Designing a locost style Lotus 7 Replica

Caffeine · Postby **Caffeine** » Tue May 27, 2008 3:28 pm

Started rebuilding the SolidWorks model of the car, based on discussions and ideas for impreovements we had with Bigdog on the weekend.

Now that we've decided to go with an NC as the donor car I'll be adding a simple, visually approximate but dimensionally accurate model of the NC drivetrain and suspension to the solidworks assembly, and adjusting the chassis to suit the NC hardpoints (i.e. engine / gearbox / diff mounts, suspension pick up points etc)

Has anyone got an NC they don't mind me disassembling to measure stuff? :shock:

what fun this is!

FMS01 · Postby **FMS01** » Tue May 27, 2008 5:59 pm

I would give some consideration to extra bracing, there's a few non-triangular areas in your chassis model.

This is what ours look like

Alex · Postby **Alex** » Tue May 27, 2008 9:44 pm

Caffeine wrote:Started rebuilding the SolidWorks model of the car, based on discussions and ideas for impreovements we had with Bigdog on the weekend.

Now that we've decided to go with an NC as the donor car I'll be adding a simple, visually approximate but dimensionally accurate model of the NC drivetrain and suspension to the solidworks assembly, and adjusting the chassis to suit the NC hardpoints (i.e. engine / gearbox / diff mounts, suspension pick up points etc)

Has anyone got an NC they don't mind me disassembling to measure stuff?

what fun this is!

do it

and keep the plans for me, thinking about starting something like this in about 5 years

Caffeine · Postby **Caffeine** » Tue May 27, 2008 10:28 pm

FMS01 wrote:I would give some consideration to extra bracing, there's a few non-triangular areas in your chassis model.

Oooohhh nice

I'm still working on traingulating and bracing, the screenshots from before were very early works in progress...

Looks more like a bird's nest now!

Caffeine · Postby **Caffeine** » Tue May 27, 2008 10:50 pm

And when the sketches are converted to tubes...

Postby **Okibi** » Tue May 27, 2008 11:14 pm

I found a prefabbed frame just long enough for you Liam :mrgreen:

Boags · Postby **Boags** » Wed May 28, 2008 10:41 am

FMS01 · Postby **FMS01** » Wed May 28, 2008 10:55 am

you'll need a fair amount of room to get the exhaust out the side of the chassis

unless you go over the top.

Make sure you've got enough room to get the engine/gearbox in in one piece, be a bastard if you couldn't. We made a removable cross brace for the engine bay where the rear of the top wishbones connects the top and bottom frames which helps keep things tied together and makes for easier engine removal. Try and add a diagonal in to the open section where your steering tie rods go through the sides.

Cheers,
Julian[/img]

Caffeine · Postby **Caffeine** » Wed May 28, 2008 12:19 pm

Awesome, thanks for the tips

Had a quick email conversation with Don (the guy building the NC based locost on page 1), he's given us a few ideas too, and a note to find out whether we need an Australian delivered NC engine to pass emissions checks...

Mokesta · Postby **Mokesta** » Wed May 28, 2008 2:26 pm

Take special care with the connection details at the nodes. The solid model shows node connections and all square tubes, whereas the photos show the typical Chapman style round diagonals mounted to one tube, not intersecting at the node.

From chassis work a mate of mine did for a widenend Westfield with a Ferrari V8, the connection detail has a huge influence on overall chassis stiffness. For example a node and beam FEA model will typically predict chassis torsional rigidity that is nearly twice the value measured when the car was B&T tested. The car needed lots of gussets at nodes and more diagonals to pass.

You can use the alloy walls to give stiffness but there is a trade off where you need to drill too many rivet holes to mount the sheets. Once the tubes have that many holes they lose their stiffness.

You'll get better results with all tubes going to the node and putting tapered gussets at all nodes.

M

FMS01 · Postby **FMS01** » Wed May 28, 2008 3:00 pm

On that last comment from Mokesta, the FormulaMotorsport chassis (also known as an FMS chassis on other forums) you see in the photos passed the beaming and torsion test in QLD as you see it in the photo's, no paneling req'd.

Cheers,
Julian

PS. Caffeine, what weight does solidworks give you for the chassis? Ours with the CAMS rollbar and all the bracketry was 98kg before the paint went on.

Caffeine · Postby **Caffeine** » Wed May 28, 2008 4:15 pm

FMS01 wrote:PS. Caffeine, what weight does solidworks give you for the chassis? Ours with the CAMS rollbar and all the bracketry was 98kg before the paint went on.

Still haven't finished all the tubing & braces, simple tubes without end profiles, no brackets as yet...

1in by 1in by 1.6mm square tube all over, 57kg
1in round tube 'sch 40' (solidworks supplied profile, looks pretty thick walled), 111kg (Edit : just checked, it's 3.4mm thick wall!!)

Screenshot

Boost · Postby **Boost** » Wed May 28, 2008 6:50 pm

hey Caffeine, I noticed that you are drawing the members as lines and then getting SW to convert them to RHS. I never knew SW had such a feature?

Caffeine · Postby **Caffeine** » Wed May 28, 2008 6:58 pm

Boost wrote:hey Caffeine, I noticed that you are drawing the members as lines and then getting SW to convert them to RHS. I never knew SW had such a feature?

Yep, the 'weldment' feature

Very handy, just pick a sketch line, and select what profile you want, and how you want the ends to be treated (i.e. cut to planar face, or another body etc)

Then solidworks generates a cut list for you, showing you the length and end profile of every tube, and where it fits into the chassis

Boost · Postby **Boost** » Wed May 28, 2008 7:01 pm

thanks.
I'm also modelling the space frame based on the book. I've model the frame in assembly mode by drawing and extruding each individual members which is so freaking time consuming and it makes doing FEA a pain in the arse. But now with weldments its going to be such a breeze.
Thanks heaps Caffeine!