Here's the PRICELESS bit of information we learned last year- after the competition and during our programming phase from Jan- May.  The wheel size matters a lot more than you might think.  The answer here is that the larger the wheel, the easier the math computation from wheel degree to inches is, but the greater it's percentage of error! So while the largest wheel correlates into a .1 ration=1"- super easy right?-, but it also has a 14-20% margin of error when stopping.  Smaller wheels are more difficult to work the math out with, but you work the wheel equation once and we're set. Smaller wheels can have up to 1-4% error.   

    Now- have the kids come to this conclusion themselves :) Have the kids do some simple tasks even just forward & back will do the trick and a bar, or goal, where they'll aim for.  Use several different size wheels and calculate the average percent of error (How many degrees it went past "perfect", which can be easily done by going to "view" in the brick after the program has run, setting it on "rotation degree" and rolling it back so you can see how many degrees the wheel was off). Start the motor block off with 1 rotation (then move to two & three).  Mark the wheel with some colored tape or a washable marker. Start and try to stop on the wheel mark.  Try it at different speeds; that's makes a big difference too. Make it more complicated and do a couple of turns.  What the kids should be noting is that the percentage of error is accumulative. So when you're off 1% each turn, not as big of  deal, when you're off 15% each turn and you've got 4
 turns, well, I think you can figure out the frustration level of anyone trying to run that course over and over.

    This was the issue we were pulling our hair out with last season.  The robot was SO inconsistent it was cruel.  It would miss the mark, the kids would reprogram it and now it was too short, fix it and it went a totally different "wrong" that time.  Turns out- it was the wheels!  BUT now my team will never, but ever, forget about this engineering principal, and it was the first point of design on this year's robot :)

    My other tip, not as priceless : ), is to build two designs now and run the same program to see the advantages & disadvantages of each one. Picking the winner sooner than later.  If you don't have two robot sets, it's far less convenient.  The team must commit fully to a robot design because changes later on are likely to effect all the programs already made, so each significant robot change will have you start about zero.   My team kept making changes until 3 weeks out.  Not the path they hope to take this year.
Good luck, 


From: Anant S. Narayanan <[log in to unmask]>
To: [log in to unmask]
Sent: Friday, September 16, 2011 6:40 AM
Subject: Re: [VADCFLL-L] Robot to Build?


The design of the robot for this competition is entirely up to you.  The basic 9797 design (also known as the tribot) is a good place to start.

Your son will soon find that the trailing wheel design for the tribot makes it hard to steer consistently - when the robot reverses, a well made tribot's trailing arm will swing around sometimes to the left and sometimes to the right.  This will make the robot's path hard to control - especially for missions outside the base quadrant.

If he gets to this learning point, he will next redesign the tribot with a skid or slider, or take matters into his hands and build a robot entirely from scratch . . . and an engineer will be born.  Remember to be there to watch and take pictures.  The moment is priceless.

Later on will come more frustration . . . when attachments don't come on and come off, programs don't behave or time starts to run out.  It is all part of the experience.

What sounds like an enormous failure will become an extraordinary learning experience and a lesson in persistence.  I hope you enjoy the journey as must as most of us here have.

Don't hesitate to ask for help -  there are tons of resources on the web (official and unofficial).  We are all in the same boat and the success of one is a success for us all.

Best of luck.

Nari Narayanan
McLean Robotics Institute
Sent via BlackBerry by AT&T

From:  Scott James <[log in to unmask]> 
Sender:  First Lego League in Virginia and DC <[log in to unmask]> 
Date: Fri, 16 Sep 2011 00:01:56 -0400
To: <[log in to unmask]>
ReplyTo:  <[log in to unmask]> 
Subject: [VADCFLL-L] Robot to Build?
Newby here with a basic question.  We have the board and all the items built so making progress.  My son built the robot from the instruction manual that came with the kit, 9797 in the lower right hand cover of the instructions.  Then he decided to take it entirely apart to take the batteries out to replace with the rechargeable pack (not sure if it was necessary to take all apart but that was what he decided to do).  Before he rebuilds it wanted to make sure the correct design for the robot for this challenge was the 9797 build instructions.  Also, with whatever design we are supposed to build, are we better off with the rechargeable battery pack installed?
Thanks a lot for any input we can get on this,
Scott James 
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