Hand tools and fabrication machines
I've always played with Legos as a kid, but I didn't have any of the 'fancy' Legos, just classic Lego bricks. I'm also a huge fan of the Marvel Cinematic Universe (MCU) and my favourite character is Hulk. So why not combine the two, and make a giant hulk minifigures, because bigger is always better, right? So I decided to make a 10:1 scale model of the original Lego minifigures.
A Giant Lego Hulk Minifig (I guess it'd be called megafig) isn't enough I decided to have some more fun and bring it to life. I've also added some extra novel features to it that allows it to both move and speak by adding 3 servo motors, an MP3 player module and a speaker with a built-in amplifier.
Since it has an MP3 player module and a speaker, you can actually load up all your favourite tunes on an SD card and use it as a speaker too!
The electronics and hardware of this project is also easily sourced and relatively inexpensive. That way, this project is easy reproducible by the masses (and tutorials community). My estimate for the project cost is around $50-80 -- this will depend on where you source the items. If you're willing to wait for eBay or Aliexpress it'll be cheaper, if not DFRobot shipped mine via DHL and I got it in 2 days. Same argument can be said for the quality of the filament you used. Considering you can pick up a tiny one for $5 from Amazon, I'd say the price scales up quite linearly, or less given that this has way more features than any store-bought lego figures.
1kg of Green PLA (I got a ton of filament for a good deal on Kijiji, but you can get yours from Amazon or filaments.ca if you're in North America)
200g of Purple PLA (I used the CCtree brand from Amazon and it exceeded my expectations for the price point)
200g of Black PLA (I used my favourite trusted, though slightly expensive brand, Innofil)
Epoxy Resin and Hardening Agent (this is for smoothing and shining the print, you can also use XTC3D but I found them very expensive)
CA Glue and Accelerant or Superglue (the former is preferable because you can accelerate the curing time to mere seconds)
Foam Brush ( I got mine from a local art store, Curry's, who gave me a student discount!)
Pro Tip / Fun Fact: CA Glue is actually just super glue, where CA stands for Cyanoacrylate (kind of like how when you buy Tylenol vs Acetaminophen at a pharmacy, the latter being a generic brand with the actual chemical name). The benefit of using CA Glue is you can buy it with accelerant which reduces the curing time to a couple of seconds, so you don't need to clamp it or hold it until it dries.
Caution: Careful not to get any CA glue + accelerant mix on your hands though because it'll burn.
Voltage step-down converter (You can also use a 7805, but they can't provide as much current as this one, plus this works for a 3 cell LiPo too!)
1K Ohm resistor (I'm sure you probably have some lying around or you can buy a pack that'll last a lifetime)
XT60 Connector (if you choose to use a lithium polymer battery with an xt60)
JST Crimp Pins (Or you can just solder those female ends of the jumper wire -- I already owned a crimper and had JST Crimp pins, so I used this to make it look more professional)
Heat Shrink (Much neater and more professional-looking than electrical tape!)
Soldering Iron, Solder, Desoldering pump
Multimeter (For troubleshooting circuits)
Crimper (If you choose to use a lithium polymer battery with an XT60 connector)
X-acto knife - I got mine at a local art store for around $2 with a student discount
Sandpaper - 400 grit, 600 grit, 1000 grit, 200 grit
"But, I don't have a 3D printer"
No problem! You can send the STLs to 3D printing services like Shapeways and 3DHubs
I know the list looks daunting and long. I tried to make it as comprehensive as possible, while providing justifications and details as to how I went about my design choices. That way, you can pick and choose and modify the project to turn it to your own. My goal is to always enable users to be creative and make their own projects while using mine as a guide rather than simply cargo cutting, but feel free to duplicate it as well!
3D Printing is becoming more common too, so maybe you have a friend who has a 3d printer that you can use. Filaments are getting cheaper and you can get a spool of 1kg for less than $20CAD or AUD (or < $15 USD)!
This build may not seem complex, but it does encompass the fundamental blocks of robotics -- electromechanical, circuitry, and embedded programming. As such, some preplanning would greatly help in the build.
I've separate this build into 5 segments:
- Design and 3D printing Phase
Divide and conquer! While you're waiting for your prints to finish, you can get started with the electronics and coding.
Since my Fusion360 skills are limited, I got a friend to help me CAD these files. You don't have to design your own if you follow this guide exactly. Simply go to the next step, and 3D print them. All the dimensions are metric!
However, if you do choose a different PCB or speaker, then you may need to resize the holes and cut extrusions where the components are supposed to be.
However, if you do want other Lego minifigs who isn't the hulk, then feel free to CAD your own. Someone, please make a giant Lego batman version of this!
Pro Tips: Design with 3D printing in Mind
(1) Tear drop shaped circles can be printed with no supports, so incorporate tear dropped shapes for circular cutouts instead of circles
(2) 45 degree angles or steeper can be printed without supports so make your overhangs have 45 degree angles to support them.
This step is pretty straight forward, grab your SD card, save the gcode from your slicer for whichever STL file you want to print and print it or just order it from Shapeways or 3DHubs.
The total print time for all the prints was around 80 hours. It used up around just over 1kg of material in total using black, purple, and green filaments -- mostly green because hulk is green, duh. You can always print it mono-coloured then spray paint the individual pieces which is another method of smoothing it (see next step).
Pro Tip 1: Fighting the Translucent Filament
If you have a transparent looking filament like I got for my green, you can get away with it still looking opaque by (1) increasing the shell thickness or (2) using a dynamic infill set to fill up to 50% in 5% increments. Unfortunately, since resin is transparent, it doesn't cover up the transparency of the filament.
Pro Tip 2: Dealing with Non-Plastic Deformation
For parts that need to flex slightly, print it at a higher infill than the default setting, around 50%, so it is not too brittle when you have to squeeze the pins together. You can leave the default wall thickness. It took me around 5 tries before I got the right combination of infill and wall thickness. Also use high quality filament. The CCTree filament from Amazon is excellent since it allows for a non-plastic deformation on the pins.
Pro Tip 3: Reducing Print Time
There is no free lunch if you want to save time 3d printing. There is almost always some tradeoff you have to make. Here's a few that I used that didn't affect the print quality much:
(1) Use a higher layer height -- around 0.2mm is acceptable for the head and front of the body and 0.3mm for everything else.
(2) Lower the infill density to around 5-10% or use dynamic infill as stated in ProTip 1.
(3) Turn on Combing Mode for reducing travel times.
(4) Use brims or rafts -- It may be counter intuitive to use brims and rafts, but it'll save you time from failed prints that came off the print bed from the nozzle striking some slightly off z-axis prints repeatedly.
(5) Use less supports. For prints that require a large number of supports like the hair, use a lower density supports around 5-10% will still yield a successful print.
This is a long and onerous process, yet very rewarding. You don't have to do it, but it makes the end result look so much better. Following BrittLiv's guide, I chose to smoothen my print with epoxy coating, except I decided to sand it down to 1000 grit first (preferable 2000, but I didn't have any).
Mix epoxy with a 30 minutes to 1 hour working time to allow you to get all the pieces done before it hardens. Then it'll take another 24 - 48 hours to cure, depending on how thick a layer you used.
Caution: Wear gloves when epoxying. You can get allergic to epoxy which will result in contact dermatitis, so you don't want any on your hands. Plus, you don't have to painstakingly sand your fingerprints away on your print job that just took 12 hours to print.
This step is rather long and verbose, though the actions taken to smoothen the print is quite simple. There were many techniques that were used and tried throughout the process, and I wanted to share all the lessons I've learned.
Pro Tip 1: Levelling the CoatUse a paper plate or any flat surface as a 'palette' prior to painting, as opposed to dipping the foam brush onto a cup full of epoxy. This will allow you to control and apply even coating onto the print job.
Pro Tip 2: Use a Foam BrushI have no prior knowledge in the arts or anything related to it, so when it came to picking a brush from a local art store, I had no clue what to pick so I asked for help. A very good point was brought up to me, if you use a typical brush, the strokes from the bristles will be visible, so use a foam brush since there are no bristles.
Pro Tip 3: Prevent stickiness by mixing the proper ratio and measuring accurately
Use a scale to measure the proper ratio of resin and hardener. Contrary to online advise of mixing more hardener for it to dry faster, always use the proper ratio. It's simple science, or chemistry rather. Resin and hardener being mixed together is a chemical reaction -- in fact, you can tell it is an exothermic reaction because the epoxy heats up as you mix them. The ratios suggested are the stoichiometric ratios that allow all the resin and hardener to react together to form the epoxy, thus anything in excess will not react and you will be left with a layer of stickiness.
1) Do not soak in water once done
I didn't have a good surface to put the 3d printed parts onto, so I just placed it on top of scrap paper. As expected, the epoxy dripped down and bonded with the paper. It's actually not hard to remove because you can just soak the paper in water and rub it off -- that is if you didn't put epoxy on the area making contact with the paper (you shouldn't). Unfortunately, soaking the epoxied print in water made it look spotty -- like a car that you tried to wash but didn't dry properly.
There was nothing I can do to get rid of the spottiness even if I dried it properly. The only solution was to sand the whole thing again -- and sanding epoxy is not fun at all -- until it is smooth (sand up to 2000 grit), then coat it again in epoxy which means more waiting.
There is a the silver lining though, after I repeated the tedious process of smoothing and epoxying, the end result looked significantly better! I can imagine there is a point of diminishing returns to this and at some point there's no point repeating this, where the first coat has the highest impact.
2) Do not heat gun
Do NOT use a heat gun to make epoxy cure faster. The plastic will soften and deform even if you are heating it from a distance. I had a sample piece of PLA and I learned that it's better to just have patience and wait.
3) Keep Sanding
I was reluctant to sand it at first because it made it look white and scratched up and I was worried that when I cover it in a coat of epoxy it'll maintain it's dull scratched colour. I was wrong. In fact, sanding it down until it is smooth and very scratched up yielded the best results.
How does it work?
When you sand it, you are getting rid of any imperfections and bumpiness, so you get a smooth print, but it doesn't fill any of the gaps and crevices. When you apply epoxy to a print, you're effectively filling all the gaps left by the layers and any unevenness in the print. Notice, if you dip the 3d printed part in water it's much smoother in appearance while wet -- that's because the water filled in the gaps, but it evaporates. The resin fills it in permanently and doesn't leave any discolouration since it's colourless.
There are some electronic components you do not need to solder thanks to the modular PCB design I provided. These are the servo motors and the speaker module. Since the servo motor and the speaker module is independent of the body, we can place those in the head and finish the head assembly.
Place the speaker on the front of the head. There are pegs for the speaker to screw into but since these two pieces are going to be sandwiched together by the servo and the hair, there's no need to screw it in -- and it won't come apart unless you force it to.
Solder the PCB based on the schematic provided. I've also added the Fritzing document so you can open it on Fritzing and run auto-routing for the PCB and get it printed if you do not want to solder the bus paths yourself.
To make the circuitry neater and modular I employed a few techniques noted below:
- Use female pin headers as custom IC sockets for the Arduino Nano and the DFPlayer Mini.
- Use male pin headers for plugging in the servo motors and speakers. This way they are not soldered directly on the PCB and can be removed at any time.
- Add male pin headers for battery input and voltage step-down converter input and output. This way you can easily route and add more bus paths to the appropriate voltage. This isn't necessary but it makes the wiring simpler and allows for less wires dangling on the voltage step-down converter. As you can see, I only used 2 pairs.
This does require a moderate amount of soldering experience and skills due to the number of bridged connections you have to make and how close the pins are to each other.
So how do you get a good result on soldering the PCB?
Get a good soldering iron with temperature control and a PCB with square pads. Use a chisel tip (flat) iron to increase the contact between the component and the pad. I also like to use 2/3 tin and 1/3 lead since lead has a lower melting temperature which makes soldering a tad easier.
The output of the 2 cell LiPo battery is though XT60 connector, which is a standard in RC Airplanes. I didn't want to cut it off because XT60 is the standard for a lot of plugs for brushless motors that I use and can also handle up to 60A of current -- which I need for other applications.
1. Solder XT60
So instead, I opted for a more modular solution. Solder an XT60 Adaptor with an XT60 Male to JST Female (labeled above) -- negative to negative (black wire) and positive to positive (red wire).
2. Crimping JST Female Pins
Place the uncrimped pins onto the crimper and tighten it so that it holds the pins firmly while still allowing the wires to slide through -- it'll form an open cube. Insert the stripped wire onto the open cube and then crimp it. Repeat this for both the red and black wires then slide both crimped pins into the JST housing.
3. Heat Shrink the Connectors
Be sure to heat shrink the connectors so they don't accidentally short. These Lithium-based batteries will make some beautiful, albeit not so nice, fireworks if they short
Pro Tip 1: Soldering XT60s
When soldering the thin wires to the XT60, tin the wires first, then fill the cavities of the XT60 with solder half way. Keeping the iron on the connectors, dip the tinned wires in and remove the iron, whilst still holding the wire. Keep it still for a few seconds and heat shrink it once it's cooled down.
Pro Tip 2: Preventing Connector Deformation
To prevent the XT60 connector from deforming from high heat, slot the female and male (unsoldered connectors NOT the batteries!) to each other before soldering. That way they'll keep the connector shape and prevent the conductors from moving since it's a tight fit.
Download the code attached and upload it to the Arduino Nano. This is responsible for running 4 different motions modes from the servo as well as looping sound effects through the MP3 module. The MP3 module plays the sounds based on which order the MP3 files are uploaded onto the SD card.
If you want to use it as a speaker, just use the following function for playing random music files in a loop.
For more information on all the commands that can be given to the MP3 player, you can find it from the manufacturer's specification.
In my case, all that is needed is playing a specific MP3 file. The way I ensured the MP3 module to play the appropriate file rather than relying on the order is using the built-in method, which assumer it is in the folder called MP3 (not case-sensitive):
where the argument 1 is the file name, 0001.mp3.
Using the method that relies on the file upload order:
assumes that it is in the root folder and does not require a specific file name.
We're going to start with the PCB and the electronic components, then moving onto attaching the servo motors.
First, to make assembly easier, label all the pin headers and unplug the components.
Notice how there are some hexagonal cut extrusions to fix a nut on the body and head of the Lego piece. This is where the nut should be glued using CA glue -- be careful when gluing it that you don't accidentally add glue on the threads.
Then place the PCB in and align the holes to the nuts and screw it in with M3 bolts. This should be a rather quick and trivial task.
There are two things that need to be attached to the servo motors physically (1) The circular metal servo horn (labeled above) and (2) The servo body to the body of the Lego piece. The screws used for this entire project is standardized; they are all M3 nuts and bolts.
There hare 3 servo horns that needs to be attached in the body. One for the head and two for the arm pins which will be driven by the servo motor. There is a particular order they should be put together such that you do not have to awkwardly position your hands.
- Screw in the servo horn for the head at the top of the body using 4 m3 screws towards the horn.
- Screw the arm pins onto the servo horn then onto the 180 degree servo motor using the screws provided with the servo. Screw it in towards the horn since the holes on the horn are threaded.
- Place standoffs at the sides of the body where the servo is to be mounted. The standoffs are to address the gap between the servo and the mounting platform due to design error. This will be fixed and you do not need to do this step.
- Then, simply screw in the servo motors chassis and servo horn to the body as shown in the images. If you're not using standoffs you will need self-tapping screws which will be provided with the servo motor. The servos in the body are quite a tight fit so you need to fiddle with it until you can get both of them in.
The last thing we need to do is just assemble all the pieces together just like classic Lego.
- Glue the two halves of the legs, below (green PLA) and above the knee (purple PLA) together using CA glue
- Snap the legs together to the hips.
- Snap the arms together to the arm pins (labeled)
- Push the hands against the arms -- the arms may need some sanding depending on the tolerances of the 3d print.
- Push down the speaker and servo wires through the hole on the body and plug it in to the appropriate pin headers you soldered.
- Screw the head servo onto the body's servo horn to complete the assembly.
- Then, place the chest plate on top of the body.
You're done! Power it on and enjoy your Lego Hulk Mega Figure!
I entered this to the Big and Small contest, so your votes would be highly appreciated if you enjoyed this. Here's the link to the Instructables contest: https://www.instructables.com/id/Giant-Hulk-MiniFig-101-Scale-With-a-Twist/