I'm taking courses at my university, and we just received our class project: a simple robot that will follow a curving white line. Extra points will be given to the fastest two robots.
I'm turning to your collective wisdom again as a method of checking my logic.
Since this is a motor (modified servos actually) driven project, I'm assuming that I want to keep the total mass as low as possible.
I think the real advantage can be gained in wheel design. There are no limits on what we can do or use for wheels. Am I correct in assuming that I want high diamater, low mass wheels?
Since this is a student project, I have access to all kinds of machinery. Everything from lathes to CNC machines!
Any and all advice is welcome!
- Stan Pope
- Pine Head Legend
- Posts: 6888
- Joined: Sat Jul 05, 2003 7:01 pm
- Location: Morton, Illinois
Seriously, I would put priority on traction, stability and agility, The smallest radius of curvature of the line you must follow will determine the limits on speed. You absolutely want to avoid any slippage in the drive wheels. That limits your ability to respond to direction changes necessary to maintain high speed in the face of path changes. And you want zero directional interference from all non-drive wheels.
Slippage risk increases, when it can be least afforded (following a curve path), if the CM is high in the car. The reason is that a turn with CM high shifts weight from the inner wheel and onto the outer wheel. The vehicle will understeer and must slow dramatically to maintain contact with the path. So, stability aids agility and is essential to speed.
Since you are dealing with "powered movement", you may have plenty of energy to overcome wheel rotational inertia, so that may not be as big a factor. However, the CM of a wheel is at the axle, and you probably don't want the CM that high in the car lest stability be reduced.
Logic to decide direction gets harder as the complexity of the line increases. Are there sharp angles? Acutely angled paths? Path crossings? Some specs on the path would be helpful in making that algorithm effective.
Can your vehicle look both at the near path and the far path, keeping speed up when it can see that the path is smooth and reducing speed if the path curves sharply?
"If it's not for the boys, it's for the birds!"
So I echo what Stan says - traction and agility (control) is likely way more key than raw power/speed/mass/cog/etc.
The sensor designs and the software side of the project to determine steering and maneuvering - is where I would start. That being said, a sturdy and well-aligned base vehicle will only help, in that the robot can concentrate on the follow-line and not compensating for a pull to the left, or a delay in steering response, over a tendency to over-steer, etc.
- Site Admin
- Posts: 4656
- Joined: Fri Jun 20, 2003 12:46 am
- Location: Highlands Ranch, CO
Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
- Master Pine Head
- Posts: 266
- Joined: Mon Feb 12, 2007 12:30 pm
- Location: Montreal, Quebec
Any PWD racers knows that the first step is to find the loopholes!
My university had robot sumo wrestling. Two robots in a circle, one needs to put the other outside the circle.
I got banned from competition after reading the rules and explaining my planned entry to the people in charge.
I was going to put a round, flat, taper-edged lead block with rubber feet in the ring. Why? Because a tie got 1 pt, a win got 2 pts, and there was a 1 pt bonus for the robot if it was autonomous. I would have won hands down.
IIRC they got me very drunk over the weekend before registration deadline. :p
And the next year the rules specifically defined autonomy and the point structure was changed.
For my project, there are no rules. But there is a grade, so it has to be in reason. I'm a little hesitant to post everything about it because it could be construed as cheating if I use too much of your advice.
There is a "suggested" way of building the robot, but he isn't giving us all the details in advance. He's releasing details a little at a time. If you follow the suggestions, you'll get an A, but you won't win the bonus points.
The wheels they supplied are HEAVY 1.5 inch hard rubber caster wheels. The wheels weigh more than the servos. Which is why I'm concentrating on the wheels at this point.
They also supplied a heavy ball-type roller, and a parallax basic stamp for controling it.
with the robotics experiment! Let us know how it turned out.