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Grant Imahara’s Hollywood Dream Machines, and the Spider Robot that Almost Killed Him

From R2-D2 to the Energizer Bunny, Mythbuster Grant Imahara has assembled some incredible robots. Here are his build notes about a few of his favorites, including one surprisingly dangerous arachnid.

My love of engineering goes way back. When I was 3 years old, I got my first Lego set. I would say it changed my life, but at that age, I really didn’t have much experience to go on, so better to say it helped shape the way I look at solving problems. I learned to work within a modular system and to use the parts at my disposal to build what I imagined. And what I imagined, essentially, was a career in engineering.

[This article first appeared in Make: magazine Volume 39, on pages 38–45.]

When I was in high school, there were no STEM (or STEAM) programs. There were no Lego Mindstorms kits or kids’ robotics programs like FIRST. In fact, I only learned what an engineer was from a college guidance counselor. When she described it, a light clicked on in my head, and I said, “Yes, that’s what I want to do.”

Over the years I have blown up home theater equipment, helped create feature films, and used science to debunk urban legends. And while special effects, explosions, and car crashes are exciting, the thing I have enjoyed most is making robots. All kinds of robots. From mundane to downright dangerous.

Here are just a few old friends and favorites.

“The Spider”

m39 imahara opener Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed Him

This monster started with the idea to create a large-scale walking robot strong enough to carry a person. I began in May 2007, with a six-legged design based on a Lynxmotion hexapod kit. I scaled up the joints and used a waterjet to cut the leg sections and body panels out of 5/8″-thick 6061 aluminum.

Each leg has a heavy-duty motor to lift it and a lighter-duty motor to move it forward and back. The leg design went through several revisions. I tried four different sets of motor/gearbox/external gear combinations before arriving at just the right speed and torque for the lifting movement. My external gear choices were limited due to space in and around each leg, and I eventually ended up using wheelchair motors with built-in electromagnetic brakes.

The control system is built around a Parallax BS2p40 microcontroller and PSC servo controller connected to an even dozen Vantec RBSA23 servo drivers. The microcontroller also runs a set of solid-state output modules that automatically engage and disengage the motor brakes so the robot won’t waste power holding itself up while standing still.

Testing the Spider — certainly the heaviest robot I’ve ever created at more than 625lbs — proved to be a tremendous challenge. Working late at night by myself, there were a few too-close calls when the robot almost crushed me.

PRO TIP: Don’t do what I did. Never work alone around heavy or otherwise dangerous equipment.

Control glitches also proved costly. I went through several $100 cast-iron gears when the legs bottomed out against their stops and the motor kept trying to turn, resulting in gear teeth shearing off and raining down on the floor like Tic Tacs. What has kept the project on the shelf for the past several years is inadequate torque in the motors that swing the legs back and forth — unfortunately, the major part of the “walking” movement. They were selected for their compact size, but they will need to be replaced with larger, more powerful motors before the project can move (literally and figuratively) to the next step.

KEY COMPONENTS

» Parallax BS2p40 microcontroller

» Parallax PSC servo controller

» 6 × NPC B81/B82 motors

» 6 × NPC EJ818 motors

» 12 × Vantec RBSA23 (“Bully”) servo amplifiers

» 6 × ODC5 solid state output modules

» 2 × NPC-B1812 12V 22Ah sealed lead-acid AGM batteries

FUN FACT

Moving the Spider into my garage at home was a touch-and-go process. Loading it onto the truck was done in minutes (thanks to the MythBusters forklift), but unloading it at home took 4 people almost 6 hours, and is one of the most dangerous non-work-related things I’ve ever done.


 

bb sf00 3657 003 Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed Him

“Deadblow” (Battlebots)

At the 1995 Robot Wars in San Francisco, I saw an awesomely powerful, relentless hammer ’bot named “Thor” that inspired me to design something similar, but using pneumatic (air) power rather than hydraulics. My version uses a paintball nitrogen tank for compressed gas storage, an air accumulator, and a high-flow, high-speed valve to drive the air piston back and forth, swinging the hammer.

2003deadblow Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed HimWe were up against robots with intimidating names like “BioHazard” and “Vlad the Impaler,” so I decided to name my hammer robot “Deadblow,” after the tool of the same name. (A dead-blow hammer is one designed to minimize recoil after a strike.) I drew up a 3D CAD model, then laser-cut the prototype from acrylic. When I was satisfied with the fit of all the components and panels, I used a CNC mill to cut “final” parts in aluminum.

But then, competing with fighting robots is a life of constant upgrades. I ended up going through three or four armor configurations, six different drive systems, and tons of minor and major weapon-arm and air-system tweaks to squeeze more performance out of my parts.

People often ask whether it’s worth it to put so much time and money into something that’s likely to be destroyed. My response? BattleBots is like a really cool party where your robot is your ticket to enter. It’s about testing your ideas against smart, tough competitors, and about the thrill of combat. Taking damage is part of the fun. And bringing home a giant nut (the trophy) isn’t bad, either.

KEY COMPONENTS

» 6AL4V titanium armor and weapon arm

» 2024 aluminum superstructure

» S7 tool steel hammer head

» NiMH battery packs

 FUN FACT

Deadblow was so popular that it spawned a line of official toys, and I was asked to write a book, which I called Kickin’ Bot: An Illustrated Guide to Building Combat Robots.


 

grant with r2 hi res Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed Him

“Artoo”

The time: May, 1997. The place: Leavesden Studios, UK. Filming of Star Wars: Episode I, was about to begin, and things were not going smoothly on the Theed hangar set. Specifically, the R2 units were not going smoothly — they kept getting caught in the door track. My team at Industrial Light & Magic had scant weeks to get the aging prop robots in shape for production.

r2 5 Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed HimUp to then, all the R2 units had some form of caster wheel in the front foot pod. Our solution to the door problem was to use a larger-diameter wheel that wouldn’t fall into the crack, and mount it on an axle that would be actively steered along with the rest of the robot. We used wheelchair motors for locomotion, which are quiet and precise. I handled the power electronics and the radio control system, including the mixing for the new steering components.

Before filming of Star Wars: Episode II, I was called on to update the electronics on the whole R2 fleet, starting with the dome lights (aka “logic displays”). Previously, big bundles of fiber optics terminated at a rotating color wheel illuminated by a bright halogen lamp (unchanged since the early ’80s), which gave a swirling appearance. I replaced the halogen/color wheel combo with two hockey puck-sized LED arrays driven by a microcontroller running pseudo-random PWM sequencer code (originally developed for the warp engines on the Protector in Galaxy Quest). I also made up a custom PCB to combine all the lighting functions in one neat little package.

KEY COMPONENTS

» 2 × Invacare Power9000 wheelchair motors

» 2 × Seiko Tonegawa SSPS-105 servos (dome and steered wheel)

» RC receiver

» Microchip PIC16C series 8-bit microcontroller

» Vantec RDFR33 electronic speed control

FUN FACT

The R2 unit we made for Episode I eventually became the “hero” unit — the one most used in filming close-ups.


 

bunny2 hi res Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed Him

“The Energizer Bunny”

In early 2008, the Eveready Battery Company commissioned Industrial Light & Magic to build a new generation of Energizer Bunny mascots for TV commercial production. My eight-person team had a three-month timeframe to complete three new mechanical bunnies plus two nonmotorized “posers.” My responsibility: all of the electronics and radio control systems.

Each Bunny has a custom circuit board and custom RC relays, with multiple 8-bit microcontrollers for interpreting the radio control commands and executing multistep movements — for example: stop beating, raise arms, twirl sticks, stop twirling, lower arms, and resume beating.

The internal structure is aluminum, with a vacuum-formed styrene outer shell. In total, the Bunny has 10 servos, 3 accessory motors, and 2 drive motors, and needs three operators: one for the head, one for the arms, and one to drive.

bunny 1 Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed Him

bunny1 hi res Grant Imaharas Hollywood Dream Machines, and the Spider Robot that Almost Killed Him

One of the most challenging parts of the project was that (for legal, truth-in-advertising reasons) the Bunny had to actually run on consumer-grade Energizer batteries. But with more than a dozen onboard motors — including two heavy-duty drive motors — the Bunny had massive power requirements, far outside the capacity of off-the shelf batteries and battery packs. My solution was to wire tons of them in parallel. I stuffed a total of 44 AA batteries into a banana-shaped pack, like an AK-47 clip, which hides along with all the other electronics in the drum body.

KEY COMPONENTS

» 3 × RC receivers

» 2 × Microchip PIC16C series 8-bit microcontrollers

» 4 × RC speed controls

» 10 × Futaba S9402 servos

» 44 × AA batteries

FUN FACT:

The Bunnies have names! They are E, F, and G — aka Earl, Floyd, and Garth.


 

IMG_9222

“Geoff Peterson”

In 2010, Craig Ferguson asked me to design and build a “robot skeleton sidekick” to help him host The Late Late Show on CBS. “Keep it simple,” he told me.

I used a standard plastic biology classroom skeleton, but replaced the torso with an aluminum plate where I mounted the servos and other electronics. “Geoff” is equipped with three high-power servos — one for each arm and one in the neck — capable of delivering 27 foot-pounds of torque each. There’s also a smaller hobby-type servo in the head, which flaps the jaw.

IMG_9224

Originally, Geoff had a complex, iPad-based wireless control system and onboard wi-fi router. A microcontroller interpreted trigger commands sent from the iPad and played a corresponding sound file, as well as orchestrating a set of synchronized servo movements to give Geoff the illusion of life. Basically, you would push a button, and the robot would respond on its own. Before each show, the producers would load up a bunch of preprogrammed clips and then select from that library to respond to Craig. (Incidentally, this is how “balls” became one of Geoff’s catchphrases, since it could be used in many different situations.) Lately, they have been operating Geoff with a live puppeteer, which allows greater spontaneity and many more comedic options.
Upgrades are always planned for Geoff, and recently, he got the ability to blink his eyes.

KEY COMPONENTS
» Parallax Basic Stamp microcontroller
» Parallax Propeller servo controller
» SparkFun MP3 Trigger
» Wi-fi router
» 3 × Seiko Tonegawa SSPS-105 servos
» Futaba S9402 servo
» Wiznet Ethernet interface
» 2 × switching power supplies

FUN FACT
Craig himself recorded the first version of Geoff’s voice. He sounded like a Dalek with a Scottish accent. Then actor Josh Robert Thompson took over voicing and controlling Geoff and does so to this day.


 

IMG_8010

“Oddjob”

The weapon of choice for the evil henchman of James Bond’s nemesis in Goldfinger is a razorrimmed bowler hat he throws with deadly speed and accuracy. For the MythBusters test, we built our own bowler-chakram with a sharpened steel ring inside. Unfortunately, it turned out to be too heavy for a human to throw accurately.

We needed superhuman strength, speed, and precision, so I built a steel-framed robot with a throwing arm powered by a massive pneumatic cylinder. The arm had an “elbow,” a second air cylinder to snap the “forearm,” and a pneumatic “finger” at the end that held onto the hat. The cylinder was pressurized ahead of time and the arm was held under tension by a 1-ton quick release latch. The trick was that the timing had to be extremely precise. I used limit switches to trigger the air valves; as the main arm swung ’round, it hit these switches, which caused the forearm to extend and the finger to release the hat at just the right moments.

KEY COMPONENTS

» 4.5″ dia. × 24″ stroke pneumatic cylinder

» 2″ dia. × 10″ stroke pneumatic cylinder

» 1.5″ dia. × 6″ stroke pneumatic cylinder

» 2 × high-speed, high-volume pneumatic valves

» 1-ton quick-release latch

» ANSI #80 sprocket and roller chain

» Limit switches

FUN FACT

The steel-rimmed hat actually lopped the head off the target statue on the second try, and we were incredibly excited … until we discovered that our “solid marble” statue was, in fact, hollow. Subsequently, we used a solid concrete statue, which the hat was only able to chip.


 

IMG_8458

“The Bride”

In Kill Bill, Uma Thurman’s character The Bride is buried alive in a wooden casket. Rather than accept her fate, she uses her martial arts skills to punch the coffin lid over and over until it collapses, and then she digs her way out. For the MythBusters test, we needed someone who could punch repeatedly for hours — with phenomenal strength — without giving up. The list of human volunteers was surprisingly short, so we opted for a robot.

To build it, I used a small air tank as an accumulator and attached a large, high-speed/ high-volume air valve as well as four smaller air valves. The main air valve handled the powerful punching stroke, while the smaller valves handled the retraction. We connected them to a squat(but powerful) air cylinder equipped with a fist cast from ballistic gelatin. The whole thing was connected to a giant external air supply and controlled by a pair of digital interval timers.

IMG_8466

We fired the robot up, and it proceeded to go THUMP, THUMP, THUMP on the coffin lid for hours. After approximately 600 punches, it did actually create a crack in the wood, but it didn’t punch through. Sorry, Uma! Rest in peace!

KEY COMPONENTS
» Dual OMRON digital interval timers

» 4 × small pneumatic valves

» High-flow/volume pneumatic valve

» 4.5″ dia. × 10″ stroke pneumatic cylinder

FUN FACT
The main high-speed/high-volume valve was borrowed from special effects company M5 Industries, and several smaller air valves came from my personal fighting robot, Deadblow.


 

Grant Imahara

Grant Imahara

As a co-host of Discovery Channel’s MythBusters, Grant has swum with sharks, spun a merry-go-round with a shot from a sniper rifle, hung beneath an airborne helicopter, fired cheese from a cannon into the San Francisco Bay, let two dozen tarantulas tap-dance on his head, dropped a BMW from a Sikorsky, cut a car in half with a rocket sled, and built many awesome robots. All in the name of science.
Before MythBusters, Grant lit the lights in R2-D2’s dome and gave the Energizer Bunny his beat as an animatronics engineer and model maker for Industrial Light & Magic. His work appears in several blockbusters including The Matrix sequels, Galaxy Quest, Terminator 3, and Star Wars: Episodes I-III (though he is in no way responsible for Jar Jar).


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