Capture The Flag

[crazydude]

Could someone help me with the problem statement of this event..?? I am thinkin of building a robot for this event.. could someone please help..  the link to the statement is...

http://www.shaastra.org/n/events/Robotics

The name of the event is capture the flag...



 

[HDL_CinC_Dragon]

Wow that is awesome. That sounds like a REALLLLLYYYY fun event...

What exactly do you need help with CrazyDude?

[crazydude]

i actually want a method by which i can detect the opponent robot... i am thinkin of usin a basic line follower principle in the automatic robot... but cannot think of a method to detect the opponent's manual robot..

also, the flag is situtated at a certain ht.. so i am thinkin of usina an extendable arm for it... but have to get it in without detection..

my budget is around 150$ so i dunno whether i will be able to fit all this..

[HDL_CinC_Dragon]

On thing you could do is have a basic line follower and then then hook up a range finder to it with the range finder facing outwards of the circle and have it quickly running around the circle drawing a map of its surroundings and then anytime it gets a reading thats significantly closer than what its map says, it stops following the line and tracks the target. If suddenly the target drops out of viewing range, it goes back to following the line until it picks up its target again.

just a thought

[Rebelgium]

150$ is quite low budget if you want to buy a robot arm to.
You're going to have a real hard time selecting your components to stay under the budget... You should try to build as much as possible yourself (base, maybe even the arm) .

[crazydude]

i am thinking of using a strong permanent magnet for lifting the flag... will i be able to lift it... or can i use a gripping mechanism for lifting the flag...?? will it be within my budget..??

and will the range finder be useful since the robot will be movin in circles..

will the range finder detect objects that are in the same level as it is or otherwise..???l
 

[HDL_CinC_Dragon]

1) A magnet should work but you just have to hope it doesnt get hit hard enough to fall off the magnet. I dont think you will have any problem with the magnet interfering with anything on the bot. You can just simply take the magnet of the back of an old speaker you might have laying around and use that for the magnet

2) the rangefinder will be useful in this case because it will constantly be taking readings in front of it and since its moving in circles it will be able to make a map of its surroundings and then whenever something changes in its surroundings that doesnt match up with its map, it will know that the attacker is nearing and can then use the servo that its mounted on to track and know the location of the manual bot as it moves

3) The range finder is conventionally mounted on a servo or a group of servos(You must do this your own or find a premade kit for it) for pan as well as tilt. Using one or more servos, your robot can look virtually in any direction it wants!


Hope this helped!

[crazydude]

do i have to have two servos for pan and tilt..??

in the problem statement it is given that the autonomous robot must remain within two barriers which are 60 cm apart... only if the manual robot enters this region the autonomous robot must frag.. else it is invalid(we are thinking of usin a LED or alarm for showing the detection. so the range finder can be of what range n can we program the bot such that it detects only when it comes into that region..??

[HDL_CinC_Dragon]

You will need 2 servos yes. 1 for Pan, 1 for Tilt but I doubt you will need the tilt

What you can do is have sensors on the bottom of the robot that detect color so that while it does not see anything out of the ordinary, it can just follow the red line in circles around its territory. Then when it detects a target(the enemy robot), it can stop and watch the target but also get in front of it so the target cant enter the area safely. You can have your robot sit on the very edge by detecting the black rim and just sit in front of the enemy bot so that if you took a picture from the top of the arena and drew a line from the enemy bot to your flag, the line would pass through your robot.

[crazydude]

i want a mechanism to take the flag from the pole..the flag is magnetic... i cant seem to think of any mechanism other than a robotic arm.. but it would become too costly if i use one... can someone help me???

[HDL_CinC_Dragon]

dont bother with an arm. From what I understand the manual robots can go wherever they want so theyre not bound by the restriction of the black area. Just put a small post on the front of the robot that is of the height of the flag and put a small magnet on it. Now of course I think that might exceed the maximum height restriction but all you have to do is mount the little pole (roughly the size of lets say a radio antenna or something) on a servo so normally its laying down unless you press the button telling to servo to turn 90 degrees which would raise the pole, grab the flag, and possibly lower the pole again so that the flag is basically cradled by the chassis for safety so it doesnt fall off or something.

[crazydude]

your idea is very good thanks.. but i think that there could be a problem.. the flag is mounted on a disc that is 20cm in diameter.. so the rod that i have o use should be very close to the tip of the robot and the magnet has to be large enough to touch the flag... so if the rod i s large enough it will add to the weight of the robot.. so is there a way to overcome this.. or can i use a mechanism to tilt the rod at some angle to touch the flag..

and is there any way i can use to evade detection..?

[HDL_CinC_Dragon]

well most likely your going to need an 'L' shaped thing where the magnet is on the end of the '_' part and the servo is attached at the free end of the '|' part.
Hope you know what I mean

As far as detection goes. Im not gunna just give you a straight answer on this one. But I will guide you through in making the decisions.
First thing to do is think about the most common types of object detection: Sonar and IR range finders. Sonar is sound, and IR is light. What do you think would be a good idea to use to fool these methods?

[crazydude]

which would be more accurate in detecting the other robots..?? a range finder or a Proximity Sensor(TSOP Sensor)..?

I am thinking of using only two wheels in the autonomous robot..(like stampy). i am thinking of using the same method to turn as the one used in stampy.. so if i have to move quickly would my wheels be able to rotate in the opposite direction to provide the turn that quickly .. or is there a chance of the robot moving out of range of the red line in centre..??

[HDL_CinC_Dragon]

A)
Range Finders and TSOP sensors are basically the same thing. They both use InfraRed and such.... detecting them is really the easy part but your going to have to get creative on how to actually track them successfully... At the moment I cant really offer a suggestion for that cuz im just not too sure as to what would be an efficient method that would be available to you... (Perhaps someone else can interject here and give a few suggestions/guidelines?)

B)
the two wheels approach can be both a blessing and curse. You get a faster response when you need to turn since your motor can just start cranking electrons across its brushes in the opposite direction at the drop of a fews 0's and 1's. Two wheels I think is also a lot easier to program and work with since you can use point to point control where you can turn around on a dime where as a typical steering system you have to confine your abilities to your vehicles turning radius...

The two wheel approach is definitely the way I would go with your robot... you might even want to do that with both the autonomous bot and the manual bot just because of the better control you get...

Heres what I would do for the autonomous robot:
Have 3 sensors on the bottom of it lined up in a row horizontally. So that when your robot is traveling on the track, it can better see where it is... ill try to illustrate
███████
███████
███████
███████
███████
██[---]██ Where each '-' is one sensor
so when your robot is driving, this is what hell see:
(S1 = Left Sensor, S2 = Middle Sensor, S3 = Right Sensor)
Scenario 1
S1: '█'
S2: '█'
S3: '█'
  ~ Derived Statement: Im somewhere within the black zone but I dont see the red line... Ill drive in a Zig Zag pattern until I find it
  ** You dont really even have to have it drive in a zig zag since its going to be on a circle. You can just set him down (on the line or not) and tell him to drive straight until he picks up something on his sensors like the green felt or the red line. See below for details:
Scenario 2
S1: '█'
S2: '█'
S3: '█'
  ~ Derived Statement: I hit the grass zone, I had better turn right so I dont run into it too far!
  ** Since he doesnt know where the line is, you could have him turn at a 90 degree turn and that should face him right at the red line...
Scenario 3
S1: '█'
S2: '█'
S3: '█'
  ~ Derived Statement: I see the red line! Im a bit too far to the left of it though, I had better tell my right wheel to slow down just a smidgen so I slowly turn onto the line!
Scenario 4
S1: '█'
S2: '█'
S3: '█'
  ~ Derived Statement: Perfect! Im centered on the red line! Now if I can just keep that as centered as much as possible!
Scenario 5
S1: '█'
S2: '█'
S3: '█'
  ~ Derived Statement: Ut oh! I drove a little too far to the right of the line! I had better tell my left wheel to slow down just a smidgen so I slowly turn onto the line!

So hopefully you can see what I mean... you could even get super crazy and put 5 sensors for even more assurance that your bot wont stray from the red line once he sees it... of course your going to have to put in some lines of code so that when it detects a robot, it basically ignores its red line protocols but does NOT ignore its green patch protocols so it can prepare to brick wall the attacker from getting to the flag...



~ I hope this helped!!!

-EDIT-
Also, for avoiding detection on your manual bot, just cover the surface of it with VERY reflective materials angled as closely to 45 degrees as possible... just something so that when the IR beam of light hits it, it does not return to the receiver thus basically blinding the enemies bot of your existence... or if your enemy uses sonar, line the outside of your bot with sound absorbing foam stuff... if you can... all in all, you should hope your enemies dont use a regular camera with image recognition (not sure if something that uses image recognition would be small enough to fit within the regulation restrictions)... but im not familiar with camera image recognition...

[crazydude]

thanks very much for that reply...i have another doubt..
if i am to use a sharp IR range finder.. can i use a dc geared motor instead of a servo motor for controlling the pan of the range finder..??

[HDL_CinC_Dragon]

you can but I think that would make it much more difficult for you. I would just go with a servo if I were you...

[crazydude]

could you elaborate why it would be difficult if i use a dc motor..??

[HDL_CinC_Dragon]

To use a DC motor you would have to put an H-Bridge on it so that it could work like a servo or you would probably have to use an encoder so the robot would know in which direction it was looking in.

Anything you use, the robot needs a way to know where its looking or it wont know where to place the data and how to read it properly and then drive in the direction that it needs to...

do you see what I mean?

[crazydude]

i seem to have a problem in selecting a proper dc geared motor for my autonomous nd manual bots. do u have any suggestions as to what motors i might use..??
i am thinking of makin the autonomous bot faster so that i can cover greater region in a shorter time.. can u help??

EDIT: i am thinking of usin dc geared motors for the autonomous n manual...

[HDL_CinC_Dragon]

Well if you use a regular DC motor for your autonomous vehicle, your going to need encoders so that your robot can track itself so it knows how far its moved... To understand what I mean, try closing your eyes and take a few steps in a few directions and then try to guess where you are before opening your eyes. Of course we humans cheat b/c weve got some basic accelerometers and such in our brains but thats beside the point lol

Anyway, for the autonomous robot I think you should go with a design similar to the $50 robot tutorial. Use servos so you can control exactly how far it goes. And the best part is, if you use a servo thats more powerful than you really need, you can just put a set of gears to get more speed out of it. But remember, if you decide to go with this idea, The more speed you gain from a gear ratio, the more torque you lose and vice versa.

For more speed, you want a large gear on the spindle shaft of the servo and that large gear would drive a much smaller gear on the spindle of the wheel.
For more torque, you want a small gear on the spindle shaft of the servo and that small gear would drive a much larger gear on the spindle of the wheel.

Hope this helped you at all? If not tell me and Ill rephrase everything/explain things better

-EDIT-
OH! And yeah, DC motors would be fine for the remote controlled robot b/c the robot doesnt need to know how far it went, thats your job as the operator

[crazydude]

i understand what u are talking about..
do u think i can use the servo listed in this website

http://www.iurs.org/shop/

go to the motors and wheels page in this website...

would this one be correct for my appln..??

[HDL_CinC_Dragon]

ummm you could if you really wanted to do but I dont know how much that costs b/c the cost tells me its like "rs.550.0" or something like that... w/e the heck that means lol
plus the torque on that servo is a lot weaker than even the HS-311 so I wont recommend using that....

You can find stronger servos here:
http://www.servocity.com/html/hitec_servos.html

they are very cost effective and I would recommend using the "HS-311" under "Standard Servos" backgrounded in Blue. You could also find higher torque ones in the same spot. Just look around for what youll need. It all depends on the weight of your bot.

Hope this helped!

[crazydude]

well the torque on this servo seems to be really good. but what about the speed?? it says 0.19 sec for 60 degree rotation..well isnt it kind of low??

[HDL_CinC_Dragon]

wellll yeah

The HS-311's I recommended have a Torque of 3.7kg/cm and a Speed of .15s/60 degrees at 6.0v
The site you posted appears to be down at the moment so I cant look up the specs on it at the moment but I know they were a little bit lower... thats all I do remember lol