Hardwiring your NXTs... with LEGO

As I posted about a while ago, I've been interested in making a quadruped robot with animal-like motions. I started working on different designs earlier this summer, but haven't been able to get something that works because of the sheer number of motors involved and the expense of TETRIX parts. (i.e. about $80 for a single rotation sensor!). However, while I was working on robot prototypes, I ran into an interesting problem with NXT-NXT communications. In one of my designs I wanted to use three NXT bricks which would all need to communicate with each other. But RobotC, the programming language I was using, only supports Bluetooth communication between two NXTs.

To get around this problem, I looked into ways to hardwire the NXTs together; there are some pretty amazing homebrew solutions out there that various people have come up with. However, as I lack the technical/electronics skills required to make such devices, I looked for a way to do it purely with NXT pieces. I came up with an interesting two-way serial communications cable that simply uses two light sensors to send and recieve data.

The two sensors are connected facing each other with a shield around them to block out ambient light. Each sensor is connected to a different NXT. One NXT sends data to the other by blinking its light sensor on and off, which the other light sensor picks up. The key advantage I found was that these blinks can be picked up over very short intervals of time (~30 milliseconds). This makes simple communications quite fast - perhaps faster than Bluetooth.

Here's a video demonstrating the "LightComm" cable. One NXT sends the position and power level for the motor to the other NXT, and then both NXTs move their motors accordingly. In the video, the NXT beeps when it starts sending each message, to give you an idea of the speed of the communication link. In the last part, I opened the casing around the light sensors so you can see the blinks.

One advantage of this cable is that you can customize the method of communication to be the most efficient for each application. One method would be to have the light blink on and off like a digital link to send "bits" of information. In the above video, I used an analog method, where the data is sent by the time duration of each blink. The light blinks a total of two times. The first blink gives the target position of the motor, and the second gives the power level. Amazingly, the recieving light sensor can accurately measure the duration of the light to milliseconds! Thus, each millisecond in the duration of the blink represents a degree in the target position or a unit of power. As you can see in the video, the message is usually transmitted with an accuracy of about +/- 2 degrees, which should be ample for most applications.

-Jonathan

Celebrating MINDSTORMS with a Remix - Part 2

The ROBOTMAK3RS continued their celebration of the 25th Anniversary of MINDSTORMS through these summer and fall remix projects. Each ROBOTMAK3R was tasked with selecting one LEGO set of their choice and combining it with a MINDSTORMS set. Below are the five amazing models they came up with. Remote controlled material handle r by Jozua van Ravenhorst (aka Mr Jo) This remix combines the LEGO Technic Material Handler (42144) with MINDSTORMS EV3 (31313) It uses the power of pneumatic cylinders to move objects around. By using a bluetooth remote control, very precise movements can be made with this model. Touch sensors in the base chassis prevent the turret twisting the cables that go through the turntable to much. The program has several protections to prevent over pressurizing the system for each of the 3 individual pumps and valves that control the 2 booms and claws. The real version of this machine is mostly used in waste material sites to bring the material to machines that sort and

Celebrating 25 Years of MINDSTORMS

In celebration of the 25th Anniversary of MINDSTORMS, we take a trip through history. Please also visit ROBOTMAK3RS Community every week as we highlight different projects all through 2023 in celebration of the anniversary. Some of the early history is based on the content shared by Coder Shah in our MINDSTORMS EV3 Community Group . Some of the text and links may have been edited from his original posts for consistency and clarity. 1984 - Kjeld Kirk Kristiansen watched a TV program called "Talking Turtle," where MIT professor Seymour Papert demonstrated how children could control robot "turtles" using LOGO, a programming language he developed. 1988 - The collaboration between MIT and LEGO resulted in LEGO TC Logo in 1988, which allowed students to control LEGO models using computer commands. The video shows Papert demonstrating TC Logo. 1990 - LEGO TC Logo was hampered since the robots you built had to be tethered to a personal computer. LEGO and MIT

MINDSTORMS Retires!

2023 is the 25th Anniversary of the MINDSTORMS brand. For 25 years, MINDSTORMS has educated and inspired a generation of robot builders, both children and adults. Unfortunately, the LEGO Group decided to end the line on December 2022. Many ROBOTMAK3RS have been passionately involved with the development of MINDSTORMS through the MUP and MCP programs. Even with the newest Robot Inventor line, several ROBOTMAK3RS were invited to submit additional bonus models that were included in the official app. Regardless of the retirement of a major LEGO robotics product line, ROBOTMAK3RS continue to MAKE-SHARE-INSPIRE using all LEGO robotics platforms available to us. Here is the official statement from LEGO. Since its launch in September 1998, LEGO MINDSTORMS has been one of the core ‘Build & Code’ experiences in the company’s portfolio, carrying with it significant brand equity and becoming a stand-out experience for the early days of consumer robotics and leading to current Build & Code

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