Bi-Pedal Walker Robot

The rest of the tutorial is presented as follows: Objective Parts List and Sources Constructed Parts Construction Programming Final Words

Objective

    There are many research programs that deal with automated vision and also locomotion; each separately. The objective of this project is to combine vision and locomotion. I will attempt to do this using a bi-pedal walker robot as seen in the picture above. The bi-pedal that is going to be used in this project was constructed according to the specification provided in the five part article named "Bi-Pedal Walker" written by John Iovine in the magazine Poptronics. The related website to this is http://www.imagesco.com/catalog/biped/walker.html

Parts List and Sources

Parts For Bi-Ped Robot

Parts For Bi-Ped Robot Stand

Constructed Parts

 

Servo Shaft:     The servo shaft can be fabricated out of metal, plastic, or wood. I have used Aluminum because it is easy to cut and drill holes in. As indicated in the images, the dimensions of the component is 0.781 x 1.625 x (3/16) " thick. The diameter of the hole is (7/32)". The center of the hole is located 1.23" up from the bottom of the piece and 0.390" away from the side of the component. The size of the counter sink is (7/16)" wide and 0.075" deep. (Click on the picture to enlarge the image)

 

Connector Component:     This component, like the servo shaft, can be made from metal, plastic, or wood. Again, I have used Aluminum because it is easy to cut and drill holes in. The dimensions of the component are 1.1875" x 0.781" x (3/16) " thick. The diameter of the holes is (1/8)" and their counter sinks are of (1/4) " wide and 0.075" deep.  (Click on the picture to enlarge the image)

 

U-Bracket:     The U-Bracket must be constructed from metal. I once again used a Aluminum sheet. Click on Image A under U-Bracket for the location of each holes. In order to keep the drill bit from walking on the metal, make a small indent on the metal using a nail and a hammer at the position of the holes. The dimensions of this part is 1.25" x 4.75" x 0.05" thick. The location of the holes are drawn to scale but the size of the holes are not. The hole on the bottom portion of the bracket is 0.25" wide. The holes in the middle of the bracket are of (1/8) " wide. The holes on the top portion of this component of two different sizes. The smaller holes are all of (1/8)" wide and the hole in the middle (the larger one) is of 0.29" in diameter. When bending this component, make sure to bend them all in the same direction. (Click on the picture to enlarge the image)

Construction Steps

Bi-Ped

Step 1: (Part types)

             Machine the three components mentioned above under the constructed parts. Once each part is machined, they should look like the pictures below. Once each part is machined; connect each component to servo motor as described below.

Step 2: (Connector Component)

            In order to glue the connector component, first put a 4-40 x 3/8" machine screw through each hole. Then spread the epoxy on the component and stick it on the bottom of the servo motor as shown in Figure B below. repeat this step for each of the eight motors. As the epoxy dries, make sure the screws remain straight. Before continuing, wait till the epoxy dries. 

Step 3: (Servo Shaft)

            Next, put the barrel of the 8 x 32 screw through the hole in the servo shaft. Once again using the epoxy, glue the servo shaft to the back of the servo motor. Make sure to align the barrel to the drive shaft of the servo motor. As shown in Figure A below. 

Figure A

Figure B

Step 4:

            Now, change the round piece on the drive shaft of the servo motor to the piece that resembles a airplanes propellers. This is shown in Figures C below.

Figure C

Step 5: (connecting motor to U-Bracket)

            Next attach the servo motor to the U-Bracket as shown below in Figure C. In order to do this, first slip the barrel into the single hole on the shorter side of U-bracket, as shown in Figure F below). Then slide the rest of the motor into the position.  Using the sheet metal screws, connect the propellers to the U-bracket. This is shown in Figure D & E below.

Figure D	Figure E
Figure F	Figure G

Step 6: (making the leg)

Figure H

Before connecting one subcomponent of the leg to the other, file off the plastic part on top of the servo-motor. This part is circled in figure G. Do this so that when you attach the subcomponents there will be no off-set.       Next connect the two screws on top of the servo motor to the U-Bracket which is connected to the bottom of another servo motor. The connections should be made using appropriate nuts.

Step 7: (The Feet)

    The feet are one of the easiest components to make. They are made from the 12" wide x 12" long X (1/4)" thick acrylic plastic. Their dimensions are as follows:

•  length: 4.25"
• width : 2.125"

    Place the 4th and the 8th motor slightly towards one end of the foot. The exact specs are shown in Figure J below along with what they will look like once they are connected to the legs. The way I drilled the holes is to place a U-bracket in their position and then color in the holes with a marker. I found this method easier than actually measuring the position of each hole. The counter sink for the holes will be the same as the counter sink for the connector component (The diameter of the holes is (1/8)" and their counter sinks are of (1/4) " wide and 0.075" deep). The counter sink will go on the bottom of the foot so when you put the screws in they will not make the legs unstable.

Figure J

(picture of the finished product soon to come) Figure K

The Finished legs

     The finished legs are shown separately below. They are arranged next to a Pepsi Bottle to show the scale of the legs.

Figure L

Step 9: (The Hip Bar)

Figure M

    For the hip bar, I used a scrap piece of metal that had the following dimensions: (You may use any thing that is convenient for you, but the suggested material is some sort of metal for durability)

• length : 10.5"
• width : 1"
• thickness: 0.142"

   The place of the holes are as follows: (location of holes from right)

• first pair: 3 and 5/8 inches
• second pair: 6.5 inches

The diameter of the holes are the same as the hole drilled in the feet as well as in the connector component (The diameter of the holes is (1/8)"). There is no counter sink required for this. The distance between the holes should be also the same as the distances in the connector components. 

Figure N

Construction of the stand

    The construction of the legs is pretty simple. It is almost like putting to gather a puzzle.

Step 1:

    Cut the 2 x 10' PVC pipe into:

• 1 piece 3 feet long
• 1 piece 2 feet long
• 2 pieces 1 feet long
• 6 pieces 0.5 feet long

Step 2: 

Connect the 0.5 feet long pieces into the PVC-T. It should look like the letter I when it is finished. This can be seen in the figure below.

      Figure O

Step 3: (The Base)

    Connect a piece of the PVC-90's on each side both the 1 feet long pieces an example of this is shown in below in figure P. The finished bottom of the stand should look as shown in figure Q.

Step 4: 

    In the largest piece, the 3 feet long piece, drill a hole 7 and (3/8) inches from the bottom of the piece and another one 18" from the bottom of the piece. Both pieces will have a diameter of 3/8 ". Both holes will go all the way through the PVC Pipe. Connect this component to the base shown in figure Q. A rod will be placed through the holes to support the legs during testing. I used a scrap steel rod that I had laying around. You may use anything similar.

Figure R

Step 5: 

    The next step is to connect the 2 feet long piece to the big PVC-T using the two different scale down connectors. This is shown in Figure S. The whole piece is shown in Figure T. Once this is complete, slide it down the pole that is attached to the base.

 

Figure S

Figure T

Step 6: 

     Next attach the robot to the arm using the Ring type clamps as shown in figure U. Figure V show the final product.

Figure U

Figure V

Programming

     I used P-Basic Stamp to initially get the robot to walk. I used this because it worked well with the controllers that I have. I am using controllers that I have from US-FIRST Robotics Competition. The picture of these are shown below. More information on these controllers can be found on the Innovation First website. Once I have a definite idea on the legs should move in order for them to walk properly.

Trials: 

• TRIAL 1: This is the first trial to get the legs to walk. This trial was initially done to understand the motion of each motor. The trial took place on the week of 07/09/2003.

  • Front view

  • Side view

• TRIAL 2: In this trial, the first step was take on the ground. The trial took place on the week of 07/09/2003.

  • Trial 2

• TRIAL 3: In this trial, the took full strides, in air. This part is not yet perfected. The trial took place on the week of 07/14/2003. This will continue through the week of 07/21/2003/

  • Full Walk

Now that I have a descent idea of how the legs should move, I have developed a PIC circuit to move the legs with. In this circuit, Tai N. He has developed a tutorial on the PIC. To view this tutorial click here. The circuit that we have developed is shown. The Picture on the left is schematic of the circuit, and the following  video explains how the circuit was created on a bread board. The bottom picture shows what wire of the servo motor should be connected to what.

PIC Schematic

Final Words

    Unfortunately due to lack of time, I was unable to finish this project. If I had continued with this project, I would have taken out one of the servo motor from each leg. This will make each leg consist of only three joints. By doing this, it will make it easier and less complicated to control motion of the legs, and it will also help balance the legs because the center of gravity is lower. Since our primary goal is not to have the legs maintain balance while walking, another suggestion I would make is to add a wheel to help keep balance while in motion.