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

3. LESSON 04

4. LESSON 04 STARTER Parts list Quick task: Discuss in pairs all the parts shown. Agree the the function each of these parts in the Tumbler power, and write your description in your parts list. 7.2V 2000MAh Battery Battery Strap

5. ADDING POWER Learning objective: Understand how power can be used to achieve functional robotics and how batteries differ and can be used for VEX. Introduction to batteries When a device is connected to a battery, a reaction occurs that produces electrical energy. This is known as an electrochemical reaction. Inside the metal or plastic case is a cathode, which connects to the positive terminal, and an anode, which connects to the negative terminal. Between them is where a chemical reactions occur. A separator creates a barrier between the cathode and anode, preventing the electrodes from touching but a medium called an electrolyte allows electrical charge to flow freely through it between them. Positive Negative

6. Electrolyte Inside the battery When a robot is turned on, a circuit is completed (the switch closes the circuit) The anode instantly experiences an oxidation reaction in which two or more ions (electrically charged atoms or molecules) from the electrolyte combine with the anode, producing a compound and releasing one or more of its electrons. At the same time, the cathode goes through a reduction reaction in which the cathode substance, ions and free electrons also combine to form compounds. This may sound complicated, but its actually simple. The reaction in the anode creates electrons, and the reaction in the cathode absorbs them. The electrons moving is what current is, which powers the robot! Anode Cathode ELECTRONS ADDING POWER

7. Non-rechargeable batteries are known as primary cells. Rechargeable batteries are known as secondary cells. Both produce current in exactly the same way: through a electrochemical reaction. However in a rechargeable battery the reaction is reversible. When electrical energy from an outside source is applied to a secondary cell, the negative-to- positive electron flow that occurs during discharge is reversed, and the cell's charge is restored. VEX batteries NiMH batteries, like those used with VEX robotics, care tricky to charge and maintain. You must be careful: - not to overcharge them (as this could lead to decreased capacity) - trickle the charge slowly to the battery - Recondition the batteries by completely discharging and recharging them again every once in a while to minimise any loss in capacity ADDING POWER

8. Lithium-ion batteries (rechargeable) Lithium chemistry is often used in high-performance devices, such as cell phones, digital cameras and even electric cars. It is perfect for VEX Robotics which need to perform to high levels instantly and repeatedly. The make up of a Lithium-ion battery is a combination of lithium cobalt oxide (cathode) and carbon (anode). ADDING POWER

9. Use the Step by Step build guide – POWER 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… Fit the motor in place tightly and connect. Bend and fit the bar to the right position on the chassis. ADDING POWER

10. Alternative to bending the metal bar Can alternatively cut your metal bar to remove the excess. Here is how. Step 1: You will cut off three from each end (or 6 from one end). Mark this with a scribe (or marker pen) and steel ruler. Step 2: Cut the metal by clamping in a metal vice and using a hacksaw. Step 3: Use a metal file and file in one direction the end until all burs and rough edges are removed. ADDING POWER

11. LESSON 04 PLENARY As a class, let us consider the following questions? A. What are the two elements of a battery that react to create electron flow (current)? B. What is between them allowing the flow of electrons through it? C. A primary cell is what type of battery. What is a secondary cell? D. What happens in a rechargeable battery when it is charged?

12. SUMMARY Today you have:  Learnt about how batteries work and rechargeable batteries restore their charge.  Applied power to your Tumbler for the first time.  Developed knowledge of how to work with metal to shape and form it accurately. Learning objective: Understand how power can be used to achieve functional robotics and how batteries differ and can be used for VEX.