Personal Project: Biomimetics
Inchworms - Crawling
Click Here to Go See Performance & Analysis
Research
http://www.wisegeek.com/what-are-inchworms.htm
The peculiar movement style of inchworms is the result of its lack of legs in the middle portion of the body. Inchworks have two or three paired sets of legs on each end of the body, but none in the middle. As a result, inchworms propel themselves forward by drawing the back end upward to form a loop shape, then reaching forward with the front portion of the body. When disturbed by a potential predator, inchworms often freeze in place so they resemble a still twig.
http://www.the-scientist.com/?articles.view/articleNo/33339/title/Next-Generation--Robotic-Inchworm/
The tricky part came when designing the legs themselves, Bashir said. In order to achieve inchworm-like movements, “the back leg has to adhere and the front has to move forward, then the front one has to adhere and the back one has to move forward,” he explained. “So there has to be an asymmetric change in surface adhesion.”
Guide:
http://www.nxtprograms.com/inch_worm/index.html
Robot Building
I started making the robot following the guide from http://www.nxtprograms.com/inch_worm/steps.html. I don't know what mechanism it uses, but I'll just build it first and think of it as my prototype/ experiment.
1. I've finsihed building around 1/3 of the robot.
2. I've finished building the robot following the guide.
3. I've programmed the robot using the file I download from the guide website.
The programming is very easy and I can understand why the robot should be programmed this way; however, the following text, which came along with the program, I would need to think about it more.
Analysis:
40 tooth gear : 8 tooth gear
1 : 5 rotation ratio
Therefore 1 rotation : 5 rotation = 80 degrees : 400 degrees.
400 degrees rotation in 8 tooth gear = 80 degrees rotation in 40 tooth gear.
4. I've done some test drive of the robot to see how its mechanism works. But the robot doesn't seem to work so well. I would need to need to analyze its structure to find out about its mechanism to come up with a solution.
Key components of the robot's mechanism:
5. Analysis
The lego brick should prevents the adjoining gear from rotating in unwanted direction, and this should only allow the wheels to roll towards the right (blue arrow); however, the mechanism doesn't work as it should. It is because the lego bricks cannot be fixed well enough to prevent the gears from rotating.
6. Coming up with a solution: Ideas
I need to come up with another way (mechanism) to only allow a gear rotate in one direction.
Idea 1:
Similar to the original design (from the web) in a way that it uses a lego brick to only allow a gear to rotate in one direction.
Idea 2:
Similar to 'Idea 1'. This design is an improvement from the original design from the web. The thin, pliable part of the brick would only allow the gear to rotate in one direction, and stop it from rotating towards another.
Idea 3:
A design that I think might work. I'll have to do some experiments to find out.
Idea 4:
As the lego brick attached to the gear rotates, it would get stuck if the gear rotates in unwanted direction.
7. Coming up with a solution: Experiments
Excluding ideas 1 and 2 that require a 3D-printed lego brick, I've experimented with idea 3 and 4.
Idea 3:
Failure. The beam(s) prevent/allow the gears to rotate the same amount in both directions.
Idea 4:
Works fine, but it requires some power when the lego pieces slide past each other.
While experimenting more with 'Idea 4', I've come up with a good mechanism that does what I want.
This mechanism perfectly prevents the gear from rotating in one direction while allowing it to rotate in another.
8. Modifications to the robot
I've made changes to the robot using the mechanism I've found. In the process, I inevitably had to add more gears and beams, which made the robot longer than before.
9. Test drive
Turns out that the gear-stopping mechanism at the robot's hind body is hardly used, and is probably unnecessary.
It seems like that the robot's fore gear-stopping mechanism is what's important.
I think this happens is because I've made the robot longer, changing its center of gravity. Since the robot's hind body got much more longer than its fore body, when the robot bends it's joint, the center of gravity is more towards the front, making the robot move forwards.
What was expected: What actually happened:
1. When bending its joint, the robot's fore gear-stopping mechanism allows the robot pull its hind body forwards.
2. As the robot straightens its body, the hind gear-stopping mechanism doesn't allow its hind body to move back to where it was, and makes the fore body to move forwards.
3. As a result, the robot has moved forward.
1. When bending its joint, the robot's fore gear-stopping mechanism allows the robot pull its hind body forwards .
2. As the robot straightens its body, its center of gravity (which is located more towards the front) makes the robots move more forwards than backwards (making the hind gear-stopping mechanism useless). The center of gravity forces the fore body to move.
3. As a result, the robot has moved forward.
