Futuristic movies usually portray a world where robots are commonplace and yet here in the present they’re not nearly as accessible, at least not the humanoid ones. If you just want a robot that can vacuum your floor read no further! One of the major things in humanoid robots is the development of linear motion devices. If you want something that spins we’ve got that covered but making something move in a line, now that’s a bit more difficult. There are ways to do it and some of them would make great muscles for robots!
First off, there’s the idea of having a motor drive a screw and use that to move a nut back and forth. This is a pretty common way of getting robust linear motion into many applications especially where accuracy is a concern. This is because for every turn of the motor the nut is going to move a small and easy to determine amount. However these can be slow and can wear out rapidly.
Next let’s look at hydraulics, these are pistons powered by piping high pressure fluid into them and forcing the piston to extend or contract. They are very powerful and can be made fairly accurate, used commonly in industrial applications for lifting things. They can also be miniaturized to fit onto a robot, unfortunately they require a fair amount of piping and a powerful pump.
Thirdly lets look at a nickel titanium alloy that goes by the brand name Nitonol. This material will contract if the temperature is raised due to a transformation in it’s internal crystal structure. Essentially the atoms that make up the material shift around and reorder themselves into a more tightly packed structure reducing the length of the overall wire. This means that when electricity is passed through the wire it will heat up due to it’s resistance and the heat will cause it to contract. This allows for linear actuation in a very small package, however the change in length is also quite small.
The world of tomorrow will probably have more prevalent humanoid robots, and they just might be flexing muscles made with one of these actuators!