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    <TD><FONT size=+4>Lego Robots Tips and Tricks</FONT> 
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      <P>
      <H2>Sensors</H2>
      <H3>Putting light and touch sensors on one input</H3>It is easy to put 
      touch and light sensors on one sensor input. In this case better set the 
      sensor mode to raw. In nqc this can be done as follows: <PRE>   SetSensor(SENSOR_2,_SENSOR_CFG(SENSOR_TYPE_LIGHT, SENSOR_MODE_RAW));
</PRE>Now a value below 100 is a touch sensor event. Values above this 
      correspond to light levels (the higher the darker). 
      <H3>Using the IR port for proximity detection</H3>It turns out that the 
      light sensor is very sensitive to the infra-red light produced by the the 
      IR port on the robot. To uses this, mount the light sensor above the IR 
      port, pointing forward. Now regularly send messages. When there is a wall 
      close in front of the robot, you can notice this by high intensity changes 
      in the reading of the light sensor (preferably in raw mode). The closer 
      you get, the higher the fluctuations become. After a bit of tuning you can 
      rather accurately predict the distance. Here is a simple <A 
      href="http://www.cs.uu.nl/people/markov/lego/tips/ping.nqc">nqc 
      program</A> to demonstrate how this works. Thanks to Dave Chen and Simen 
      Svale Skogsrud for finding out about this. 
      <H2>Design</H2>
      <H3>Front and back</H3>All designs that come with Lego MindStorms use the 
      IR-port side of the RCX as the front. This is not a good idea because you 
      normally add a lot of stuff at the front, making the IR-port almost 
      invisible. Also, for balance reasons, it is good to put the motors under 
      the middle of the RCX. Finally, if you use a swivelling wheel, put it at 
      the back, not at the front. Pulling a swivelling wheel gives a much 
      straighter motion than pushing it. 
      <H3>Drive-Steer mechanism</H3>
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          <TD><IMG src="Lego Robots Tips and Tricks_soubory/step3.jpg"> </TD>
          <TD>This mechanism is based on the adder-subtractors of <A 
            href="http://carol.wins.uva.nl/~leo/lego/diff.html">Leo </A>and <A 
            href="http://www.phred.org/~alex/lego/">Alex </A>. It must be driven 
            by two motors; one connected to one of the four gears on one side, 
            and the other connected to one of the three gears on the other side. 
            One motor makes the wheels move in the same direction. The other 
            sterrs by making the wheels move in opposite direction. My design is 
            acccording to me stronger than the other ones. More pictures can be 
            found <A 
            href="http://www.cs.uu.nl/people/markov/lego/tips/Differential1/index.html">here</A>. 
          </TD></TR></TBODY></TABLE>
      <H3>Double motor power</H3>
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          <TD><IMG src="Lego Robots Tips and Tricks_soubory/twomotors.jpg"> 
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          <TD>If you need extra motor power, and you have enough motors, 
            connect two together. You can out them both on the same output to 
            drive them simultaneously. This is especially good for heavy robots 
            or if you want your robots to go fast. I assume you can do the same 
            with three or more motors, but I am not sure how many you can 
            connect to one output. </TD></TR></TBODY></TABLE>
      <H3>Bumpers</H3>
      <P>
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          <TD><IMG src="Lego Robots Tips and Tricks_soubory/bumper1.jpg"> </TD>
          <TD>Here is bumper I designed that uses only one touch sensor. 
            Instructions for building it can be found <A 
            href="http://www.cs.uu.nl/people/markov/lego/tips/bumper1/index.html">here</A>. 
          </TD></TR></TBODY></TABLE>
      <H2>Internals</H2>
      <H3>Free memory</H3>After loading the firmware, it seems that there is 
      about 6K of memory available for programs. You can use the <B>RCX Command 
      Center</B> to free this memory when required. 
      <H2>Programming with SPIRIT.OCX</H2>
      <H3>Using the joystick</H3>Here is an <A 
      href="http://www.cs.uu.nl/people/markov/lego/tips/RCXJoystick.zip">example 
      program</A> (in Delphi 3) of how you can use the joystick to steer the 
      RCX. It comes with full source and is freeware. It is a simplified 
      stand-alone version of the joystick window in my RCX Command Center 
      version 2.0. 
      <H3>Registering SPIRIT.OCX</H3>If you don't want to install the lego 
      software on your system but still use programs like the <B>RCX Command 
      Center</B> you must register the OCX. Copy the spirit.ocx file from the 
      lego Cdrom to you harddisk and use the Run command in the windows Start 
      menu to execute <PRE>   REGSVR32.EXE spirit.ocx
</PRE>This will register the ocx on your machine. (You might need to 
      specify the path of the ocx in the above command.) 
      <H3>Bugs</H3>There is a bug in the OCX: When polling the mode of a sensor 
      (e.g. Poll(11,0)) you don't get the right mode but 32* the mode. 
      <P>There is another bug in the polling command. Polling the watch gives 
      you the total time in minutes, and not divided in hours and minutes as the 
      doc suggests. </P></TD></TR></TBODY></TABLE></BODY></HTML>
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