Hi All.

I have been lurking for a while and learning heaps of good stuff. My intention is to build a BEC project and as you see I have opted to make it front-mid-engined as I think that the irritation of reverse is best solved with a Quaife reversing box and not a big mess of gears and electric motor and other Heath Robinson stuff. Id be interested in your opinions of the initial design. Click on images for a larger size.






I'm planning to construct the chassis with a steel called Hi Lite made here in Australia. The larger tubes will be 50x2mm and the smaller diameter will be 35x1.5mm.
Thanks to information off the forum I'll also be looking for a Freelander diff and driveshafts for the rear. All suspension will be pushrod coilovers and unequal length 'A' arms.

[Edited on 16/12/07 by Benonymous]

[Edited on 17/12/07 by Benonymous]

Make sure you can buy Hi-Lite where you are in WA I never managed to find a small volume supply of the stuff.
I resorted to the more common GR350 material.

I am in NSW, right next to Port Kembla steel works. I reckon I can get Hi Lite but if not, I'll settle for mild steel in similar dimensions. BTW Doug, I've looked at your website and I really like what you're doing I won't be starting this project for real until next year as my shed is filled up with unfinished sea kayaks ! Don't you have a onesteel outlet in WA?

[Edited on 16/12/07 by Benonymous]

Hi Nice concept - great name too! Looking at your frame sketch the area between the front suspension pickup looks a little open. Have you considered how you will pass the loads into the chassis yet?

It is this front "box" that often seems to be the fist area to be strengthened when people set out to make Locost chassis stiffer. The catering-van (another great name!) CSR introduced a load of stiffeingin this area.

http://en.wikipedia.org/wiki/Caterham_CSR
Rescued attachment Caterham_CSR_Suspension.JPG

We have One Steel over here but they wont bother stocking the stuff unless you want a rail car full it seems.

The difference between the materials is actually not as big as it looks, I spoke to a tech guy at one steel and apparently as even though the Hi-Lite has a UTS of 450mpa it develops an equal amount of strain at lower loadings to GR350, so probably the only benefit you will see to it is in horror situations.

I had been trying to get the stress / strain graphs out of one steel but gave up when getting the stuff was obviously going to be too hard.

Thanks for looking at the website, I sometimes wonder if anyone does.

BTW amongst all the other crap in getting a car registered in Aus, you'll have to pass a 4kn per degree torsion test. So you might want to think of doing some stress analysis on the design before you get cutting metal.

A book locost wont do 4kn and neither will many other UK kit cars (not sure about the Atom) and there is no such requirement in the UK. So just be careful where inspiration is drawn from.

I like the design if it were me though I'd put the engine in the back and either forget about reverse of use one of these:



They're double the price of the reversing unit though.

Thanks for the feedback. Puk I'm going to use a laser cut sheetmetal part in the front of the chassis, less hassle than a load of small tubes. I hear what you're saying with regards to the steel Doug. I'm not married to the idea of using the Hi Lite. Actually the whole idea started off as a mid-rear but I thought if it's going to be a modern Lotus Seven style car it really should be mid-front. I wonder how many production cars would pass 4Kn too. You just have to wonder at our bureaucracy here in Aus. What are they trying to achieve with these enthusiastic targets? maybe it's just to discourage us.

Looks nice.
Do you have some dimensions? (track, wheelbase)
I would make the passenger entry a bit larger though.

Yeah, that's been bugging me I think I need another 100mm for the passenger compartment opening front to rear. This is the second draft of the chassis and there will probably be others. The basics will stay pretty much the same though.

This is actually the third draft of the chassis. I really should post a pic of the one where one of the cross members on the top of the frame went through the occupants!

Anyway, the passenger opening is larger now and I've put in a draft of the bulkhead for the suspension in the front. An identical one would be in the back. I had a look at the Caterham CS chassis and they've put a couple of pyramid structures in the front, very stiff! There is a bunch more triangulation to go into my effort, and a transmission/propshaft tunnel. Comments are welcome






BTW Track and wheelbase dimensions are shown on the reference dimensions in the images

[Edited on 19/12/07 by Benonymous]

Your track is very wide. So big lateral G's is no problem

Mind the propshaft, though.
You will need in this config a split one. Since you not connecting @ the crank, but at the transmission.

Still you are at the right direction.

Keep the progress!

Yeah, I figured on a split propshaft with the quaife reversing box acting as a centre bearing. If it ends up putting the reversing lever in a difficult place I'll just remote it.

Hmm, that's not a bad idea.
I think I will use the split prop shaft in my design as well.

A little progress. I have dealt with a couple of issues. The main one was that the rear wheels lacked sufficient clearance from the vertical tube at the rear and the curved top tube. I thought about it for ages and decided to extend the wheelbase 200mm to move the diff centre back. I also ditched the curved tubes at the top and bottom rear and went with straight ones. Much simpler. I have also added a truss that goes in to tie the rear suspension subframe to the top rear cross tube.



Comments and suggestions are welcome :-)

[Edited on 14/1/08 by Benonymous]

[Edited on 14/1/08 by Benonymous]

quote:

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Originally posted by Benonymous
......you see I have opted to make it front-mid-engined.......

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quote:

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Originally posted by Benonymous...I have also added a truss that goes in to tie the rear suspension subframe to the top rear cross tube...

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Neo7 - truss comment GIF

I hadn't considered that Puk. It looks good in the plane you've drawn in but that leaves a quadrilateral between the tubes you've added.

Its all speculative at this stage however so I'll make a version like you've suggested and include it in the testing later on.

I based this choice on a local builder who has been keeping a build diary on his 'Godiva' project. It was surprising to see that in a similar area of his car that this truss assembly is superior to a pair of crossing (X shaped) tubes in the same area.

As he points out. If the angle of the crossed tubes is too acute, it's stiffer to have a truss, closer to 45 degrees in the corners.

This whole thing is a great learning exercise for me and the joy of using SW is the fact that I can load the chassis and get a really good idea of the torsional strength before laying down a single weld.

I was looking at Dennises car (DP Cars) a couple of days ago and I was very surprised to see how little triangulation he had included in his chassis. He has used stressed aluminum skins for stiffening.

Hi B'

I'm wary of the long term strength of stressed skin steel frame, even though early 7s did use that technique. I've got no direct experience but two issues appear to me:

1 if bonding - difficult to be certain that you have a structurally sound joint.

2 if you discount bonded joints you are left with mechanical methods - rivets. Rivet holes experience high local stress which leads to strain and a loosening of the joint. Perhaps wrapping the skin around the tube before riveting would give a better stress distribution - difficult to model though??

That said I'm designing chassis that will use composite aluminium panels, and am hoping to find some mechanism for creating a reliable bonded joint. Jaguar are mass-producing riv-bonded aluminium chassis so it must be achievable.

Have you considered approaching Dennis to ask him how he mitigated against these risks?

Cheers,
Puk

B- just reread your response and you pointed out that my solution wasn't triangulated in the horizontal plane. Guilty as charged.

Thinking further though, wouldn't the horizontal loads be introduced by the reactions at the inboard ends of the suspension wishbones? If so horizontal triangulation in the plane between the inboard suspension pickups might allow you to get away without a diagonal brace higher in the frame. Maybe count the diff as a stressed component tying the inboard suspension pickups together. FEA or long hand truss analysis would help untangle that lot.

Cheers,
Puk

Hi Puk. I'm actually not proposing to use any stressed skin in my chassis. I used Dennis as an example just because I found it interesting that he chose that route.

I agree with you on the stressed skin issues. I built a locally produced Seven replica many years ago and when I put the floor skin in I used bathroom silicone as an adhesive. Unfortunately I had to remove the skin and the silicone was unbelievably tenacious. Got it off but it was buggered.

I think I could go bananas putting triangles into the chassis and then having to redesign around inconvenient items like shock absorbers and steering racks and the like

While the basic layout will not change, I feel there may be more versions of this as I go on. More versions from scratch. It's fun to do and with the FEA in SW I'll be able to give it all a good twist!

Kindered spirit:

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