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  1. Parts
  2. Dimensions and Constraints
  3. Motion Analysis

Representing Parts in Crayola

In Crayola CAD we are working to develop the design of moving mechanisms to assure fit in size constraints and to be compatible with other structures on the robot. The completed cad can also be used to determine abilities of the robot in the game, such as scoring height etc.

All parts are represented by 2 dimensional basic shapes such as lines and circles. so our most used tools will be Line and Circle, press L to get Line tool and C to get Circle, esc releases each tool.

For a structural part usually the length of the line is the length between holes in the part. This way the end of the line is 1/2 inch shorter than the real part if using the center line or 1/4 inch shorter if using a side row. Alternatively and more accurately you could make the line the full length of the part and add points to represent holes that you will use.

Shown here is a line 4 inches long representing the distance between the holes on the center row. The 4.5 inch line represents the distance between holes on the side rows. The C channel is a 10 hole length that is 5 inches total. the distance between each hole is 1/2 inch. Depending on your design objective you could use lines of any of these lengths to represent this part.

Gears are represented by a circle that is on the pitch diameter where the teeth mesh. This is somewhat smaller than the physical outer diameter of the gear. When two gears are meshed together and two circles are tangent the distance between axels will be correct.

Dimensioned 36 tooth gear showing pitch diameter and outer diameter.

The vex gears are 24 diametrical pitch, meaning that a gear with 24 teeth would be 1 inch in diameter. The 36 tooth gear is 36 / 24 = 1.5 inches in diameter. The outer diameter is slightly larger by the size of the teeth. All the gears have the same tooth dimensions so we just add a constant to diametrical pitch. For the vex gears the outer diameter is 0.084 inch more than the pitch diameter.

Putting it all together, we have a small 2 bar lift using 10 hole long c-channels and a 12 tooth gear driving a 60 tooth lift arm gear.