T4-K9 Dancing Dog - aka Cog The Dog Tamiya T3-01 Hackmod

Tamiya has started something exciting when it released the T3-01 chassis it developed for the Dancing Rider, that quirky 3-wheeled leaning trike they released late 2017. In fact, elements of that design are in the new Lunchbox Mini I reviewed HERE. The leaning setup adds an entirely new dimension to Tamiya models that hint at interesting ideas in robotics and chassis dynamics. So where, then is the T3-02?

Sometimes innovation comes from without. "I was inspired by the Sony Aibo, but wanted something faster. Something more outdoors, something more dog." says Brian Gunning, the creator of this serious hackmod he's dubbing the T4-K9 Dancing Dog - aka Cog The Dog.

The business end of the T4-K9 is unchanged from the stock T3-01. Gunning uses a Traxxas 370 and Hot Racing ball differential with Yeah Racing metal shafts for durability and top speed. Gunning's current setup means Cog has a top speed of 25.4 mph, (measured by strapping an iPhone to his back). Tires are Tamiya hop-ups and the chassis has full bearings throughout.

Gunning used two T3-01 kits to build the T4-K9. Two forks are in use, one for each arm, and the "radio platform" was used twice to create a Ducati-esque space frame topped by the dog's head. The chassis is still fully suspended, by two independent front forks and the stock rear torsion shock.

The head is built from the stock battery cover part flipped upside down and drilled for cooling. The top platform of the radio deck forms the jaw, and a portion of the original plastic shell for the eyes and head are painted in Kawasaki GPZ livery. "It was my first bike, I still love the colors." The FreeSky receiver, light controller, and micro servos to control the head are all inside.

The standard T3-01 chassis uses one standard servo to lean, allowing the front fork to change angle by gravity. The T4-k9 uses the same principal, but adds two more servos...one for each fork. Gunning used a table saw to notch out the existing frame at the current neck position to make room for two back-to-back servos.

Those servos are bound to the chassis via threaded rods passing through a small metal plate added in the center, between the chassis halves. "I added holes for the existing chassis screws and the threaded bolts for the servos, but I didn't measure anything. It's pretty much all eye-balled and assembled with hand tools."

Gunning is using a FreeSky i6s transmitter and all 6 channels of the receiver to control his creation. Channel 2 controls the hip servo, and is mirrored to the head L/R servo with a small reverse circuit. 3 and 4 control the shoulder servos, and are Mixed with each other and Channel 2 to blend servo actions similarly to a Delta-wing setup. Channel 5 is set to the left VR pot to control the head up/down, and 6 is reserved for the linear micro servo in the jaw. "He will be able to pick things up soon." Gunning promises.

Check out Cog the Dog in this excellent video


There is no direct steering for Cog. Like walking a dog, the steering input is more a suggestion, and for the most part the dog is agreeable. Each fork is lightly sprung to center, but still uses shopping cart caster technology to make steering work. Here you can see Cog set up for a high speed corner with the chassis leaning slightly right, right fork all the way forward, and left fork nearly vertical.

The twin-fork setup allows Cog to act more like a dog, too. He can drive tight slow circles with the forks upright, or lay them out flat for high-speed driving and stunts. Moving the legs together with the right stick changes the steering dynamics from twitchy oversteer to lazy understeer while you drive. Dynamic indeed.

Cog's head turns with the hip servo, giving a lot of life to the model as it looks into turns, using the head's weight to counter-balance the corner and toss the frame deep into turns. The head is attached using an AdaFruit standard micro-servo gimbal frame, with up/down controlled off the left VR pot. "I've had entire conversations with people from across a parking lot, just using Cog's body language" Gunning notes. "He's really expressive. Kids just love Cog."

This hip dog cruises the streets of Wausau Wisconsin bringing smiles and the inevitable question, "Can I pet it?" everywhere it goes. Gunning has plans for more versions of his wheeled dog creation. "I've already made a few Lego versions," he says "and I'm hoping to have a version using micro servos and Erector set parts by this winter. He's like my personal suit of Iron Man armor. I'm just going to keep building them until I come up with one that can fly. Wouldn't that be cool?" 

No word yet on Tamiya making RC dog kits, but Gunning (And Myself) remain hopeful. :)

Thanks to Brian Gunning for such an inventive build article.. I cannot wait to see what is next :)