See How This Versatile Robot Can Scale Vertical Surfaces with Ease

This project from Jegatheesan Soundarapandian was inspired by observing how lizards are able to walk along walls. Upon getting this initial idea, he then applied it to a problem, which was how to efficiently take some small tools to the top of a tower. After searching for a solution, he came across a few wheeled robots, but those have trouble moving up stairs. So, he used the movement of lizards to determine how his robot would work.

Theory of Operation

Lizards are able to climb up walls by using tiny hairs on the bottoms of their feet to stick to the surface. Since hairy robots aren't quite a thing yet, he went with a pair of electromagnets instead. To move in a certain direction, one foot's magnet is deactivated, it is rotated in the requested direction, and then the magnet is reactivated. This cycle continues for as long as the user wants.

Necessary Hardware

Since the user interacts with the robot with a phone, there is a base station consisting of an Arduino Nano, HC-05, and RF transmitter. This is because Bluetooth alone might not have enough range to reach the robot, so it's better to use a lower-frequency transmission system instead. The robot itself also has an Arduino Nano and RF receiver, along with a DC-DC step-up converter, four servo motors, and a pair of electromagnets. Power is provided by two 18650 batteries in series.

3D Design and Fabrication

The robot's chassis was designed with Tinkercad, and it can be found here. The chassis is quite simple, consisting of two halves that each contain a pair of servos. One servo motor in each pair is responsible for rotating the robot, and the other tilts the robot up so it can pivot freely. The batteries and electronics are housed in the middle to keep the center of gravity balanced and low, which means the robot will be less likely to fall.

How the Robot Program Works

Commands for movement come in from the RF receiver module and get decoded. If the robot is going to the right, the left leg lifts up and moves more than 45 degrees, depending on how far up or down the robot is moving simultaneously. The right leg then moves to line up with the left leg in a straight line, so that line ends up being perpendicular to the desired direction. The reverse is also true, in that moving to the left causes the right leg to pivot around and then the left leg matches it. Commands are encoded by a single ASCII character. For example, 'D' corresponds to down and 'K' corresponds with down-right.

Control from a Phone

Communication with the robot is first started by the user's phone, where an Android app first connects to the base station's HC-05. Then, it sends a specific character to the base station depending on which button was pressed via Bluetooth. When the base station receives the command, it relays it to the robot via a simple RF module.

Assembly and Testing

Once Soundarapandian received his 3D-printed parts, it was time to assemble. The electromagnets slot into the bottom of each foot, and then those two assemblies get attached to the rotational servo mounts. There is a bracket that spans from each piece, and they are connected together in the middle.

After adding the electronics and starting the app, he stuck the robot onto a metal wall. Sadly, the robot tends to fall off when walking, so the creator chalks this up to using magnets that are too weak. To solve this, he plans on adding better magnets and a larger battery pack.