how you could join frame sections. As i don't have any engineering chops i am looking for some specific info on where the Locost chassis might be best split into three. I'm thinking front suspension (control arms forward), engine bay/cockit, rear end starting at seat back. I'm thinking the front end style used on the Collin's frame would be easier to turn into a module?

http://www.locostusa.com/files/Collins.pdf

Maybe a construction style like the Lotus 49 with front and rear bulkheads (while still using the tube frame center)?
Any input would be appreciated!
Cheers
Allan


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PostPosted: October 14, 2018, 12:17 pm 
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I think the simple answer is:
It adds weight to have brackets/bolts to allow for modular chassis. There is no reason why you couldn't weld up different sections as units, then weld the units together when able.

That being said, for the majority of the build (assuming a street car), you will want it together so you can fit things on the very small car.

If it helps, the locost frame will fit through a doorway w/o a rollbar.

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PostPosted: October 14, 2018, 1:22 pm 
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Another alternative is to get your final chassis designed with accurate measurements (preferably in CAD) and the layout and tack weld certain sub-assemblies together in your small space, later welding them into a cohesive unit on a full size build table.

I took your reference chassis and used colored marks in MS Paint to illustrate my point. Other builders, including myself, have used the layout and tacking of sub-assemblies to do portions of the chassis.

Parts with the same color are done together in my example. I did it pretty quickly, so I'm sure there are pieces that should be build in a slightly different order. However, you could use the "hide" feature available in just about every CAD programs to figure out what the actual, practical order should be.

Cheers,
Attachment:
File comment: Locost chassis divided up into sub-assemblies for modular construction in a small space.
Sub-assemblies.jpg
Sub-assemblies.jpg [ 170.38 KiB | Viewed 670 times ]

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: October 14, 2018, 4:50 pm 
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Shevalev, who hasn't posted in a while, is building his car in the living room of a high-rise apartment builting. He built the frame in sections that bolt together, so he can eventually get it down to the parking deck in pieces via the service elevator.


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PostPosted: October 15, 2018, 8:14 am 
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Consider building the locost in one of the sheds. It seem to be a popular way of building a locost in England is to use the garden shed. They add bracing between the roof sides [ i.e. roof rafters ] that support lightning and it also adds some above storage. The only thing I would say, is differently use a HD extension cord for running power to the shed. DaveW


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PostPosted: October 15, 2018, 7:23 pm 
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Thanks to everyone for input, greatly appreciated!

To clarify my thinking.

This will only be a street car so i am not overly concerned about any extra weight added by this approach. As well, i only need it modular once. When completed it can be fully welded and never has to come apart again. I'm thinking that the structural requirements needed to just to hold things true until fully welded vs a modular design meant to be disassembled in use are different (hopefully lighter)?
My goal is to be able to complete each section independently in a small space. In my large shed i can setup a build table of about four foot by four foot at the biggest with enough room left to get around. Lots of smaller shed space to squirrel things away separately. No shed big enough to do the complete frame in. The pic below shows what i was hoping to accomplishment:

Attachment:
proposed modules.png
proposed modules.png [ 179.54 KiB | Viewed 560 times ]



It seems the bulk of the project is working out everything in what i call modules 1 and 2. The tricky part of the build for me will be sorting out the suspension geometry and wishbones. This is what i would like to accomplish this winter. The suspension bracket labeled in the picture below makes splitting off module 1 awkward (sorry for the mix of Book frame in one pic and Collins in the next, at this point i am thinking a Collin's style frame with Book dimensions).



Attachment:
front suspension bracket.jpg
front suspension bracket.jpg [ 35.57 KiB | Viewed 560 times ]


If i'm understanding the sequence suggested by Lonnie-S it seems to be a great way to make the frame up in parts but doesn't really give me the ability to 'complete' each section independently? Will study more.

That 'shop' view for Shevalez is something else. I could make the frame in my living room and get it out the picture window, trying to convince my wife is something else entirely!

C10Corey, I see you are in White rock, any chance i have seen your car on the Sea to Sky? Seen quite a few 7 variants on there this summer (i live in Squamish and commute the Sea to Sky daily).

Cheers
Allan


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PostPosted: October 15, 2018, 11:48 pm 
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atone wrote:
Thanks to everyone for input, greatly appreciated!

To clarify my thinking.

This will only be a street car so i am not overly concerned about any extra weight added by this approach. As well, i only need it modular once. When completed it can be fully welded and never has to come apart again. I'm thinking that the structural requirements needed to just to hold things true until fully welded vs a modular design meant to be disassembled in use are different (hopefully lighter)?
My goal is to be able to complete each section independently in a small space. In my large shed i can setup a build table of about four foot by four foot at the biggest with enough room left to get around. Lots of smaller shed space to squirrel things away separately. No shed big enough to do the complete frame in. The pic below shows what i was hoping to accomplishment:

Attachment:
proposed modules.png



It seems the bulk of the project is working out everything in what i call modules 1 and 2. The tricky part of the build for me will be sorting out the suspension geometry and wishbones. This is what i would like to accomplish this winter. The suspension bracket labeled in the picture below makes splitting off module 1 awkward (sorry for the mix of Book frame in one pic and Collins in the next, at this point i am thinking a Collin's style frame with Book dimensions).




C10Corey, I see you are in White rock, any chance i have seen your car on the Sea to Sky? Seen quite a few 7 variants on there this summer (i live in Squamish and commute the Sea to Sky daily).

Cheers
Allan


I've certainly seen some non-locost racecar builds where the front suspension basically get's welded onto a box that is later welded into the rest of the chassis. There is no reason why you couldn't do similar built to locost dimensions. If you are trying to follow locost chassis as close as possible, you may want to try to build from the foremost vertical "H" tubes forward in one piece and just have some temporary braces to keep them square. Not sure if that fits your needs though.

My car basically just goes to autoX and gets abused locally :รพ Haven't done the Sea-Sky in it yet. Maybe next Summer. There are a few people on this forum that live near it though.

Cheers.

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PostPosted: October 16, 2018, 1:19 am 
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For some reason I can't see any of the pics or the file you uploaded except what some others have posted, but why the heck not!?!?!?!

The weight added would be negligible, but here's the tough part, how would you fasten them together so that you knew they wouldn't come apart later? Of course we do that all the time with the suspension so why the heck not?!?!?!

Make a front suspension module, a rear suspension module and then the passenger compartment module.

An added bonus is that, if you did it properly each of those joints could become a "break away" point for an accident and help absorb some of the impact. Break away isn't an accurate description in that I mean the modules might deform under impact at the joint level.

Now make the joints at a diagonal and you have a way for the passenger compartment to rise above the other parts should you have an accident.

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PostPosted: October 16, 2018, 10:16 am 
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Perhaps you need to think outside the box, a little.

Here's a recent prototype from Westfield, in the UK, that uses a monocoque centre tub with bolt-on 'subframes' front and rear:
Image

Image


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PostPosted: October 16, 2018, 11:32 pm 
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Thanks for the pics of the Westfield, that is pretty close to what i was trying to imagine in my head but with a tube frame mid section. Funny it didn't come up when i google 'monocoque 7', i got Robin Hoods, Centaur and PRB .
This thread has given me some great ideas to chew on. Now I just have to figure out if starting now with the space i have and building a modified frame to accommodate will save me anytime over waiting until i have a large enough shop to build the frame the tried and true way.
Cheers


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PostPosted: October 17, 2018, 9:50 am 
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I'd do it in three pieces: center tub, firewall-forward, and seatback-back. You're looking at about four feet each for the long sectiond, two and a half for the back.

Double up the bulkhead frames at the two joints. If you want it to stay disassembleable - say, for repair after a crash - use tabs for alignment and weld some tubes or pipe in to keep from crushing the tubes at the bolt joints. Otherwise, drag it outside, line things up with C-clamps, and weld it up.


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PostPosted: October 18, 2018, 8:21 am 
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In the large pics posted of the blue chassis...

looks very well done. However, in the first pic, unless I'm misinterpreting, it looks like the bolts used to secure the front section are in shear.

I'd much prefer a fastening method the had the bolts in tension.

Actually, if I were to do it, I'd probably set it up with locating pins and/or a system of tabs and receivers, so the only function of the bolts was to hold the parts together, but all the other loads were transferred through other means.

Or just weld it...


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PostPosted: October 19, 2018, 10:37 am 
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chrisser wrote:
In the large pics posted of the blue chassis...

looks very well done. However, in the first pic, unless I'm misinterpreting, it looks like the bolts used to secure the front section are in shear.

I'd much prefer a fastening method the had the bolts in tension.

Actually, if I were to do it, I'd probably set it up with locating pins and/or a system of tabs and receivers, so the only function of the bolts was to hold the parts together, but all the other loads were transferred through other means.

Or just weld it...


I'm not sure I can agree with that. Bolts in shear = shear strength of steel. Bolts in tension = strength of threads/nuts to resist pull out. No same-same, me thinks.

It does look to me like the compressive forces of that blue sub-structure will first enter the monocoque edge-on by one side of the RHS, but I'd have to know more about the chassis than one photo to really know - just guessing.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: October 19, 2018, 7:10 pm 
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Lonnie, I think I would prefer bolts in shear too, but to say that tension is weaker may be questionable. Think of head studs: if you overtorque them the threads don't fail, the stud yields. But in a thin-walled structure, fasteners in shear are less likely to distort the structure locally.

Back to the OP. If you are going to build in subassemblies, use the plans for conceptual guidance only. The structural tubes would be organized differently to support front and rear subassemblies. AirFrame Fixer did that in the beginnings of his build. The intermediate structure then just links the various subassemblies and distortions in them can be 'fudged' away.

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PostPosted: October 20, 2018, 3:20 am 
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Warren Nethercote wrote:
...in a thin-walled structure, fasteners in shear are less likely to distort the structure locally.

This.

The Westfield is a blood awful design...but in fairness, it's the material that you're feeding the loads into that you need to worry about, not the bolts themselves.

You must feed loads into the thin skins of a carbon monocoque in pure shear, or as near as makes no difference.


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