[WIP] Supercar in 1:8 scale

[Erik Leppen]

I took myself on the quest to create a new supercar, in a new scale.

Normally, when I build suprecars I aways use the wheels from 8070, 42039 and the like, which is about a 1:10 scale. This is smaller than many cars by other builders, who use the larger tyres from 42000 or more recently the Porsche.

 

So I set myself the challenge to build a car in the somewhat larger scale of 1:8. Which is, I'll be using these wheels which I'd bought myself as a little present :)

It won't be a particular existing model, but I used a plan of a Ford GT to find the measurements relative to the wheels. It will be 27 to 29 wide. This is quite a bit larger than I'm used to, so this will be interesting. I'm relatively good at doing the chassis, so the largest challenge will be the body. It will not be motorized.

 

Here's the front axle.

I want to have it all-wheel drive, so the rear axle will be similar, except the steering.

The arm for the suspension on the lower wishbone is relatively long, which means the suspension travel is just about one stud. I always try to limit the suspension travel, because then the wheel arch will not need to be so huge. Also, with less travel, the suspension will be stiffer, so that one spring per wheel will still hold the weight.

 

The second unit I started is the gearbox and interior.

As usual, I try to do something with color, and I selected green for the interior. I got myself a few extra small panels, which are super useful for finishing touches to almost everything.

As you can see, the seats are adjustable; they slide on an axle and the backrest can be inclined (no gearing though). Similar to ye olde 8865 :)

The gearbox will be 5+R with 1, 3, 5 forward and 2, 4, R backward, just like in some real cars. The gearing is a known design I used previously, I believe it's not even my design but it's perfect, so I just copy it. It uses the old driving rings, so that explains the 1/2 stud offset.

 

So far, this is sort of the progress/plan. The connection between the two modules is temporary, because the space between them is way too large. The whole seats unit will move forward, but I'm not sure yet how much. The position of the rear wheels is guessed to be approximately there.

 

(Yes, I know the tow truck isn't finished yet. I'll finish it, but my local LUG has a meeting soon and I want to present more than one model, so I will take this one there aswell.)

[1gor]

Erik, it is interesting approach using green for interrier, but don't you think that Tumbler tires are "to fat" for a supercar? Perhaps ones used in silver champion could be better suited for supercar; even classic like GT40?

Edited June 22, 2017 by I_Igor

[TechnicRCRacer]

This is interesting! Keep building! I like the green interior!

[Didumos69]

Great WIP! I like the front suspension a lot. How are the thin 3x5 levers attached to the lower wishbones?

[Alex Ilea]

This looks like a very interesting build ! To be hornest i hate the green interior (just my opinion), the front axle looks very good (one of the best i've seen) . 

[Lipko]

Engine placement?

[Lakop]

I suspect engine will be at the rear. I like the middle section with the gearbox but not sure about the wheels on this one. Look forward to progress.

H

[Leonardo da Bricki]

I like the unusual color choice. Can you make an LDD or some close-up photos of the gearbox? I would love to see it.

The front suspension looks nice, how stiff is it?

[PorkyMonster]

9 hours ago, Erik Leppen said:

The arm for the suspension on the lower wishbone is relatively long, which means the suspension travel is just about one stud. I always try to limit the suspension travel, because then the wheel arch will not need to be so huge. Also, with less travel, the suspension will be stiffer, so that one spring per wheel will still hold the weight.

 I seriously don't get your point  because IMO less travel does not translate to stiffer suspension... unless you pre-compressed the shocks, which doesn't look like the case in your pictures. But even if you DID pre-compress the shocks, I think one shock per wheel for a 1:8 model will still be quite a challenge... u gotta build really light 

Edited June 23, 2017 by PorkyMonster

[Didumos69]

2 hours ago, PorkyMonster said:

 I seriously don't get your point  because IMO less travel does not translate to stiffer suspension... unless you pre-compressed the shocks, which doesn't look like the case in your pictures. But even if you DID pre-compress the shocks, I think one shock per wheel for a 1:8 model will still be quite a challenge... u gotta build really light 

I think what Erik means, is that the complete compression of the shocks translates into 1 stud vertical travel of the wheels, which is quite direct (the shocks themselves also travel 1 stud), but I agree that if the whole model is going to weigh around 2kg it might not be enough.

As a reference: For my rugged supercar (1.9kg) I used double hard shocks to gain 2 studs travel for all wheels. For the front this turned out sufficient, but in the back I had to add torsion bars to avoid too much compression under the vehicles own weight.

Edited June 23, 2017 by Didumos69

[PorkyMonster]

1 hour ago, Didumos69 said:

I think what Erik means, is that the complete compression of the shocks translates into 1 stud vertical travel of the wheels, which is quite direct (the shocks themselves also travel 1 stud), but I agree that if the whole model is going to weigh around 2kg it might not be enough.

As a reference: For my rugged supercar (1.9kg) I used double hard shocks to gain 2 studs travel for all wheels. For the front this turned out sufficient, but in the back I had to add torsion bars to avoid too much compression under the vehicles own weight.

Hmm... even if 1 stud vertical wheel travel translates into 1 stud shock compression (doesn't look like it though...), I wonder if the fact that the shocks are mounted horizontally weaken the spring strength (lever effects)... and if there is no 1-1 correlation, only the weaker parts of the springs will be used before bottoming out...

Now assuming that spring strength is unaffected, and based on the shocks I have currently, I just measured that each yellow shock can take on 1.5 kg before compressing fully - (so 4 x 1.5 = 6 kg!!!) not bad indeed... 

Edited June 23, 2017 by PorkyMonster

[Didumos69]

9 minutes ago, PorkyMonster said:

I just measured that each yellow shock can take on 1.5 kg before compressing fully - (so 4 x 1.5 = 6 kg!!!) not bad indeed... 

Maybe a bit off-topic, but it would be interesting to know how much weight they can take before compressing by 25% up to 33%, which is the ideal range under the vehicles own weight in my opinion.

Edited June 23, 2017 by Didumos69

[PorkyMonster]

25 minutes ago, Didumos69 said:

Maybe a bit off-topic, but it would be interesting to know how much weight they can take before compressing by 25% up to 33%, which is the ideal range under the vehicles own weight in my opinion.

At 25%-33%, weight is about 700 gm... which came as a surprise to me... I've always thought that spring rates are either linear, or hardens progressively (for variable rate springs). But for this Lego yellow shock, its seems to soften progressively!

So I did a google search to find out more... didn't find anything that answers my SHOCK (LOL), but I found this thread by @Doc Brown about 3 years ago, and his results corresponded to mine as far as the yellow shock goes... 

But bear in mind that all these measurements assume 100% direct/vertical compression. 

[Erik Leppen]

Wow, that's a lot of replies so quick. I see there's a lot of discussion about the springs. Let me clarify what I meant. See also the attached image at the bottom of the post. The spring has a fixed strength. If the attachment point is far away from the hinge, it has a large arm of momentum, meaning each millimeter of vertical travel will compress the spring by a large amount, which requires a large amount of force. In the left image, 1 mm of vertical travel may compress the spring only 1/3 mm, which requires little force. In the right image, 1 mm of vertical travel will compress the spring 1 mm, which requires 3 times as much force. So it holds 3 times as much weight, but with 3 times as little travel.

@PorkyMonster: you're right that springs compress linearly, but the spring in a Lego shock is pre-compressed. If you would dismantle it, the spring would be longer than in the part. The precompression force will be about 500 g or so, so that's why 25% is about 700g, because that's 25% on the way from 500 to 1300. (numbers are approximate for clarity). Also, as a Lego shock absorber has only two pinholes, it's a two-force member, so it's always in "direct compression" (if it's free to move). The only place where force can be lost, is friction.

Anyhow. Progress!

I copied the front axle, but replaced the steering by fixed links. I could have used non-steering hub parts, but I liked the similarity between both modules. Engine is placed, @Lipko, between the gearbox and rear axle. And I found a way to connect the seats unit to the front axle unit with much less distance between. The central console has been widened to 7 to allow the two long green beams to run through to add strength. These have to be lengthened in some way to the back (over the engine probably) to have a continuous beam from front to back to add more stiffness. Also, HOG is added (12t gear behind front axle), and steering wheel is added (white beam is temporary). It's an easy change to put the steering wheel on the other side.

21 hours ago, IA creations said:

This looks like a very interesting build ! To be hornest i hate the green interior (just my opinion), the front axle looks very good (one of the best i've seen) . 

If the front axle is one of the best you've seen, than you haven't seen very much, because it's nothing out of the ordinary. No camber, no caster (whatever those are), not even Ackermann steering. Just the same properties as that of 8880. Lots of axle modules by other people are much more imaginative and interesting than this. There's even a bit of play in the steering rack because it had to move out of the way of the differential and the support beams (so it's "["-shaped). I'm not entirely happy with the steering rack, but I don't think there're many better options.

Also, no problem you don't like the color. It's unusual, that's why I like it, but it's not very realistic

18 hours ago, Leonardo da Bricki said:

I like the unusual color choice. Can you make an LDD or some close-up photos of the gearbox? I would love to see it.

Does this help? But again, I don't think it's my design. It's a while old already, I don't know where I saw it first. I don't know if you can see it, but the 16t side of the diff drives 1st, 3rd, 5th gear 16t clutch gears. The 20t (on the axle of the 8t gear) drives the reverse-gear. Because it's 3x as fast as the diff, reverse gear has similar speed as first gear. The other 20t (on the same axle as the whtie gear) drives the 2nd, 4th gear clutches. The level above it, with the clutch gears, is the same as in set 8448 (directly next to the 5x7 frame you see the two pairs of 12-20).

22 hours ago, Didumos69 said:

Great WIP! I like the front suspension a lot. How are the thin 3x5 levers attached to the lower wishbones?

Does this help? The 2L axle at the bottom holds two 2 x 0.5 beams and the hinge axle has a 2L beam too.

Some more images:

More on the Brickshelf folder: http://www.brickshelf.com/cgi-bin/gallery.cgi?f=570177 (not public directly after any uploads)

[Jeroen Ottens]

Shaping up very nice. Interested to see what you will do with the bodywork...

[syclone]

Very interesting car, it is looking great so far . I do like the green interior 

Edited June 23, 2017 by LXF

[TechnicRCRacer]

This is awesome and has inspired me to attempt to make my own super car! 

Just now, LXF said:

do like the green interior 

(pic)

What??? 

[Myers Lego Technic]

1 hour ago, TechnicRCRacer said:

 What??? 

If you are supersede by the Lambo interior, I would palace money in the fact that it is photoshopped. 

Carbon fibre doesn't usually glow...

[Lox Lego]

This is a great build. Seems to have quite a few functions already, everything is compact. I like the interior!!

[TechnicRCRacer]

@Myers Lego TechnicThere was a different pic before with an actual green interior of another car.

[Aventador2004]

3 hours ago, Myers Lego Technic said:

If you are supersede by the Lambo interior, I would palace money in the fact that it is photoshopped. 

Carbon fibre doesn't usually glow...

That is a virtual Lamborghini configurator, I messed around with it to make one for if I ever have the money for one .

[PorkyMonster]

@Didumos69 and @Erik Leppen, thanks for explaining how this suspension works - I get it now .

And tweaking this setup can even allow for stiffness beyond what compressing a shock perpendicularly can give... that's something I've never thought of... 

[Didumos69]

6 hours ago, PorkyMonster said:

And tweaking this setup can even allow for stiffness beyond what compressing a shock perpendicularly can give... that's something I've never thought of... 

Indeed. I tried to reason what @Erik Leppen's 'arm' means for my rugged supercar suspension and came to the conclusion that my setup (left in the image below) behaves as if the spring was positioned as in the right half of the image below. I actually translated the springs along the suspension arms away from the wheel. The red parts indicate the 'arm'-length. EDIT: I corrected the image.

Edited June 24, 2017 by Didumos69

[Didumos69]

16 hours ago, Erik Leppen said:

I copied the front axle, but replaced the steering by fixed links. I could have used non-steering hub parts, but I liked the similarity between both modules.

I like the similarity with the front module too, but I think you could also obtain similarity with fixed links. This will give a lot of unnecessary slack in the rear wheels.

If I'm not mistaken the steering links are secured to the chassis using perpendicular axle pin connectors, but these can easily slide off the axles they are attached to, they are only friction-locked and not form-locked to speak with @Jeroen Ottens' terms.

If you could find a way to secure these links better or even give them a little tightness by offsetting the connection at the chassis-side with half a stud lengthwise, I think it would make a much better rear module. (The steering links can handle such offset easily, because of the slack they have.)

Edited June 24, 2017 by Didumos69

[PorkyMonster]

4 hours ago, Didumos69 said:

... that my setup (left in the image below) behaves as if the spring was positioned as in the right half of the image below. I actually translated the springs along the suspension arms away from the wheel...

Hmm... had you actually positioned the spring as in the right half of the image, you would have had stiffer suspension... So I think they (the left and the right setups) don't behave the same way. Of course, the fact that the top of the spring in the right image setup is not static adds some complications.