Project Overview  Introduction  Frame Build  Motion  Power  Control  Sensors  Advanced Sensors  Open design challenges  Project evaluation

LESSON 02

Metal parts (various) LESSON 02 STARTER Delrin Bearing Flat Keps Nuts 8-32 Screws Parts list Quick task: Discuss in pairs all the parts shown. Agree the function each of these parts in the Tumbler frame, and write your description in your parts list. Pop rivets

FRAME BUILDING Building strong structures When joining many parts together, it is important to consider how they join and in what shapes, to ensure the structure created is strong. Strong structures resist deforming, impact, and help to direct forces acting on them. Below is an ideal triangular frame and a square frame. The load, in blue, is acting on them both. In the case of the triangle the compression and tension of the frame will stop it deforming. This is not the case for the square frame which will deform as shown, pivoting from the corners. LIKELY DEFORMA TION UNDER LOAD TRIANGLE SQUARE Learning objective: Develop an understanding of simple frame design and the building techniques required to create simple robot design solutons.

Building strong structures Joining metal parts for strength is easy, by simply adding two or more screws between frames. Here are examples on one face (the X) and a second face (X then Y). If you join a material by fixing it in the X, Y and Z axis, this will be joined without opportunity to move at all. This is the same in CAD part assemblies (see Autodesk Inventor project). Insufficient fixings Sufficient fixings (1 axis) Sufficient fixings (2 axis) Excessive fixings FRAME BUILDING

Building strong structures Looking at the metal chassis parts and angles, they have patterns of holes. This is not a pretty pattern. Why are the holes arranged like this? Answer… Arranging the holes in patterns of 5 (like a dice face) allows you to fit screws into two or more holes, and creating multiple fixed points between the two parts, adding strength by preventing compressive and tensile forces twisting the frame as the robot moves. In this way we can create a solid frame to mount other parts to. FRAME BUILDING

Building strong structures The square frame of the Tumbler can be reinforced to prevent it deforming when under load in two simple ways. 1. Use one screw on one axis, and one on a second axis to prevent any twisting. 2. Add a second chassis frame inside the first, creating four parallel pieces of metal. FRAME BUILDING

Building strong structures With the Clawbot (the next VEX project) you can see that the frame has been built to create fixings on different axis, so that it does not twist or move when in operation. The red circles identify points where fixings (screws and nuts) have been used to assemble the frame. They appear either in pairs or on two axis to prevent a frame from twisting. In the case of the claw however, not there is only one fixing through one axis, resulting in movement about that fixing. These pins become pivot points around which joints can move, or in the case, allow the claw to open and close. For the Tumbler, the frame must be rigid and tough to prevent twisting or deforming under load, and there follows the pair or 2 axis rule. FRAME BUILDING

Building strong structures Whole class design task: Using just angle sections of metal from each Tumbler kit, how would you create a very tall but very strong structure? THE SOLUTION FRAME BUILDING

Watch this short demonstration video that will take you through the simple elements that make up a more complex VEX Robot build like those above. Starter video (click to launch in Vimeo) Building strong structures Building with the VEX system can lead to some exciting, large, and complex robot builds like these below. These both use the basic frame principles to ensure a sturdy build, and the following techniques which you can watch and learn about now. FRAME BUILDING

Getting Started Layout the metal parts as follows - 4 x Chassis Rails - 2 x Angles - 1 x bar (used later) You will also need a hand full of: - Screws - Bearings - Pop Rivets Tools you will need are: - Allen Wrench 5/64” - Allen Wrench 3/32” - Open End Wrench Chassis Rails Bar Angles FRAME BUILDING

Use the Step by Step build guide - STRUCTURE Follow the instructions on page one of the build guide. Use the tools provided by your teacher and remember to check all the time that you are being accurate and working as a team! Key to getting it right… Tighten the screws using an allen wrench and open wrench at the same time. Fit the pop rivets tightly with a “pop” sound. The bearing should not wobble. FRAME BUILDING

LESSON 02 PLENARY As a class, let us consider the following questions? A. How do we create strong structures with any materials? B. When building a VEX robot, what has been designed in to help you achieve strong structures? C. Why have the extra chassis pieces been included in the Tumbler square frame? D. What do the axis X, Y and Z relate to?

SUMMARY Learning objective: Develop an understanding of simple frame design and the building techniques required to create simple robot design solutons. Today you have:  Learnt how to assemble a strong chassis frame for your robot Tumbler.  Used a range of tools to join materials temporarily  Developed an understanding of how structures can be strong or strengthened