Bob the constructionrobot

Our robot consists of a chassis with two drive wheels that allow it to turn precisely in place. To keep the balance, it is supported by four ball casters.


Bob the construction robot orients itself with LDR sensors that detect the brightness of the ground and thus the lines.  The component recognition is done by two touch sensors in the lifting element.

Bob thus moves to the building element and scans it. Since the walls differ in the arrangement and number of windows, they can be distinguished.
The lifting element at the front of the robot carries the electromagnet, which holds the components, the touch sensors and a guide.

Hoist

The lifting unit detects the walls and can raise and lower them, placing them in the right places. In order to realize this process smoothly, sub-functions such as component recognition, lifting and transport had to function properly. The lifting is performed by a trapezoidal threaded spindle. The spindle is supported at both ends by plain bearings. To ensure almost frictionless descent and ascent, a threaded nut made of tribologically optimized plastic is used on the spindle. Torque transmission between the spindle and motor is ensured by a toothed belt drive.

Component detection

There were two options for component detection: The first solution was with a camera. However, since a camera takes up a lot of space, this option was ruled out. The second, more complicated option was to design a magnetic fixture that performs several functions at once. In the center of the mount is the electromagnet, which has a force of 280 Newtons. Two guide nipples were designed to fit the dimensions of the components.

According to the specifications, there are two different roofs and three different types of walls on the playing field. They include door, window and glass front. In order to distinguish the components, there are two tactile sensors above the magnetic holder. Depending on the configuration in which the touch sensors are actuated, the robot recognizes which part it is.

Bumper

In order to ensure unhindered lifting of the components, very precise centering is required and the possibility of moving differently close to the storage site and the construction site, because the components have to be lifted and set down differently close. This was achieved with the extendable bumper. It can move horizontally forwards and backwards. After many considerations and tests, it was decided that the system should be driven by a servo motor.

A servo motor is mounted on the base plate. The motor has a 3D-printed wheel with an eccentric cylindrical heel that moves 90 degrees in a circle. The motor is connected to the moving bumper, by a 3D printed element which has a long vertical recess. Since the heel of the wheel is in the vertical recess, the 3D printing element is pushed from front to back, and the rotational motion is thus converted into a horizontal longitudinal motion.
Thus, we are able to move the bumper in and out at will.
In addition, the bumper has prongs at the ends that center the robot at the build site and at the storage locations. Lastly, near the prongs are two touch sensors, they are actuated when the component is touched. This distinguishes whether the robot has reached its destination or not.