csclub@shep (11/18/90)
Each year, UC Davis has a "Micro Mouse" contest in which student teams compete in a timed maze-run using small robots they have constructed. A few of us are playing with design ideas, but would be pleased if we could bounce ideas off of the membership of this newsgroup. If this is an inappropriate topic, or if there is a better discussion group for this, please tell me. Further, perhaps comp.robotics would appreciate the stimulation of such a discussion. To this end I am including a brief description of the contest and some design considerations The Problem: The robot must maneuver through a large (8" corridor) wooden maze, and in order to reach the point in the maze designated as the target, must be prepared to cover the entire maze in the fastest possible time. Some Design Considerations: - Awareness of surroundings, memory of where it has been - Ability to maneuver quickly in at least 4 directions, or turn easily - Ability to correct itself if it gets into weird orientations - Well developed algorithm for mapping the maze In particular our team is concerned with how we can make the mouse move in 4 directions without having to pause for turns. We had thought of using 2 DC motors (stepper motors won't be fast enough), to run two central wheels; this would allow us to turn quickly, and could elminate back-ups since we could switch direction. Another idea is a large central track ball, which could virtually eliminate turns. Are we overlooking other superior ways in which we could accomplish 4-way movement? Thanks for your input, Devon Tuck tuck@iris.eecs.ucdavis.edu
mwtilden@watmath.waterloo.edu (M.W.Tilden, Hardware) (11/19/90)
In article <9322@aggie.ucdavis.edu> tuck@iris.eecs.ucdavis.edu (Devon Tuck) writes: >Each year, UC Davis has a "Micro Mouse" contest in which student teams >compete in a timed maze-run using small robots they have constructed. > >A few of us are playing with design ideas, but would be pleased if we >could bounce ideas off of the membership of this newsgroup. If this is >an inappropriate topic, or if there is a better discussion group for this, >please tell me. I can't think of a better place to bounce mouse ideas. I'm currently engaged in re-tackling the problem myself after competing at the North American Micromouse competition in Toronto (great time. Lotsa fun. Strongly recommend it). >Some Design Considerations: > - Awareness of surroundings, memory of where it has been > - Ability to maneuver quickly in at least 4 directions, or turn easily > - Ability to correct itself if it gets into weird orientations > - Well developed algorithm for mapping the maze > >In particular our team is concerned with how we can make the mouse move in 4 >directions without having to pause for turns. We had thought of using 2 DC >motors (stepper motors won't be fast enough), to run two central wheels; this >would allow us to turn quickly, and could elminate back-ups since we could >switch direction. Another idea is a large central track ball, which could >virtually eliminate turns. > >Are we overlooking other superior ways in which we could accomplish 4-way >movement? Superior? Loaded question. Well, my mouse uses the guts of four regular Microsoft mice to make a frame which could independantly raise and lower wheels in either x or y directions. The 90 degree roller axes were mounted on a cross frame and grommets added to the round contact switch sensors (yes, these were old style mechanical mice, not IR). A motor on each side of the square mouse drove two grommet wheels by band drive, and a single motor looked after the raise/lower mechanics. The result was a mouse that was perfectly four-way symetric with a change-direction speed of less than a 20th of a second. Four of the eight wheels were in contact with the ground at any one time giving maximum stability and traction. Such a mouse has advantages, not the least being that as it does not have to turn around, control is simplified to just staying orthogonal to the maze walls. This was done by simple speed regulator circuits on each edge motor, the inputs coming from rolling tactile wall sensors. As the mouse moved down a corridor, the carefully adjusted sensors thus forced the mouse to stay dead middle. They did the same thing every time the mouse had to make a turn, keeping the mouse from hitting the walls in a corner. Fact is, this design took away so many control headaches that my mouse did not even need a processor, just a simple 3 chip state engine. A processor is going on the next one (maybe) but it was nice to see what could be done without it. I tried using the idea of a single ball driving the floor but came across two problems: One, the drive ball must be under pressure from the perpendicular driving shafts just to maintain friction. As this happens in 4 places around the ball, the energy losses of rotating the rubber ball surface over two inert areas I think mounts up to 30%. Two, because of One, the balls don't last too long and your mouse gets hot. Conclusion, using a mouse as a position sensor is all it's good for. Regarding algorithms, the competition I entered did not use a connected maze, so the simple right-hand wall following rule would not work. My system used a slight modification to this which was... prime = 3 Right-hand rule, turning left (if possible) every prime. every (tee or cross) junction, increment the prime to the next prime. when goal reached, lock current prime in place. I haven't tested this algorithm rigorously, but it seems to work. It was the best non-random algorithm I could implement on my hardware. It turns out the algorithm you use will change drastically depending on if you use over-the-wall looking sensors or low sensors which can only see the immediate walls around it. Over-the-wall sensing means you can fill up your internal maze map with less travel, but the weight of the sensors typically makes for a very top-heavy mouse which cannot turn quickly. An interesting discovery by MIT during their recent racing in Singapore was that a mouse which aggressively seeks the center of the maze without checking to see if there might indeed be a faster path eleswhere does have a better overall chance of winning. 'Mapping' a maze takes time which will count against you in the final scoring. Simulations on lots of previous competition mazes proves this out. In terms of mouse designs, the MIT two-wheel-two-castor cart design is the current world record holder. The main motors are small and close to the center of mass, as are the drive wheels. Balancing castors are placed at a distance to stabilize the outfit. It makes for a very low and light engine which can cut corners effectively. There are also close competitors which use powered outside castors to hasten the mouses turns. The speed is equivalent, but the mouse can be made significantly heavier if you need it to be so. My current design ideas include the following: a motorcycle mouse (wide wheels, high traction, bi-laterally symetric, small), a mouse 'ball' (large sphere which changes internal centre of balance to move. Won't be fast but will make a good 'demonstration' mouse), a 'jet' mouse (built in ducted fan to assist acceleration and also suk the wheels onto the deck for better traction), a Lamborgini mouse (made from a posi-track Tamaya model kit. It'll fit and look good) and a 'mouse' mouse (a mouse built out of a single ordinary computer mouse, using the trackball to give positional information to a 68C11 uP. Two motor, two castor drive), and, of course, improvements to my first mouse. One of the interesting things about micromousing is that, like potato chips, you can't have just one, you've gotta build another. My preferance is to go the unorthodox route and build no two mice alike (there's an awful lot of cart designs around. It's good but it's peaking in effectiveness IMHO. Don't be afraid to go wierd). The other reason to go unorthodox is that in two years the next International Robot Olympics will be held, and modifying mice to enter one or more of those events will be a must for those that can (I just got a brochure of some of the competitors. Most look like an explosion in a Meccano factory. Just beautiful). Of course the whole reason to get into micromousing is not the competition so much as the fun of doing it. Most people who got into robotics were not inspired by robot assembly lines, but by Star Wars and Silent Running and other shows which showed robot creatures doing neat things. Robotics needs industrial efficiency to make it pay, but after hours, micromousing is one way to keep the imagination greased. Anyway, I have all kindsa information (including full on line rules) if anybody's interested. Videos may soon be available if I can get my butt in gear. Is all. -- Mark Tilden: _-_-_-__--__--_ /(glitch!) M.F.C.F Hardware Design Lab. -_-___ | \ /\/ U of Waterloo. Ont. Can, N2L-3G1 |__-_-_-| \/ (519) - 885 - 1211 ext.2454, "MY OPINIONS, YOU HEAR!? MINE! MINE! MINE! MINE! MINE! AH HAHAHAHAHAHAHAHAHA!!"
mgobbi@cs.ubc.ca (Mike Gobbi) (11/19/90)
If the maze is guaranteed to only contain 90 degree corners, here is a
quick method:
have 8 wheels on the robot - 4 pointing north/south and 4 pointing east/west.
The two sets are on separate frames, and are set up so that only one set is
lowered at a time.<< forgive the noise. SOmeone just picked up
the phone>>
Thus, to go north, spin wheels in one direction. To go south, spin the other
way. To go east or west, lower the e/w frame and raise the n/s frame, then
turn wheels in appropriate direction.
Using solenoids to raise and lower the wheels allows for almost instantaneous
transfers. The biggest flaw that this robot has is that if it gets out of
alignment somehow (careening off a wall is a good way...) it cannot recover.
--
__
/..\ In quest of knowledge...
--mm--mm-- Mike Gobbimwtilden@watmath.waterloo.edu (M.W.Tilden, Hardware) (11/20/90)
Just so everybody knows, the next two micromouse competitions
(that I know of) are:
APEC 91 Micromouse contest
5th annual contest at the Hyatt Regency hotel in
Dallas, Texas, March 13, 1991. Approx start time: 2:00 pm.
Contestants do not have to register for the conference if
they don't want to.
Additional info can be obtained from
Melissa Widerkehr
Courtesy Associates
655 Fifteenth Street, NW
Washington D.C.
20005
(202) 347-5900
...but not until January. Until then, contact Dave Otten at MIT,
(617)253-4691 for details. (Dave is the current world record
Micromouse holder and the creator of MITEE 1 through 6. He
has also written several 'build your own mouse' articles in
Ciarcia'c Circuit Cellar, so look them up.)
------------------------
IEEE 91 Micromouse Competition (Canada)
First annual contest sponsored by the University of Waterloo,
Ontario, Canada in May, 1991. Details pending. For more
info, e-mail mouse@sunee.waterloo.edu.
If anybody has details of other events, please post. Nothing inspires
action like a deadline.
Is all.
--
Mark Tilden: _-_-_-__--__--_ /(glitch!) M.F.C.F Hardware Design Lab.
-_-___ | \ /\/ U of Waterloo. Ont. Can, N2L-3G1
|__-_-_-| \/ (519) - 885 - 1211 ext.2454,
"MY OPINIONS, YOU HEAR!? MINE! MINE! MINE! MINE! MINE! AH HAHAHAHAHAHAHAHAHA!!"jc7k+@andrew.cmu.edu (Jeffrey C. Chen) (11/20/90)
On 19-Nov-90 in Re: Micro "Mouse" discussion? user M.W.Tilden, Hardware@wat writes: > ...but not until January. Until then, contact Dave Otten at MIT, > (617)253-4691 for details. (Dave is the current world record > Micromouse holder and the creator of MITEE 1 through 6. He > has also written several 'build your own mouse' articles in > Ciarcia'c Circuit Cellar, so look them up.) You wouldn't happen to have Dave's email address? -Jeff ================================================== jc7k@andrew.cmu.edu jcc@cive.ri.cmu.edu Jeffrey Chen Jeffrey Chen Box 1566 Field Robotics Center 1060 Morewood Ave Carnegie Mellon University Pittsburgh, PA 15213-3890 Pittsburgh, PA 15213-3890 USA USA (412) 268-4876 Aspired to become a vending machine technician... ==================================================