Bi-Pedal Walker Robot
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The rest of the tutorial is presented as follows:
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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 For Bi-Ped Robot
PART NAME | PART # | SOURCE | QUANTITY | PRICE (US Dollars) | |
16F84 PICmicro controller | 145111 | jameco | 6 | $ 5.95 | |
Hitec HS300 42-oz Torque servo-motor | 12 | $ | |||
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8975K22 | McMaster | 1 | $ 8.79 | |
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89015K14 | McMaster | 1 | $ 7.73 | |
Barrel
diameter = 0.203' head = 0.406" length = 0.570" |
100 | $ | |||
screw 8 x 32" | 100 | $ | |||
(3/8)" long binding head post screew | 90277A108 | McMaster | 100 | $ | |
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92196A108 | McMaster | 100 | $ 4.31 | |
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90480A005 | McMaster | 100 | $ 0.70 | |
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91102A72 | McMaster | 100 | $ | |
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90190A108 | McMaster | 100 | $ | |
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8589K81 | McMaster | 1 | $ 3.63 | |
Parts For Bi-Ped Robot Stand
PART NAME | PART # | SOURCE | QUANTITY | PRICE (US Dollars) |
2 x 10' PVC Pipe | Home Depot | 1 | $ 2.88 | |
1/4" PVC Coupler | Home Depot | 1 | $ 0.49 | |
1.5" PVC - T | Home Depot | 3 | $ 0.84 | |
PVC 90's (90 degree angle connection component) | Home Depot | 4 |
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.
Servo Shaft:
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Connector Component:
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U-Bracket:
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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
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![]() Figure E
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![]() 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.
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Figure I |
The fourth and last motor from the top of each leg will be perpendicular to the rest of the motors. This is shown in the picture on the left in Figure I. |
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.
Figure P |
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 |
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.
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 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/
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
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Servo Wire Designation
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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.