Structure Assembly

Structure Assembly

How to assemble the skeleton

Here are the parts we will need:
metal and fasteners for assembly

assembly of bearings with rivets
We first assemble some bearings on the frame using pop rivets, as described in the previous lesson. Make sure you put the bearings in the correct places by counting the number of open square holes. Insert two rivets in each bearing, leaving the center hole open. We need two metal pieces with three bearings on the inside, and two metal pieces with two bearings on the outside.

The L Subassembly

join 2 pieces to make an L
Join two pieces of metal to make an L shape, like in the picture above. We need two of these for our robot, so make two identical L shapes. As we assemble everything, it is best to not tighten the screws too tight. When using many screws we follow a tightening sequence. Put all screws in partially tightened, then tighten each one little by little. This will make it easier to assemble since it will keep the pieces flexible. It will also assure that everything is tightened equally.

Assembly

marry the two L pieces
Now we join the two L-shaped pieces together. If you followed the directions, it should fit perfectly. If not, make sure you didn't tighten the pieces too soon. Also, check to see the L-shaped pieces are lined up properly. The pieces should be on "top" of each other, not "underneath" each other. If they're not lined up properly, this is probably the reason why.

Double-checking your work is very important. This is called systems engineering, making sure everything in the system works. Every individual must make their parts correctly and double check their work in order for the parts to perform as a system. When working together as a team, we should all take the attitude that "It won't fail because of me" -- a slogan that developed during the Apollo moon missions. If we can get these small details correct, one day we may participate in something big like the assembly video below:

http://www.youtube.com/embed/yLLF13IuAMI

This is the International Space Station that is currently orbiting the earth. It was built piece by piece in space. The pieces, or subassemblies, were made all over the world, by teams of engineers with different languages, cultures, creative desires and even different measurement systems. When it all got to space all the pieces fit together and it all worked. Amazing, isn't it? This is what great systems engineering can accomplish. If you like this, there's lots more where that came from here:
http://www.nasa.gov/mission_pages/station/main/index.html

The Square

a square base robot frame

We now have a square. As we saw in our study of shapes, the square is a special kind of parallelogram: Four sides that have two sets of parallel lines. When the corners are perpendicular, it is a square. It is one type of polygon. Polygonal shapes are shapes made up of lines and angles. You can learn more about these shapes here: Mathisfun.com

The square is not a very stable structure for a frame. Any change to the angles at the corner and it is no longer a square. We can strengthen this shape by adding a brace.

The Brace

brace the square structure for strength
Adding the brace across the square prevents it from deforming into a parallelogram. You will see this type of bracing on truck and trailer frames. You will also see this if you see a new house under construction in California. Why in California? Metal bracing is put in the walls to prevent the rectangular frames from moving too much during earthquakes. For our case, bracing will help our robot to be stronger, roll straighter, and as a side benefit, it provides a nice place for mounting other robot parts later.

Motors

add motors to our robot frame
Now add the motors to the frame. You want to attach it to the metal frame that has three rows of holes, NOT the one with two rows of holes. You attach the motor in the middle of the frame, which is eight holes in from the edge in the middle row. Be careful: the motor screws are a slightly different size than what we have been using for the framing. The are size 6, and use the smaller hex wrench to tighten.

Sliders

sliders to hold the robot wheels
The sliders with the pre-assembled wheel bearings are installed using the two spacers on each side. Complete this and we are done. We have a completed frame. Now go around to all the screws and nuts and make sure they are tight. Use the wrenches and tighten everything so it won't fall apart later.

STEM Education Standards

  • STEM Engineering StandardMaterials and Tools
    Identify and explain the properties of materials and where to use them. Plastic, Metal.
    No Metal Moving on Metal
  • STEM Math StandardGeometry
    Identify polygonal shapes up to 10 sides
    Identify and draw parallel and perpendicular lines
    Two Points Make a Line