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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- saved from url=(0054)http://www.cs.uu.nl/people/markov/lego/tips/index.html -->
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<HTML><HEAD><TITLE>Lego Robots: Tips and Tricks</TITLE>
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<META content="MSHTML 6.00.2800.1226" name=GENERATOR></HEAD>
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<BODY background="Lego Robots Tips and Tricks_soubory/back.jpg">
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<TABLE>
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<TBODY>
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<TR vAlign=top>
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<TD>
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<P><IMG src="Lego Robots Tips and Tricks_soubory/logo.gif"></P>
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<P><A href="http://www.cs.uu.nl/people/markov/lego/index.html"><IMG
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height=58 alt=[Home] src="Lego Robots Tips and Tricks_soubory/homeoff.gif"
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width=78 align=ABSCENTER border=0></A></P>
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<P><A
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href="http://www.cs.uu.nl/people/markov/lego/challenge/index.html"><IMG
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height=58 alt=[Challenge]
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src="Lego Robots Tips and Tricks_soubory/challengeoff.gif" width=78
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align=ABSCENTER border=0></A></P>
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<P><A href="http://www.cs.uu.nl/people/markov/lego/rcxcc/index.html"><IMG
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height=58 alt=[RcxCC]
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src="Lego Robots Tips and Tricks_soubory/rcxccoff.gif" width=78
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align=ABSCENTER border=0></A></P>
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<P><A href="http://www.cs.uu.nl/people/markov/lego/robots/index.html"><IMG
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height=58 alt=[Robots]
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src="Lego Robots Tips and Tricks_soubory/robotsoff.gif" width=78
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align=ABSCENTER border=0></A></P>
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<P><A href="http://www.cs.uu.nl/people/markov/lego/tips/index.html"><IMG
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height=58 alt=[Tips] src="Lego Robots Tips and Tricks_soubory/tipson.gif"
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width=78 align=ABSCENTER border=0></A></P>
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<P><A href="http://www.cs.uu.nl/people/markov/lego/links/index.html"><IMG
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height=58 alt=[Links]
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src="Lego Robots Tips and Tricks_soubory/linksoff.gif" width=78
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align=ABSCENTER border=0></A></P></TD>
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<TD><FONT size=+4>Lego Robots Tips and Tricks</FONT>
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<P><IMG src="Lego Robots Tips and Tricks_soubory/divide.gif"></P>
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<P>
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<H2>Sensors</H2>
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<H3>Putting light and touch sensors on one input</H3>It is easy to put
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touch and light sensors on one sensor input. In this case better set the
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sensor mode to raw. In nqc this can be done as follows: <PRE> SetSensor(SENSOR_2,_SENSOR_CFG(SENSOR_TYPE_LIGHT, SENSOR_MODE_RAW));
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</PRE>Now a value below 100 is a touch sensor event. Values above this
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correspond to light levels (the higher the darker).
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<H3>Using the IR port for proximity detection</H3>It turns out that the
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light sensor is very sensitive to the infra-red light produced by the the
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IR port on the robot. To uses this, mount the light sensor above the IR
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port, pointing forward. Now regularly send messages. When there is a wall
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close in front of the robot, you can notice this by high intensity changes
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in the reading of the light sensor (preferably in raw mode). The closer
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you get, the higher the fluctuations become. After a bit of tuning you can
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rather accurately predict the distance. Here is a simple <A
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href="http://www.cs.uu.nl/people/markov/lego/tips/ping.nqc">nqc
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program</A> to demonstrate how this works. Thanks to Dave Chen and Simen
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Svale Skogsrud for finding out about this.
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<H2>Design</H2>
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<H3>Front and back</H3>All designs that come with Lego MindStorms use the
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IR-port side of the RCX as the front. This is not a good idea because you
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normally add a lot of stuff at the front, making the IR-port almost
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invisible. Also, for balance reasons, it is good to put the motors under
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the middle of the RCX. Finally, if you use a swivelling wheel, put it at
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the back, not at the front. Pulling a swivelling wheel gives a much
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straighter motion than pushing it.
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<H3>Drive-Steer mechanism</H3>
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<P>
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<TABLE>
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<TBODY>
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<TR vAlign=top>
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<TD><IMG src="Lego Robots Tips and Tricks_soubory/step3.jpg"> </TD>
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<TD>This mechanism is based on the adder-subtractors of <A
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href="http://carol.wins.uva.nl/~leo/lego/diff.html">Leo </A>and <A
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href="http://www.phred.org/~alex/lego/">Alex </A>. It must be driven
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by two motors; one connected to one of the four gears on one side,
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and the other connected to one of the three gears on the other side.
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One motor makes the wheels move in the same direction. The other
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sterrs by making the wheels move in opposite direction. My design is
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acccording to me stronger than the other ones. More pictures can be
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found <A
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href="http://www.cs.uu.nl/people/markov/lego/tips/Differential1/index.html">here</A>.
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</TD></TR></TBODY></TABLE>
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<H3>Double motor power</H3>
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<P>
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<TABLE>
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<TBODY>
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<TR vAlign=top>
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<TD><IMG src="Lego Robots Tips and Tricks_soubory/twomotors.jpg">
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</TD>
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<TD>If you need extra motor power, and you have enough motors,
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connect two together. You can out them both on the same output to
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drive them simultaneously. This is especially good for heavy robots
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or if you want your robots to go fast. I assume you can do the same
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with three or more motors, but I am not sure how many you can
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connect to one output. </TD></TR></TBODY></TABLE>
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<H3>Bumpers</H3>
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<P>
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<TABLE>
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<TBODY>
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<TR vAlign=top>
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<TD><IMG src="Lego Robots Tips and Tricks_soubory/bumper1.jpg"> </TD>
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<TD>Here is bumper I designed that uses only one touch sensor.
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Instructions for building it can be found <A
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href="http://www.cs.uu.nl/people/markov/lego/tips/bumper1/index.html">here</A>.
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</TD></TR></TBODY></TABLE>
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<H2>Internals</H2>
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<H3>Free memory</H3>After loading the firmware, it seems that there is
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about 6K of memory available for programs. You can use the <B>RCX Command
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Center</B> to free this memory when required.
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<H2>Programming with SPIRIT.OCX</H2>
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<H3>Using the joystick</H3>Here is an <A
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href="http://www.cs.uu.nl/people/markov/lego/tips/RCXJoystick.zip">example
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program</A> (in Delphi 3) of how you can use the joystick to steer the
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RCX. It comes with full source and is freeware. It is a simplified
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stand-alone version of the joystick window in my RCX Command Center
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version 2.0.
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<H3>Registering SPIRIT.OCX</H3>If you don't want to install the lego
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software on your system but still use programs like the <B>RCX Command
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Center</B> you must register the OCX. Copy the spirit.ocx file from the
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lego Cdrom to you harddisk and use the Run command in the windows Start
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menu to execute <PRE> REGSVR32.EXE spirit.ocx
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</PRE>This will register the ocx on your machine. (You might need to
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specify the path of the ocx in the above command.)
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<H3>Bugs</H3>There is a bug in the OCX: When polling the mode of a sensor
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(e.g. Poll(11,0)) you don't get the right mode but 32* the mode.
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<P>There is another bug in the polling command. Polling the watch gives
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you the total time in minutes, and not divided in hours and minutes as the
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doc suggests. </P></TD></TR></TBODY></TABLE></BODY></HTML>
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