Team 2886B-- John Hardin High School

Make it Real CAD Engineering Challenge

For our CAD Engineering online challenge, we decided to create a latching mechanism. Earlier in the year, we were contemplating an intake design that had both a fixed position to stay within specifications, and second mobile position to fulfill its functionality as an intake. However, since there’s no official VEX latch, we had to design our own with other various VEX parts. Although we got the job done, it ended up being too heavy, too complicated, and too bulky. This did bring to our attention, however, that teams all around the world could be having the same issues we are. Therefore, we planned to remedy the absence of a VEX latch by making one ourselves.

Part Specifications

Our VEX latch is a 4.5 inch long by 0.7 inches tall by 0.6 inch wide rectangular piece made of acetal resin. It has 6 holes on the side at the standard increments of 0.273 inches; the holes go all the way through the part. There is a groove on the top of the part that starts just after the last hole, about 3.273 inches from the start of the part. The groove is 0.4 inches deep, 0.3 inches long, and the width of the part at its base. It is open on both sides, but is enclosed in the front and back because of the part itself. The front of the groove is simply a wall at a 90o angle, while the back surface is about 0.48 inches long at a 126.8o angle relative to the top of the part. The part ends at an angled surface that is about 0.9 inches long at a 135.5o angle that is also relative to the top of the part.

How it Will be Used

The original idea for usage on a robot was to create a system that would allow a fixed mechanism to become mobile with a simple movement. It would optimally be used with a standoff or other part that could rest in the channel of the part, denying it the axis of motion to extend into its active position. Then with a simple jerking movement, the latch would release the standoff, restoring its axes of motion, and putting it into an active position.

We also brainstormed several other uses along with the original. A very practical use for this year and years would be a passive catapult launcher. VEX challenges consistently require some sort of launcher to throw scoring objects in some sort of manner. Our part would be used in tandem with a high strength gear in the same manner as a medieval catapult. As the gear turns, the latch would turn with it until it reaches a release point, where the arm would swing forward with the help of rubber bands-- thus a passive catapult. Finally, it can be used in other applications where a mechanism needs to have the ability to transfer from a fixed position to a mobile one, a prime example being wheelie bars.

How We Used Inventor

We used the 2016 version of Autodesk Inventor Professional to design and 3D print our part. We used the basic 3D part building tools such as the 2D Sketch tool, Extrude tool, Fillet tool, Measure tool, as well as several others in the design of our part. We also conducted stress analysis simulations as to check our part’s weak points, and see how it would perform under the conditions of being on an actual robot. We also referenced other CAD parts such as the C-channel so we could provide accurate measurements and spacing. Finally, our part was created as a standard .ipt file, the same format as the parts we already have.

The dimensions of the holes are equal to the cam gear.

After conducting a 5 lbs stress analysis simulation on the vital area which we assume will receive the most force, we were able to discover weak points in its design

Another angle showing the possible warping of the latch under stress.

The overall dimensions of our latch.

The latch will be lipped and thicker to give more structural support similar to the high strength spur gears.

Design Process

When we decided our team would be undertaking this challenge, we had several ideas that we wanted to investigate. Therefore, we used design matrices to decide which idea we wanted to throw our full support behind. After we settled on the latch idea, we went about trying to find the optimal design that would not only suit our purposes, but the purposes of other teams in the future. After several iterations and much debate, we settled on our current design, which we consider the optimal design for a latch.

We redesigned the original latch to give it more support on key weak areas, after simulations we determined that the redesign provided more drastic weak areas than the original design.

We also simulated a stress analysis on our redesigned part to see if the new design

proved to be better, which it did not.

Conclusion In past years, our team has always been encouraged to use Autodesk Inventor in tandem with our other design tools; we will continue to use CAD in the design of future robots just as we have in the past. Using CAD modeling to conceptualize a robot design is always a good practice for any design process. The model can serve not only as an accurate design for references, but a comprehensive build-guide and easy to access parts list. Having proper CAD skills can also be very useful in the future workplace. Jobs that require STEM disciplines, especially engineering jobs, have a high likelihood of requiring some sort of CAD modeling. Any good design team will certainly use CAD in the design of a product, so already having skills in 3D design would be a great skillset to bring to an engineering career path.