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3D Modelling A Slot Car - Dodge Monaco


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#1 choc-ice

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Posted 23 April 2011 - 06:09 PM

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.

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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 :angry:

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.
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I put some shape to the sides
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Then made it hollow (shelled), and put a few more features on
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Verdict? Looks awful!

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
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Now we'll put the roof in
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Now extrude the roof out to the side
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This isn't going anywhere..... it still looks rubbish.

Shall we see where the chassis bits go?
3D modelling a slot car - Dodge Monaco

#2 choc-ice

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Posted 23 April 2011 - 06:16 PM

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.
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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.
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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.

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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.
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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
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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.
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Want to see it lean in a corner? B)
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3D modelling a slot car - Dodge Monaco

#3 Mohawkk

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Posted 23 April 2011 - 06:45 PM

Very interesting cant wait to see the end result

Kai

Edited by Mohawkk, 23 April 2011 - 06:46 PM.

Love,
Kai Posted Image

#4 choc-ice

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Posted 23 April 2011 - 07:02 PM

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

Then I had a breakthrough! The 3D model worked without surfaces overlapping...
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This is the point I found a 1:32 model kit :unsure: Do I continue with the 3D model, get a rapid prototype made and go from there, or shortcut everything and use the model kit bodyshell instead? It would be quicker, cheaper, easier and a better finish.....

Then was a day on the phone ordering parts.

Penelope Pitlane wheels and tyres of the correct size - 20mm x 7mm. They'll take inserts so hopefully I can do something appropriate.
Rear axle
Mabuchi motor, I don't want too much speed at the moment!
Axle bushes, these are for the rear axle and to let the front and rear suspensions pivot
Bag of springs, suitable for 1970s American barges at 1:32 scale.

I tweaked the chassis to fit, narrowed the track to fix the front wheels fouling inside the fenders when turned, but I didn't want to order the chassis until I got the wheels, then I can check the offset.

Contact made with someone to resin cast the body, bribe allocated for someone to turn down the front stub axles so I can get a circlip on.

Then it was time to get the chassis quoted. The kind of rapid prototype technology I use means that all the parts get made in one go, you model the hub with half a millimetre of clearance from the steering arm and they easily break when the parts are made.

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.
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10 days later, the chassis arrived!
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Put some paint on, then gently rub it down. Here you can see the 3/32 axle front and rear of the motor pod that lets it pivit. The front crossmember has the same kind of thing, running in nylon bushes
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And in it all goes!
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Edited by choc-ice, 23 April 2011 - 07:03 PM.

3D modelling a slot car - Dodge Monaco

#5 choc-ice

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Posted 23 April 2011 - 07:10 PM

Then a day later, look what was waiting for me!
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After the pinion on my motor wasn't meshing properly I changed the motor, the wires on this one weren't long enough either so it's still got the eyelets from an old Scalextric car into the guide blade. On the track for the first time and..... nothing.

Fiddle around with the braids, still nothing. Back on the track and it farted into life, then nothing again. Turned out to be a break in the wire where it goes into the eyelet, so a dig into my box of dead cars found another wire. Onto the track and it works! The track isn't always making good contact so it's tricky to get a smooth lap in, but the first impressions are it's very easy to drift with those Ninco classic tyres.

The steering works well, it's not always easy to see in fast corners but you can really tell when you hang the tail out which is just the effect I was after. One advantage of the track contacts being a bit ropey is that it came out of a corner and the straight was dead, this is how it looked
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Body mounts on! These are resin so I cut them to length, drilled and mounted them to the chassis then blobbed some glue to hold them in place. Note the welding kit under the bench in case I need to take drastic action
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The glue has dried, so let's give it a go on the track. Steering right...
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And steering left. It's just like doing your driving test again
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Let's get the power down and see how long we can hold the tail out. Drifting around a right hander
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And around to the left. Yes, it's just like taking my driving test again
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I took these shots when the car is stationary; I'm not good enough to slide the car with my left hand, nor take a photo with it. And digital cameras take an indeterminate time between pressing the button and taking the picture.... However it looks like the car isn't leaning enough in a turn, you can hardly see it lean at all. Tomorrow I'll try some ballast and softer springs, until then I'll get some paint on!

This scrap shell was worthwhile to see where I could (and couldn't - look at that radiator grille!) take material out and the best way to get the flash resin off. I'll do a proper shell next.

Other things to do: sort out a way of mounting the police light bar, drill the back of the wheel centres and take a brave pill to get the windows out and try the glass in. There's no interior so I'll use translucent painted glass instead.

To get it leaning more I took the front springs out for some more track testing and with ballast it does roll, but not as much as I'd like. I think I need more clearance on the rear too, the front end can roll over 15 degrees but the rear will only do about 10.

Looks good when it rolls. All four wheels are on the ground here, that's just suspension movement.
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Comparing size with Starsky's Torino
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Hmmm, something's not right in this picture?
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Right up to date, prototype chassis number 2 arrived on Thursday, this has got more clearance around the hubs for better steering lock and it's made from ABS plastic done by a 3D printer. This gives much better surface finish so the hubs don't need any work (by me!) to get them smoother. However I could keep the cheaper SLS and use a nylon washer between hub and front crossmember instead...

The other advantage is all the holes come out at much tighter accuracy; the SLS chassis needed a drill run through to clean all the powder out but the ABS one is clean straight off the printer.
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I'm very impressed, but the cost is almost twice that of an SLS chassis. Worth doing to investigate the technology, and it gives me a second chassis to get testing.
3D modelling a slot car - Dodge Monaco

#6 BMR

    wheres the tape measure ?

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Posted 23 April 2011 - 07:41 PM

Wow - sorry I mean double wow wow , looks fantastic , you realise your probably gonna get bombarded with requests for all types of odd ball bodies that people want now .

Im looking forward to more , also interested to see how the chassis goes agaist the regular designs we all are used to seeing .

#7 eagleby flyer

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Posted 23 April 2011 - 10:22 PM

Did someone say requests ? Well I need one to chase Bo & luke around, a couple to chase the Bandit's Trans Am. Like the man said, WOW, awesome.

#8 kalbfellp

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Posted 23 April 2011 - 10:42 PM

Nice project But do tell us the cost if getting the chassis made on the 3d printer.

Edited by kalbfellp, 23 April 2011 - 10:46 PM.


#9 TJ_Tas

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Posted 23 April 2011 - 11:25 PM

Choc-Ice,

You and I are definitely treading the same ground. I have my own 3d printer on order which should be arriving soon. Its interesting to see that it is possible to do what I am working toward. Maybe when I get closer to my goals you and I can share some notes?. I've just got the rest of my setup together:- My Workshop!.

#10 choc-ice

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Posted 24 April 2011 - 01:54 AM

View PostBMR, on 23 April 2011 - 07:41 PM, said:

Wow - sorry I mean double wow wow , looks fantastic , you realise your probably gonna get bombarded with requests for all types of odd ball bodies that people want now .

Im looking forward to more , also interested to see how the chassis goes agaist the regular designs we all are used to seeing .
It's only got a Mabuchi 18000rpm motor and narrow Ninco classic tyres. Quick it's not, but a huge amount of fun to power slide around corners. I can almost hear the tyres screeching on dirt roads now :P


View Posteagleby flyer, on 23 April 2011 - 10:22 PM, said:

Did someone say requests ? Well I need one to chase Bo & luke around, a couple to chase the Bandit's Trans Am. Like the man said, WOW, awesome.
That's the kind of thing I had in mind!

View Postkalbfellp, on 23 April 2011 - 10:42 PM, said:

Nice project But do tell us the cost if getting the chassis made on the 3d printer.
If you already have a 3D printer (and that's around £18,000 or 28,000 Australian dollars - yikes!) then the cost is very reasonable, less than £10 or 15 Aus dollars per chassis. Unfortunately for those who don't have one and use an agency it's more like 3 or 4 times that. But ordering in quantities brings the price down a lot. Instead of making a dedicated chassis for the Dodge Monaco, I might do better making the chassis adjustable wheelbase, then I've got a chance to sell more so it's more affordable.

View PostTJ_Tas, on 23 April 2011 - 11:25 PM, said:

Choc-Ice,

You and I are definitely treading the same ground. I have my own 3d printer on order which should be arriving soon. Its interesting to see that it is possible to do what I am working toward. Maybe when I get closer to my goals you and I can share some notes?. I've just got the rest of my setup together:- My Workshop!.
Happy to share notes, as a design engineer I know lots, as a slot car designer I know very little, but I'm getting a thrill from the steep learning curve!

Edited by choc-ice, 24 April 2011 - 01:57 AM.

3D modelling a slot car - Dodge Monaco

#11 BMR

    wheres the tape measure ?

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Posted 24 April 2011 - 10:43 AM

Call that a workshop - not one Samantha Fox poster to be seen anywhere :lol:

Be a good idea if you can get a generic chassis working , even two or three chassis than can cover a wide range of bodies would keep the costs lower .

I was wondering about the way the chassis would handle with spring loaded front end , I would guess the spring tension will need a bit of playing around with - but there's another marketing aspect I suppose , sports suspension , cruise suspension ? How about a 63 chev impala with magnets that raise the body when the powers on but drop to just clear the track when the powers off :lol:

Cool concept , good luck with it all .

Steve

#12 Ember

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Posted 24 April 2011 - 10:47 AM

View PostBMR, on 24 April 2011 - 10:43 AM, said:

Call that a workshop - not one Samantha Fox poster to be seen anywhere :lol:
Gawd! That's a bit of carbon dating there.

Choc-ice, it'd be great if you can configure the body roll and steering into an adjustable chassis. Got a few kits of old American cruisers that would look really great with some proper wallow around corners.

Embs
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#13 inveterate retiree

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Posted 24 April 2011 - 01:44 PM

Thanks Choc-ice.

This thread has been a real education, for me at least.

I look forward with great interest to see just what comes out of your design & production endeavours.

I used to be surprised that I was still surprised by my own stupidity, finding it strangely refreshing.
Well I don't now.
I'm over it!

Photos of my track in progress.


#14 choc-ice

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Posted 24 April 2011 - 06:08 PM

View PostBMR, on 24 April 2011 - 10:43 AM, said:

Be a good idea if you can get a generic chassis working , even two or three chassis than can cover a wide range of bodies would keep the costs lower .
I think you're right, I'm coming around to the idea of making the chassis adjustable.

View PostBMR, on 24 April 2011 - 10:43 AM, said:

I was wondering about the way the chassis would handle with spring loaded front end , I would guess the spring tension will need a bit of playing around with
It zips around the track really well, I've no idea how it compares to race car handling but that's not what it's for. It's to make something that's really easy to drift with authentic wallowing in the corners :P

View PostBMR, on 24 April 2011 - 10:43 AM, said:

- but there's another marketing aspect I suppose , sports suspension , cruise suspension ? How about a 63 chev impala with magnets that raise the body when the powers on but drop to just clear the track when the powers off :lol:
The sports suspension should be easy to do, but the hydraulics effect is a lot more trouble than I can do! My suspension only lets the car roll, not lift. To make it lift would probably need ball joints rather than just pivots...

View PostEmber, on 24 April 2011 - 10:47 AM, said:

Choc-ice, it'd be great if you can configure the body roll and steering into an adjustable chassis. Got a few kits of old American cruisers that would look really great with some proper wallow around corners.
If you can do a quick measure of the wheelbases, that would be great. With the motor in line, there's only so short I can go on this chassis. Otherwise I'll have to do a sidewinder which might not be as easy to corner Hollywood-style
3D modelling a slot car - Dodge Monaco

#15 Ember

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Posted 24 April 2011 - 07:41 PM

View Postchoc-ice, on 24 April 2011 - 06:08 PM, said:

View PostEmber, on 24 April 2011 - 10:47 AM, said:

Choc-ice, it'd be great if you can configure the body roll and steering into an adjustable chassis. Got a few kits of old American cruisers that would look really great with some proper wallow around corners.
If you can do a quick measure of the wheelbases, that would be great. With the motor in line, there's only so short I can go on this chassis. Otherwise I'll have to do a sidewinder which might not be as easy to corner Hollywood-style
Will run the verniers over them in daylight on the morrow.
Computers. They'll never catch on.

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#16 choc-ice

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Posted 24 April 2011 - 07:54 PM

Cool, thanks!

The Dodge is about 88mm wheelbase, and I can reduce that to perhaps 73mm but no smaller.

The chassis is 41mm wide so hopefully narrow enough to fit under any bodyshell, the track (centre of left wheel to centre of right wheel) is 47mm. Wider is ok, but narrower is difficult because of the front crossmember.

I'd be interested to see how it fits under a selection of typical shells
3D modelling a slot car - Dodge Monaco

#17 Ember

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Posted 24 April 2011 - 08:28 PM

Given the selection I had in mind include an Impala, a T'bird, a Fairlane Skyliner and a Bel Air I don't think reduction of the wheel base will be at issue.
Computers. They'll never catch on.

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#18 TJ_Tas

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Posted 24 April 2011 - 10:31 PM

You probably want to take note of the size of the wheel wells. With the steering you may run into problems with rubbing/binding.

#19 choc-ice

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Posted 08 May 2011 - 06:49 AM

Thanks to ember for the measurements, I've now got an adjustable chassis designed. In other news I've spent the last couple of weeks getting things wrong. After brush painting the bumpers, lights and grille it looked awful so I cleaned the paint off and sprayed it. Then I applied some Maskol fluid and sprayed white over the whole shell. What I should have done is thrown the Maskol fluid as far as I could, possibly with a run-up. So I took the paint back again, sprayed the front and rear silver again and used Tamiya masking tape. That looks much better.

Other things I got wrong, I thought I could keep the resin windows in place like some of the Scalextric cars do, this would keep the shell stronger, save me a stack of work and hide the fact there's no interior. Wrong. So I took the resin out and I'm starting to put the vac formed windows in place. If anyone knows where I can get a roughly-Rosco shaped figure to put in the driving seat I'd love to hear from you.

Finally I got the springs wrong. I had a great idea to use plastic leaf springs because the coils I'd used were too strong. I then found some weaker coil springs which turned out to be very similar to the ones I had a couple of weeks ago! But then some good news, I realised I could soften the springs by moving them inboard; closer to the centre pivot. This afternoon I've been busy filing off the existing spring mounts and fitting new ones.

Pendle came up with the goods for another set of parts so as we stand right now the glue is just drying so hopefully by tomorrow I can have car number 2 on the track with its soft suspension and prove the leaning works. The steering is as before (with some extra clearance) and I'm happy that works.

If it's all good, I can finalise the design changes I've made to the chassis which are:
1. Make the motor pod have better clips for the bearings
2. Change the motor mounts to make it easier to remove the motor
3. Move the springs inboard
4. Add clearance around the axle gear
5. Make the motor pod a little longer because the datasheet I used from Mabuchi has a different shaft to all the slot car motors
6. Make the wheelbase adjustable
7 to 25 just loads of other stuff. Not bad for something that worked ok first time out....

Want to see some pics?

The resin parts including windows
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Front axle built up, rear axle built up

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Possibly a better view of the improved paint masking, but maybe not. At least it shows the running gear progressed and better wire for the motor!
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3D modelling a slot car - Dodge Monaco

#20 choc-ice

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Posted 11 May 2011 - 08:12 AM

Well..... I'm not too happy with the height of the guide blade and the steering needs a little work to smooth it out but it definitely works cool.gif

Looks like the new springs and spring mounts allow for lots of travel. Citroen 2CV owners would be intimidated by this amount of lean


Axle tramp - we don't want no stinking traction here, we want a live axle trying to jump out of the car. Amazingly you can't sense the axle moving when you drive, but it does show how soft the springs are

3D modelling a slot car - Dodge Monaco





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