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

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

Celebrating MINDSTORMS with a Remix Part 1

In honor of the 25th Anniversary of MINDSTORMS, we asked ROBOTMAK3RS to combine a LEGO set of their choice with a MINDSTORMS set. Here is what these five ROBOTMAK3RS came up with. MINDSTORMS Chess Assistant by Arvind Seshan Overview: When you are new to chess, it can be a challenge to remember which pieces go where. Now, you can use machine learning and LEGO MINDSTORMS Robot Inventor to build a tool to help you learn where all the chess pieces go on the chess board. Sets used: LEGO® Iconic Chess Set (40174) and MINDSTORMS Robot Inventor (51515) Review: I really like how the chess set base can store all the pieces underneath and that the board neatly splits in half for handy storage. The chess pieces themselves are very sturdy and well built. My only criticism is the building of the box itself. It was quite difficult to see what pieces to use and since the entire box is made mostly of thin plates, it took a lot of time and patience. I would have liked the storage area to be sliding dra

Machine Learning Meets MINDSTORMS

Machine Learning Extension LEGO MINDSTORMS announced today a brand new feature that is sure to excite all users. Machine Learning Extension is coming to the software in August 2022. This will allow users to implement new applications that were not possible before. Machine Learning has become exceedingly popular in recent years with applications in all sorts of industries from robotics to financial services to climate change. Now, even the youngest of robot enthusiasts and programmers have access to the world of Machine Learning and Artificial Intelligence. Comparing two classes Machine Learning on MINDSTORMS will work with both images and audio. For instance, you could train your model to recognize smiles and frowns on your face and have the emotion displayed on your hub. You could train your model to recognize when a red ball is present or not or identify a particular LEGO element. You can control your robot with audio commands that use your own voice. It is exciting to see what new p

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