Two major systems of every robot on the planet are the structural systems and mechanical systems. Mechanical systems allow some or all of the robot to move.  Before we get into how to design a mechanical system we are going to go through all of the things FRC, FTC and Vex robots have been asked to do over the years.

Tasks in FRC

 

Tasks Unique to  FTC or Vex

When you are doing research look up the past games to get an idea of what the various types of tasks were and what the game pieces looked like.  Next we will go through some of the popular mechanical systems that teams have used to do all of the above tasks.

 

Mechanisms Examples

 

Passive vs Active Mechanical Systems

You can design a mechanism to be completely active, meaning that all functionality is a result of powered motion as demonstrated above. Or you can design a mechanism to be partially or completely passive meaning all functionality is a result of the shape.  The benefits of passive mechanism are that the reduce the likelihood of mechanical or human failure occurring. Here are some examples of passive mechanisms;

  • Intake mechanisms
    • Passive claw: tote
  • Robot lifter mechanism: example 1

 

Understanding Motion

Once you have selected the desired capability you will need to select the type of motion you need.  Here are the different types of motion you are most likely to see in FRC;

  • Linear motion – motion in a straight line (example: train on a track)
    linear_motion
  • Rotary motion – circular motion (example: the hands of a clock moving, or a wheel on an axle)
    engineanimation

 

Mechanical Joints

A mechanical joint is a section of a machine which is used to connect one mechanical part to another. Mechanical joints may be temporary or permanent, most types are designed to be disassembled.

 

Mechanical System Design

Mechanical Systems  need to be able to withstand the expected structural loads over an expected number of cycles. Teams will need to follow these steps necessary to design their mechanical system.

  1. Sketch out a idea
  2. Build prototypes
  3. Refine the sketch
  4. Refine the prototype
  5. Create a free body diagram
  6. Understand the loads
    1. Understand ultimate load case for each type of loading
    2. Understand the number of cycles for each load case
    3. Do the math
  7. Select materials that can resist the loads
  8. Define the shape that will resist fatigue and is manufacturable

Note – steps 3 and 4 may need to be repeated many times to find the right combination to reduce weight and fabrication complexity

 

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