Society of Robots - Robot Forum
General Misc => Misc => Topic started by: frodo on February 02, 2009, 05:22:39 PM
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hi, i am thinking of doing the challenge with webbot and wondered whether anyone had anything to say about it.
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hi, i am thinking of doing the challenge with webbot and wondered whether anyone had anything to say about it.
Ok - so a bit of clarity. Check out http://www.micromouseonline.com/ (http://www.micromouseonline.com/) - its a 'maze solving' competition aimed at schools.
Lots of cool videos etc out there (Google) and lots of 'off the shelf robots' at a price - Nah! - lets build one.
But to make it clear: 'we' wont be entering the contest - but we intend to mentor a local school to help them to take part. They take the glory and the failure - we just learn by mentoring. They've got lots of cool fabrication machines - hhmm may just help us out in return.
Can't see why a $50/Axon kind of circuit wont do the trick!! So: I hope you guys/gals are 'all in' to help 'mentor the mentors' - and lets all become contest winners!!!!
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'we' won't be entering, just mentoring others
thats what i meant, just not good at wording stuff :P
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As I promised you, Webbot . . . micromouse video, hopefully useful for someone . . .
[youtube]bproY7G2t4o[/youtube]
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COOL!!!!!!!!!!!!!!!! :o did they use servos or something? because i have never seen a robot move so fast, it actually made me go a bit dizzy!!
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Most micromouses adcance onto using stepper motors.
here is another site hosted by birmingham university and midlands robotics club http://www.tic.ac.uk/micromouse/ (http://www.tic.ac.uk/micromouse/)
It contains past competition times and results aswell as a gallery etc... there are some videos but they dont seem to be streaming today (i dont know if they have been deleted but they used to work).
Also there is a basic competition for schools where the maze can be solved just by following one of the walls (like tracking the left side) so your first entry need not be overly complex, you could easily build a robot for this category and then work on improving it for the next competition.
There are other categories and competitions too
****GOLDEN CHEESES FOR THE WINNERS!
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so the stepper motors are used as the motors on the wheels?
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yeah, they help with controlling the position.
Once the robot has recorded the map into its memory, it might for instance know that it has to move forwards 45cm and then turn right. Using stepper motors and knowing how many steps per rotation along with the circumference of the wheels will let it be able to move 45cm whereas if you use modified servos you can only turn them on.
You could use encoders along with motors or modified servos but that means the microcontroller has to deal with a lot of interrupts, most mouses progressively use stepper motors. (you cant get exactly 45cm with stepper motors because they all have a max number of steps. say you have a stepper motor that steps 56 times per rotation and 45 cm falls inbetween steps 51 and 52 and not dead on either of them, you lose a bit of accuracy).
You have to decide what level of accuracy you want before choosing the stepper. The more steps the more accuracy or resolution you get from them but it takes longer to complete a rotation. its a play off between speed and accuracy .....again ..... it always is
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Stepper motors are kinda like a DC motor with a built in encoder: With a DC motor you use the encoder to count the steps, with a stepper motor your code issues the steps. As paulstreats says.
However: this make several assumptions:-
1 - That each stepper motor step achieves a physical movement (ie the motor doesn't stall at all) and the 'bot doesn't skid
2 - That the diameter of the wheels are exactly the same. If the robot covers say 2/3rds of the maze then it has actually covered a considerable distance so any imperfections in the wheel diameters may become significant.
But its all a bit simpler than that.
The micromouse environment is somewhat 'artificial' in that its world is made up of a fixed sized grid of squares. So you don't need to use encoders/steps to work out exactly where you are relative to your start position - you only need to know which grid square you are in.
IR sensors pointing N/S/W/E and NE/NW/SE/SW can aid the robot to move in parallel to the walls between each grid.
When moving down a long 'corridor' then errors could build up but the corridor can only max out at the maze width. Normally there would be at least one 'gap' in one wall. Detecting this gap can then help to 'reset' your encoders to know that you are at a cell border. So the encoders only need to be as accurate as the number of cells across the map.
Stepper motors tend to be quite big, bulky. I think the videoed robot probably uses mini-dc motors with a 'crude' encoder.
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I also noticed that when it gets to the high level competitions that the winning factor is due to the cooefficient of the tyres meaning less friction. youll notice that some robots start messing up then the "owner" cleans the wheels off and starts again... also algorythms to turn corners efficiently are also a major factor as well as making sure the back isnt heavy to prevent slide. All is down to removing errors....
Stepper motors tend to be quite big, bulky. I think the videoed robot probably uses mini-dc motors with a 'crude' encoder.
possible, but i have had the pleasure of seeing a few micro micromice and these use very small stepper motors(the downside being they cost around £280 each.... most micromouse enthusiasts dont mind spending this amount on their hobby especially if it mens winning the golden cheese ;D). You know if they are steppers because of the ringing sound they make when they are moving fast enough.
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Webbot, my assumption is that they use data from the IR sensors to slowly correct for the drift from the encoders/steppers.