Connecting LEGO Technic beams in three dimensions remains a difficult task. While it has become easy to connect beams in one and two dimensions, it remains difficult to extend this to the third dimension.
I first designed a new LEGO Technic connector that features pins. The design was compact and stable, put the pins were too fragile. It was also very difficult to get the support material out from the holes.
My second design had no pins but still the option to firmly hold a technic beam. With this new 3D printed corner part it is possible to build a perfectly stable cube with a minimum of parts. The additional holes provide options for further strengthening the cube or to connect other parts to the cube.
Racing LEGO cars down a ramp is a popular attraction not only in the LEGOLAND Parks, but also at Brickshows and classrooms around the world. The physics around the race are well understood, but experiencing them in practice is a great learning experience for students.
We setup a little ramp race at home and I would like to share our setup and results with you. We put two base plates together as the ramp and inclined it at ten degrees. We then measured four meters from the starting point up the ramp to the finishing line.
Of course, you can race multiple cars at the same time but then you might encounter collisions and photo finishes too close to call. A reliable and precise measuring system is a much better solution. The SpeedClock App is just what you need. It allows you to measure the speed of a car with a smartphone. You can for example place the phone at the end of the ramp to measure the LEGO car’s maximum speed. You can also synchronize two phones running the app and measure between a start and finish gate. We tried both methods. All races were completed three times and the times and speeds reported are averages.
We started with a typical LEGO car (150gr) and it took it 4.42 seconds to complete the four meter distance. We then started to use my special Ramp Racer. It uses Mindsensor’s ball bearings, large wheels and a heavy battery pack (324gr). It’s maximum speed was 4.3 km/h and it took 3.4 seconds to complete the four meters distance. The same car without the batteries (148gr) had a maximum speed of 4.06 km/h and it took 4.2 seconds to complete the full track. Last we tested the Ramp Races with another set of wheels for which I also had rubber tires. With the rubber tires it took 3.7 seconds to complete the race and 3.6 seconds without.
In conclusion, the ball bearings make the car significantly faster and large hard wheels are best. The heavy batteries conserve the kinetic energy and result in a winning car. For a fair competition a maximum weight should be set. Since the ball bearings used were not from the LEGO company a policy on using third party parts is also advisable.
Ever since I created the Spirograph Automaton I remained interested in drawing machines. For this years Christchurch Brick Show I wanted a more compact, easier to build version of the Spirograph. This time I used three motors instead of just one. Controlling the speed of both arms and the table was very easy this way. The Spirograph worked reliably throughout the whole show. The MinuteBot baseplate makes the construction even easier. The building instruction are available for LEGO Digital Designer. More information is available at Rebrickable.
You can play TicTacToe with this LEGO Mindstorms EV3 robot. It uses three motors to drop the balls into the right field. It uses a NXTCam to view the board and then calculates the best move using a MiniMax Algorithm. All future moves are explored an rated according to their winning chances. The work is based on the TicTacToe code of Thomas Kaffka. An IR sensor detects your hand when you drop your ball. The robot is using red balls and the human player uses blue balls. The Java code is available over at Github. The building instructions are available for LEGO Digital Designer. I used the MinuteBot baseplate, which is useful for building static Technic/Mindstorms models.
LDD does not have all the required pars in its database. You will have to replace 22961 with 27940. You will also need to add a worm wheel 27938. In addition you should use a lamp to provide consistent lighting. I used a USB powered LED circular lamp the can be powered through the USB port of the EV3. I only had to take out the lens in the middle so that the camera fits through the hole. A rubber band holds the light in place. To calibrate the robot I added a little arm at the end of the base plate against which the robot arm rotates. The position of the camera can be centered on the board using the wrench and through sliding along the axles.
You can also find information about the robot over at Rebrickable. The inventory there is correct and complete. Except for the base plate of course.
Bringing back your old LEGO Mindstorms RCX to life is easier than you might expect. The bottleneck is being able to communicate with the RCX using the Infrared Communication Tower. Version 1 used a tower that was attached to the computer using the old serial port (RS232) while version 2 used a USB tower. The later is much easier to use these days since most computers still have plugs that are compatible with USB1.1. For this tutorial you will need:
We will setup a virtual machine on your host computer (Mac or PC) and install Windows XP on it. We will then install the original Robotic Invention System (RIS) so that the USB driver is correctly installed. You can then use RIS to program you RCX or you can setup many other programming environments/languages. Another problem you might encounter is that the cables used to connect the sensor and actuators to the RCX have become brittle and the isolation comes off easily. You can still buy some new cables from Bricklink.
