VEX IQ Curriculum Mechanisms Lesson 07

MECHANISMS In your current groups, clean up your boxes. Take all of your last robot apart and put pieces neatly into your box.

MECHANISMS The purpose of this lesson is for students to learn about robotic mechanisms, their design, and the corresponding math and science concepts.

Task 1 : Matching exercise Fill in the missing gaps on your worksheet by picking words from the word bank at the top of the page. Learning objective: Learn about DC Motors. Learn about and apply knowledge of Gear Ratio. Learn about Drivetrains. Learn about Object Manipulation. Learn about lifting mechanisms. LESSON 07 STARTER

Actuators are used to act upon an environment, usually for moving or controlling a mechanism or system. Actuators drive everything that moves on a mobile robot. The most common type of actuator is a motor; in particular, VEX IQ utilizes Direct Current (DC) Motors. DC Motors convert electrical energy into mechanical energy through the use of electromagnetic fields and rotating wire coils. When a voltage is applied to a motor, it outputs a fixed amount of mechanical power (usually to a shaft, gear, and/or wheel), spinning at some speed with some amount of torque. LESSON 07

Motor Loading Motors apply torque in response to loading. Motor Loading happens when there is any opposing force (such as friction or a heavy mass) acting as a load and requiring the motor to output torque to overcome it. The higher the load placed on a motor output, the more the motor will “fight back” with an opposing torque. However, as you learned in the Key Concepts Unit, since the motor outputs a fixed amount of power, the more torque the motor outputs, the slower its rotational speed. If you keep increasing the load on a motor, it eventually stops spinning or stalls. Motor applies torque to overcome the friction of a wheel turning against the ground Current Draw A DC Motor draws a certain amount of electrical current (measured in amps) depending on how much load is placed on it. As the load increases on the motor, the more torque the motor outputs to overcome it and the more current the motor draws. LESSON 07

Build the gear ratio simulator, as shown in the handout. 1.Build the Basic Gear Assembly (steps 1 – 4) 2.Build the Assembly with Compound Gear Reduction (steps 5 - 9)

LESSON 07 Work in the following groups A- Dawson, David, Jake B- Allana, Bryce, Jackson C- Brock, Ethan D- Cole, Jacque, Jason E- James, Brodie

Task 2: Build and experiment with the VEX IQ Gear Ratio Simulator. Gear Ratio Basics Making a Gear Ratio change is one of the easiest ways to change Mechanical Advantage in a mechanism or system to achieve desired speed and/or torque. Gear Ratio expresses the relationship between a Driving Gear (the gear connected to the input power source, such as a motor) and a Driven Gear (the gear connected to the output, such as a wheel or mechanism) in a system. When you have a system with a Driving Gear that is SMALLER than the Driven Gear you will increase Torque and decrease Speed: LESSON 07

When you have a system with a Driving Gear that is LARGER than the Driven Gear you will increase Speed and decrease Torque. Making this kind of change to Mechanical Advantage is helpful when you are trying to lift or move faster mechanically, you don’t require the ability to lift heavy objects, and/or you favour agility over pushing ability in a drivetrain. LESSON 07

Expressing Gear Ratio and Gear Reduction Both Gear Ratio and Gear Reduction are mathematical expressions that describe the relationship between a Driving Gear and a Driven Gear. However, It’s important to understand the different, but similar ways they are expressed. Both use the number of teeth on each gear as key values, although their order is reversed. Gear Ratio is expressed this way: (Driving Gear Teeth) : (Driven Gear Teeth) Gear Reduction is expressed in reverse: (Driven Gear Teeth) / (Driving Gear Teeth) Note: Gear Reduction is seen as a fraction that is often reduced to simplify the expression LESSON 07

So, given the example right of a 12-tooth Driving Gear and a 36-tooth Driven Gear: Gear Ratio = 12 : 36 “12 to 36 Gear Ratio” Gear Reduction = 36 / 12 or 3 / 1 “36 to 12 Gear Reduction” or “3 to 1 Gear Reduction” Mobile and Competition robots will vary greatly depending on the tasks they are designed for. However, one thing common among them is that they usually have some method for moving. The robotic subsystem that provides the ability to move is often known as a Drivetrain. Drivetrains may come in many different forms – two examples are wheels or treads (like a tank). The wheeled, rolling drivetrain is the most common one found in competition robotics and one of the most popular in the entire industry… LESSON 07

Gear Trains and Idler Gears A simple Gear Train is a connected set of rotating gears that transmits power from an input (like a Driving Gear connected to a motor) to an output (like a Driven Gear connected to a wheel or mechanism). Simple Gear Trains can have any number of gears in a single row. All gears in between the Driving Gear and the Driven Gear that only transmit power are known as Idler Gears. Idler Gears have NO EFFECT on Gear Ratio or Gear Reduction, regardless of the number of teeth they have. Example Gear Trains: In all three of these example Gear Trains, the Driving Gear is 12- teeth and the Driven Gear is 36-teeth, thus the Gear Ratio for all three examples is the exact Gear Reduction, they just same - 12:36. Size and number of Idler Gears have no effect on Gear Ratio ortransmit power! LESSON 07

Compound Gears and Compound Gear Reductions In certain situations, a design may require more mechanical advantage than a single gear ratio can provide or is otherwise impractical. For example, if a VEX IQ robot design requires a 12:500 gear ratio it is a problem because there is no 500-tooth gear available. In this situation, a designer can use multiple gear reductions in the same mechanism. This is called a Compound Gear Reduction. In a Compound Gear system, there are multiple gear pairs. Each pair has its own Gear Ratio, and a shared axle connects the pairs to each other. The resulting Compound Gear system still has a Driving Gear and a Driven Gear, and still has a Gear Reduction. However, it’s now called a Compound Gear Reduction and is calculated by multiplying the gear reductions of each of the individual gear pairs. LESSON 07

Quiz on Monday Ten questions, taken from some of the previous shown here

Brain Storming Defer judgement. You never know where a good idea is going to come from. The key is make everyone feel like they can say the idea on their mind and allow others to build on it.

Brain Storming Encourage wild ideas. Wild ideas can often give rise to creative leaps. In thinking about ideas that are wacky or out there we tend to think about what we really want without the constraints of technology or materials.

Brain Storming Build on the ideas of others. Being positive and building on the ideas of others take some skill. In conversation, we try to use “and” instead of “but.”

Brain Storming Stay focused on the topic. Try to keep the discussion on target, otherwise you can diverge beyond the scope of what you're trying to design for.

Brain Storming One conversation at a time. Your team is far more likely to build on an idea and make a creative leap if everyone is paying full attention to whoever is sharing a new idea.

Brain Storming Be visual. Nothing gets an idea across faster than drawing it. Doesn't matter if you're not Rembrandt!

Brain Storming Go for quantity. Aim for as many new ideas as possible. Crank the ideas out quickly and build on the best ones.

LESSON 07 As a group, you will design a robot to play soccer. Think about speed and agility, also think about pushing your opponents. Your group should brainstorm together. Each person should draw out ideas in their own notebook, but all must agree on one final idea and this must be presented to a teacher before you may build

LESSON 07