3D Modelling a slot car - Dodge Monaco Options

[choc-ice]

So, if your modelmaking skills are good enough for an Airfix kit but too rubbish to make something from scratch like the guys here, what do you do? Play to your strengths, in my case design it using 3D CAD (computer aided design) and get it made by rapid prototyping.

CAD is a handy thing, but let's remember it's only a tool. The actual designing still goes on in your head, same as it always did. Where do we start? How about the design brief, same as ever.

I'm not a slot racer, although I love slot cars and I was a demon electric R/C racer as a teenager. While going faster is a noble aim, a fast car isn't always the most fun, or your favourite car. To make my fun car, I want it to be like car chases were as a kid – with a good sized American car, loads of lurid tail slides, burnouts... as much as I can get. Back when Sony launched the first PlayStation everyone was making a racing simulator, then came a game called Driver where the cars were slow but wallowed brilliantly in corners and could slide around corners with only a modicum of talent from the player. That's my target.

To the car. I love the shape of the '77 Dodge Monaco; it's got a fine history in TV and films, looks a good shape and nobody does one at the moment.


Now for the specification – it should have suspension that lets it lean realistically in a curve. The roll centre of a solid rear axle is easy to find, we'll make the roll centre of the front suspension at the same height so it doesn't have a roll gradient.

It should have steering, this is essential when doing huge power slides and even just when on tight corners. I just think it looks fantastic, so you'll have to humour me. You don't mind?

Finally, when you hit the throttle what does any chase car do? A burnout! I can take or leave the noise but I like the idea of smoking tyres so that's what I'll do. How hard can it be?

Let's get going with the design proper. I can do the chassis and body but I'll reuse a motor, rear axle and perhaps a guide blade. That means they should be the first things to model up. Sod that – I want to get going with the body!

I use Solid Edge almost every day, it's pretty rubbish but at least I can use it at lunchtimes. For 12 years before I used ProEngineer which was much more powerful, if I had a copy I'd much prefer to model things using that, but you use the tools you have around you. First tool is some graph paper.

I went to http://www.the-blueprints.com/ and found a 1977 Dodge Monaco, but beware when using these sites because the plan view doesn't always line up with the side view. How I laughed when I found that out

Using my friendly copy of PaintShop Pro, I resized the picture so it printed out 2:1, then I transferred it onto graph paper (see how high-tech and modern this is?). Then I could get the outline shape measured with more accuracy, and I could sketch it in Solid Edge.

I started by doing a plan view, because the car is tapered front and back, then I sketched the side profile.


I put some shape to the sides


Then made it hollow (shelled), and put a few more features on


Verdict? Looks awful!

[choc-ice]

I tried a few different methods, but the place to start seems to be the front and rear screens, then the roof. The rest is comparatively simple. The screens are bounded by 3D curves, so it's time to get started with Solid Edge's surfacing capabilities which are quite limited.

Let's start with a trajectory which is curved in plan view, and the side profile of the car (waistline above the wheelarches) in its path


Now we'll put the roof in


Now extrude the roof out to the side


This isn't going anywhere..... it still looks rubbish.

Shall we see where the chassis bits go?

[choc-ice]

Front axle first! I'll have a metal axle which allows the whole assembly to pivot, it's not real suspension but it'll let the body roll around as I want it to. After lots of thinking and other opinions taken (because it's better to use someone else's good idea than a rubbish one of your own) I decided to use trail steer rather than linking the guide blade to the steering arms. This means I can use a standard guide blade.


A 2mm pivot should be strong enough to let the suspension roll, with a 1mm pin to pivot the hubs on. The back end of the hubs point to the middle of the rear axle for proper Ackerman steering.


Nylon bushes (from a long dead Scalextric car from my youth) will let the axle pivot, and the steering arm needs to clear the guide blade for full movement. The advantage of 3D CAD is you can try different steering positions easily to check for interference.

[stevie7v]

Love it!

Can't wait to see the bit where it manifests into a real material. What material will it be? Looks like you might have to make it out of a material that you can hand-sculpt a bit to get the results you want.

But then, you could get yourself (or build yourself - like here or here) a vaccuum forming rig. That way, you could 3D model using any material and then vaccuum form the body in lightweight lexan (the clear polycarbonate stuff).

Persevere choc-ice, you're on the right path.

Regards
Steve

[choc-ice]

I'd always imagined using a spring like an antiroll bar, simple, cheap, easy to adjust, what's not to like? Unfortunately when it came to packaging the whole lot in it was a nightmare so I plumped for coil springs. I modelled one compressed and one extended to check it was feasible.


Rear axle next. The idea is that the axle and motor will be held together, and the whole lot will pivot. This is an upside-down view, the motor is the old Mabuchi from the long dead Scalextric Porsche 911


I'd thought the chassis would be a few small sections which would then attach to posts from the bodyshell, this would be simpler to produce. But once I'd drawn them up, the torsional stiffness looked dreadful so I went for a more conventional chassis instead. Tall box sections make for more stiffness if you remember your second moment of area calculations from Maths. Better to start off strong and whittle parts away than have to add bits I thought.

I took a keen interest in chassis design when I did my HND in Automotive Engineering so I'm aware of the limitations of a ladder frame, but it's not all bad.

[choc-ice]

Want to see it lean in a corner?


More later!

[sacesta]

I like your idea for the motor mount. Simple but practical design. Nice job!

[UshCha]

who are you going to use to do the prototyping? Some charge a $1.6 per cc, that would cost a lot.

[bwaminispeed]

Coil Springs in a big Dodge, you're kidding me, right?????

Nice CADding.

[Knacki]

Future of scratch "building" .
Cool start.

[Datto]

"Movie Smoke" is acetic acid and ammonia. Combine the two and you get cold smoke (no fire). This is what they use for smoking clothes and the like. Smells like the devil. Someone on another board has the source of the burnout in the track. He has a Mexican Airfield with drug cartels and Federales going at it. He has a 'donut' section of his track and can control the smoke from the driver's position. Don't know if it's oil smoke or dry-ice.

You might consider the little springs used for HO slot car pickups for your coils. They're tiny and soft, and readily available from vendors.

When you've finished your body shell, will you be casting it in resin, or directly using the digital print? I've done some 3D printed chassis, but the rough finish of the printed material is pretty much hidden in that case.

Good luck, and have fun!

[Datto]

That Acetic acid/ ammonia smoke would probably be corrosive on track rails, axles and motors, though...

[Spa67]

I'm really interested in this topic. I've been working on getting some 1/43 diecasts scanned and printed in 1/32. It's not easy communicating with the folks remotely, as they have no idea what I'm really trying to accomplish. Does anyone on this board have easy access to a 3D scanner?

[choc-ice]

But then, you could get yourself (or build yourself - like here or here) a vaccuum forming rig. That way, you could 3D model using any material and then vaccuum form the body in lightweight lexan (the clear polycarbonate stuff).

I'm not sure about vac forming, I've had it done for work stuff before and they struggle with undercuts. I'll have a look at the links later though, thank you!

who are you going to use to do the prototyping? Some charge a $1.6 per cc, that would cost a lot.

Luckily I've got a mate with a rapid prototype machine he bought for his own company. Otherwise I'll use a few agencies I use with work - Arrk Europe, 3T SLS, Malcolm Nicholls or Rapitypes

Coil Springs in a big Dodge, you're kidding me, right?????

I know, I'm hanging my head in shame It's really just down to packaging, even though my idea of basically an antiroll bar (sway bar in the US) seemed simpler. You just never know until you get into the design and cram it all in.

"Movie Smoke" is acetic acid and ammonia. Combine the two and you get cold smoke (no fire). This is what they use for smoking clothes and the like. Smells like the devil. Someone on another board has the source of the burnout in the track. He has a Mexican Airfield with drug cartels and Federales going at it. He has a 'donut' section of his track and can control the smoke from the driver's position. Don't know if it's oil smoke or dry-ice.

I've done a few tests with onboard smoke units on the bench. One is made primarily for model tanks and turned out to be rubbish, another is made for model trains and worked much better. It pours out a fair amount when you give it 12V but takes a second or two to warm up. I asked a tame electronics designer to do me a circuit which keeps 5V at the smoke generator, then 12V when you open the throttle fully. That'll go inside the car.

You're not at full throttle very often so I hope it'll work ok, testing will tell me more.

You might consider the little springs used for HO slot car pickups for your coils. They're tiny and soft, and readily available from vendors.

I use springs in mechanisms at work so there's a boxful I can try, there are plenty of manufacturers that do small quantities too.

When you've finished your body shell, will you be casting it in resin, or directly using the digital print? I've done some 3D printed chassis, but the rough finish of the printed material is pretty much hidden in that case.

Got any pics of the chassis you had done?

The body will probably be done in resin. I picked the brains of some experts here and they said it should be strong enough. I'll probably get an SLA master made, then ask someone who's much more talented than me to cast it. The chassis could be either, but obviously the rough finish of 3D printing or SLS wouldn't matter.

[choc-ice]

I'm really interested in this topic. I've been working on getting some 1/43 diecasts scanned and printed in 1/32. It's not easy communicating with the folks remotely, as they have no idea what I'm really trying to accomplish. Does anyone on this board have easy access to a 3D scanner?

I considered that when I was tearing my hair out with the bodyshell. You can try a local search for rapid prototype bureaus?