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3D Modelling a slot car - Dodge Monaco. On the track!

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  • 3D Modelling a slot car - Dodge Monaco. On the track!

    A few months ago I posted this thread about steering and received some very helpful replies. The idea was to make up a slot car that wasn't done by the other manufacturers, not a race car (because I'm not a slot racer) but capturing the spirit of my youth watching TV on a Saturday afternoon.

    When you're a kid growing up in England during the late '70s, the homegrown TV is pretty tame. American TV on the other hand was much more exciting, there were car chases and crashes - Starsky and Hutch couldn't drive more than 5 minutes without a huge burnout and tail slide, the Fall Guy was even more so and of course The Dukes of Hazzard was 50 minutes of weapons-grade action.

    Unlike racing, the key attributes seemed to be wayward handling, taking every corner with the handbrake, tyre squeals on dirt, soft suspension and burnouts. Let's see how many we can capture in 1:32 scale!

    My craft skills are ok for a model kit but there's no way I can sculpt a bodyshell from scratch. Let's get the subject matter sorted first, the 1977 Dodge Monaco


    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!
    Last edited by choc-ice; 04-17-2011, 06:51 AM.

  • #2
    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?

    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.


    Last edited by choc-ice; 03-27-2011, 05:25 AM.

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    • #3
      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 studied Automotive Engineering in university so I'm aware of the limitations of a ladder frame, but it's not all bad.



      Steering turned, suspension on full lean which is about 10 degrees

      Last edited by choc-ice; 03-27-2011, 05:25 AM.

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      • #4
        Over the next week the daily progress followed a similar path
        10 Have a go at getting the bodyshell modelled correctly in Solid Edge at lunchtime in work.
        20 Try a bit more in the evening when my better half has finished with the laptop.
        30 Fail. The software says it can’t trim a surface, or something similarly frustrating. Consider throwing my shoe at the laptop in anger.
        40 Go to bed, figure out some other way of doing it.
        50 Goto 10

        At last, a breakthrough!





        All the base features are in place, I can put in the details that make it - the peaks along the middle of the hood and trunk lids, and the very distinctive rear bumper.

        I might do some more tweaking to the shape, I had a very rough guess on how the rockers curve under but it's close enough to know that it works.

        A bit more progress, excuse my indulgence on colouring bits in!



        And this is the point I found a 1:32 scale model already existed! I didn't know to be happy or sad, but I got the kit just in case....

        Wheels next - resin casting an insert is possible but as a base some Penelope Pitlane wheels with Ninco classic tyres Fitted to the chassis. Time to check out clearance issues soon, full lean and full lock will make the tyre foul on the front fender

        Quote came back after a couple of days, I almost spat out my coffee when the e-mail arrived. The price was a bit steep, but by the time you add on delivery and VAT, it went from 110 to 150 for one set.

        Lunchtime was mostly spent sending it out to other companies, and eventually I settled on Materialise. You upload the CAD model and it generates a price on the screen. You can change the material, how many you want any surface finishes, and it spits out the price. From there you can pay just like any other site, it's very slick indeed.




        Doing all the parts separately was quite expensive, so I put them all together with thin support structures and the whole lot came out at just over the cost of the chassis on its own. There's no point making this if it's not affordable, so I'm quite pleased with the result so far, can't wait for it to arrive!
        Last edited by choc-ice; 03-27-2011, 05:27 AM.

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        • #5
          Oh man..! is anybody else seeing this ???
          You are doing some very cool things here
          I had no idea that it was possible to export a 3D model file to someone and they would build 1.
          Looking forward to seeing pictures of this in the flesh. Don't know if it will be fast but I don't think it will matter if it does what you are designing it to do

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          • #6
            This is pretty cool. Can't wait to hear / see how it works out.

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            • #7
              Amazing, cant wait to see the result of all your work.

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              • #8
                very very useful post! thank you...

                I have made similar beginnings in modelling bodies in SolidWorks - haven't gotten nearly as far as you have! Great work! I like your steering front end too....

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                • #9
                  Wow that is impressive !
                  Racer9

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                  • #10
                    Originally posted by mrossmassler View Post
                    I have made similar beginnings in modelling bodies in SolidWorks - haven't gotten nearly as far as you have! Great work! I like your steering front end too....
                    Let's see what you've done - get some pictures up!

                    EDIT: Just looked at the steering and suspension in your gallery - I'm very impressed



                    I had an e-mail through from the chassis supplier yesterday; some small ribs had broken, was this a problem?

                    I put the ribs in to hold the steering arm to the front crossmember and the chassis, just to support it all while the laser is sintering the material together. Once the chassis arrives I'd just snap it off anyway.


                    Nice to be told though and I can't wait for the parts to arrive! First job is to blow away the surface powder, then I'll get some paint on to seal the surface a little.
                    Last edited by choc-ice; 03-31-2011, 05:58 AM.

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                    • #11
                      This is really impressive...and yes..to quote from one of your posts.."BREAKTHROUGH" (for you..my computer skills rival my building from scartch skills, which are simliar to the Titantic's ability to stay afloat)

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                      • #12
                        All ready subscribed

                        I really like this chassis. Laser printed? Right. I have liked steerable cars since I first got into slots. Suspension to boot. An a cool body. What a package. It don't have to be fast but it don't look slow. Good luck and keep us posted.

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                        • #13
                          Originally posted by madmax16117 View Post
                          I really like this chassis. Laser printed? Right. I have liked steerable cars since I first got into slots. Suspension to boot. An a cool body. What a package. It don't have to be fast but it don't look slow. Good luck and keep us posted.
                          The chassis is SLS which is selective laser sintering. Good strength but the surface finish isn't good enough for a bodyshell, which is why that will be resin cast.

                          Parts arrived today, woo-hoo!

                          Or at least some parts arrived. The main chassis parts are there but still no axles, and no motor pod either so it looks like it fell out of the file during the translation. I'm just investigating where the error was made (mine or the supplier) but I'll get one ordered by Monday.

                          Want to see how it looks?


                          I've pulled the front crossmember out, gave a gentle cut with a scalpel and the steering linkage and front hub all came out nicely. The Scalextric guide blade is a snug fit so I'll open the hole up a little with a drill. The surface finish is quite powdery so it needs a paint, quick rub down then varnish to be smooth enough for one surface running over another.



                          The holes for the axles to allow the suspension to pivot are a bit snug, but I'd rather be able to gently file for clearance than have to glue bits in. Springs fit ok but seem a bit stiff, I'll hunt around for some softer ones for the full "wallowing in a corner" effect.

                          Tomorrow morning I'll get some paint on and see how the steering feels. Bodyshell is being prepared for moulding and I can't wait to see how the resin cast ones turn out

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                          • #14
                            Very awesome! Can't wait to see this thing fly around your track. Hope you can make a video and put it up on youtube. How cool would it be to have a whole library of 3d car models that anyone could download and "print" out at home???
                            -=Randy

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                            • #15
                              Tools outside, making the most of the sunshine. 3/32" brass to make the front stub axle and a die nut, and I'm not afraid to use them!

                              No 1mm rod so I can't make the steering link yet.


                              Here's the parts tied together temporarily

                              It's 3/32 rod that allows the front and rear axles to pivot, so they fit in standard bushes. The roll centre is at the same height for front and rear, which is where the roll centre would be for a real car like this with a solid rear axle.

                              But with only 3/32 I can make the motor end up. Axle in first, the support for the nylon bushes looks a bit feeble so I'll get some epoxy in there, and make a note to improve the next one. Wires soldered to the motor and it clicks firmly into place. Ask me why the wires are too short, go on, I dare you to ask me


                              Penelope Pitlane wheels and Ninco classic tyres give the right size for a typical '70s American sedan.

                              Springs on, it feels great but I'll only know if the rate is correct when I get the bodyshell on and get it on the track.


                              Tomorrow I hope the 1mm rod will arrive so I can pin the steering assembly together, then clip it in place.

                              Bodyshell should be done by the end of the week!

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