3 August 2017

Digit Evo 1 - One Small Step for Robot Kind

Digit Racing Against the Clock
In 2006, an event occurred called the UK Robotic Games, which had a biped walking robot category.

After about 2 nanoseconds of thought I, decided that I must enter as it was just too tempting to make a walking robot.

So after much sketching and head scratching I came up with a design and Debs christened it Digit, a name that stuck.

Digit was quite utilitarian, in that there was no attempt to make it animal like or human like, it was just built to race.

It is a statically stable biped, which relies on keeping its centre of gravity over it's feet at all times.
To do this it leans one way to raise one foot off the ground then moves that foot forward. It then proceeds to lean the other way, then raises its other foot off the ground and moves that forward etc.

Movement of the stride and the leaning are done by 2 servos. The control of the servos is by pulse width signals coming from a Microchip micro-controller.

To make the servo change position at the required rate, a sequence of positions are read from a table and translated into pulses at the correct time.

The correct table is selected depending upon a second micro-controller, which decodes the signals from a radio control receiver, such as forwards and the speed, as well as direction.

I programmed 3 speeds for digit, which had to be carefully tested, as stability becomes an issue when leaning side to side, because if you're not careful, it can throw the robot over because of the momentum.

Mechanically the robot has 2 large feet, legs are in 2 parts for rigidity, and to keep the foot parallel to the ground.

At the body the leg parts pivot front and rear with 1 degree of freedom, as there doesn't want to be any sideways motion at the body leg joint.

At the feet there are 2 degrees of freedom, in the form of hinge type joints, the sideways twist and a swivel. After getting Evo 1 to a walking state, I was inspired to evolve the design, and so set to work on Evo 2.

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