Rocco – Frame and Parts

Rocco was designed in Tinkercad.  The model can be found here:

It should not be printed to a 3D printer currently because the holes don’t line up quite right.  When I started assembling the first leg I had to widen most of the holes and even move some of them.  This is possibly because the servo dimensions aren’t exact.  I will try to fix the model when I build the rest of the legs.

Below is a description of all the materials and components currently used to make the robot.

Drill Bits

Any drill bits meant for plexiglass will work, but these are the bits I’ve used:

R&H 3/16″ Plexiglass Acrylic & Lexan Drill Bit

1/8″ Drill Bit for Plastic

5/64″ Carbide Small-Diameter Drill Bit
(M2’s actual outer diameter is 1.9mm = .0748in = use 5/64)

3/32″ Carbide Small-Diameter Drill Bit
(M2.5’s actual outer diameter is 2.4mm = .0945in = use 3/32)


You can order acrylic sheets anywhere, but I have a lot left over from prior projects.  I have previously ordered them from U.S. Plastics.  You can cut plexiglass by scoring it repeatedly with a box cutter along a heavy straight edge.

Acrylic Sheet 24″ x 24″ x 1/16″ (.060) Thick

Plexiglass Cuts

18 @ 20mm x 100mm – mid-leg and outer leg lengths (shared size)
6 @ 10mm x 132mm – longest leg pieces
12 @ 10mm x 42mm – knee servo side mounts
18 @ 10mm x 32mm – knee servo top and bottom mounts
12 @ 35mm x 35mm – hip top and bottom plates
6 @ 12mm x 35mm – hip mid-panel
2 @ ? – hexagonal body top and bottom (no exact dimensions currently)
Other – there may be other plexiglass cuts added later

Wood Block

I needed some spacing material to fill an area in my design and provide support.  I also needed to be able to cut it by hand, so I just got a stick of wood from the hardware store.

6 @ ~27mm x ~22mm x ~11mm (length, width, height)

The wood is then cut to an “L” shape.  I’ve only made one so I’m not sure how much I cut out.  Let’s just call it “some”.

Frame Hardware

I designed the mounting hardware solution around getting as many of the components as I could from one place.

I was able to do this such that I got everything from McMaster-Carr.  Most of the components are shown to the right:

According to the link below, the “spline screw” that fits in the center of the servos I’m using (TowerPro MG90s) is an M2.5 size.  I needed longer screws than the ones that were supplied so that I could put plexiglass between the screw heads and the servos.

I also needed some threaded rod that I could cut to specific lengths using a dremmel.  The threaded rod and the the metal hex nuts for it are the heaviest parts of the mounting hardware but it is necessary to keep the hip/shoulder “square” and keep it from flexing.  To keep the weight down, almost all the mounting hardware is nylon.

Metric Pan Head Phillips Machine Screw
Black-Oxide 18-8 Stainless Steel, M2.5 Size, 8mm Length,.45mm Pitch

Type 316 Stainless Steel Fully Threaded Rod
M2 Thread, 0.4mm Pitch, 1 Meter Long

Type 18-8 Stainless Steel Thin Hex Nut – DIN 439B
M2x0.4 Thread Size, 4mm Wide, 1.2mm High

Metric Nylon Pan Head Phillips Machine Screw
Black, M2 Size, 16 mm Length, 0.4 mm Pitch

Nylon 6/6 Hex Nut
M2x0.4 Thread Size, 4.2mm Wide, 1.5mm High

Nylon Flat Washer
M2 Screw Size, 2.2mm ID, 5.0mm OD