Assembling the Legs

You will need to assemble four legs, two right-hand variants and two left-hand variants. Left-hand variant is shown above.

Requirements

ToolsHardwarePrinted Parts

• Phillips (one small, one medium) and Flat Head (medium) Screwdrivers
• M4 hex key
• Pliers
• Scissors
• Knife (X-acto or small blade)
• Soldering Iron (pencil tip)

• 8x M2x6 machine screw (comes packaged with A1-16 servos)
• 4x M2 nuts (comes packaged with A1-16 servos)
• 4x M2 washers
• 1x M3x6 machine screw
• 9x M3x8 machine screw
• 1x M3 locknut
• 1x M3 threaded insert
• 1x M5x20 machine screw
• 1x M5 locknut
• 2x 625 ball bearing
• 1x M3 threaded rod
• 2x M3 rod end bushings
• 1x Adhesive grip pad
• 1x Ziptie

• 1x Calf
• 1x Calf Bushing
• 1x Thigh Inner
• 1x Thigh Outer (Left and Right variants)
• 4x Thigh Spacer
• 1x Servo Horn
• 1x Servo Horn Spacer

Assembly Instructions

Calf Assembly

The calf assembly is the same for all four legs. Repeat these steps four times, once for each leg.

1. Press Calf Bushing into Calf. You may need to use a knife to scrape or debur the edges, and it may be helpful to use pliers while pressing in the bushing. Make sure the bushing is inserted completely such that the bottom of the lip is flush with the calf.
   

2. Melt M3 threaded insert into the top hole of the calf. You will need to use a soldering iron, preferably with a pencil tip, set to medium-high heat. Make sure the top of the threaded insert is flush with the top of the plastic.
   

3. Using scissors, cut adhesive grip pad into a 1cm x 7.5cm strip.
   

4. Remove the adhesive backing from the grip pad, and adhere the pad onto the bottom of the foot such that the pad is equally spaced around the bottom center of the foot. Secure pad by wrapping a zip-tie around the ankle.
   

Thigh Assembly

The thigh assemblies for the right and left sides of the dog are mirror images; the "Thigh Inner" parts are different for the left and right leg variants, and assembly is mirrored. Make sure to assemble two copies of the right leg and left leg. Steps with variations during assembly are indicated.

1. Press a 625 bearing into the end of the Thigh-Inner and Thigh-Outer parts.
   Thigh Outer:
   
   Thigh Inner:
   
2. Insert M2 nuts into each of the four top corners of a servo. It may be helpful to use the side of a flathead screwdriver. Secure the servo to the Thigh-Inner using four M2x8 screws in the location where the nuts were inserted. These screws come packaged with the A1-16 servos. It is not necessary to use a washer here.
   
   
   Note: It is not necessary to use a screw in each hole - only the four corners.
   Note: The Left leg variant is shown here. The procedure is the same for the Right variant. Make sure the protrusion on top faces in the same direction as the servo's rotating platform.
3. Make sure an M3 screw threads smoothly into each end of four "Thigh Spacers". Depending how these parts were printed, you may need to self-tap these ends by screwing an M3 screw halfway into each end. Apply downward pressure when doing so. It may be helpful to debur or chamfer the screw hole with a knife, and it may be helpful to hold the part with pliers while working with it. If you need to scale and re-print these parts, ensure that the height remains 12mm.
4. Insert an M3x8 screw into each of the four countersunk screw holes of the Thigh-Inner. Screw a Thigh Spacer onto the other end of each of the four screws. Ensure that the spacer if flush with the thigh part.
   
   
   
   
5. Secure the Thigh-Outer to the assembly by inserting an M3x8 screw into each of the countersunk holes of the Thigh-Inner and securing them to the four Thigh Spacers. Make sure the Thigh-Inner is flipped on the correct side - the screw heads will be recessed inside the countersunk holes.
   
   

Leg Assembly

1. Use an M5 screw and M5 locknut to secure the calf through the bearings of the thigh assembly. Make sure that the protrusion of the calf is facing the Thigh-Inside. The protrusion should slide within the curved slot on the inner thigh when the leg is extended. Make sure the nut is attached on this same inside. A left side leg is shown here.
   
   
   
2. Use four M2x6 screws and washers to secure the Servo Horn and Servo Horn Spacer to the thigh servo. Make sure the single mark on the servo rotation platform faces in the direction of the servo horn. It is important that you use all four screws and use washers in this step. Make sure the Servo Horn Spacer is 0.5mm thick, scale and re-print if necessary. It is recommended to an SLA printer or to use PETG and 100% infill for the Servo Horn if possible.
   
   
   
   See the single servo rotation platform marking. Make sure the servo horn faces in this direction.
   
3. Set aside the leg assembly. Cut a piece of M3 threaded rod to approximately 60mm in length.
   
   
4. Screw M3 rodend bushings onto each end of the threaded rod. Screw rodends on such that the length of the showing M3 rod is approximately 38mm. Make sure each rodend is screwed in an equal amount.
   
   
   It may be helpful to use a hex key or screw driver through the bushing to assist screwing on the rodends.
   
   This value will change in the next step.
5. Secure one end of the threaded rod to the top protrusion of the calf by using an M3x8 screw through the rodend bushing and the threaded insert on the calf.
   
   Notice there may be a difference in height between the top of the protrusion of the calf and on the tip of the servo horn. Use M3 washers between the rodend and the calf's threaded insert to eliminate this difference. As shown above, 2 washers were used to eliminate this difference.
   
6. Use an M3x6 screw and M3 locknut to secure the other rodend to the servo horn. The servo horn has a recess for the M3 nut. Make sure the locknut is installed in the correct orientation, with the tapered portion facing outwards.
   
7. Make sure the calf moves freely when the servo horn is facing upwards in the direction of the Thigh-Inner curved slot.