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November 2009


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Wed, 4 Nov 2009 13:08:05 -0800
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Never Hold Robot Tires with Hands. Use a vacuum cleaner or a piece of clean cloth from soft t-shirt to clean up the Field Mat and Robot tires. This should be your regular practice to keep the consistency of the mat and robot tires physical property (surface smoothness and friction of the contact area of the tires and the surface). Same as to fully charge the battery, you must do this every time you work on your robot on the field. And every time the robot starts acting abnormally vacuum the field mat and wipe the residue/dust off the tires!!! The tiny residue from tires may be left on the field mat after a few runs and if the robot drives over the residue or dust it will act crazy! Now let’s talk about how to carry the robot. When you absolutely have to carry the robot with hand such as move it from the carrying box onto the field mat, hold on non-tire portion of the robot. Holding on the robot tires directly with hands may make tires wet and sticky!
 As the result, it dramatically changes the friction between the tires and the surface, the consequence is all pre-programmed turns will NOT do what they are expected!
Use Wait Block (Time) for cancelling motion momentum, relieving the distortion from elastic bending and for testing NXT Program segments or subsets. Insert a wait-on-time block between two move blocks even if it seems unnecessary at the time. It is a simple but very effective way to improve the consistency of the robot movement. The robot and its parts may need additional time to “calm down” or to “relive from stress” after executing a move block and the “program counters reset” can be consistent with real robot movement. With deliberate increase of the value in the wait-on-time block the robot can take a long pause before executing next block; or you can terminate the program if you want to tune the movement executed so far before making adjustment on the remaining movement without breaking the block link. Therefore, the method can also be used for program diagnosis and fine tuning.  
The gravity center of the robot is better to near "the middle point of the line segment from the left driving motor to the right driving motor". How to build a 2 wheel (active) drive NXT robot (using wheel & tires, not treads) that can turn at ease? Assuming that you have designed your robot's "3rd-wheel-support" correctly (such as pivot wheel or least frictional sled surface, etc.), your robot still struggles with the turns – it cannot make turn with the low level of power and the turns are not consistent with the slight variation of the contact condition and the power level. In general you will find the gravity center of your robot is somewhere between the front edge (or back end) and the driving wheels. If this is the case, re-configure your robot to shift the gravity center towards the driving wheel – one way to achieve this is moving the NXT Block, the single largest mass of the robot!
Use Level of Power properly. Observe the behaviors (moves and turns) of robot with the different level of the power percentage and select the optimum level. Always fully charge the robot battery – set a thread hold of your own standard for battery level stability – how about no lower than 7.5v? A good practice is that if the MOVE block is for making a turn, set the power level around 50% 
Bump/Hug/Rub/Touch Walls and use walls for Robot Angling / Orientation. In reality no matter what you do to follow the previous stated methods the robot will still perform inconsistently. So you need to apply other reinforcement to make the robot to move in a predictable way! It is the most commonly used method to align and re-align the robot during the progress. One of the key elements is to use LEGO L-shape beams and rollers to build mechanical bumpers/aligners, which are not only provide the orientation alignment but also space (position) alignment for a particular mission execution. A combination of “bumping wall, driving away from wall a bit, and turning into wall with a move block on time” may provide a decent orientation resetting. Are there any other objects on the field that can be used for robot position/orientation alignment? 
Use sensors as many applicable places as possible! Checking black strips (lines) on the field mat with light sensors provide the most fundamental POSITION RESETTING method in FLL robot games. You may apply “a light sensor checks black strip edge” to a turning alignment under a suitable situation. Check distance with Ultrasonic Sensors whenever it is applicable.
Turn on Sensors only when the robot is near the intended check point. Don’t turn on the light sensors or ultrasonic sensors when the robot is still relatively far away from the intended check point because that may introduces some unintended responses. Instead, use a move block on degrees to travel a estimated distance to close in first, then continue on with “move-block-unlimited with  wait-on-light /distance-change-blocks”   
Calibrate or adjust Key Values on Different Tables. Recognize the variability that has no way to be completely eliminated (wall-to-wall distance on different tables, lighting condition, etc.), you may intentionally imbed or identify some blocks in the program that may need to be adjusted at the tournament. Once your table assignment is handed over to you at the tournament day and you are given a preliminary round opportunity, use it for calibrate your robot on the table within allowed the time – record the change of the value and go back the pit area to update your programs! And also keep in mind that THERE MAY BE MACHANICAL SOLUTIONS TO DEAL WITH THE VARIABILITY! Can you design your attachments that are intentionally imbedded in adjustable elements?  Of cause the best way to deal with this is your robot design and your game execution plan will minimize the impact of the change of the environment to your mission executions!!! For the light sensor
 position it very closer to the ground or surround it with other LEGO parts SO THAT THE LIGHT SENSOR WILL ALWAYS STAY IN SHADOW NO MATTER WHAT TABLE LIGHTING CONDITION IS – imagining whether you place the table under SUN or place it under totally dark the reading on your light sensor should stay the same!  
Apply move-block-on-time to preventing robot from “stuck” – Frequently we observe that when a robot is stopped by an obstacle it cannot finish the motion (value of the degrees or rotations) defined in the move block and it cannot move on to the next action. It is stuck. How to avoid this? Remember that “The Time will pass and The Robot will move on! Don’t get stuck on walls, on models or even on the robot self if you improperly use move block on degrees!” Use move-block-on-time!


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