5: CAD Design Principles for Electric Vehicles

Learning Objectives

• Students will learn to think about design parametrically in CAD systems.
• Students will understand the concept of a feature, basic feature types and their properties.
• Students will understand what part families are and how they are used.
• Students will be introduced to Additive Manufacturing (3D Printing).

CAD Model of the PLUS II

• PLUS II is an electric vehicle
• Made of several components including chassis, bodywork, windshield, electronics, door, steering system, front wheels, drivetrain, back wheels
• Example of CAD model used to design these components

Drivetrain

• Example component of PLUS II
• Composed of electric motor, wheel, suspension

Example part from Kyburz: Motor Shaft

• Motor shaft is an example of design using CAD features
• The motor shaft is broken into various parts with different function and material properties
• Parts are indicated by different colours eg, orange - bearings, green-sealings, blue-drive shaft, pink-coupling motor, red-differential drive, grey-gears, transmission
• Drivetrain is a key component of electric vehicles.

Question: Modeling operations

• The question asks about the best way to represent the basic shape of a part in CAD, using geometric modelling operations
• The options are either 1. Extrusions only, or 2. Revolves only

How can we encode the engineering meaning of geometry?

• CAD features can be used to encode engineering meaning of geometry
• This is referred to as "Design-by-Features"
• This makes designing easier to understand, manage and modify
• Example of this is in the design of a gear
• A gear is a complex shape, with many features such as key seat, chamfer, centre hole, locking pattern, groove
• Features are built up on top of basic geometry to create complex shapes
• Example of features: chamfer, round, mirror geometry

Assembly and Tolerance Features

• Assembly features allow parts to be assembled and constrained in CAD software
• Example of assembly feature - co-axial assembly features, where parts are aligned and attached to each other
• Tolerance features are used to control dimensional accuracy of parts
• Tolerance features ensure that a part is within specified limits
• Example - profile tolerance feature

Feature Verification

• Feature verification is important to ensure CAD features work as intended
• Features can sometimes interact with each other, creating unexpected geometry
• Example - fillet and round feature, where the round overwrites the fillet
• Model History can show how a model was created
• History can show a breakdown of the features used to create the model

History Dependency and Interaction

• CAD models have 'history' meaning they remember how they were created
• History can be used to modify a model easily
• Changes to a model can have cascading effects on other features
• Example: modifying a hole feature can affect a pattern or shell

Question: Alternative Model

• This question asks about modifying a sequence of modelling steps in CAD
• Modifying the sequence of steps can change the outcome of a design
• Example - switching the order of 'shell' and 'hole' operations can create a different result

Sketch and Parametric Modeling Overview

• Parametric modeling allows for flexible and dynamic design
• Parametric modelling uses constraints and parameters to define geometry
• The relationships and constraints define how geometry should behave
• The model automatically updates when parameters change
• Example: changing the length of a line can affect the position of other geometric entities

Question: Parametric Modeling

• This question asks about how a parametric model responds to changing its parameters
• Changing parameters can change the model because of defined relationships
• The constraint solver will find the new solution and update the model accordingly

How to Create a Parametric Model

• Parametric models are created by linking geometric entities using parameters and constraints.
• Constraints define relationships between different geometric entities in a CAD model.
• Example constraints include:
  • Lines parallel to lines
  • Lines perpendicular to lines
  • Circles tangential to lines or other circles
  • Points constrained to a specific location.
• Parameters are used to define specific values for the constraints.
• Example parameters include:
  • Angles
  • Lengths
  • Radii.