2. Second BIRD Prototype

The second prototype built included adding a frame to the mechanism. For the original idea, we wanted to combine flapping and rotating bird flight patterns. However, pursuing each mechanism requires two separate projects because it would take two motors for both degrees of freedom, as well as advanced programming to combine the two mechanisms in unison. Therefore we designed our prototype to focus more on the flapping motion and gear assembly on a frame resembling a robotic bird. The design shown below exemplifies the crank rocker motion attached to the gear assembly which will be run by an AC brushless motor. The motor was chosen by performing a reverse analysis in order to calculate the amount of torque required to fly the bird, as discussed more below. In the attached excel spreadsheet, the torque was calculated by solving for the amount of lift required to fly the bird. The inputs were based on worst possible circumstances meaning heaviest material possibly used as well as most inefficient design possibly used. The torque was also calculated with a double gear system in mind as seen the second prototype picture. In other words, the torque the motor produced must apply enough torque to both input gears for each wing.

Torque Analysis

To calculate the necessary torque that our motor would see we decided to plan for the worst and fit the torque for the worst case scenario with the dimensions that we came up with. This meant a solid rectangular prism like body with solid rectangular prisms as wings. This would make our torque calculation very conservative as the weight is much higher than expected and the areas are blunt. After we calculated the mass of our prototype, minus the mass of the motor, we then assumed that the center of mass would be in the middle of the bird body and that the lift force from the flapping motion would be acting 2/3 away from the center of the body. Again this is conservative as in actuality the lift force should act closer to the body of the bird. We then multiplied the weight of the bird by the distance to where the lift force was acting. Again to be conservative, we said that this was the torque that the motor would be seeing (no mechanical advantage from gear trains). We then solved iteratively to find the motor that matched up. We knew that when buying a motor this value would be unrealistic, so we divided it by 25 because we figured that this was a reasonable mechanical advantage for the space that we have.

Torque analysis based on weight of design:

Torque Analysis.xlsx

Second Prototype:

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20131118_204127.jpg