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abhinavnalluri

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Post Edited (abhinavnalluri) : 11/4/2009 7:29:13 AM GMT

Mike Green

1) The BoeBot is normally intended to run off 4 AA 1.5V cells. These power the servo motors and the BOE Stamp controller. If you want to use rechargable batteries, these are usually 1.2V and 4 of them only make 4.8V. Normally, you'd use a 5th rechargable cell to make a total of 6V. Parallax has an add-on for mounting this 5th cell or you can just buy a single AA battery holder (like from RadioShack), wire it in series with the 4 AA battery holder that comes with the BoeBot and glue it or otherwise mount it on the chassis. You'd have to make sure the 5th cell is allowed by the contest rules. They may only allow 4 AA cells even though that would not provide 6V if you used rechargable batteries.

2) The wheel motors on the BoeBot are what are called "continuous motion servo motors". These can be made to stop or to move at variable speed either forward or backwards and the BoeBot could stop very quickly (if it is not moving too fast ... it could slide or slip if so). You don't have to reverse the motor.

3) The BoeBot can time its movement. The timing isn't absolutely precise, but should be more than accurate enough for your purposes.

4) There is a whole tutorial on using a remote control with a BoeBot to send any kind of commands you want. It would be easy to use this to command the distance to move and to start the movement.

5) There is an "encoder" add-on to the BoeBot that provides for much better control of distance travelled than with a "stock" BoeBot. Have a look at the documentation that comes with it.

6) In summary, you need to download and look at several tutorials (Robotics and IR Remote for the BoeBot) and you need to download and look at the documentation for the wheel encoder for the BoeBot. The tutorials are available through links on the BoeBot page here: www.parallax.com/Store/Robots/RollingRobots/tabid/128/ProductID/302/List/1/Default.aspx?SortField=ProductName,ProductName.
The wheel encoder information is here: www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/List/1/ProductID/80/Default.aspx?txtSearch=wheel+encoder&SortField=ProductName%2cProductName. The BoeBot page I indicated is for the serial version. There is an almost identical USB version as well for PCs without an RS232 serial port.

Post Edited (Mike Green) : 11/14/2007 6:33:17 AM GMT

Bean

If they give you enough time it would be easier to just re-program it on the spot with a laptop.
You should only have to change one value to get the required distance.

The encoders will be the way to go. They will not only give you the distance travels, but they will help keep the bot going in a straight line. You just have to watch out for wheel slip.

Sounds like a great project.
Good luck.

Bean.

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www.iElectronicDesigns.com

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bobledoux

If you plan on using a robot with differential drive, like BoeBot, plan on adding a trailer wheel on an extension. Use readings from the wheel to keep it in a straight line.

BoeBot is a differential drive robot. It can turn in its own diameter, but driving in a straight line is not its strong suit. Even with encoded wheel sensors you could see significant errors in directional control. If you have to drive to a line a set distance away directional control would be very important.

Adding an extended third wheel permits much more precise directional control.

Selecting one of eleven distance options would be simple. It could be performed using a five switch DIP switch. That might require five input pins.

Franklin

curious_roboticist, Or something. They were written for high school students to design a vehicle on their own that encompasses the goals within the rules. I'm pretty sure the boebot was not singled out as the platform required.

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- Stephen

SRLM

To program a distance you could just use two buttons and an LCD: the LCD displays a distance, the left button accepts that, and the right rejects and scrolls to the next. As for dirrection control, the BOE-BOT, when adjusted, is very good about keeping a straight line. A gyro might help, but that might be over kill. As for the extended wheel: how will you read the change in dirrection? A pot would have too much friction and anyway, the boe bot is pretty light.

How is the contest scored? I'm assuming that they grade based on how close you are to a destination point, and the speed at which you arrive.

Franklin

SRLM, the rules are on the Siecne Olympiad site (if they are still up as this post was from 11/07)

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- Stephen

SRLM

Hmm. I guess I didn't look at the date. Well, *if* I were to build a robot that had to go in a straight line for a certain distance, thats how I would do it.


With chagrin.

Franklin

If you're still interested here is a link to the contest for 2008. www.soinc.org/events/electricveh/index.htm .

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- Stephen

erco

If you only want to go in a perfectly straight line and no turns are required, don't even consider a differential drive robot (such as Scribbler or BOE-bot). Just make a fixed axle, straight-line vehicle with 3 or 4 wheels that goes straight. You can modify a toy car or make your own. By mechanically eliminating the turning variable, you will simplify your task immensely. You'll only need two I/O pins: one for an encoder to measure wheel travel (counting pulses from a slotted disk or equivalent), and one to control your motor/servo. Perfect job for a BS1! In fact, you'll have so many left over pins that you can add pushbuttons and LEDs to enter the distance desired in lieu of using a laptop.

Plenty of online info to draw off of:
http://www.societyofrobots.com/sensors_encoder.shtml
http://www.seidata.com/~llingle/computer/trak.html
http://www.acroname.com/robotics/info/mini_faq.html
http://www.active-robots.com/products/motorsandwheels/wheelencoder-details.shtml


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·"If you build it, they will come."