3 DOF Leg Assembly Instructions Rev. 3.

Updated 03/16/2006.

Safety first! Wear eye protection and never touch a powered robot!

Note: Do not use Loctite or thread locks on the assembly. They are not necessary and may cause damage to the Lexan.

Important! If you are building legs for the EH3-R using the Bot Board / Basic Atom 28, and SSC-32, then you need to build three right legs and three left legs. This is also true if you are building for a standard insect looking hexapod such as the EH3. However, if you are building for the EH3-R using the ServoPod then you need to make 6 right legs.
Image of completed Right (robot's right) leg.

 
Step 1.
Drop the servo in through the hole, and use four nylon rivet fasteners to hold it in place. The servo tabs should be on top of the Lexan, and the rivet fasteners should go in from the top, through the servo tabs and then the Lexan. Do not take the rivet fasteners apart.
 
4 x  
 

Figure 1.

 
Step 2.
Turn the assembly over and place the two Lexan spacers onto the assembly as shown.
Figure 2.


Step 3.
Use three 4-40 x 1/2" screws and three acorn nuts to hold the spacers and second leg panel together with the first. The screws should go in from the top, with the nuts on the bottom.
 
3 x 3 x

Figure 3.

 
Step 4.
Slide the robot foot rubber end cap onto the end of the leg. It might be a tight fit, but if you wiggle it, it will fit.
 
1 x  
 

Figure 4.

 
Step 5.
Clean the bottom of the servo with alcohol and allow it to dry. Then peel the green plaid cover off the tape on the hinge, and line the hinge up with the edge of the servo. Press the hinge onto the servo very firmly for a full ten seconds to insure a good bond.
 
1 x  
 

Figure 5.


Step 6.
Using four of the nylon rivet fasteners, attach two of the "L" brackets as shown. Push the rivet fasteners in from the back (bottom of panel as shown).
 
4 x 2 x

Figure 6.

 
Step 7.
Use four rivet fasteners to attach one servo as shown, pushing the fasteners in from the top. Make sure that the servo's mounting tabs are on top of the "L" bracket.
 
4 x  
 

Figure 7.

 
Step 8.
Put the second servo in through the servo hole as shown. Use four rivet fasteners to hold it in place.
 
4 x  
 

Figure 8.


Step 9.
Clean the bottom of the servos with alcohol and allow them to dry. Then peel the green plaid cover off the tape on the hinge, and line the hinge up with the edge of the servo. Press the hinge onto the servo very firmly for a full ten seconds to insure a good bond.
 
2 x  
 

Figure 9.

 
Step 10.
Use four 4-40 x 3/8" hex socket head cap screws to attach the 1.0" nylon spacer bars.
 
4 x 4 x

Figure 10.

 
Step 11.
Attach the rear panel using four of the 4-40 x 3/8" screws.
 
4 x  
 

Figure 11.


Step 12.
Assemble the leg cross member as shown using the 1 7/8" aluminum standoffs. Use two 3/8" hex socket head cap screws.
 
2 x 2 x

Figure 12.

 
Step 13.
Finish the cross member assembly as shown. Use two 3/8" hex socket head cap screws.
 
2 x  
 

Figure 13.

 
Step 14.
To make the assembly go easier, the servos need to be moved to their center of rotation using the Bot Board, SSC, or other servo controller or microcontroller. We have set up a tutorial to guide you through this step. If you are using a different microcontroller, consult your electronics documentation for help with this step. If you are using a ServoPod, leg calibration will be done in the robot programming tutorial.

Note, centering a servo simply requires generating a 1.5mS positive going pulse that repeats every 20mS.
Figure 14.


Step 15.
While the servo is centered, install the servo leg lever onto the servo horn. If necessary, you can drill the indicated holes with a 1/16" drill bit. Use two #2 x 1/4" Phillips head tapping screws. Use the servo horn holes as illustrated. The bottom edge of the lever and the bottom edge of the main panel should be parallel.
 
2 x  

Figure 15.

 
Step 16.
While the servo is centered, install the lower leg onto the servo horn. Use two #2 x 1/4" Phillips head tapping screws. Use the servo horn holes as illustrated. The lower leg should be perpendicular to the leg lever.
 
2 x  

Figure 16.

 
Step 17.
With the leg positioned as shown, remove the screw and tuck the servo wire under the rear panel. You've now completed the assembly of a robot's right leg! Left legs are simply a mirror image of this assembly.
Figure 17.