Simple CAD to get sizes and movements defined.
Jump to Section:
Double Reverse 4-Bar Tutorial
Tools to Learn
Select a Plane, The sketch we are making will be 2 dimensional so you ned to select a plane to draw on. When you click create sketch three planes are kighlighted in yellow. Click on one to select it. usually I will pick the plane that is the x, y axis plane.
L activates line tool. Click one point then the next, click the check mark when done. esc to leave line tool.
You can type in a value for the length of the line here. In designing the robot the length of the line is usually a distance between holes.
Click for center, then drag for approximate diameter. Enter a value to set the diameter. esc to leave circle tool.
DimensionD activates dimension tool. Click a feature and drag mouse to create dimension line. Right click to get other options. Click when placed correctly. Enter a value and click enter to finish. This will constrain the size of the feature to that dimension. esc to leave.
ConstraintsCoincident A coincident constraint is made when a new line is started on an existing point. A blue box indicates this. Equal Makes 2 lines , arcs or angles constrained to be equal. Parallel Makes 2 lines parallel Tangent Makes a line and an arc tangent or two arcs tangent.
Knowledge to Use
GeometryChord of circle. Equal chords give equal arcs. Can use to create gear motions on gear constrained lifts. See DR4B
Constrain features as a real build. Imagine screws as constraints and lengths of parts fixed.
Hole spacing is ½ inch so try to use lengths in ½ inch increments.
Gears are 24 dp, meaning a 24 tooth gear would be 1 inch in diameter.
So for the VEX 60 tooth gear the diameter would be 60/24 or 2.5 inch.
So when you use gears in Crayola cad use the correct diameter circles. Note that this is the pitch diameter , where the gears mesh. If you measure the diameter at the end of the teeth it is larger. Meshed gears are drawn a circles with the pitch diameter and tangent to one another.