Tutorial O: Grasshopper basics, sphere and cylinder

Video	Bastian Wibranek, Rhino 3D and Grasshopper - Basics Tutorial (YouTube)
Application	Algorithmic Modeling (Katydid)
You learn	Opening the canvas, adding components by name, sliders, wiring, two results from two inputs, Bake, warnings, saving
Sizes	Millimetres: a sphere of radius 7.5 and one of 3, 40 mm apart; a cylinder 5 × 8

The video teaches Grasshopper inside Rhino. Here the same steps run on Katydid’s canvas inside FreeCAD NX-Style: Katydid plays Grasshopper’s part, FreeCAD plays Rhino’s.

Step by step

1. Open the canvas

Application › Algorithmic Modeling. The canvas opens as a floating window over the graphics window, as Grasshopper’s floats over Rhino’s viewports.

Grasshopper’s Display › Draw Full Names has no counterpart: Katydid writes each component’s short name on it and shows the full name, every input and its type in the tooltip.

2. A sphere

Double-click the empty canvas, type Sphere and press Enter. A red preview sphere appears at the origin in the graphics window: the preview is not a document object yet.

A Sphere component and its preview at the origin

Grasshopper’s Sphere also has a Base (B) input for its position; Katydid’s Sphere sits at the origin, so the next step moves it.

3. Move it

In the video a point drawn in Rhino is referenced into the sphere’s Base (Set one Point) and dragged with the Gumball. Katydid cannot reference a FreeCAD point yet, so a Move after the sphere does the moving:

Double-click, Move, Enter.
Drag a wire from the sphere’s output S to Move’s G.
Double-click, Number Slider, Enter. Double-click the slider to name it X and give it the range −50 to 50, value 20.
Wire the slider into Move’s X.
Right-click the sphere and switch its preview off, so only the moved sphere shows.

Drag the slider and the sphere follows, live.

4. A slider for the radius

Add a second Number Slider, name it Radius, range 0 to 10, and wire it into the sphere’s R. At 7.5 the sphere’s volume is 1767.1 mm³, as 4/3 π r³ gives.

5. Two spheres

The video references two points (Set Multiple Points) and copies the radius slider. Here a second X slider (−20) goes into Move’s X and a second radius slider (3) into the sphere’s R, each wire dragged with Shift held so it is added, not swapped. Lists pair up item by item: radius 7.5 at x = 20 and radius 3 at x = −20.

Two spheres from two radius sliders and two X sliders

6. Bake

Home › Algorithm › Bake (or Bake on the canvas) turns what is previewed into ordinary Part features. Move 0 and Move 1 appear in the Part Navigator and stay when the canvas is closed.

The two spheres baked into the Part Navigator

7. Exercise: a cylinder

Clear the canvas, add a Cylinder and two sliders, Radius 5 and Length 8, and wire them into R and L. Its volume is 628.3 mm³ (π r² h). The baked spheres stay in the document, grey; the cylinder is still a red preview.

A Cylinder with Radius and Length sliders

In Grasshopper, typing 5 into the search box makes a slider at 5. Katydid’s search finds components only, so the slider is added and then set.

8. Warnings

A component that misses an input turns orange. Add a Move with nothing in G: it says "Input parameter G failed to collect data" when you hover it. Wire the cylinder into G and it is grey again.

9. Save

Grasshopper keeps its definition in a .gh file beside Rhino’s .3dm, and both have to be opened together. Katydid saves the canvas inside the part: one Save, and the .FCStd holds the baked spheres and the canvas (the Katydid object in the Part Navigator).

The replay

Every step above is done by the tutorial replay (--tutorials O): it double-clicks the canvas and types each name, drags each wire between grips, types the slider values into the slider’s dialog, and checks every result by its volume and position.

#	In the book (NX)	In FreeCAD NX-Style	Result	Notes
O1	Open Grasshopper from Rhino’s toolbar; the canvas floats beside the viewports	ribbon 'Application › Design > Algorithmic Modeling'	same	Katydid’s canvas opens as a floating window over the graphics window (floating True); the document is Unnamed
O2	Display > Draw Full Names, so components show 'Sphere', 'Radius' …	-	differs	Katydid draws each component’s short name on it (Sph, Cyl …) and shows the full name, every input’s name and its type in the tooltip; there is no names/icons switch. Tabs ['Params', 'Maths', 'Sets', 'Vector', 'Curve', 'Surface', 'Transform', 'Intersect', 'Tolerance']
O3	Double-click the canvas, type Sphere, Enter: a preview sphere at the origin	double-click + 'Sphere' + Enter	same	sphere volume 523.6 mm^3 = R 5 (Katydid’s default; Grasshopper’s is 1); inputs ['R (Radius)']. Grasshopper’s Sphere also has a Base plane (B) input; Katydid’s sits at the origin
O4	Reference a Rhino point (Point > Set one Point) into the sphere’s Base; drag it with the Gumball	stand-in: 'Move' after the sphere, a slider 'X' into its X; the sphere’s own preview off	missing	sphere centre x = 20.0. Katydid has no Point parameter that follows a FreeCAD point yet (asked for); dragging the slider moves the sphere live, as the Gumball does in Rhino
O5	Number Slider into the sphere’s Radius ®; double-click the slider’s name for its range: 0 to 10	double-click + 'Number Slider'; double-click the slider: Name, Minimum 0, Maximum 10, Value; MB1 drag from the slider to R	same	radius 7.5 → volume 1767.1 mm^3 (expected 1767.1)
O6	Two points (Set Multiple Points) give two spheres; copy the slider and Shift-wire both into R	stand-in: a second X slider Shift-wired into Move’s X; a second radius slider Shift-wired into R	differs	spheres (centre x, radius): [(-20.0, 3.0), (20.0, 7.5)]. Shift + MB1 drag adds a wire, as in Grasshopper; lists pair up item by item
O7	Right-click the sphere’s output > Bake…: real Rhino objects	ribbon 'Home › Algorithm > Bake' (Katydid’s own Bake on the canvas does the same)	same	baked ['Move 0', 'Move 1'], volumes [113.1, 1767.1] mm^3; they are ordinary Part features in the Part Navigator and stay when the canvas closes. Baked 2 object(s) into the document
O8	Exercise: Cylinder with sliders 5 for the radius and 8 for the length	double-click + 'Cylinder'; two sliders typed 5 and 8; wired to R and L	same	volume 628.3 mm^3 (expected 628.3). Grasshopper makes a slider when you type '5' into the search box; Katydid’s search finds components only (asked for)
O9	An orange component: an input is missing; its balloon says why	a 'Move' with nothing in G	same	state warning: ['Input parameter G failed to collect data']; Katydid colours it orange and shows the message in the tooltip (hover the component)
O10	Save the Rhino model (.3dm) and the Grasshopper definition (.gh), and open both together	one save (Save As, named by the replay): the canvas is saved inside the part	differs	Katydid_Basics.FCStd holds the parts and the canvas (a Katydid object in the Part Navigator); there is no separate definition file to keep next to it

In the book (NX)

In FreeCAD NX-Style

Result

Notes

Open Grasshopper from Rhino’s toolbar; the canvas floats beside the viewports

ribbon 'Application › Design > Algorithmic Modeling'

same

Katydid’s canvas opens as a floating window over the graphics window (floating True); the document is Unnamed

Display > Draw Full Names, so components show 'Sphere', 'Radius' …

differs

Katydid draws each component’s short name on it (Sph, Cyl …) and shows the full name, every input’s name and its type in the tooltip; there is no names/icons switch. Tabs ['Params', 'Maths', 'Sets', 'Vector', 'Curve', 'Surface', 'Transform', 'Intersect', 'Tolerance']

Double-click the canvas, type Sphere, Enter: a preview sphere at the origin

double-click + 'Sphere' + Enter

same

sphere volume 523.6 mm^3 = R 5 (Katydid’s default; Grasshopper’s is 1); inputs ['R (Radius)']. Grasshopper’s Sphere also has a Base plane (B) input; Katydid’s sits at the origin

Reference a Rhino point (Point > Set one Point) into the sphere’s Base; drag it with the Gumball

stand-in: 'Move' after the sphere, a slider 'X' into its X; the sphere’s own preview off

missing

sphere centre x = 20.0. Katydid has no Point parameter that follows a FreeCAD point yet (asked for); dragging the slider moves the sphere live, as the Gumball does in Rhino

Number Slider into the sphere’s Radius ®; double-click the slider’s name for its range: 0 to 10

double-click + 'Number Slider'; double-click the slider: Name, Minimum 0, Maximum 10, Value; MB1 drag from the slider to R

same

radius 7.5 → volume 1767.1 mm^3 (expected 1767.1)

Two points (Set Multiple Points) give two spheres; copy the slider and Shift-wire both into R

stand-in: a second X slider Shift-wired into Move’s X; a second radius slider Shift-wired into R

differs

spheres (centre x, radius): [(-20.0, 3.0), (20.0, 7.5)]. Shift + MB1 drag adds a wire, as in Grasshopper; lists pair up item by item

Right-click the sphere’s output > Bake…: real Rhino objects

ribbon 'Home › Algorithm > Bake' (Katydid’s own Bake on the canvas does the same)

same

baked ['Move 0', 'Move 1'], volumes [113.1, 1767.1] mm^3; they are ordinary Part features in the Part Navigator and stay when the canvas closes. Baked 2 object(s) into the document

Exercise: Cylinder with sliders 5 for the radius and 8 for the length

double-click + 'Cylinder'; two sliders typed 5 and 8; wired to R and L

same

volume 628.3 mm^3 (expected 628.3). Grasshopper makes a slider when you type '5' into the search box; Katydid’s search finds components only (asked for)

An orange component: an input is missing; its balloon says why

a 'Move' with nothing in G

same

state warning: ['Input parameter G failed to collect data']; Katydid colours it orange and shows the message in the tooltip (hover the component)

O10

Save the Rhino model (.3dm) and the Grasshopper definition (.gh), and open both together

one save (Save As, named by the replay): the canvas is saved inside the part

differs

Katydid_Basics.FCStd holds the parts and the canvas (a Katydid object in the Part Navigator); there is no separate definition file to keep next to it

Result	Means
same	The book’s NX steps work as written.
differs	It works, but the FreeCAD way is different; the notes say how.
limit	The book’s way fails in FreeCAD itself; a workaround follows in the next steps.
missing	FreeCAD has no such function; a stand-in follows.
skipped	Not replayed; the notes give the reason.
FAILED	Did not work.

Result

Means

same

The book’s NX steps work as written.

differs

It works, but the FreeCAD way is different; the notes say how.

limit

The book’s way fails in FreeCAD itself; a workaround follows in the next steps.

missing

FreeCAD has no such function; a stand-in follows.

skipped

Not replayed; the notes give the reason.

FAILED

Did not work.