Green Living
ISDN2001/2002: Second Year Design Project
Topic: Independent studies on suspension for chassis
Background
The suspension system should align with the selection of the wheelbase and the characteristics of the usage. Throughout the project, the wheelbase had kept changing and led to different variations of suspension.
Above all the circumstances, the wheelbase was meant to maneuver freely in all directions as it could map out the cleaning area at the highest efficiency. By looking into the existing vacuum cleaning robots, they mainly use two wheels and a roller bearing to achieve the movement.
At the same time, we investigated similar products such as those window cleaning robots and wall climbing toy cars. They used tank belt, or two wheels aligned in a normal four wheel with only one wheel on one side respectively.
At the same time, we investigated similar products such as those window cleaning robots and wall climbing toy cars. They used tank belt, or two wheels aligned in a normal four wheel with only one wheel on one side respectively.
Apart from the above-mentioned methods, using omni wheels or Mecanum wheels may also meet our goals.
Design Process
The first suspension system was designed for a robot that has full automation. According to the calculation of my groupmate, the suction plate could have provided a 5kg carrying weight. And by estimation, the whole robot would not exceed 2kg.
By calculation, the force exerting towards the wall was 0.3N which the robot would fully stick to the wall with a maximum of 5kg carrying weight. The robot would not drop in ideal case. According to the product specification of the wheel motors originally used, the motors could provide 1.5kg/cm. The motors need to overcome the friction between the suction plate and the wall to move.
As the friction ration of silicon is around 1, the force from the wheels which was attached to the motor should eliminate the frictional force in order to move freely.
First Stage
This design could maintain the wheels attaching to the wall while the suction plate was approaching to the wall.
Before calculating the horizontal spring system, calculation was done on vertical spring system to prevent complicating the problem.
By calculation, the k value should be 0.015 N/mm. With the formula of spring stiffness, the material was aluminum, the wire diameter was 0.5mm, the coil mean diameter was 6mm. These numbers were used as they could reduce the weight and the complexity of the system. The result turned out to be unsatisfying which the number of effective coils were way less than 1.
Therefore, the plan was suspended.
First Stage Results
The robot was then changed to a 3 omni wheel chassis with a handheld machine. As there might be calculation errors from the value obtained, direct testing was used in the second stage.
The usage of the robot was changed to handheld rather than moving by its own. When the user was holding it, more force would be exerted to the wall than only the suction system. This part was not easy to calculate. Therefore, many generations of the suspension were built.
Second Stage
