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Discussion Starter · #1 ·
This is a guide to how I built my 3DP popsicle chassis. It's aimed at the complete beginner to 3D design and Windows 10 users (sorry Apple fans)

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This is to show that you don't need lots of drawing or CAD skills to be able to produce useful, but simple, designs for 3D printing and that you shouldn't be put of having a go.

When I bought my first 3D printer, I had no idea what I would do with it and treated the purchase more like buying an expansive man toy. I certainly had no thoughts about designing my own objects for printing, my drawing skills are still very basic and at the time I had no desire to learn to use a CAD program.

Over time I have printed a few things with the printer but never made full use of it. Over time the range of available slot car items that can be down loaded and printed has grown considerably and II started to down load any suitable chassis I could find and the odd body but I had the need for a simple chassis that would be adjustable in wheelbase and also width, I also wanted it to take any motor type and have adjustable mounting points. I have I have a few PCS and MRRC adjustable chassis that meet the first two requirements and even a few Revell Ladder chassis the meet the first one but none of these allow for the other options. While browsing the forum an article was posted that included a popsicle stick chassis and I realised that it should be possible to make a plastic printable version that would be fairly simple to adjust as required and meet all four of the above requirements.

So, let's build a simple chassis. First let me say that this is aimed at Windows 10 users as I don't know if any similar software is available for Apple users, although you should be able to do this using many of the free CAD software.

To follow along you will need Windows 3D Builder.

A basic popsicle stick chassis just two rectangular sticks held apart with cross braises that hold the motor and guide flag in place, so where do we start?

The most important thing to remember, to simplify construction is to keep the centre of the rear axle on 0 for its X axis and the centre line of the chassis and motor on 0 for its Y axis. With this in mind we will start with the rear axle as all other parts are measure front the centre of the rear axle. Insert a cylinder and rotate in to 90º roll, the diameter isn't that important at the moment and can be set to either that of your axle or a bearing. My rear axle is set to a X and Y measurement of 5.2mm, which on my printer gives a good push fit for the bearing.

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The next thing we need is two chassis side members, these are mad from a cube so insert a cube or if you want rounded end to the chassis use the custom option. You can adjust any of these measurements to suit your own requirements. If using the custom option, the only change is to set the roundness to two and then add, the starting measurements are X=70, Y=2.8 and Z=10. The under the object menu select settle for the side bar. At this point change the Z position of the rear axle to 5mm so it is in the middle of the side bar.

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A couple of points to remember. At the end of each process use the deselect circle in the right-hand selection menu, just to be safe. All changes to position are based on the centre of the object selected. All changes to the size of the object will keep it centred on the same point. If you make a mistake just undo it.

We now need to position the side member in relation to the rear axle and we need a rear overhang of about 10mm, you can adjust this later to suit your crown gear and body. The new X position for the side bar is 35, half the side bar length less the over hang of 10 and less half the axle diameter 2.6 which is 22.4, which we can round down to 22.

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I find it easier to colour code parts as I build the chassis to make it easier to know what parts linked and I use red for parts that will later be removed.

The side bar now needs positioning relative to the centre line and for this you need to know the width of you motor. The centre of your motor will be on the Y=0 so the side bar needs to be at Y=0 plus half the motor width plus some clearance, say 0.5mm, plus half the width of the side bar, 1.4, which for me is 11.5mm. Change the side bar Y to 11.5mm. We can now make and position the second side bar, with the side bar only selected from the object menu select duplicate and set the new side bars position to the same X and Z as the first and the Y to the same but negative value, in my case -11.5.

As long as the we have an identical positive and negative value for these parts anything on Z=0 will be in the centre.

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Using the required wheelbase, we can place the front axle. I use a diameter of 2.65 for the front axle so it's position will be the wheelbase, say 68mm, less half the rear axle diameter, 2.6mm, less half the front axle diameter 1.32 which is 64.08. You can duplicate the rear axle and change its X and Y dimensions to both be 2.65. then set its X location to 64.08 and here you will notice a problem in that the axle is in front of the chassis, this isn't a problem as we need to duplicate the side bars so we can extend the chassis and at the same time make it wider. Select just the two side bars and duplicate them. Now click so that you can see them paint them a different colour, say black. Then drag them to the right, using the green arrow until the rear is just past the rear axle.

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We need top make these bars further apart so select the top bar and add 2.5mm to its Y position and make the front bar thew same negative value. This gives an overlap of about 0.3mm at the join of the bars.

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Discussion Starter · #2 ·
To add some strength to the chassis and as a body mount fixing point, we will add a block to the rear of the chassis. Insert a cube with a X dimension of 3, a Z equal to the side bars, you can leave the Y for now. Settle the block and drag it the rear of the chassis. With the block selected you can now set the width, Y, click on the dimension icon and then on the Y dimension, the Y arrows will turn green. Using each arrow in turn resize the block so that a little bit of each side bar can be seen.

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Duplicate this block and move it to the front end of the grey side bars and drag the ends out so it is inserted in to the black side bars. This block can be removed or moved it required later.

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Discussion Starter · #3 ·
Next, we need to think about the motor brackets. These can just be open at the top so the motor clips in but tolerance need to be good so I prefer a two-part bracket.

Duplicate the rear block and change its colour. For the moment we are going to set the motor along the centre line of the chassis height, which is what the axles are set at. You now need to take some measurements from your motor, you will need to measure the outside diameter of the bearings at both ends and the distance from the motor body to the end of the pinion shaft. Using this last measurement, we will position the rear motor bracket. The X position for this will be this measurement lest 1.5, being half the width of the block, we are using plus half the diameter of the crown gear where it meets the pinion shaft plus some clearance, say 1mm, in my case this is 13.5mm. Now change the Z dimension to half the side bar height less 0.5mm and settle the block.

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Duplicate this block and set it X position to the first motor bracket plus the length of your motor plus 3mm, the thickness of the bracket, plus a little clearance, say 0.5mm, in my case this 42.5mm.

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Discussion Starter · #4 ·
Before we add the top brackets, we will make the motor bearing cut outs and do a test print. Insert a cylinder and give it a colour and rotate it on the pitch by 90º.. Set its Y and X diameters to the diameter, it's been rotated so the Z is now the X, of the motors rear bearing plus a little bit for clearance, for me 10.0mm. Set it's x position to that of the rear motor bracket and its Z to that of the axles. Duplicate this bar and resize to the front motor bearing plus a little clearance and position it over the front bracket lit the rear one.

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If you look at the model you will see a little problem at this point in that the rear motor bracket will have no thickness at the bottom when we remove the bar so select both bars, both brackets and both axles and add about 1mm to the Z height, 6 in my case.

We can now do a test print but first we need to change a couple of bits. Make sure you have saved the model. If you have some single flange bearing you can leave the rear axle as it is otherwise change the rear axle diameter to match the front axle. From the edit menu select the rear axle and subtract it then do the same for the front axle and both the motor bars, you will need to deselect all then select the item to remove. Save this as a STL file and the you can slice and print the model, I do this with 5% fill on a course print setting and you will need supports for the motor brackets.

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to be continued...
 

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Discussion Starter · #6 ·
Having done you test print check that everything fits. The rear flange bearings should be a tight snap fit, I have to use a pair of pliers to get them snapped in. the front axle should be fee but not loose. The motor should fit fully in the brackets and be able to rotate very slightly. If anything is wrong make any adjustments and do another test print, repeating as required.
 

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That's very kind of you to give up so much time. 3D Builder is great for quickly throwing shapes together, adding/subtracting, hollowing and to some extent smoothing...it can hang forever if you're importing files but for an intro to 3D modelling it's surprisingly useful.
 

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Discussion Starter · #8 · (Edited by Moderator)
If you have got this far, I will assume that everything is now fitting.

Now select the rear motor bracket and duplicate it, colour it the same as your axles. Then give it the same X location as the rear motor bracket, then lift it up until it's top is level with the top of the chassis sides. Repeat this for the front motor bracket.

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Select both top motor brackets and click the dimensions icon and using the top Z arrows raise the top of the brackets slightly above the chassis sides.

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Select one of the motor brackets and duplicate it. Change its Z height to 2.5mm. Change its Z position to your chassis side height plus 1.3mm and set the X position to the same as one of the motor brackets. Clear all selections and then select both inner chassis sides, note their Y dimension, this will be from the outer edges and set the y dimension of the last part we made to this value. Duplicate this piece and place over the other motor bracket.

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Insert a cylinder and resize it to X=2, Y=2 and Z=10. Then place this at the same X as one of the motor brackets parts. Select both pieces of the chassis on one side and note the Y position, then set this to the same for the pin we have just made and then lower the pin until just a little bit is above the motor brackets.

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Duplicate this pin and set to the same X position and opposite Y value (+/-). Then select both of these pins and duplicate then change the X position to that of the other motor bracket.

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Now select all four of the pins and duplicate, change their colour so you can easily see. Select each pin in turn changing their dimensions to X=5, Y=5. Now select all four original pins and note the X location and the select only the four new pins and change the X location to match.

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With all four still selected change the Z height to 2.5 and the Z position to your chassis height plus 1.25. It should now look like the following picture. Change the colour of all these eight parts to the colour of your axles. That completes the motor brackets.

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Discussion Starter · #10 ·
From this point onward there are different options available for mounting the guide and for the location of body mounting points.

We'll start with the guide flag and will first use a standard clip-in guide. We will build the guide bracket at the bottom of the chassis as it is easier this way but it's height can be adjusted later. Select and duplicate the front crossmember and move this to the front of the chassis and change its height to 3mm and settle. To add a little bit of extra strength to the front of the chassis I also have a plate at the front of the chassis, duplicate the bar you have just made and resize to X=7mm and Z=2mm and place it under the front bar and level with the front of it. You can resize this plate as required, the thickness is controlled by the front axle height and you can stretch it back all the way to the front motor bracket if you want.

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Now select one of the round disks and pins on a motor bracket and duplicate them. Select just the outer disk and resize the X and Y both to 6.5mm and Z=3.0 then set the Y location to 0 and settle. I would also change the colour to match the bars at the front of the chassis. Select the pin and resize the X and Y to about 4.1mm, you may need to adjust this depending on you printer but if it is too small it's quite easy to enlarge the hole this will make with a round file later. Finally change the Y location to 0 and move the pin down so it projects under the chassis, this will insure you have a clear hole when it's removed. Select both parts and move back on the X axis until the pin just touches the front bar.

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Let's now add some mounting points. The simplest to add use normal body mounting posts. Select and duplicate the bottom bar at the front of the chassis and slide this to the rear of the chassis but leave it slightly under the chassis. Change the Z thickness to 2.5 or 3mm. The X and Y dimension need to adjusted to match your body and over lap the rear body posts.

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Select and duplicate the guide flag pin and drag to the required position for one of the rear body mounts and resize the X and Y to just give some clearance for the screws you will be using. Now duplicate this post and the Y location to the opposite value (+/-) and same X value.

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You can adjust the height of the mounting bracket as required, just select both posts and the bar and move up as required. If you just need one screw hole just place it on the centre line. With all three parts selected duplicate them and move to where you need the front bracket and again move or delete the pins to match the body mounting posts. You may need to move or remove the crossbar at the front of the chassis.

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Your basic build is complete so save this as your master file. This file can be use to make any size chassis with any wheel base and can use any motor, JUST NEVER MOVE THE X LOCATION OF THE REAR AXLE as all measurements are taken from the centre of the rear axle. We will look at making changes to the wheelbase, motor, guide and mounting points later but first there is one thing we need to do.
 

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Discussion Starter · #11 ·
Select all six top parts of both motor brackets and duplicate them and move to the side of the chassis. Now rotate these on the roll by 180 º.

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Select each pin one at a time and subtract them. Then select all four remaining parts of one bracket top and settle it and repeat for the other bracket.

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Now select the large top part of each bracket and change the Y dimension to be about 1 or 2 mm smaller than the width of your motor. This will allow the top parts of the motor brackets to fit inside the chassis over the bottom bracket.

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I normally print these brackets as separate items as I find they print better with a brim and set the infill at 100% were as I print the chassis with 75 or 80% and supports but no surround. Just delete all the main chassis parts and save a separate file for the brackets.

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You need to do this last step for every change you make to the motor brackets which is why it's the last part you do.

To print the chassis, we now subtract the following parts. The rear screw pins, rear axle, all four motor bracket pins, the front screw pin(s), guide flag pin, front axle and both the bars in the motor brackets so it should look like the below picture.

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You can now delete all the upper motor brackets parts. The chassis is now ready to be printed.

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Once printed the motor is held in place by screwing the top brackets to the chassis.

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This is the chassis in its simplest form, if there is interest I can show how to add adjustable front axle brackets and other types of mounting brackets and pick-ups.
 

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Discussion Starter · #13 ·
I tend to save the file every time I make a change, on the original build I had over 30 files and again over 30 file when I adapted it to fit the Super Shells Ferrari 156. It was about the same when changing it to fit the Airfix Beetle body, the latest for the Alpine is only about 10 as most of the work was already done. Change and save is my moto.
 

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I have several TinkerCAD files set up the same way.... multiple iterations I have used for various cars. It's easier to move guide and body mounts that way, and narrow cars or those with short nose profiles present those challenges.
Sometimes it's easier to print what you need rather than cut/glue what is already available.
 

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Discussion Starter · #16 ·
When I first designed the chassis it had bars for attaching to the sides of the chassis and my Beetle version has pans on the side and are both simple additions to the basic design.

This is where we have got to with a fully working chassis.

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The original mounting I had was a simple pair of bars across the chassis. To add these, insert a cube and resize to Z=3, X=6 and Y to what suits your body, then settle the bar and move to the required position on the chassis. The duplicate the piece and move to the second required location. In this form you will need to avoid the motor bay, although they can go under the motor brackets.

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An alternative is to add four shorter bars that are built in to the sides of the chassis as these can be placed anywhere along the chassis

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For the screw holes just duplicate one of the other screw hole pins and drag to the required position in one of the bars and then keep duplicating and dragging.

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The other side mounting option as I used for the Beetle chassis is based on the above but with rectangular plate each side. For this you insert a cube and resize Z to a thickness of 2-3mm as required, the X and Y dimensions will need to be adjusted to suit the body you are using. When making any adjustments to the side pans make sure you have both selected the they will both be the same. The Y dimension when both are selected will be the overall outside width of both parts so this can be set to match the inside of you body less a little clearance.

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The hight of these pans can also be adjusted to be anywhere up the chassis sides, just select all the screw hole pins and both pans and drag up to the required position. This also applies to the bars above.

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If the screws need to be close to the chassis sides you can add an extra cylinder around the pins to give clearance for the screw head. To do this select all screw pins and drag the tops above the top of the chassis. Then duplicate them with all the pins still selected. Now select one of these new pins at a time and change the X and Y dimensions be slightly bigger than your screw head. Then select all four of the original pins and note the X and Y location of them. Deselect these and reselect all four of the new ones. I would change the colour of these so you can see them easier and then change their Z height to 10mm or whatever your chassis height is. Now set their X and Y locations to what you noted earlier for the original pins. This should place then around the original pins. With all four of these sleeves still selected drag them up and down until they are just touching the side pans and then reduce the Z location by small amount but no more than 0.1mm.

When subtracting these parts remove the smaller pin first and then the sleeve, this will leave hole in the pan and a groove down the side of the chassis.

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When using these methods you can remove the mounting points from the back and front of the chassis if required but thew front on does and extra strength and a little weight to the front of the chassis so you can just remove the pin. These parts are removed just by deleting not by subtraction.
 

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Ok, so let's make the chassis a little more versatile and add an adjustable front axle.

I'll start again with our basic chassis.

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Select and duplicate the front axle, give it the same X location and set Y to 7.5. Then repeat this setting the Z location to 2.5.

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Select the two front motor mount screw pins and set their X location to the same as the front axles. The select each one individual and set the Y value to match the front chassis sides. Then select the size icon and with both pins selected drag the bottoms down until the come out below the chassis.

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Insert a cylinder and paint it a different colour the size it X=5, Y=5 and Z=12. Give this the same X and Y location as one of the axle ins and settle it. Repeat this for the other side.

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Now insert a cube and size it X=2.5, Y=7.5 and Z=5 and paint it a different colour to the other front axle parts. Give it the same X and Z location as the middle axle and the same Y as the axle screw pin or front chassis side and repeat for the other side.

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When you come to subtract these parts you need to be careful or the program will hang for ages. First select both screw pins and with the dimension icon selected drag the bottom of them up until above the axles. Then delete, don't subtract, the middle axle, then select each block and subtract them and then you can subtract each axle. Once all these parts are gone you can drag the screw pin bottoms back down below the bottom a of the chassis and subtract them to leave.

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The little bits that may appear to be left behind don't print out.

If you want a smaller movement range just adjust the position of the top and bottom axles and the size of the blocks or you could just use two axles
 

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