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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> |
| <P> |
| <TABLE> |
| <TBODY> |
| <TR vAlign=top> |
| <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> |
| <P> |
| <TABLE> |
| <TBODY> |
| <TR vAlign=top> |
| <TD><IMG src="Lego Robots Tips and Tricks_soubory/twomotors.jpg"> |
| </TD> |
| <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> |
| <TABLE> |
| <TBODY> |
| <TR vAlign=top> |
| <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> |