Jinny                                                                                               

Hand Shaped Ostrich Robot at Kinetica 2012

Recently while cruising the undernet, I ran across this intriguing image of an animatronic bird-thing pulling a small cart. The image is so cool, I thought about trying to duplicate this bot.  Maybe I'd use a hefty 6 volt acid-lead battery to power some micro-controlled stepper motors.

The bird-thing image started me thinking about legged robotics again. What is the best way to pull a load anyway, with bird legs (knees hinged towards the back) or with mammal legs (knees hinged towards the front)? Seems like all real-world pack animals have front facing knees, just like humans do. In fact, it is still common in some parts of the world  for humans to pull loads around with rickshaws. Hum... robotic legs pulling a rickshaw. How about robotic legs strong enough to pull me around in a rickshaw. Strong legs would need a lot of power; generating power adds more weight. Seems like a portable air compressor in a rideable cart and big leg pistons could be a way to go. So once again, what started out as a modesty sized rational project has morphed into a crazy-big-ass-over-engineered circus. I have bravely cleaned out  a 4x8 foot work space in the garage and I'm ready to dive-in. What can I say; this is where my muse is taking me; I can either follow where she leads me or loose my creative way.

Wiki says  the word rickshaw originates from the Japanese word jinrikisha, where jin = human, riki = power and sha = vehicle. From the word jin, I am naming this project Jinny. I am committed now.

This is a big project that may take as long as two years to complete. I will break the project up into three parts:

Cart sketch.

In phase one, I will build a rideable rickshaw that has a portable air compressor hidden under the seat. I have pretty much settled on a design. I already have a 2 hp four-stroke engine (26 lbs) that will drive a Craig's list compressor unit (39 lbs) and I also have a pair of sturdy 14" wheelbarrow wheels. I need to buy a half sheet of  plywood, some 1" thin-walled  electrical conduit, some weldable metal rods and some miscellaneous hardware. The cart will have a foot powered mechanical break system.

Servo follower pneumatic piston.

In phase two, I will build two human sized pneumatic driven legs. My current idea is to use only one pneumatic piston per leg, probably made out of 3" PVC pipe. Thirty PSI would give me 212 pounds of force to use, at a rate of about one stroke per second. The knee joint will be the only actively powered part of the leg mechanism. The piston will be of a servo follower type, where the piston's position mimics the position of a standard servo. This is a design I developed years ago and it is a marvelous actuator solution. I plan to use magnetic angle sensors to monitor the free wheeling upper leg position (hip joint) and to use air pressure sensors to monitor the weight that each foot is supporting. The direction of the leg swing (forward and back) is fixed until changed by the rider (pulling on a set of reins. (Yeehaw!).

Phase three will be writing the arduino uno micro controller program that runs things. This will be the most formidable part of the project, especially since I skipped building a smaller version of the project where I could have developed control loops without accidentally bashing into my wife's parked car. Indeed, the compressor easily produces 100 PSI which could generate over 700 pounds of force at the piston heads. I will have to have several levels of safety built into the design and still be very careful.