The Attractnid has four feet that each consist of a magnetic foot and a sliding assembly. These specially designed feet are the basis for the robots unique ability to stick to and walk on vertical magnetic surfaces.
The foot assembly houses our mechanical magnetic switch. The servo on top activates and deactivates the magnetic switch, allowing the foot the stick or un-stick. The foot also has a bearing which allows it to pivot.
Our robot’s feet needed to have a strong attraction with the metal wall as well as release easily for motion. Initially we planned to use electromagnets to achieve this, however, we realized the large amount of electricity necessary to run them would prevent us from untethering our robot from an external power source. Our solution was to create permanent magnet feet that could be switched on and off with a servo.
We found through research and experimentation that we could reverse polarity in half of a magnetic assembly to cancel out the magnetic field holding the foot to the wall. The assembly is made up of an H magnet closest to the wall and a reversible A shaped magnet that rests on top of it. When the A switch is in the on position (attracting) the polarity of the two halves align reinforcing the magnetic field and attracting with almost double strength. When the servo flips the A switch 180 degrees into the off position, the poles on the halves are misaligned. The opposing poles on each side of the magnet pull toward each other instead of reinforcing the attraction with the wall. This lets the foot easily drop off the wall and the leg can be moved. This is shown in the magnetic field diagram.
The slider assembly lets the robot move and pivot in place while keeping its feet fixed to the walls. The constant force spring at the front of the slider allows for the foot to always retract to the outermost position. There is also a slight angle built into the slider. This makes the foot pop off the wall when the foot releases.
The frame of the robot is designed for tight packaging of all the components. The robot on the underside carries its battery and its power converter. From this view you can see the magnets in each foot and the gripping pads used to prevent the robot from sliding down the wall.
