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Learning how to build Lotus Seven replicas...together!
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PostPosted: March 27, 2018, 12:49 am 
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Joined: March 15, 2018, 6:03 am
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Hi cheapracer...
Many thanks again for your erudite replies.
The suspension layout is a bit complicated because... well, it’s just a whim... which is what much of these projects are. I first learned about suspension design in the early 60s when racing cars were turning to rear-engines. It became ‘fashionable’ for lower wishbones to have a long trailing arm and for the upper to have a long leading arm - for me, now, it’s just a caprice, to see if I like it - or just to be different.

The positions of the two shorter arms are determined by the ball joints on the spindle, and I wanted to have these arms perpendicular to the chassis so I can run the heims straight into the tube and not have to weld on a short piece of tube - as I'll probably have to do with the forward and rearward arms...

There are two verticals in the middle because the inner points (being perpendicular) are not inline - and I also just thought it would be stronger, as the tube walls will be much thinner than normal brackets. I think it’s known as: making a rod for one’s own back... lol.

Thanks for your comment re. my ‘magenta’ braces - sounds good. I am also wondering that, as every system (from a simple chain upwards) will have a weak link, whether one should design where the weakness will/could be - which could be quickly and easily checked after every run - bending or cracking. This was also my thinking with using the vertical tubes, and even adding a little extra strength to the longitudinal tubes, to ensure the vertical goes first..

I previously had a 10º tilt on the upper wishbone brackets but read here that ‘anti-dive’ was not crucial in these lightweight designs, and especially with rear-engine setups. In this case it was a ‘complication’ I was happy to lose - but it can go back in...

Statistics: I currently have: Caster, 6º; KPI, 8º, Camber, -1º. Upper arm is 76% length of the lower, and slopes 10º downwards towards the chassis.
In cornering, if the car rolls an ‘even’ 4º, the outside wheel will be in 2” of bump and the camber becomes +1º - the inner wheel will droop 2” and the camber becomes -2.6º.

My main problem is designing the inboard ‘quadrant’ joining the pushrod to the spring/damper. Ratio between pushrod end to pivot distance v. coil to pivot distance. At the moment I'm just playing with trial & error.
____

mangpong’ is Thai for scorpion, which was the car’s original name, when I started my design in 2002/03. I was obliged to drop my plans back then and only resurrected them a few months ago... since when the scorpion name has been taken by someone else... lol. Thai roads tend to be quite flat - relatively. Many have drains running along the centre of the road so camber would be disastrous...

Sorry about my confusion with your bearings... For some bizarre reason I was thinking the bearings were somehow joined to the shaft - apologies... lol.

Many thanks, Mangpong.
______________


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PostPosted: April 19, 2018, 1:10 pm 
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I've been taken away with other things that make money damn it.

I have been able to tinker in 3D late at night a few times and I came up with this eventually. It's more a foundation on a few large tubes rather than lots of small ones.

Being Australian where our chassis stiffness laws are tougher, and a fan of good handling cars, I am happy with the potential of this and wilol be interesting to see it's actual stiffness.

I hopefully have a week or 3 up my sleeve now, so will be getting into this starting next week. I even aquired an older Hi Lux Pickup as a donor vehicle. - and yes, that really is the licence plate number, I've had some chuckles since the F-U series came out.


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PostPosted: April 19, 2018, 1:55 pm 
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.. and carguy123 will be happy to know that 3" rear, and 5" front have been removed from the width of the bodywork.

Not quite as "Lardo" as before.

It was for reasons other than being a bit wide by the way.


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PostPosted: April 20, 2018, 5:12 am 
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Yeah, well Lardo was more a take on the name rather than any commentary on the actual size.

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PostPosted: April 21, 2018, 2:14 am 
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carguy123 wrote:
Yeah, well Lardo was more a take on the name rather than any commentary on the actual size.


Oh you say that now, but where were you all those nights I cried myself to sleep! :cry:

The slight reduction has more to do with logistics, I can fit 4 extra frames into a shipping container now and a couple of other reasons.


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PostPosted: April 22, 2018, 12:06 am 
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Funny how the brain works and you get stuck on one thing.

The 4 large diameter round longerons started off as being able to use leftover tube from the rear roll ball vertical supports, and the thought was simply to put a bend in the 2.

Attachment:
RB 00.jpg


Then I considered that consistency would be an issue, and that not using a bend having 2 straight pipes each side with some laser cut plates would be super accurate and easy, so settled on that setup not even considering the simplicity of going back to square tube. So last night drew it up as square tube and back to simple cuts without ishmouthing and other alignment issues. The round tubes sure look nice, but no one sees it under the bodywork anyway.

Better stop talking about it and build it this week I guess.


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PostPosted: April 25, 2018, 2:26 pm 
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Well I am moving into my new old factory, still a bit of a mess and the workers haven't finished the walls and floor yet, but I did get electricity hooked up last night so made a start today. I can't set up my MIG yet so had to tack it together with a little Arc welder I have. Forgot how annoying it is chipping and grinding Arc weld tacks, but better than standing around making excuses.

I designed some simple connectors where 4 main tubes intersect, looked good on the computer, the yellow thing here ..

Attachment:
main connector.jpg


.. so I lasered and folded a left and right up in the morning and stuck it together this afternoon. Very happy how it went together too. The connectors save me from the need to cut angles on the 4 ends that intersect there, the ends only have to be cut square in the drop saw. because the connectors are laser cut, accuracy is assured and the 2 sides are identical.

Attachment:
NC 1.jpg


As I mentioned, I have a few weeks up my sleeve, so hopefully get closer to this over the next few days. I lasered and folded the front suspension mounting plates this morning as well (orange plates). The main tube passing between the upper and lower arms has certianly made life easy for mounting the arms.

Attachment:
NC 2.jpg


.. and I'm going to try a new polyurethane suspension bush system the next few days too, may interest some of you.


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PostPosted: April 25, 2018, 11:36 pm 
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That's an awesome little gizmo you designed there. I'm presuming it is of a sufficient thickness that it isn't the weak link, unless that's what you wanted and were building in a crumple zone in case of a collision.

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PostPosted: April 26, 2018, 12:23 am 
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carguy123 wrote:
unless that's what you wanted and were building in a crumple zone in case of a collision.


That's some sound thinking there, I'll keep that in a brain cell in the back of my mind somewhere, but no, it's just a lazy man's connector (of suitable etrength).

Made life very easy yesterday, along with using some small front and rear jig plates, I'll take a picture of those this afternoon. Without any real effort, the sides are within 2 mm of each other, not too bad a result over 2000mm, cutting with nothing more than a cheap dropsaw.


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PostPosted: April 27, 2018, 10:51 am 
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Awesome, this thing is falling together, even the inevitable changes you need to make when transfering from 3D to the real world are minor.

I love laser!


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PostPosted: April 27, 2018, 10:58 am 
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Location: Carlsbad, California, USA
cheapracer wrote:
. . . I love laser!


What kind of laser cutter do you have? Is it one a small builder can afford, or a machine you use for business?

Cheers,

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

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PostPosted: April 27, 2018, 11:20 am 
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Nice work - I really like that you have a wood floor finish on your build table! Super classy.

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PostPosted: April 27, 2018, 12:27 pm 
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Lonnie-S wrote:
What kind of laser cutter do you have? Is it one a small builder can afford, or a machine you use for business?



Hey Lonnie.

In this case I don't, it's a professional service around the corner, one of a couple in my town. I do all the 3D (Sketchup) and conversion to 2D (dxf) and the clean up needed myself though (Librecad 2D), and the nesting, as well as buying my own sheets. There's a sheetmetal shop nearby for folding, but in reality I should have my own small folder.

Upon saying that, there's no good reason why a homebud can't get some very good results from a little cheap plasma cutter, I have one and use it often. I have a set of holes (various sized washers 8mm larger diameter than the hole I want) with handles welded on that I vice grip in position to the sheet, straight edges and various scrap curves.


RandyBMC wrote:
Nice work - I really like that you have a wood floor finish on your build table! Super classy.


Ha, they are actually floor tiles, big mistake, looks great in pictures, but they crack easy with a GClamp, and surprisingly easy to damage by welding sparks/hot slag.

Stick to a big thick sheet of ply or chipboard.


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PostPosted: April 28, 2018, 7:32 am 
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Only a few hours today, but I started laying some floor tubes.

At the last moment I have decided to shift the engine almost 2" to the right (viewed from behind) for about 1.5" wider foot room around the pedals. I had my biggest size 44 steel cap work boots on today and not an issue.

One of the suspension plates I modified with an angle grinder, but the other one either needs a new cut or add a bit to reach the inner lower tube now.


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Last edited by cheapracer on April 28, 2018, 11:51 am, edited 1 time in total.

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PostPosted: April 28, 2018, 9:29 am 
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This is some cool stuff going on here man. Its going to be really cool to see it done. Could you find a bigger work space? :D. I wouldn't be able to control myself. There would be stuff everywhere. Just had to drop you a line. :cheers:

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