Cellulo V2
Cellulo V2
The actual version of Cellulo (V2) is born from two core needs: Adapt the previous version to correct flaws and errors discovered over its use and seek to expand the functionalities to adapt to the necessities of the users.
Cellulo is a project born in 2013 as an educational tool and the digital and autonomous pen of the classrooms. After constant use by the researchers and users, it was possible to point out weaknesses in the design. Additionally, the advance in technology has opened new capabilities for the robot. The goals of the new redesign are to solve the flaws spotted, improve the functionalities of the robot and increase its capacities. The strategy to achieve those goals is based on the following factors: Usability, maintainability, cost, and scalability.
The old Cellulo had two core flaws spotted; battery capacities, mainly caused for the lack of on/off buttons, and locomotion maintenance. Additionally, it was learned that the users would appreciate having versatility in the way to interact with the robots, whether it is from a mechanical perspective or from the electronic one, which led us to the introduction of modularity. These flaws, as well as other lessons learned, are dissected in the following sections.
A schematic of the V2 is displayed below.
The biggest burden spotted in the previous version involved the locomotion system. In particular, Cellulo is based on a novel technology that enables the robot to move holonomically. A holonomic movement is such that each of the degrees of freedom is directly controllable. When using wheeled robots, this tends to be a problem, since the wheels can only be driven in one direction, and that is the reason why the Omni wheels or Mecano wheels were created since they are active in the rotational direction, but thanks to the small rotational parts in the radius of the wheel, it doesn't block the displacement perpendicular to the rotation. Seeking the same effect, the CHILI team came up with the idea to use magnets to drive the wheels. In a detailed manner, the wheel consists of a metallic ball that is magnetically paired with the shaft of the motor, and when the motor moves it drives the wheel, however, if the ball wants to rotate in a direction that is not the same as the magnet direction, the shear force would not be sufficient to interrupt the movement.
More details about the design can be found in the thesis Cellulo: Tangible Haptic Swarm Robots for Learning.
This design presents multiple advantages, however, it comes with some inconveniences. First of all, the size of the robot requires small parts, hence, the bearings and the magnet are parts that are harder to find out and accommodate in the design, i.e. the bearings are 3mm in diameter, nylon made and allocated directly in the chassis, hence, to provide adequate functionality the tolerances in the bearing hole must have small tolerances and smoothness, which is hard to produce. As for the ball, the initial design was done with metallic balls of 14 mm and a casting of 1mm to provide friction in the movement. Those balls are custom-made, and hence an appropriate supplier must be found, the last supplier used can be found in the following email: 1007785188[at]qq.com. Be aware that it is a Chinese supplier and it has limitations in the language as well as payment methods. Additionally, these design incurs a maintenance cost. Due to the nature of the movement and the design, dust and particles tend to be accumulated in the bearings, which difficult the move over time. The same movement and friction between the floor, the magnets, and the balls might cause erosion in the coating surface, which deteriorates the movement. Because of those reasons, it is required to do maintenance periodically,