Applying my PWD experience to a robot

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OneTimeRunner
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Applying my PWD experience to a robot

Post by OneTimeRunner » Wed Oct 13, 2010 9:51 pm

Greetings all! It's good to have a reason to chat with you again, even if it isn't PWD related.

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!



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Stan Pope
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Re: Applying my PWD experience to a robot

Post by Stan Pope » Wed Oct 13, 2010 10:37 pm

Well, I have no direct experience with robotics, but I've never let ignorance keep me from expressing myself! :)

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?


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dna1990
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Re: Applying my PWD experience to a robot

Post by dna1990 » Thu Oct 14, 2010 9:05 am

Also speaking from ignorance - but many of these types of challenges result in faster, by going slow (methodical at least).

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.



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gpraceman
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Re: Applying my PWD experience to a robot

Post by gpraceman » Thu Oct 14, 2010 9:39 am

In terms of the robot controller, you might want to use an Arduino. They are flexible, easy to program, have lots of inputs and outputs, and are inexpensive.


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SlartyBartFast
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Re: Applying my PWD experience to a robot

Post by SlartyBartFast » Thu Oct 14, 2010 12:33 pm

Post the rules!

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.



OneTimeRunner
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Re: Applying my PWD experience to a robot

Post by OneTimeRunner » Mon Oct 18, 2010 1:06 pm

Sorry for the delay in responding. I was having fun with my son at the Kentucky Centennial Jamboree this past weekend. (they had a 100 yd PWD track: http://www.courier-journal.com/article/ ... centennial

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.



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FatSebastian
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Re: Applying my PWD experience to a robot

Post by FatSebastian » Fri Oct 29, 2010 2:54 pm

OTR, this is completely off-topic, but over here you had once commented that a German tribologist had given you "some suggestions" that might lead to some lube experiments in the off-season? Are you still planning those?

:goodluck: with the robotics experiment! Let us know how it turned out.



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