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The points highlighted in yellow within Figure 1 are points that require grounding on some kind of cage not included in the drawing. This cage would be sturdy enough to act as a virtual ground link for the planar wing, as well as house the motor responsible for the rocking motion and be able to handle the force induced by this rocking. One major issue we had to resolve was ensuring that the rotation of the two wings remained planar, that we used the right line of action to consider rotation. In order to ensure that this new rocking rotation can be achieved, the center of rotation for the cage connection points on the wings and the center of rotation for the rocker must be along the same axis. We ended up making the hinges located on the wings attach to the cage on either wing into rings that connected to a hole in the cage. A ring through the gr planar ground pivot point allows the piece to rotate as it did with a dowel in it, but easily connects to the cage through a small hole. Adding this ring also allows for more variability in position of that rotation point if our alignment is not correct. With more rotation at this point on the upper wing, the original (now virtual) planar ground link may become larger. If this distance, from center of rotation of the driving link on the wing to the rotation point on the upper portion of the wing, becomes too large our entire device may become a non-Grashoff device causing its performance to suffer. In addition we were able to find a non continuous motor that allowed for back and forth rotation which negated the need fr a crank rocker device entirely.We also decided to exclude a complex gear system between the two wings to allow for single actuator power source, because we wanted flexibility to shift the wings in towards one another and away if dimensions needed to change on other components.
As we began to model this system in Solidworks, the difficulties arose from designing the cage. There are several essential details of the cage: first it could not interfere with the movement of the wing, it could not block the view of our device to others to extensively, and needed to be stable enough to support the movement and weight of materials as necessary. Our initial design was rectangular, but quickly the merits of arches was scene in their simplicity, elegant look and obvious ability to stay clear of the wings as they moved. Although our initial design was more baren than that seen in image 2, the premise is nearly identical except with less arch supports, base triangular supports, and longitudinal supports attaching the arches together. These elements will prove useful however as we learn more through fabrication.
Motor Selection
We decided to use the 2 Propeller Continuous Rotation Servos and 1 Futaba Standard Servo to actuate our mechanism. We chose these motors because they were relatively lightweight, and we had free access to them through the UT Austin Advanced Mechatronics lab. The continuous rotational servos have a stall torque of approximately .294 Nm, and the standard servo has a stall .431 Nm. We showed our mechanism to our TA, and after observing how little friction and inertia we had to overcome, we qualitatively decided that the motors should have enough torque to drive their portion of the mechanism.
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