3D Printed RC Tank Car, Apocalypse Style!

Intro, please read to understand a lot of the weird choices I made!

There is a good chance that you are reading this from some form of world-wide pandemic-induced lockdown, which is exactly the situation I found myself in when I built it, and played a large part in both the inspiration and techniques I used to build it.

I have always prided myself in releasing projects that are easy to print, easy to assemble and easy to source the exact parts for, this project is not one of those, but it is special in it's own way.

Now that I plan to share all of my projects I seldom start printing until the design is 100% complete in CAD and I know it is all going to work, which has its merits, but one loses some of the spontaneity of going into the shed and bash something together, one piece at a time, using whatever parts are on hand and without a clear plan in mind.

This project was a challenge to myself to let all of that go and just start building. I used bits of metal you won't have, I used laundry pegs in the electronics, an unreleased body file, and tracks from a previous project, but I hope it will be a challenge to you too to take the editable parts I will share, and create something awesome and unique to you!

Yours will be different to mine, but that's the whole point, and I hope that I will lure you in to learning a bit of Fusion360 along the way! This Instructable assumes a basic knowledge of Fusion360, but I like to think that since I am giving you a bunch of EDITABLE fusion files, some tips on how to use them, and hopefully a dose of inspiration, it will be a great opportunity to learn on an exciting project without it being too intimidating.

If you do build one, all I ask is that you credit the source so that other people can find it and get involved, and that you please tag me somehow so I can see your build, because that's the best part about sharing!

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A complete part list is not really applicable here, since the whole theme is adapting to and overcoming shortages and allowing that to spur your creativity, resulting in a unique build, but I will list what I used, which hopefully will get your brain churning!

Tools

• 3D Printer (I used the CraftBot+ for the body and the Sindoh DP200 for the tracks)
• Screw Drivers/Allen Keys
• Soldering Iron (Probably)
• Drill (Probably)
• Files (For fixing mistakes)

Software

• Autodesk Fusion360

3D Files

I used a number of files modified from my previous builds,

• Tank Tracks adapted from my DieselPunk Tractor
• Chevrolet Suburban Panelvan from an old commission

These will be discussed more in the next step! Including editable files of all of the track parts and more.

Electronics

• Receiver and Transmitter (2CH or more, I used my old Flysky)
• 1/10 Scale Brushed ESC (I used an old one I had lying about)
• 1/16 Tank Gearboxes and Motors (x2)
• Scrap Wire
• Battery (2S, 1800mAh)
• 1/10 Servo
• Laundry Pegs (yep, you'll have to read the steering step)
• ESS One Sound Module

Hardware & Materials

• Filament (I used rigid.ink PETG, and DavinciLabZA PLA mostly)
• Screws (I used a lot of M3 and M5)
• 11x5x4mm Bearings (or just print bushings - see step)
• Hot Glue
• Super Glue

Finishing

• Sandpaper (80/100/200 grit)
• Rustoleum 2X Ultra Cover
• Various Acrylics
• Sponges and Brushes
• Coarse Salt
• M1.6 and M1.4 Screws for Detailing (glasses screws)

The body that I used is a 1957 Chevrolet Suburban panel van which I designed as a commission for a friend who prints and sells bodies for RC crawlers. I printed myself a test version over 2 years ago, painted it up and kind of forgot about it.

Sadly since it was an exclusive commission I cannot share the file, but that would be boring anyway, I want to encourage you to make your own crazy post apocalyptic ride!

You could:

• Search for a suitable body on Thingiverse or MyMiniFactory
• Use my Jeep
• Use my '32 Hot Rod

• Design your own!

But why not:

• Start with my EDITABLE '32 Panel Van Fusion360 project and go bananas, make Max Rockatansky proud by re-purposing these digital scraps into an awesome road warrior's ride!
• I have also made available all of the track parts and other assorted pieces that I designed for this project
• Download the archive here (attached to this step)
• View online (and open for editing) here

I wanted to give you a head start towards creating something, so I have compiled my various editable parts, including tracks, wheels, axles and even the whole panel van as an editable Fusion 360 assembly that you can play around with.

All it needs is a chassis and something in the front. Due to how the body narrows I think it would look great as a half-track, who's up to the challenge?

As we follow through this Instructable on how I completed my own scrapyard build I hope to equip you with ideas and tools to complete your own, no mattery which route you take.

The design of a track is not trivial, and perhaps too much to go into in depth here, but it is also quite intuitive once you start playing with it, so I have provided a Fusion design in the project which demonstrates how I did it. I'll step through the basics of it here.

Core Parameters

As usual I begin by defining the core parameters. I have defined all of the variables that I will use to create a parametric sketch which defines a wheel that accepts a certain number of track segments of a certain size.

This will look complicated from this static image but if you open the file, navigate to the first two sketches and begin playing with the parameters it should make a fair amount of sense.

Since we know the length of a track segment and the number of segments in a wheel we can use that to drive the diameter of the wheel (the angle of each segment equals (360/num segments)). The images in the gallery are annotated with notes for more detail too.

Note the clearance between the teeth and the track in the wheel below.

The profile is extruded here into a single segment of the wheel (and a revolved cut was used to make the groove down the middle).

A circular pattern (defined by the "Num Segments" parameter) creates the rest of the wheel, which can then be mirrored to complete it.

Printing Considerations

I knew well enough from my previous tracked builds that cleaning up track segments gets boring really fast, so I was adamant that I would avoid supports. Each track piece prints in the orientation shown below.

By sectioning the segment you can see that there are no overhangs greater than 45 degrees, so the print will be easily achived.

Cleanup

Unfortunately there is not much to say about the assembly of the tracks except that it takes a long time!

A good pair of flush cutters and a sharp blade will help to clean up the prints, and a 1.8mm drill or small needle file will help clean out any imperfect holes.

Assembly

Find yourself something boring to watch (I chose our President Cyril's national address during the Covid19 Lockdown) and start cleaning and assembling links. Each link is held together with a short segment of 3D printer filament.

Once the tracks are assembled you can use a soldering iron to press the filament pins flat on both ends, forming a rivet of sorts. I prefer PETG or PLA for the pins, since the ABS smells like cancer when you heat it up.

The design of the roller wheels is very simple after the drive wheels, so long as the groove in the center is correct then all will be well. I thought it worth pointing out some other design choices that I made though.

Bearings

The roller wheels accept 11x5x4mm bearings which are very common in RC cars and I had quite a few of. Remember to make the recesses for the bearings slightly oversized (I used 11.3mm holes) since printers usually produce slightly undersized holes. More about these in the "Making Do" step

Halves

The wheel is printed in two halves, which means that I can hide the bearings inside, as well as the head of the M5 bolt. This was primarily because I didn't have enough M5 bolts with the same heads. The two halves also make it very easy to print without support material.

Assembly

The two halves are assembled with M3 screws. Once again I was using up my stock fasteners and didn't want to run out so I gave myself as many options as possible. There is a recess for an M3 nut in the rear of each screw hole, but I also undersized the hole in the rear piece so that the M3 screw can tap into the plastic directly and make do without the nut (for a limited number of assemblies anyway).

Now this step is going to come down to the body that you have chosen, or designed, but I have a few recommendations

Filament Plastic Choice

I recommend PETG (I used rigid.ink clear PETG for this body)

• It's lack of warp makes it much easier than ABS for the large thin pieces that usually form a 1:10 car body.
• Layer adhesion is excellent, making for a strong print
• It is slightly flexible
• It will not warp in the sun

However, don't let that stop you, as long as you understand your materials, just go ahead and use whatever you are comfortable with.

PLA will be the easiest to print cleanly, and ABS offers interesting options for vapor smoothing and acetone bonding.

Filament Colour Choice

I strongly recommend a clear colour if you are going to paint it, since scratches will not show up much at all, failing that, I would go for a neutral silver/grey/black/brown, but preferably stay away from bright colours, since the paint will get scratced up in use.

The only time I use a colour by choice is if I can match the final paint colour in filament, which then provides the same scratch protection.

Print Settings

Strength is mostly obtained through the number of perimeters (assuming optimal print settings, so make sure you are printing hot enough to get great bonds too), so I usually use at least 4 perimeters.

These are big prints, so I use 0.2mm layers with a 0.4mm nozzle. You will be tempted to up the speed or lower the quality but don't do it, you will regret it! Printing time is much less work than sanding and body-filling, so don't skimp on it.

Prep the Surface

There are many ways to tackle the paint process, but this is how I did mine

1. Sanding (80 - 200 grit)
2. Sanding
3. Body Filler (or thick ABS slurry poured into gaps in a pinch)
4. Sanding
5. Cursing
6. Repeat previous steps until your desire to be finished outweighs your desire for perfection

Once you are happy that you have a smooth surface, and you have sworn to yourself that next time you will use slower, higher quality, print settings, you are ready for paint.

Paint - Rusty Patina Style

1. A primer coat is a good idea, I prefer to use Rustoleum 2X Ultra Cover, in this case, a tan colour
2. I then used a dark coat of generic matte black, it would have been best to just use a dark primer and skip this but my plans were... fluid
3. Now for the fun bit, find all of the different acrylic browns, burnt siennas, umbers, and assorted other rust colours that you have and squeeze big blobs onto a board. Apply generously and completely with a dabbing motion of a sponge or even a cloth (don't wipe) swapping between colours a lot. Eventually it will look like a loaf of bread. This is fine.
4. Think about the areas that you think will be rusty (I chose the roof, hood, and some of the side panels) and wet them with water, the generously pour coarse salt onto these areas (I mixed in some fine salt too).
5. Once the water has dried, spray your top coats over the salt, making sure to get good coverage, a few coats if needed, before scraping the salt away, exposing your lovely patina'd rust beneath. I used a baby-blue Rustoleum 2X Ultra Cover for this too.

You can see me using the acrylic rust effect in this video of my DieselPunk Crawler, from about 3:30

The first requirement after the body is the chassis. How will we mount everything together?

Of course you can print the whole thing, but chances are you can find some scrap lengths of metal which will do the job much quicker, with some small printed braces to hold them together.

I happened to have a few lengths of u-shaped aluminium from some old rack-mountable telecoms equipment which is disassembled many moons ago.

Parameter Based Sketches

Wherever possible I try to define the most important (and likely to change) aspects of my designs as parameters (look under the "MODIFY", "change parameters" menu in F360, this makes it easy to change them at a later stage and is especially good for reusing generic parts.

A simple example is my "Rear Freewheel Mount" which you can see in the attached gallery or in the Online viewer here: https://a360.co/3gp54u2

The 1/16 Tank gearboxes that I used had a mess of mounting holes, with no discernible pattern. I decided that the easiest way to mount them would be to print a spacer which picked up the various holes and gave me four nicely spaced mounting holes which I could attach to the frame. I had visions of using a TPU spacer to reduce the noise, but never got around to that.

The most interesting part of this step is the measurements. I scanned the base of the plate with a regular 2D scanner and then use it as a reference canvas in Fusion360, I'll explain the process a little further here.

Scan

First I scanned the mounting plates along with a ruler on a flatbed scanner. It doesn't really matter what you use, as long as you have an object with one known dimension lying flat on the scanner.

Import

In Fusion you can go to the "INSERT" menu and hit the "Canvas" button to insert an image on the selected plan as a canvas.

Calibrate

Right click on the canvas in the list and select "Calibrate"

Now its time to use that object of known length in your image, in my case it was the ruler, simply click on the two points and type in the distance between them, the image will be scaled perfectly. Magic!

Model

Now it's as simple as using the regular sketching and modelling tools to complete your object. Often, but not always, you will then discover the original designers intent, expect dimensions to be clean multiples/fractions of millimeters (or inches).

On a normal project I would redesign and reprint a part that is not exactly right, but this project is unique, no one is going to build exactly the same thing as me (or you) so if you can make a piece usable with judicious application of cutting and gluing then go for it!

I trimmed, cut and drilled parts with my great grandfather's old hand tools, a wonderful convergence of technology separated by almost 100 years, and after assembly no one will be the wiser except me (and I appreciate the layers of story it adds to this build).

If you find that you have made a screw hole too small (or haven't made one), then drilling it out to size can work, but so can pressing the screw right into the plastic with a hot soldering iron.

Traditional RC Tank Steering via Mixing

Steering an RC tank with two electronic motors is usually achieved with one Electronic Speed Controller (ESC) for each motor. The transmitter (or some receivers) handles the mixing of the channels so that the relative speed and direction of each motor can be used to drive and steer the tank.

Below is a simplified diagram which shows how the control signal from the transmitter is received, then remapped to a control signal for each motor.

This traditional solution has some benefits, such as zero-point turns where one track is moving forwards and the other backwards, but it also has some disadvantages, such as requiring two ESCs and a method of mixing the channels.

Simplified Electromechanical Steering

I didn't have two ESCs available during our Pandemic Lockdown and couldn't get more so I had to come up with a solution. It came to me that I could use one ESC to control the speed of both motors and simply use a servo to actuate a switch, cutting current to one motor, which would result in steering action.

The disadvantage to this is that our hardest turn will be one motor on and the other off, no zero-point turns. The advantage to this system is that it is cheap and easy to use. There is no mixing required so the most basic two channel transmitter will do.

Implementation

Now this is all good in theory, but how to we break the current to a motor with a servo? One might think of a small normally-closed pushbutton but it is very likely to fail after a short while since switching relatively large DC currents causes a lot of arcing.

I didn't have any suitable pushbuttons so I chose to make my own with a pair of laundry pegs, simply drill some holes, thread a bit of flexible wire through and there you have it. The pictures will speak louder than words in this step.

I also printed a bracket which holds the pegs and servo in place. You will likely have to make your own of modify mine, since it is specific to my pegs, but here is the Fusion file anyway.

This step is best demonstrated in the short video you can see here: https://www.instagram.com/p/B_pJKy8gH3y

Once again, since this project had to be completed with items already in my shed I faced shortages, in specific I started running out of fasteners and bearings.

Bolts from Threaded Rod, Low Tech solutions

I used a lot of M5 bolts to fasten the wheels on to the chassis but eventually ran out. I then used sections of M5 threaded rod, cut to length and added a slot on the end with a hacksaw so it could be turned like a screw. I used M5 nylocs on the end to turn them into useful bolts, but I could have printed those too if needed.

3D Printed Bushings, High(ish) Tech Solutions

Every one of the freewheels required two bearings. One of the options was to make a custom design for each wheel to use up all the odd-sized bearings that I had, but in the end I decided to print bushings which were the same size as the most common bearing that I had (11x5x4) and replace them with bearings after the Apocalypse is it was warranted.

There are a few little tricks to take notice of here since getting the perfect fit will improve their performance dramatically.

(A) I applied a chamfer to the bottom edge of the bushing so that the slight bulge (elephant's foot) that is common at the bottom of a print wouldn't affect the fit

(B) I create a 0.2mm thick face across the bottom hole, which greatly improves adhesion during printing, but is incredibly easy to remove since it is only one layer thick. Very helpful for such a tiny item.

(C) I made the outer dimension slightly smaller than the hole that it would fit into. A distance of 0.275mm worked nicely.

Glue in Place of Nuts, Just Plain Lazy Solutions

For the rear axle holder I tried to give myself as many options as possible, one of those was to leave a recess where I could squeeze in some hot glue to hold the screw in place, it turned out to be useful when I ran out of M5 nuts.

You can't really have glass windows in a post-apocalyptic tank car, which is probably a good thing because I don't have the facility to print them yet anyway (gotta get me a resin printer right?!).

I decided the obvious answer was to armor everything. This turned out to be quite an easy task, I simply used the patch tool in Fusion360 to create surfaces that filled the window spaces, added some simple borders and printed them out in silver PLA.

Cosmetic Screws

I decided that I would embellish them with about 47 billion M1.4 screws. It wasn't the best idea, since it took forever, but it does look ok I think.

The screws can be found on Banggood etc. as 600 - 1000 pcs eyeglasses repair kits for a few dollars.

I included tiny holes in the design for the screws but some were a bit stubborn, those I carefully held with a pair of tweezers while pressing the screws in with a hot soldering iron.

Damage

I added some battle damage to the windows by poking and prodding the 3D prints with my soldering iron. No finesse here.

Paint

Paint was a simple matter of layering silver and black spray paint and white acrylics until I was happy with the mess I had created.

One trick I like to use is to not depress the nozzle of the black spraypaint properly, so that it splutters.

Of course this step is optional, but I love having a quality sound module in my rigs, the ESS ONE 2017 is my weapon of choice.

These modules are not cheap (and are not waterproof ) so I designed this simple bracket which allows me to clip the module in and out easily, swapping it between vehicles.

I did some minor modifications to the design to included screw holes, and mounted it to the base plate with a pair of M3 screws.

I think that lights add a lot of life to a car model, and they are really simple to add. These are just a pair of yellow 5mm LEDs running in series with a 75ohm resistor, powered with 5V from the receiver.

The interesting part is in the printing. It is very difficult (or impossible) to create a clear print with a FDM printer, but it is easy to make something nicely translucent if it is kept thin enough.

You can see in the attached photo how I designed the lamps to be printed at a 45 degree angle to the printbed. This allowed me to print them with only two perimeter walls and no infill, resulting in something that passes light well.