Imagine trying to make a ball-shaped robot that rolls in any direction but with a head that stays on. When I saw the BB-8 droid doing just that in the first Star Wars: The Force Awakens trailer, it was an interesting engineering challenge that I couldn’t resist. All the details for how I made it would fill a book, so here are the highlights: the problems I ran into, how I solved them and what I learned.

The Design Criteria: Portable and Inexpensive

I had two design criteria in mind. The first was to keep it low-cost. Some spend $1000 to $1500 on their BB-8s. I wanted to spend as little as I could, so as many parts as possible had to come from my existing stock and from online classifieds and thrift stores. Not counting the parts that were discarded along the way, the cost came in just shy of $300.

The second design criteria was to make it portable. It had to be something I could take on the bus or carry while walking a reasonable distance (I once carried it twenty-five minutes to a nearby school).

Both of these criteria meant that it had to be smaller than full size. A full size ball is 20″ in diameter. Mine has a 12″ ball which makes it 3/5 scale. Also, the larger it is, the more powerful and costly the motors, batteries, motor controllers, magnets, and so on.

Version One: Quick And Easy

First I tried a minimalist approach. For the ball, I found my 12″ cardboard globe on kijiji.ca. I bought an RC toy truck at a yard sale and attached a pole to it for holding magnets near the top of the globe. I then made a head with corresponding magnets under it. The head magnets attract to the pole magnets, keeping the head on. Meanwhile, the truck rolling inside the ball makes the ball move.

Making the ball roll around was easy. Making it roll around while keeping the head on was very hard. The magnets at the top of the pole attract the magnets under the head, pulling them down hard onto the surface of the globe. That essentially glues the truck to the top of the globe.

To overcome that the truck needs sufficient traction. That also means the truck needs to be heavy. And lastly, the truck’s motor needs to be powerful enough to overcome its own weight and the grip of the magnets on the ball. The alternative is to make the magnetic attraction weaker, but if it’s too weak the head falls off. It’s a tricky balancing act, in both senses of the word.

But the most dome-like head I could make stay on was just a cardboard skeleton. Anything more filled out would be heavier and require a stronger magnetic attraction. The toy truck’s motor would not be up to it.

Version Two: Drill Motors And Drill Batteries

For more powerful motors and more mass I figured I could kill two birds with one stone by going with drill motors and drill batteries in a hamster drive configuration. Using drill parts kept costs down as the batteries and one drill came from yard sales while the other drill was free through freecycle.org. Meanwhile, both are heavy.

To make sure it all fit, I drew up a 3D model in Blender, the free 3D modelling and animation software that I use a lot. In fact, finding out how to make the batteries and motors fit was the first step. They had to be as low as possible. Their large mass low down is what keeps the droid vertical, with the much lighter head at the highest point.

The drill batteries had to be easily removable for recharging. To hold them under the drive plate I simply used Velcro. Meanwhile, the drill battery stems went up through a hole in the drive plate. I made a connector to electrically connect to the battery terminals. It is a plastic rectangle with thin copper sheet metal for the contacts. Once the battery was Velcroed in place, this plastic and metal piece was lowered down onto the stem, the copper metal making contact with the battery terminals.

The Electronics

For the brains I used an Arduino UNO. To drive the motors I had all the parts for making two H-bridge driver boards, with the exception of 4 MOSFETs and some fuses. The Arduino does pulse width modulation (PWM) to the driver boards for speed control, as well as playing sounds at certain times when the motors are turned on.

For remote control, I hacked the RC receiver from the toy truck and added an extra set of AA batteries in parallel for more runtime. A problem I ran into right away though, was that the RC receiver put out voltages of both polarities based on which direction the motors should rotate, whereas the Arduino’s pins take only positive voltages. To solve that I came up with a converter board to go between them.

Getting all that to work reliably took a while. Before I added fuses, I burned a few MOSFETs. At one point I’d put an N-type MOSFET where a P-type should have gone and vice versa. That resulting problem alone took a few days of spare time to figure out.

The wheels were old Rollerblade wheels — I keep a small bucket of these in my shop. I decided I wanted the ball to roll at around 1 foot per second and doing the math, that meant the wheels would have to rotate at around 2 rotations per second or 120 RPM. I found a PWM value that would give something close to that and started blowing fuses. I started with 1 amp fuses, then 2, 5, and finally settled on 10 amp fuses.

My final hurdle was that the motors would behave oddly when the motors were told to turn in opposite directions but were fine when they were told to turn in the same direction. This turned out to be a bad assumption on my part about how the RC receiver was wired internally — none of the output wires were common inside. After some changes to the circuit, I now had stable electronics.

I had basically been treating the RC receiver as a black box, but when I asked for help about my converter board here on Hackaday, it was pointed out that the receiver likely contained H bridges. Opening it up, that’s exactly what I found. The converter board works fine for now, but in the near further I’ll use one of the suggestions from that Hackaday post to eliminate the board altogether. I might even try all of the suggestions, just for fun.

The Drive System

The motors were too long to fit in line between the wheels and so had to be mounted off to the sides. To transfer rotation to the wheels, I drew up some gears in Blender and 3D printed them at our local University of Ottawa Makerspace. In the print settings I used 2 shells and only 50% infill. The gears are held firmly onto the shafts solely using nuts and washers on either side. They’ve held up amazingly well, even with slipping and grinding during development.

For the bearings for the center gears and the wheels I used an old trick of making bearing blocks from hardwood.

I wanted to keep as much room as possible on the drive plate available for adding things later and so initially I’d mounted the motors at only three points. But this allowed the motors to move a little causing the gears to slip. To fix that I later added a fourth mounting point and haven’t had any slipping since.

At the end of the shaft for the drill motors is a hole that a screw goes into. That’s part of how the chuck is kept on a drill motor, and that’s how one gear was kept on. However, this screw had a tendency to get loose. Putting a little Loctite on the threads fixed that.

Stability

Given that I was trying to fit a lot in a small droid, I had to mount some things higher than I’d have liked to. When the droid stops, mass high up causes the droid to wobble. In the BB-8 droid used for promotional events they’ve gone to a great extent to keep the majority of the mass as low as possible. Originally I had the Arduino batteries and the RC receiver with its extra batteries fairly high up. I later mounted them much lower. When holding the internals in my hands I could tell the difference but it didn’t make a noticeable difference with the wobble.

Instead, for that I added Adafruit’s BNO055 inertial measurement unit (IMU) board. With it I could tell what angle the droid was at when stopping and experimented with PID loops and other algorithms of my own to minimize wobble. That helped.

The Ball

As I said, I used a 12″ cardboard globe. To increase the traction of the wheels inside the globe I sprayed the globe’s interior with an anti-slip spray from a hardware store. This made a huge difference. However, over time the anti-slip coating vanished, and so I’m looking for another, more permanent coating, perhaps urethane or something. If anyone has any suggestions, please let me know in the comments. It also has to stop off-gassing eventually. The anti-slip spray had an odor for a long time.

But the main problem with the cardboard globe was its thinness. With the huge weight of the internals pushing down on it where the wheels are, it warped significantly and required a lot of effort and a copious amount of tape to keep the two hemispheres together. This large amount of tape also made an uneven ridge for the head to slide over, making it get stuck. At that point either the drive system continued to move while the head fell off or the drive system couldn’t move at all.

The solution was to carefully coat a new globe in three layers of fiberglass. I took my time doing this, over a month and a half, applying one piece at a time and then sanding before putting the next piece. The result was a fantastic improvement. It no longer deformed and now it takes a minimal effort to attach the two hemispheres with only eight narrow strips of transparent duct tape.

The Never-ending Saga

My BB-8 is now at the point that I can call it finished. At least it’s finished as far as all the engineering is concerned, and that’s usually where I call it quits.

While the paint job worked out well, up close you can see that the details are painted on. It’d be nice to have at least the lines on the head be actual grooves. Also, these drill motors are brushed motors and I’ve since learned that doing high frequency PWM to brushed motors damages them over time. I’d like to replace them with brushless motors. And as anyone who’s use cordless drills a lot knows, drill batteries don’t last long, and so it’d be great to switch to LiPos.

But for now, the reactions I get from both kids and adults is beyond my wildest expectations. Kids threat it like a friend while adults have petted it and called to it like it was a baby or a dog wagging its tail. I’d call that a success.

In skateboarding, the ollie is a fundamental trick used to leap onto, over or off obstacles, or over gaps of unfriendly terrain such as grass or stairs. But how do you know just how sick your ollie actually was? Josh Sheldon has a solution.

The Maker has built a device that judges the sickness of your ollie and visualizes your score, rewarding the best ones with the chiming of a cowbell. Sheldon describes the project as something “like one of those hammer games at carnivals, but instead of trying to hit that thing with a hammer as hard as you can, the goal is to land the sickest ollie.”

The aptly named Sick Ollie Machine consists of two parts: a stand with LEDs and the skateboard itself. Underneath the board is an Arduino Uno, a 9V battery, and an accelerometer. The stand is equipped with another Arduino, a relay, and an RGB LED strip that goes up mast, as well as a solenoid on top. When the relay closes, the solenoid hits the bell. Both units also contain a wireless transmitter, allowing them to communicate with one another.

Watch Sheldon discuss his project in more detail below!

Unlike most cars today, deepsyx’s old Opel Astra did not have a tachometer. So what’s a Maker to do? Build your own, of course.

To accomplish this, deepsyx used an Arduino Uno along with a few LEDs. The first LED turns on at 4000 RPM, while the others light up with every 500 RPM increment. At 5800 RPM, however, all the LEDs flash as a warning. There’s even a serial output of the RPM value, so logging real-time data can be a possible enhancement down the road.

I started by cutting a 5cm x 1.5cm piece of an old credit cart, drilled 4 holes in it, painted it black and glued 4 LED diodes to it. Then I soldered 220ohm resistors to each positive LED pin and used a common ground. I connected them to an Arduino via 5 x 30cm jumpers and hid the Arduino in a hole under the wheel. I connected the Arduino data pin via voltage divider to the signal pin of the coil and used an old phone charger to power the Arduino. In order to work, I shared the phone charger and Arduino’s grounds.

Intrigued? You can read more about this project on deepsyx’sGitHub page and over on Hackaday.

[Stanley] wanted to make a laser projector but all he could find online were one’s using expensive galvanometer scanners. So instead he came up with his own solution that is to be admired for its simplicity and its adaptation of what he could find.

At its heart is an Arduino Uno and an Adafruit Motor Shield v2. The green laser is turned on and off by the Arduino through a transistor. But the part that makes this really a fun machine to watch at work are the two stepper motors and two mirrors that reflect the laser in the X and Y directions. The mirrors are rectangles cut from a hard disk platter, which if you’ve ever seen one, is very reflective. The servos tilt the mirrors at high speed, fast enough to make the resulting projection on the wall appear almost a solid shape, depending on the image.

He’s even written a Windows application (in C#) for remotely controlling the projector through bluetooth. From its interface you can select from around sixteen predefined shapes, including a what looks like a cat head, a heart, a person and various geometric objects and line configurations.

There is a sort of curving of the lines wherever the image consists of two lines forming an angle, as if the steppers are having trouble with momentum, but that’s probably to be expected given that they’re steppers controlling relatively large mirrors. Or maybe it’s due to twist in the connection between motor shaft and mirror? Check out the video after the break and let us know what you think.

The video’s in three parts: looking at the laser beams in action as you’d see them on a dance floor, then watching the projected images while looking at an insert of the Windows application, and then watching the steppers and mirror doing their rapid movements.

As for the expensive galvanometer scanners we mentioned above, check out this impressive laser projector that uses them. Another method is to use a spinning wheel with mirrors set to different angles, like this one that draws a marquee using a pill box as the wheel. And how about one with no mirrors at all, instead attaching the laser directly to servo motors, though that one does take longer to draw.

Bouncing a laser off of a spinning mirror creates an amazing effect with smoke and fog, but YouTuber “Normal Universe” made it even better with an Arduino.

This video starts out by introducing the concept of “laser sky,” which seems like a fun idea. There is, however, a chance that the mirrors wouldn’t spin, potentially pointing a laser continuously at a bystander, possibly damaging his or her eyes. To prevent this, the YouTuber added a photoresistor and LED to sense the spinning mirrors, then programmed an Arduino Uno to cut off the laser if it’s stopped for whatever reason.

Normal Universe goes on to explain the electronic concept behind it as well as the Arduino code involved, so even if this effect isn’t your cup of tea, the photoresistor/voltage divider setup could still be quite useful.

You can find a detailed breakdown of the project in the video below!

After an accident, Ethan Kadish was paralyzed. His friend, 14-year-old Jacob Smilg, came up with a simple device to help him communicate.

Several years ago, Kadish was struck by lightning, and lost control over his body. Communication with the world took the form of eye blinks for “yes” and “no,” which gave Smilg an idea for a revolutionary, Arduino Uno-based gadget that could help him communicate with people not familiar with this method.

It uses two pads, which Kadish can press with his head. When pressed, the device displays “yes” or “no” on a small LED screen. This allows him to have conversations in a more natural way, which, as seen in the video below around 4:00 it appears to make him very happy!

You can read more about the project on Make:, and keep up with Kadish’s story and progress on the Team Ethan blog. More pictures and videos can be found on Smilg’s Facebook page.

After recently meeting each another in Cologne, Simone Giertz and Laura Kampf decided to put their creative minds together to build a cartoon-inspired robot for Kampf’s dog, Smudo. The idea is fairly straightforward: a device that “makes a dog walk itself” by dangling a piece of sausage in front of their head.

The contraption consists of a lightweight, ergonomic aluminum harness that bends over Smudo, along with an Arduino Uno and a servo motor tasked with wiggling the hot dog around.

You can see how it works and hear more from the creators themselves the video below!

Starting a new project is always an effective way to hone your skills while exploring circuitry and programming. To help improve his engineering chops, Joop Brokking recently bought an inexpensive oscilloscope (a device for visualizing voltage over time in an x-y graph) and connected it to an Arduino Uno. He then shared his findings in a detailed tutorial on YouTube.

In the video below, Brokking is using a Hantek 6022BE 20MHz dual-channel oscilloscope and provides three examples to better understand what can go wrong when building a simple Arduino setup.

Les Boites Mécaniques are a set of four automated boxes that produce music out of wood and metal. These experimental instruments enable anyone to explore the magic of making sound by pressing buttons on a remote, which activate each respective device to vibrate, knock, and rub materials.

The boxes were developed by Kogumi‘s Anatole Buttin and Yan Godat for educational electronic music workshops, and can be played either solo or in unison. There’s even a mode that allows users to control it all via MIDI notes on a computer.

In terms of hardware, each box is equipped with an Arduino Uno, a TLC59711 LED driver, step motors with AccelStepper library and a 3D-printed microstep driver.

You can watch how it all comes together to create a unique sound below!