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Movement in Robotics

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by | Feb 13, 2019

One thing that I find particularly fascinating in robotics is the constant problem solving in movement. Generally, at least in my head, when you mention “robot” I have a biped in my head. Something with two legs that walks like we do. This sort of movement brings a whole host of challenges that (I bet) you hadn’t even considered.

We all take the fluid movement of walking for granted, we can walk in an S shape without having to stop and re-evaluate movement prior to turning. Many robots would have to stop, think about the next movement, turn at a certain angle and THEN return to moving forward (rinse and repeat for our S shape). Our pattern is a smooth curve vs. a robots rather jagged looking S shape.

Another challenge? We are able to remain static and upright, walk in a straight line (sometimes, maybe not on a Saturday night) but also walk up and down stairs. We achieve this by constantly changing our centre of gravity and lots of dynamic movement (swinging our arms like pendulums). Imagine how many sensors must be required for a robot to constantly be aware that it has moved, is off balance and now needs to change its centre of gravity before it falls over. A lot! This is a challenge enough for walking on a flat surface, add in a gradient (or stairs!) and it would become an even bigger sensory challenge! This has been achieved though by ASIMO, a robot developed by Hondas. This impressive robot can store walking patterns in real time, calculating where to place its feet each step, acceleration/deceleration and steady speed: all of which creates a fluid movement vs. previous robotic attempts which can appear stiff and overthought. If you watch closely, you’ll also notice that ASIMO’s torso shifts slightly with each step, allowing it to readjust its centre of gravity (as we do!). ASIMO can walk up and downstairs because of this ability to real time walk.

Even more impressive, Boston Dynamics have created a humanoid, biped known as Atlas which can not only keep its balance on uncertain ground, it can actually stop itself from falling even when its centre of gravity is completely off after tripping and if it does fall, it can get itself back up. Something which I find marvellous is it can also jump! See here.

Bipeds are popular, however there are also robots with six legs known as Hexapods. These are fantastically stable because at all times there are three legs on the ground, creating a triangle of stability each time it moves forwards. Quadrupeds have four legs and are also popular, although a few of these remind me of the robot dogs in Black Mirror. Quadrupeds are four legged robots and are able to negotiate uneven ground. Boston Dynamics, again, created BigDog which was designed to carry heavy loads on its flat back in uncertain environments, a great benefit for getting supplies etc to troops (if required). Impressive as it is, I still have the heebie jeebies every time I look at it (the quadrupeds in Black Mirror were not friendly).

How else can robots get around? Many small robots are wheeled. They are steered differently than a cars wheels, which predominantly use a rack-and-pinion steering. This mechanism doesn’t allow for tight turning (in circles) so smaller robots tend to have two wheels, one on either side, and are differentially steered. Each motor, and therefore each wheel, is controlled independently. So to rotate, we could turn one motor off and one motor on and vice versa. This is how my university simulated robot is controlled, wee Simon! The issue with these robots is they are not exactly space saving! So they would be useless for, say, a robot intended for pipework. The wheels also don’t offer a lot of stability on rough terrain, think of a fiat (or similar) trying to off road, yikes!


This does give the robot a range of motion as shown:

Robots can also be tracked, but this seems inefficient to me as a lot of energy is lost through friction and there is not a lot of control over movement. However, there is a place for them as tracked robots have the upper hand on difficult terrain than wheeled robots.

Robots have also been made to hop, swim, fly and even climb. A Professor at Nagoya University, in Japan, even created a robot known as “The Brachiator‘ which gets around by swinging! The robot even has the ability to lear how much of a “swing” it needs to grab the next bar. People are really steeping out of the “robot box” though and robots have even been designed to move in a similar way to animals such as snakes which have an incredible amount of Degrees of Freedom.

Side Note: The idea of “Degrees of Freedom” is used to describe the range of motion a robot has. e.g a human hand would have more than 20 degrees of freedom, one degree of freedom for the ability to make each finger move around (rotation, forwards and backwards) and one per joint. A elbow joint moves around one axis and has one degree of freedom. 

We have even started to make robots that mimic the way plants grown and climb! Most recently researchers at Istituto Italiano di Tecnologia in Genoa created a “soft” robot which climbs in a similar way to a vine growing. You can read the research here or find the short and sweet summary here 

Needless to say, all of this movement requires some sort of force behind it, known as its actuator. Many robots remain electrical, however actuators such as hyraulics or pneumatics are increasingly popular. These are summarised well in this article but the simplest way to remember them is that hydraulics uses  pressurised fluid, pneumatics works using air pressure and electrical actuators turn electricity into torque (power). 

A bit of a whistle stop tour, but hopefully it’s got you thinking about other ways we could make robots move. Maybe something from the plant kingdom will be the next huge leap forwards for movement in robotics!