M.O.T.M Ring

_concept

The basic concept of this project is combine the open tensegrity structure with membrane, also develop it into a moveable structure. We take the basic idea of the bicycle wheel structure, which is showed in Fig. 1. The simplest tensegrity work can be formed with one strut and four cables, and you can get more complex sets when you combine these simple elements. This kind of tensegrity structures work well in plane, but they get unstable when out of plane, so an additional structure is needed, like a frame to hold the structure. It looks like a limit of the structure, but we try to take the benifit of this limitation. We seprete the frame into three layers, then use the track to make them could be rotated around a same center. By attaching the tension cables at different layers, we could change the angle between the tension cables by rotating the frame. By changing the angle of the tension cables, the compression members will move radially, so the inter ring of the structure will open and close. This is the basic movement of the structure we want to achieve. We can consider this structure as a roof system that could be open and close.

_system

The basic system could be consider as a roof structure, which could be light weight and could be open radiusly. Which could be a structure solution for stadium.The system is easy to acturate when the tension member could change the length. Which is the typical way to acturate the tensegrity system.

_structure

The axon diagram showed the major element of the whole structure system. Which the membrane applied on the top and the bottom layer which doesn‘t consider as a structure element (even it could hold the tension load). The frame hold the whole system by tension. 8 compression members arraied by circle, an elastic member in the center which creat the deformation of the openning. The section structure diagram showed the force applied in the system, which only tension and compression in the system, no bending moment exist. Then compression member‘s height is .6m which is close to the golden ratio 0.618 to the radius.

_joints

For the actuator, we decide use manual control the whole system, we will set up a hand knob to twist the frame. To maxiam the deformation of the structure, we try to figure out a way to slove the problem caused by the two tension cable when they met together. We propose to layer them in different level, so that they won‘t conflic each other.

_mechanism

The structure consists of two wheel-shaped frames. The outer frame has a C-shaped section detail and the inner wheel is located within the hole of that „C“. There is a lateral opening in the outer wheel that allows a small handle to come out from the inner frame. This handle acts like the actuator of all the system, since it makes the inner wheel rotate independently from the outer wheel. In the center of the whole set there is a rubber band. In between the double wheel frame and the rubber band, there is a group of poles and strings. The vertical poles are under compression stress, while the strings are under tension stress. All the poles are linked to the inner wheel, the outer wheel and the rubber band by a series of strings. This principle makes that, when the inner wheel rotates and the outer wheel stays still, all the poles relocate themselves and they make the rubber band expand, making the hole in the middle grow. Over the whole system, membranes can be placed to cover the space below the structure.

_parameters

To design the whole system, we start with the number of the compression members. Based on our study and calculation, the deformation of the center circle related to the numbers of the compression members (more compression ebers, less deformation). Considering the visualization and the deformation, we chose 8 compression members system. That means the angle between two moveable tension cables could reach 45 degree (with the improved join method, the angle could reach larger). The section diagram shows the deformation value in the whole system, which x is the deformation of the elastic member, and the y is the deformation caused by the elastic member, z is the deformation caused by the angle change of the tension cable a. The diagram showed the the relationship between the different member of the structure. Based on the simple way to calculate the length between the frame and the compression columns, „a„ should be 1/2 c. But the deformation should be able to express by a non-linear function. Which means we can find a best range of deformation to make the „c„ more efficiency.

_system Parameters

cable1 length: s1= 50 cm

cable2 length: s2= 48.6 cm

horizontal gap: a= 38.3 cm

horizontal gap: b= 37.6 cm

column height: h = 60 cm

Opening Angle: a = 0 - 45°

Deformation radius: q = 31cm