CAD Techniques

Preface: Haven’t really seen any threads about this so I figured I may as well start one. Also, I’m well aware of the Vex CAD discord server, but not all forum users or competitors are actively on discord.

When I first started CAD, I didn’t know where to begin. I kind of just used the inspect tool and field appendix dimensions to get an assembly started –– almost like trial and error. But it wasn’t terribly inefficient, and it actually lent me some decent results. But then I got to college…

Understanding how CAD actually works and is intended to be used lends a whole array of opportunities (especially for robotics). Working around defined design constraints and real-world physics allows for some fully optimized geometries.

Examples from my Change Up Sketches
  • Chassis - Intake Geometry
    Screen Shot 2021-01-03 at 7.43.46 PM
    dimensions and constraints visible
    Screen Shot 2021-01-03 at 7.44.23 PM
    dimensions and constraints hidden

  • Uptake Geometry
    image
    fully optimized for uniform contact (given the constraints)

When I see intricate assemblies like these these (notably 5225a), I’m curious to know what kind of mindset goes into designing and cadding something of that caliber. So, all that being said, how do you approach CAD?

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Preface; I am an Inventor user, I acknowledge the benefits to Fusion(and others) but prefer Inventor for Vex assemblies and design. I do use Fusion for 3D printing and to share stuff with my team though.

For the intricate assemblies that you mentioned, its completely different. What Boots and other people that work on Remembering The Best do is take images and videos of robots that we see as the best, and make assemblies of their designs. I personally have made 929U TP, and 62A ITZ as well as started 5225A ITZ(until Boots beat me with his insane skill) and am currently working on AURA SR. This is a different process from designing a new robot however because we have the photos of what the original designers did and we are just working to recreate it digitally.

I can’t speak to other contributors of the project do for their process but I always start by watching reveals and other videos, scrubbing through and taking screenshots of different portions of the robot, and compiling as many of these photos as I can into an album. I then reach out to different people on the forum, and Discord to see if there are any photo repositories. I know this is how Boots did a large portion of the Pilons’ robot. From there it is just sitting down and working through the robot. It appears that Boots makes sub Assemblies of different portions of the robot which are then all placed into a larger assembly for export and rendering. I know Zach 929U does a similar process in Fusion 360 although I do not know how the heck he did 169A’s robot. I personally have found this to be the best process though and although it takes some trial and error, it works if you can commit to it. After that, you just render, I started in Inventor, then learned to use Fusion to Render, and now I use Blender.

As to designing a competition robot for the current season. It is the same as you would design a robot in person. At least for me. You start with the base; you have the idea of what you are looking for, the specifications you want to meet and your personal design strategy/aesthetic. From there, onto the intakes. This is just trial and error for the most part. You constrain parts together, see how field elements interact, change the components, and then keep moving. I like to make one functioning side of the robot, and then mirror grounded components to the other side. You continue this process of placing, constraining, measuring, and adjusting parts and assemblies until you have a robot.

From there, I upload it as a .step file to Fusion 360 since it has an iPhone app that my team can use to build off of. Fusion also gives nice renders with little effort.

With this strategy, you save a ton of time of actually building and can also come out with a much more intricate design. Just be aware that some things are going to be different in person because of using round pegs to affix square holes…

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I was referring to designing a robot from the ground up, I think CADing an already built robot is pretty intuitive. I agree with your general process though –– normally starting from the chassis up makes the most sense. The precision of the 5225a passive intake (and more generally machined parts) requires more than trial and error with CAD, though.

One of the most efficient ways to CAD is by projecting geometries of surfaces from already existing Vex parts/assemblies (kind of like the images above, a combination of optimized geometry as constrained by Vex parts). I know many people don’t utilize the CAD sketch tool for Vex assemblies often (mostly because you’re confined to Vex parts, not custom).

People also forget that Vex parts can be heavily modified –– for example, no one is stopping you from machining a custom piece of 5 wide :thinking:

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the great thing about CAD is that you don’t necessarily need to start from the ground up. you can figure out important geometry, and worry about how you’re going to make your build fit the geometry afterward, not the other way around, and I find this leads to a more efficient and better performing build in the end.

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To add to this, I like to design around the scoring elements directly. For example, change up intakes could (and should) be designed around the extreme points of the goal zone. This will allow to have maximum torque at the high contact points on the goals and overall allow for a more efficient system.

TL;DR I don’t think there’s any one chronological or end-all-be-all method to CAD

Even then, what other CAD skills are necessary to design an efficient system? Like, knowing how to use cross-section views is really useful for compact builds.

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Typically I figure out motor distribution and subsystems before I even start cadding. Then I figure out the limits and most effective way to do each one in a file. Then start throwing everything into a main file and adjusting things to fit.

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In regards to CAD techniques, it really just becomes more apparent as you start to design more often. Understanding what the game requires out of a robot and what your goals are in a match can greatly help understand what you want to do with your design.

The 5225A CAD was designed through the team’s extensive Google Photos album which I had access to. This allowed me to go through and understand what structural components went where and how certain mechanisms worked within the robot. (I have linked the album at the end of the post for anyone curious.)

In regards to this:

This is fairly accurate for a majority of the time, but something that can help is creating a semi-complete mockup through CAD, physically building it as a prototype, and playing around with it to understand how different manipulations can change the outcome. Through this, you can approach designing a second version much easier as you have the groundwork laid out for what has to be changed and what can remain the same.

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I really like this idea. Tapping into different learning centers of the brain to understand patterns and relationships between the problem at hand and the design (in this case, kinesthetic learning center is optimized).

This is interesting because normally people insist on one end of the extreme –– people either follow CAD to the tee without allowing for new ways of thinking or the opposite where someone won’t plan anything beforehand at all. Speaking from experience, most novice engineers (for lack of a better word) won’t plan much of anything beforehand, and even now I tend to rigidly stick to my CAD regiment. I’m starting to realize that engineering is a hugely dynamic field where art and creativity meet science.

There is no one way to get good results, but the best way probably involves a little bit of everything.

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friendly reminder to fully constrain your c channel’s FEA study

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Ethan, it needs to be all one part to have structural analysis done…

you can do FEA on assemblies…?

besides what i was implying was that you should conduct a study on each hole c channel to find what the optimal length is for the forces described lmao

That’s what I was saying. It has to be a single part. Not an assembly.

but…you can do fea on assemblies

FEA –– “Finite Element Analysis” (for those just scrolling but too lazy to ask)

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I don’t think so? The button’s not available for me.

i mean i’ve been doing it all day for my 250 lb’er

Inventor limits what you can use FEA for depending on your system specs I believe. I have a desktop that’s very powerful that can do large assemblies but a weak laptop that can only do small parts.

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Not exactly a technique, but this is still within the essence of this thread:


Useful CAD Definitions:

Definitions
A

Application

A computer program. A CAD application, also called an add-on or plug-in, can carryout complex tasks specific to a particular drawing problem. CAD applications run in tandem with the CAD software to perform specialized or automated tasks. Some examples of CAD applications specific to theatre include programs to automate the drawing of construction drawings and light plots.

Arrowhead

The part of a dimension or leader which points to an object or extension line. Arrowheads usually can be drawn automatically in several styles or shapes.

Attribute

  • AutoCAD : Information or data about a drawing object which can be hidden or appear in the drawing as text. Often this information can be extracted from the drawing and used in a spreadsheet or other program.
  • Vectorworks : Color, Pattern, or Marker Style of an object.
B

Bezier Curve

A curve defined by endpoints, tangent lines, and control points at the ends of the tangent lines. Altering the length and angle of tangent lines alters the shape of the curve.

Bitmap

A pixel based graphic or image inserted in a drawing. Bitmaps can be sized but not edited with most CAD programs.

C

CAD

Computer-aided design. Common CAD programs include: AutoCAD, Vectorworks, Microstation. Programs differ greatly in features, complexity, cost, and hardware requirements.

CADD

Computer-aided design and drafting.

Cartesian coordinates

See coordinates.

Center point

The defining point at the exact center of a circle, arc, regular polygon or ellipse.

Chamfer

A diagonal line which connects points on two intersecting objects such as an angled corner. The chamfer tool is an editing tool.

Class

A category of objects (Vectorworks) to which objects can be assigned and then manipulated as a group.

Color

A property of any drawing object which defines the color in which it appears on the screen and (possibly) the color in which it is printed. Color is often associated with an object’s layer or class assignment and can be used to determines how that object will appear on a printout with regard to line thickness and line type.

Component

(Generic CADD terminology) See symbol.

Constraint

A drawing tool which limits drawing to a particular point, line or angle. Some common constraints are snap to grid and ortho.

Control points

Points determining the path and shape of a Bezier curve.

Coordinates

A sytem of numbers used to locate a point or object in a drawing.
In the Cartesian coordinate system 2 numbers x and y are used to describe the location of a point in the horizontal and vertical dimensions respectively. 3D CAD programs add the z coordinate which describes distance in the third dimension.
In the Polar coordinate system a point is described by a distance and an angle where 0° exends horizontally to the right.

Cursor

The screen symbol or icon which represents the current mouse location relative to the drawing window or viewport. The cursor may appear as crosshairs or another symbol based on which command is active.

Curve

A complex entity created by the definition of endpoints of spline curve sections. Note, the type of curve you use determines the types of editing tools or functions that may be performed on it. See also Bezier curve

D

Datum

A temporary coordinate point set by the user which can be used as a snap point or reference point when drawing.

Dimension line

A line, usually with an arrow indicatiing the direction and distance of a drawing dimension. See also extension line.

Drawing database

The central part of a CAD drawing. A list of all objects which exist within a drawing along with all parameters and definition points.

Drawing units

See units.

Drawing window

See viewport (AutoCAD).

DXF

Drawing exchange format created by Autodesk. An ascii text file format describing drawing data and settings to translate drawings between programs and formats. Note: DXF is not a standardized format and different programs convert or ignore different entities found in a DXF file.

E

Edit

The process of modifying a drawing object or entity.

Editing tools

A class of drawing commands used to modify drawing entities or objects. Common edits include: trim, rotate, move and stretch.

Ellipse

A CAD drawing object defined by a major axis, minor axis and centerpoint. An ellipse may also be constructed out of arcs and line segments. An ellipse created in this way is not mathematically a true ellipse but is an easier object to edit.

Environment

The over-all setup of a CAD program including all drawing settings, colors, units, tool palettes, etc. comprise the drawing environment.

Explode

A common command which break objects apart into their component pieces. Explode most often works on symbols, breaking them back into their component pieces. In some CAD programs other entities are explodable such as text lines, polylines, or other complex objects.

Extension Line

The line which extends from a measured line or object to the dimension line, showing the extent of the measured distance.

F

Fillet

(Rhymes with skillet). An arc connecting endpoints of two intersecting lines or objects, often a rounded corner.

Fill

A complex object defined by a series of points or a bordering object such as a circle or polyline which fills the defined area with solid color. The display of a fill is highly dependant upon the display or printer/plotter being used. See also hatch.

Font

The typographic style property of text. Fonts may be drafting style (one line thickness) or typographic such as that being used in this document. Fonts are commonly managed by the operating system, not the CAD program and can be difficult to translate from one computer to another or one CAD program to another.

G

Grid

A drawing tool which is usually a pattern of regularly spaced dots or lines which make the alignment and drawing of objects easier. A snap to grid tool constrains or locks all drawing to grid points only.

Group

A collection of objects which can be manipulated as one object.

H

Handles

See object handles.

Hatch

A complex object defined by a series of points or a bordering object such as a circle or polyline which fills the defined area with a repeating pattern of lines. Hatches have a scale property which determines the size and density of the repeating pattern. See also fill.

L

Layer

A property of any drawing object. Usually objects are organized onto different layers for organazational purposes and ease of drawing, viewing and editing. Layers often can be named and can have default colors or other properties associated with them. Vectorworks Layers have the added ability to have associated properties of scale, view, and projection. These added properties of Vectorworks layers are similar in function to AutoCAD paperspace.

Leader

A line with an arrowhead and attatched text pointing at another object.

Leader line

The line portion of a leader connecting the shoulder to an arrowhead.

Line

A CAD object defined by two endpoints.

Line type

A property of any line, circle, curve, or arc. Line type describes a repeating pattern of lines and spaces. Lines may be solid, dashed, alternate, etc. The additional property of line type scale determines how often in a given distance a pattern of lines and spaces repeats. Scale may or may not be affected by the scale of the drawing view.

Line width

A property of any line, circle, curve, or arc. Line width describes how thick a line or other object appears on the the screen or on a printout. Different CAD programs use different schemes for acheiving line width.

Locus

A drawing object with a single reference point and no physical dimension.

M

Macro

A sequence of commands recorded and saved for easy playback. Well designed macros can save a great deal of drawing time. See also script and application.

Major axis

The longer axis of an ellipse.

Manual entry

The process of entering points manually by typing coordinates as opposed to clicking within the viewport or workspace.

Markers

A line marker is used to mark the end points of lines.

Minor axis

The shorter axis of an ellipse.

Move

A drawing editing tool which moves objects or selection sets to a new drawing location by changing all definition points by a given distance.

N

Nested

Objects inside of other objects. Symbols may be nested within other symbols. Drawing commands can be nested or executed while other drawing commands are active. Macro programming objects can be nested in terms of their control structure.

O

Object handles

In a windows CAD program the handles which appear when an object is selected. Handles often allow objects to be stretched, rotated, or moved.
Note: in AutoCAD handles refer to arbitrary names assigned to each drawing entity in the drawing database so that macros and applications may refer to specific entities directly.

Offset

The distance between two objects. Offsets are often used to draw parallel lines or determine the location of a dimension. In AutoCAD a command which creates a duplicate of an object at a specified distance.

Origin

The point in a drawing with the x,y coordinates of 0,0.

Ortho

Short for orthagonal. Usually refers to objects placed horizontally or vertically within a drawing. Ortho mode is a constraint which limits all drawing to regular 90° angles. In some CAD programs other ortho angles and modes may be set.

P

Pan

The process of altering the drawing view by moving the viewpoint laterally relative to the drawing.

Polar coordinates

See coordinates.

Polygon

A complex object composed of three or more straight lines in a closed figure. Polygons are treated differently by diffent CAD programs. Often a polygon is simply a closed polyline entity.

Polyline

A complex object composed of two or more lines, curves, or arcs which have contiguous endpoints. A closed polyline or polygon has its endpoints joined into a closed form. Polylines are more difficult to edit than a form drawn with individual line segments, but offers some advantages when editing or building surfaces and 3 dimensional objects.

Primitive

The simplest drawing objects from which all objects are built. Common 2D primitives include: point, line, circle, arc, and ellipse.

Prompt

A program message often located on the programs status line.

R

Radial copy

Also Duplicate Array (Vectorworks). An editing command which creates multiple copies of objects by copying them around a centerpoint for a given angle.

Real scale

Objects in a CAD program a drawn at full scale or 1:1. See scale.

Redraw

The process by which the video display is updated cleaning up any unwanted marks or construction points. See also regenerate.

Reference points

Points associated with drawing objects which allow an object to be selected, grouped, and manipulated. Reference points are often not visible. One example is the reference point of a text line which is often found at the lower left hand corner of the text line. To select a text entity it is often neccessary to click near this invisible point or include it within a selection window.

Regenerate

The process by which the view updated from the drawing database cleaning up any unwanted marks or construction points. Similar but more comprehensive and time consuming that a redraw. Note: on some CAD packages these processes are synonymous.

Relative coordinates

Drawing coordinates which when manually entered are interpreted as relative to the last point entered. In AutoCAD relative coordinates are entered by preceeding the coordinate pair with the @ sign such as @2,3.

Resolution

The clarity or degree to which individual elements can be discerned on a monitor or print/plot. Common monitor resolutions include 600x800 and 1280x1024 measured in pixels. Common laser printer and plotter resolutions range from 300x300 to 600x600 dots per inch. Resolution of these devices determines how accurate a printout will be or how accurate an object will appear on the screen. The actual resolution of objects saved in the drawing database is usually much higher to insure a high degree of accuracy. When drawing objects are viewed on screen or plotted their size and position is rounded to the nearest dot at the resolution of a given device.

Rotate

A drawing editing tool which rotates objects or groups of objects based on a center of rotation and an angle.

Rubberbanding

A feature of many CAD programs which shows how a line or other object will look before it is actually placed. An example is with the line command. A starting point is selected after which a line appears rubberbanded between the first point and the cursor. As soon as another point is selected the actual line is drawn and the rubberband moves to the next point.

S

Scale

  1. An editing tool which changes the size of an object relative to percentage. Some objects can be rescaled to different percentages in the x and y directions.
  2. The relative size at which a drawing is viewed on the screen or printed/plotted. Scale is often represented as a ratio where 1:1 is full scale, 1:12 = 1" =1’-0", 1:24=1/2"=1’-0" etc.

Script

A list of drawing commands which can be typed in a text editor and then loaded and executed with one command. Different scripting methods are supported by different CAD programs. Scripts are useful for performing repetitive tasks such as drawing setups.

Selection set

One or more objects selected for action with a single command. Often items are selected this way by drawing a window around them or holding down the shift key while selecting them individually.

Shoulder

The horizontal part of a leader line.

Snap

A drawing tool which locates points exactly by finding an existing point within the drawing database which is closest to a point selected with the on the screen. Some common snaps are: snap to nearest point, snap to midpoint, snap to intersection of two lines, etc.

Snap to grid

A drawing constraint which forces all points picked to fall on the currentl grid.

Stretch

An editing tool which moves some of the points which define an object and leaves others.

Symbol

A collection of drawing objects defined as a single complex entity. Defining and using symbols speeds drawing and makes drawing files more compact. Symbols are also called blocks (AutoCAD).

S
T

Trim

A drawing editing command which causes one object to end exactly at another. Trim points are calculated mathmatically so they are exact. Some complex objects such as curves cannot be trimmed to.

Tangent

A line which intersects a circle, ellipse or arc at only one point. Tangent lines to Bezier curves define the shape of the curve.

Toggle

A drawing control or setting which is either on or off. Subsequent execution of the command reverses the state of the parameter. One toggle is the dispaly grid command.

U

Units

Units of measure represented by numbers in a CAD program. Usually units are inches or feet, but can be anything from millimeters to light years.

V

Vertex

A point defining the junction of a segment within a polyline or polygon.

View

The graphical representation of the geometry stored in the drawing database which appears in the drawing window or viewport. A view has a center point and a scale or zoom. Multiple views of one drawing may be open in seperate windows or viewports simultaneously.

Viewport

The window or frame within which a view of the drawing is visible. In some complex CAD programs viewports are considered complex objects and can be placed in drawings. Many programs also support the use of multiple viewports which can simultaneously show different parts of the same drawing. This is especially important when working in 3D.

Z

Zoom

The way the view is changed by magnifying or reducing the image on the screen. Zoom scales the view only and does not affect the actual size of drawing objects.


I figured I would add something like this to the forums because I see a continual lack of awareness and general knowledge on CAD programs. I am aware that google exists, but this is usually where people go to to find vex help.

Anyways, if you see something wrong in the list, or want something added –– pm me and I’ll change it. Also, note –– these definitions were pulled from here.

TL;DR conversations about CAD will be much more productive when people refer to things specifically, by name, and when people understand what exactly is being referred to

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I think this belongs in this thread as well.

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