Personal Project: Biomimetics
Dogs - Walking
Click Here to Go See Performance & Analysis
Research
http://www.earthlife.net/mammals/locomotion.html
Dog walk - The most common four-legged locomotion which you will observe is the walk, sometimes called the diagonal walk. This is used by most hoofed animals as well as cats and dogs. In this walk, the animal uses diagonally opposing legs, i.e. front left and right back legs move forwards then the front right and left back legs move and so on.
http://www.oricomtech.com/projects/leg-anat.htm
Leg Attachments. Note that on horse, cat, and dog skeletons, the leg attachments are located high with respect to the main mass of the torso. This prevents the animals from being top heavy.
The legs, front to back, have a mirror-image conformation as in the horse above, and the joints bend in a similar manner.
Also see horse anatomy in the Research section of 'Dogs and Horses - Trotting'.
Guide:
http://www.thenxtzoo.com/4legwalk_gears.pdf from http://www.thenxtzoo.com/4leg_NXT.html
'Building robots with Lego Mindstorms NXT' from the school library
Astolfo, David, Giulio Ferrari, and Mario Ferrari. Building Robots with Lego Mindstorms NXT. Updated ed. Burlington, MA:
Syngress, 2007. Print.
Robot Building
Experiments: legs
First, I made the legs from the book to fully understand how they work.
1. I started making the base looking at the pdf from the internet
2. When making the robot following the instrutions on the pdf file, I realized the gears don't move because of motor overload
(the gears need more power than the motor's maximum output). So I added another motor.
3. I figured out the leg mechanism I'm going to use for this robot. I also figured out the the legs will always work even if they have different length as long as it has 4 hole in between the connectors.
4. When experimenting with the leg mechanism, I found out that one of the small gears fall out after rotating for some time. So I changed the way it is connected
5. I connected the legs to the gears according to the pdf file. Then I analyzed how leg movements are relate to the gear rotations and the position of the connectors. After analyzing, I changed the positions of the connects so the legs would move in the sequence I want (dog walk).
PDF: Dog Walk:
LR or L for legs raised, G for legs touching the ground, (A) for leg in the air.
6. I attached basic legs. Currently, the robot is in the right diagonal phrase of the 'walk'; however, the robot is not balanced on the two legs (right front and left rear), and is leaning backwards; it needs the right rear leg in contact with the ground for it to balance.
7. I changed the main leg pieces and made them shorter because they were too long and unstable. I made the feet wider for more stability. I then moved the NXT box more towards the front to adjust the center of gravity.
Reference:
The robot is now balanced on two legs (right diagonal).
8. I realized the leg movements aren't uniform (even if the position of the connectors and gears are the same). So I adjusted the position of the yellow beams to make the legs all move in a same way
9. I noticed that I could have reduced the width of the robot, so I made appropriate changes (I wans't able to reduce it as much as I expected).
10. I made the program for my robot, but because the NXT brick was not recognized by my computer and the school computers, I told my supervisor about this. Actually, the problem was that the NXT brick I borrowed from him was a newer version of NXT (EV-3) and it needed the newer verison of programming software. My supervisor got the software for me, and with some experiments, I was able to programm my robot.
Software older version: Software newer version:
11. I programmed the robot, but for somewhat reason the gears didn't rotate well; they rotated very slowly and sometime would stop. Maybe it was because of motor overload, however, when using the 'Motor Contorl' application inside the NXT brick, the gears all rotate fine.
With some testings, I figured out that it had to do with the number and size of gears I used.
Smaller the gears, greater the number of gears needed.
Greater the number of gears needed, bigger the friction between gears and between its connectors and the beams.
Bigger the friction, the more power it is needed from the motor, and harder it is for gears to rotate.
Before: After:
I made appropirate changes, and it now works fine.
Creating this robot was tough because I tried to make a robot within the limited number of lego pieces I borrowed from Mr. Lavigne. It was also wearisome to figure out the leg mechanism and adjust the center of gravity by trial and error. I think the hardest part about building a robot is that if something does not work the way it should, I first need to identify the cause of the problem and fix it through trial and error or testing hypotheses.
Despite all the challenges I faced (overcoming motor overload, coming up with a leg mechanism, adjusting gears, legs and center of gravity), I liked the process of building and programming this robot, and I am satisfied with the outcome.