TMR3M Grade 11 Manufacturing Technology – Robotics Unit

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Robotics

S.P.I.C.E. Design Model:
– situation: states the scenario and gives context to the project, introduce all the given information, as well as information you would have to figure out in order to complete the project, state time constraints
– problem: state all possible problems that would need to be worked through—include materials, figuring our torque/speed gear ratios
> also called a design brief, states rules that need to be followed in design
– investigation: brainstorm all possible solutions to the problem and find the best method of making it—include calculations, thumbnail sketches, prototypes, etc.—if used trial and error, include process as well as why the final design was chosen
– construct: build the design, talk about how it was built, how easily or difficult, include working pictures
– evaluation: evaluate the final design, begin testing—talk about what worked, and why it worked well

Tools and Safety:
–  when cutting axles on the band saw, use vice grips and the wooden push stick
> place a piece of scrap wood towards the blade and cut about an inch in
> use that as a platform to cut the axle—prevents it from bending when it is pushed inside the hole on the band saw base
> be sure to wear safety goggles
– Allen keys are used to tighten screws and nuts
– nut drivers are used to tighten nyloc nuts (nyloc nuts have a plastic part in them which prevents the screw from coming out even before fully tightened)
– must use a wrench to secure the nut before tightening with an Allen key

Torque:
– torque: the measure of instant force applied on an object than can cause rotation around a fulcrum, or simply put, if an object is turning another, it’s how hard the object pushed on the other
– torque = distance from fulcrum in metres x mass in newtons (T = nM)
– newton metres (Nm): are the measurement unit for torque and have to do with the force of gravity on earth—Nm can be calculated by multiplying the weight of the load in kilograms by 9.8 (which is acceleration of gravity)
– torque is calculated to determine how much power is needed to move or to lift a load. Once torque is found, gears ratios and different motor types that are needed can be determined—this can also help ensure there is more torque than needed
– example: A 200 g weight is placed 0.2 m from a fulcrum. Calculate the torque.
Nm = 0.2 kg x 9.8 = 1.96 Nm
T = 1.96 Nm x 0.2 m = 0.392 mN

Gear Ratios:
– gears are used in many ways, like to connect one motor to two or more wheels through a gear train—they can also be used to increase the torque of motors, which would make moving or lifting heavy loads easier
– to calculate gear ratio, divide the number of teeth of the driver gear by the number of teeth on the driven gear, (note than when written as ratio, the driven gear comes first)—30/60 = 1/2 = 2:1
– gear ratios can be used to increase the torque, since motors are often high-speed and low-torque—by  increasing the torque the speed is reduced, and vice versa
> to increase speed, use a large driver gear
> to increase torque, use a small driver gear
– to calculate the gear ratio of a gear train, multiply the ratios of each pair of gears in the train—60/30 x 30/60 = 2/1 x 1/2 = 1:1

Drive Programming:
– tank drive: on the controller, one joystick controls one side of the robot, while the other side controls the other
– arcade drive: on the controller, one joystick controls movement both forward and side to side
– on the PIC microcontroller, default programs for tank and arcade drive can run by hooking up the motors to certain ports—tank is 23 and arcade is 12
> this means that the motors get plugged into those ports, based on the kind of drive required
> also, remember to make sure the transmitter is set to 12 or 23 too
– tank drive is easier to program, arcade drive is a little less precise than tank, because one joystick controls all movement—reduces the amount of movement or the type of movement
– getting the hang of how to drive in arcade mode is also more difficult than tank, because with tank the movement of the robot directly corresponds to the movement of the joysticks
– with tank drive the controller is completely devoted to moving the drivetrain and nothing else—this is a problem if the team only has one controller or only one driver—would mean that they would need two separate joysticks
> if two joysticks were unavailable, arcade drive would have to be used so that one controller would control the tool and the drivetrain

Autonomous Programming:
– start by opening the application EasyC for Cortex, select “Autonomous Only Project” and press OK
– screen consists of main tab where code goes, as well as modules that can clicked and dragged over
– drag motor modules over and set their values in order to start the motors movement—if no wait time is added, then motors spin indefinitely
> values include motor port number and strength
– if the robot is not moving straight, change the values of the motors, to make some stronger and weaker accordingly
– when using sensors, need to create a variable and refer back to the variable (“retrieves to”) within the code
– when done, select “Compile Project” and then “Build and Download” when complete
* when cortex is plugged into computer, it needs to be turned off as it will turn on on its own

Teleop Programming:
– this is programming that allows control with the joystick
– just click and drag type of drive required, then fill in proper motor port number
– for example, tank 2-motor drive, would mean a chassis with 2 motors driven in tank drive
> all values for the motor ports would need to be inputted
– compile then build and download to the cortex