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Rocco – Frame and Parts

Rocco was designed in Tinkercad.  The model can be found here:  https://tinkercad.com/things/i91TkKbNDc9

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
http://www.eplastics.com/Plastic/Plexiglass_Lexan_Plastic_Drill_Bits/DB-187

1/8″ Drill Bit for Plastic
http://www.amazon.com/dp/B0011Z0I82/ref=pe_175190_21431760_cs_sce_3p_dp_1

5/64″ Carbide Small-Diameter Drill Bit
http://www.mcmaster.com/#2841a95/=w65byx
(M2’s actual outer diameter is 1.9mm = .0748in = use 5/64)

3/32″ Carbide Small-Diameter Drill Bit
http://www.mcmaster.com/#2841a96/=w65bz9
(M2.5’s actual outer diameter is 2.4mm = .0945in = use 3/32)

Plexiglass

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
http://www.usplastic.com/catalog/item.aspx?itemid=35662

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.

http://hobbyking.com/hobbycity/store/product_discussion.asp?idproduct=9392

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
http://www.mcmaster.com/#95836a255/=w65we0

Type 316 Stainless Steel Fully Threaded Rod
M2 Thread, 0.4mm Pitch, 1 Meter Long
http://www.mcmaster.com/#94185a135/=w65wf3

Type 18-8 Stainless Steel Thin Hex Nut – DIN 439B
M2x0.4 Thread Size, 4mm Wide, 1.2mm High
http://www.mcmaster.com/#90710a020/=w65wf5

Metric Nylon Pan Head Phillips Machine Screw
Black, M2 Size, 16 mm Length, 0.4 mm Pitch
http://www.mcmaster.com/#92492a110/=w65wej

Nylon 6/6 Hex Nut
M2x0.4 Thread Size, 4.2mm Wide, 1.5mm High
http://www.mcmaster.com/#93800a300/=w65wet

Nylon Flat Washer
M2 Screw Size, 2.2mm ID, 5.0mm OD
http://www.mcmaster.com/#95610a510/=w65xbz

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