3D Printed MB Jeep and M416 Trailer in 1:10 Scale

Introduction

If you haven't experienced the world of scale RC crawlers then you are really missing out, there is something really theraputic about tackling the same impossible lines until you eventually crest that hill.

One of the great benefits of crawling is that cars can be elaborately detailed without risking being destroyed in a high speed crash (low speed tumbles down cliffs are of course another story).

The downside of crawling is that it is horribly expensive to get a good-looking scale rig. I'm hoping to provide a solution to that.

I used a cheap 1:18 scale RC crawler (A clone of the more expensive Losi MRC) to supply the drivetrain (it could provide the electronics too if you are new to the hobby and don't have a pile lying about) and built a realistic 1:10 scaled MB Jeep around it (The MB jeep is tiny in real life, hence why so-called 1:18 parts work at 1:10 scale).

Features and Design Goals

• Complete assembly without glue
• Replaceable panels (for inevitable crashes)
• True 1:10 scale (most "1:10" RC's are not, since they have a common wheelbase)
• Electronics hidden in engine bay
• Working printed suspension
• Affordable
• Reliable (hence the choice of off-the-shelf axles)
• Print without supports
• Printable on hobby printer (250x200x200mm bed)

STL Files for Printing

• Jeep (myminifactory)
• Trailer (myminifactory)

Non Printable Jeep Parts

• Donor Vehicle for drivetrain (Kulak Crawler - Aliexpress) approx $130
• Tyres (AsiaTees) but you could use the tyres off the Kulak
• M2 Threaded Rod (Brass preferably)
• M2 nuts (lots)
• M2x10 screws
• M2x16 screws
• M2x12 screws
• M1.6 screws (optional)
• A kit of screws like this can be handy for these projects

Wheels

• M2x10 screws (5 each)
• M2 nuts (5 each)
• 1.9 Tyres (I just used the Kulak's tyres)

Trailer Parts

Trailer

• M2x5 (20)
• M3x40 (1)
• M2x10 (24)
• M2x16 (6)
• M3x12 (2)
• M3 nuts (3)
• M2 nuts (50)

Wheels

• M2x10 screws (5 each)
• Tyres (AsiaTees) (Or just use the Kulak's tyres)
• M2 nuts (5 each)

Consumables

• Filament, I chose PETG for durability and layer adhesion
• Primer: Rustoleum Ultra Cover
• Olive Drab Paint: Tamiya TS-28

CAD Tool: Fusion360

Autodesk's Fusion360 is in my opinion the best thing that has happened to CAD for hobbiests in recent years. It is incredibly powerful and improving every day (No I'm not paid to say that, unfortunately, I just am a huge fan).

Get it here, it is free for hobby use (or even light commercial, go have a squizz at the license)

Source Material

Fortunately the internet is chock full of source photos of the MB Jeep, so I collected a few. It was also easy enough to find the true dimensions, so I used those to scale the canvases that I imported into Fusion360.

Design Considerations

Unlike my hotrod project, which was designed to be printed in SLS nylon, I took pains in this project to make it easily printable on a hobby-grade FDM printer.

Nozzle Diameter: Since most of the body is comprised of thin wall features I designed them to all be exact multiples of my nozzle diameter (0.4mm) so that they could be printed in solid continuous lines.

Parameters: Make sure to include all important dimensions (wheelbase, wheel diameter, length, width,scale, bolt diamters etc.) as parameters (tutorial) and define everything with respect to them. If you do this carefully enough you will easily be able to make sweeping changes later, such as changing the scale altogether, the nozzle diameter or the size of the screws used.

Tolerances: When making a hole for a screw, for example, it makes sense to define it with an additional tolerance defined as a parameter, then you can easily change the parameter if the holes are too big or too small.

Sanding

The reason I put the finishing&painting step first is that it is far easier to sand the parts individually before assembly.

Especially on the flat parts the print lines can easily be removed (or mostly removed) by rubbing the parts against some 100-grit sandpaper placed on a flat surface.

Mask the Nuts

In case you have already inserted the nuts, but not the screws, make sure to mask them off to prevent the threads getting clogged by paint. The easiest way is to just temporarily insert screws (long ones that are easy to get out).

Primer

Make sure that you use a primer suitable for the plastic that you are printing, I found Rustoleum's "Ultra Cover" primer to work well (it promises to "also bond to plastic" on the tin and seemed to live up to it)

Painting

For the military themed trailer and jeep I used Tamiya TS-28, it took two tins for the jeep and trailer combined.

Nozzle Diameter

I designed all of the thin-wall parts to be multiples of 0.4mm for printing on a 0.4mm nozzle. Besides the frame rails , where I use about 40% infill, everything will be "all walls", so make sure that you use enough (I normally set the slicer to use 6 or 8 walls).

Orientation

In the attached images you can see the orientations that I used to print all of the trailer parts.

Supports

None of the parts should require any supports, although the recesses in the hitch triangle may come out cleaner with them enabled.

Brims

You may find it helpful to use a brim on the tub when printing it vertically.

Layer Height

Since there are almost no curves you will get just as nice results, a whole lot faster, by printing with 0.2mm layers.

Insert Nuts

Start by inserting M2 nuts into all of the holes in the main frame. If the holes are too tight then simply use a soldering iron to heat them up and press them in, which has the added benefit of "gluing" them in place.

There are also nuts to be inserted in the hitch triangle.

Attach end-caps

Use the M3x5mm hex bolts to fasten the two end-caps to the trailer tub. You need to use hex screws so that you can use an "L shaped" allen key inside the trailer with the nuts on the outside.

Attach Triangle

It is best to attache the triangle to the frame before the suspension brackets, otherwise things can become very tight.

There are two screws which pass through the side of the frame, fastening into captive nuts in the triangle.

Attach Tub and Suspension Brackets

Assuming that you have inserted all of the nuts into the frame you can now attach the tub and the suspension brackets in any order. It is safest to to the suspension brackets first, so that you can be sure the screws aren't too long (otherwise they will press against the floor of the tub).

Axle Rod

Insert the ~160mm threaded rod through the axle tube. The rod may have to be threaded through the tube if the tolerances are too tight, this is helpful though, because it makes it easier to tighten the wheel-nuts afterwards.

Take a look at the attached animation. The hitch "loop" and "shaft" are reinforced by an M3x40 bolt that runs down the center, fastened into an M3 nut that is held captive in the back of the shaft.

Make sure that the shaft turns freely before you tighten it all up, you may have to sand the shaft of use a round file in the tube, especially if you have a blobby PETG print.

Part Options

You will see that there are two options for the rear of the jeep wheels, one has "extra offset" in order to allow 1.9" wheels to clear the leaf springs.

Jeep Wheels (Driven)

• M2x10mm bolts (5 each)
• M2 nuts (5 each)
• 12mm Hex (4mm hole for shaft)

Trailer Wheels (Freewheel)

• M2x10mm bolts (5 each)
• M2 nuts (5 each)
• 5x11x4 bearings (2 each)

Assembly

The front and rear wheels go together in exactly the same fashion (see animation)

First insert the beadlock ring into the tyre (take a look at the cross-section picture to see what is going on inside - if it doesn't fit properly you may need to scale it and reprint), then press the two sides of the wheel in, sandwiching the tyre bead between the ring and the rim.

Fasten the two halves of the wheels with the nuts and bolts.

Filament

I chose to print in PETG since the great layer-adhesion keeps thin vertically-printed parts strong, it is also quite tough and semi-flexible.

Nozzle Diameter

I designed all of the thin-wall parts to be multiples of 0.4mm for printing on a 0.4mm nozzle

Orientation

In the attached images you can see the orientations that I used to print all of the jeep parts.

Supports

The following on the only parts that really require support

• Windshield (for the arms)
• Tub (for the horizontal portion of the transmission hump only - I plan to eradicate this issue from the design in a later release)

Brims

You may find it helpful to use a brim on the hood when printing it vertically.

Layer Height

Since there are almost no curves you will get just as nice results, a whole lot faster, by printing with 0.2mm layers.

Except for the dashboard section, which has gentle curves and embossed text so a fine layer height is preferable (I used 0.1mm)

List of Parts

As with the trailer, insert all of the M2 nuts into the frame. If the tolerances are too tight, use a hot soldering iron to press them gently into place (as an added benefit they will become "glued" into place when the plastic cools).

Attach the two halves of each side of the frame together, be careful with the assembly at this stage, since it is quite delicate.

Attach the two halves of the frame to the motor mount, front bumper and rear bumper. Follow the pictures closely to make sure that all of the orientations are correct. The assembly should be fairly sturdy by this point.

Attach the eight suspension brackets.

Fastener Choice

I chose to use M1.6 screws here for mostly aesthetic reasons, they are a fiddly nightmare though, so feel free to replace them with M2 if you like.

Rear Half

There are really no tricks to the assembly, attach the rear wheel wells to the rear bed first using M1.6 screws, tapped directly into the plastic.

Front Half

Connect that whole rear assembly to the front half using M1.6 nuts and bolts in the sides and M2 nuts and bolts at the front of the bed.

Front Fenders

Although the holes in the front fenders are currently size for M1.6, I found it easier to use M2. They are mostly hidden, so it's not a major eyesore.

Grab Handles

Here I used M1.4 screws, but actually screwing them in seemed too much like hard work so I just slowly pressed them in with a hot soldering iron.

This is the part where we rip the heart out of a perfectly good ready-to-run RC and discard the rest (or more likely keep it for future projects).

There is nothing to it besides removing screws. Collect the following and put them aside:

• Front Axle and Servo
• Rear Axle
• Transmission and Driveshafts
• Wheels (You may want to use the tyres for the trailer)

Disclaimer

It should be noted that 3D printed springs are simply not as good as a bit of steel, nevertheless, for novelty sake I decided to do it. Printed out of PETG they are suprisingly effective.

Leaf Thickness

I have provided two thicknesses of leaves, one which is sturdy but really too stiff and the other which is nice and flexible, but a little delicate.

Shackle Assembly

Each shackle is held together with a pair of M2x18 nuts and bolts (or M2x16 if you use a soldering iron to press the bolts into the plastic)

Take a look at the attached photos to see how the springs and shackles go together. Pay attention especially to which side the shackles go on (the giveaway is that they attach where the frame rails are higher).

I found it best to have the "nut" side of the shackles inwards since there is very little room for an allen key on that side once the driveshafts are installed.

Axle Assembly

The axles are a simple case of taking the stock hubs off the Kulak axle and replacing them with the 3D printed ones. Make sure to use the very short screws to reattach the hubs or the screws will jam up the axle inside the housing.

Attach Axles

The axles are attached to the leaf springs with U-bolts made out of brass threaded rod. You could use stainless but it will be much more difficult to work with. Brass rod can be bent around the axles by hand and cut to length with sturdy clippers.

Note: This is a section that I am continually reworking, it may even be best (from a steering perspective, not the "scale look" perspective), to stick with the axle-mounted servo for now. This method currently requires you to bend up a steering link from a piece of threaded rod.

Assembly

The attached animation shows how the micro steering servo (an "ALIGN Digital Servo, DS410" in my case) is attached to the support piece with 2 M2x12 screws and bolts.

Before you install the servo horn, make sure that you have powered up the transmitter and receiver, and set the servo trim to zero.

The entire drivetrain from the Kulak is transplanted into the Jeep, held in to the mounting plate using the original four screw holes.

The only change that you will need to make is to trim about 15mm from the front driveshaft (keep the leftover pieces, they may be useful in the future to lengthen the rear shaft)

Print

Print the headlamp pieces in a clear filament, I chose to use PETG. Varying the number of outer lines as well as whether you print the face of the lens on the bed or not will vary the look of the final lens.

Glue

I used superglue to glue the lenses into the grille as well as the LEDs into the lenses. This is quite final, so make sure you get it right!

Power

Place a 5mm LED in the back of each lens. I chose to power mine off the 5V BEC output with an appropriate (150ohm) resistor in series with each one. If you are unsure about wiring the LEDs just have a look around instructables, there are oodles of great resources.

The seat frames are designed to be printed in two halves each, negating the need for support, and fastened together using M1.6 fasteners (or glue).The cushions can be made with scraps of fabric, wrapped around a square of sponge, cardboard or wood (depending how pampered your driver's butt is I suppose).

The fender part includes two recesses into which you can install an M3 hex standoff (I used a 12mm standoff, you can vary the length to adjust the clearance) and then screw a shock mount ball screw into.

Since most crawler shocks are too long I used 60mm touring car shocks and removed the springs (we already have leaf springs, we only need the dampeners).