Performance Testing NXT’s Ultrasonic Range Finder

I have plans to utilize the Lego NXT system for several upcoming robotics projects. The success of these projects depends on the capabilities of the kit’s ultrasonic (US) range finder. I created a test rig with the US sensor and NXT brick and conducted several experiments in order to characterize the sensor.


Test rig: wood block, measuring tape, protractor, US sensor, NXT brick (from left to right).
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SLAM-5 Bot part 1: The Hardware

I recently purchased Lego’s new NXT hobbyist robotics kit. After familiarizing myself with the basic layout of the command module, available hardware and sensors, and third-party programing languages by building several single-task robots, I decided to use the NXT as a forum for my studies in SLAM robotics. As I have previously quoted, Dr. John Leonard of MIT says,

The problem of SLAM is stated as follows: starting from an initial position, a mobile robot travels through a sequence of positions and obtains a set of sensor measurements at each position. The goal is for the mobile robot to process the sensor data to produce an estimate of its position while concurrently building a map of the environment.

My goal and new perspective on the problem is to design a system which is as simple as possible. I immediately realize that much of the complication in SLAM systems lays in the timeliness with which the system processes information in real time. I know that some compromise between speed and simplicity had to be established, and in pursuing the most simple system, I am willing to sacrifice a lot in speed. So I have created what I am calling the “slam five robot”. The real acronym is S.S.S.S.S.L.A.M. which stands for “super-simple, super-slow, simultaneous localization and mapping robot”.

The system consists of three components: the physical hardware of the robot, the control algorithm which guides the hardware and sensors, and the post processing algorithm which interprets the sensor data. I begin here by describing the hardware and sensor setup.


Front view of the SLAM-5 bot, showing ultrasonic range finder and wiring for the drive motors.

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Meerkats Slay Muddy Buddy

This weekend, I was part of Team Meerkat in the Atlanta Muddy Buddy with my friend Katie Davis. The race was held at the Georgia International Horse Park in Conyers, GA. We won our division (Coed 45 and Under) and placed 21st overall out of 740 teams which finished. The race is one in which a 6-7 mile course is divided into five stages. For each stage one teammate mountain bikes and the other runs. Then at the stage intervals, the teammates switch positions and carry on for the next stage. Teammates are not required to stick together. In fact Katie and I only saw each other twice through out the race.
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NYC: Bike Punks and Coffee Geeks

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© demon cat

Back in February, I traveled to New York City to participate in Monstertrack and investigate the 3rd wave coffee shop scene. I drove up with my friends Seth, Gregg, and Chris. We left Atlanta at 4pm on Thursday and drove throughout the night, arriving in Manhattan about 10 am Friday morning. As soon as we pulled into the parking garage, we assembled our bikes and took off to explore the city. We had plans to stay with NY messengers Pablo and Victor, who were organizing the race, so first we dropped off most of our gear at Pablo’s house in the Lower East Side.

The race, which wouldn’t be until the next day, consisted of eleven checkpoints. Five of them were released on the internet several weeks prior, so the four of us decided to pinpoint their exact locations. Furthermore, I knew that I would need a bike helmet for the race so our next stop was one of the checkpoints: a track bike-only shop called Trackstar.
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Wankel Rotary Engine CAD conversion

3/7/2017 UPDATE: A commenter made some nice updates to both the translation and the geometry of the project. Be sure to read Martin’s comments below.

1/2/2014 UPDATE: After some interest from other folks in this project, I’m sharing all of my final Solidworks files. I’ve talked with the original sponsor and he has agreed to release them. You can download a zip file here. The files are organized by part. All of the final drawings and parts are annotated with “_finished” in the filename.  Some of the original scans are also included.

3/31/2013 UPDATE: A kind reader has found the original drawings in a model airplane magazine from 1964. I’ve included the PDF below in the Resources section. The blue prints are on pages 17-18. It is interesting to note that the model was submitted as an entry to a contest to generate an epitrochoidal engine (an epicycloid is a type of epitrochoid). However, as I show below, the chamber isn’t an epicycloid.

I have been contracted to convert the SW92 Wankel rotary engine from its original 1950’s paper format (in German) to electronic format (in English). I am utilizing Solidworks 2005 to reconstruct 13 of the 36 pieces included in the blueprints. Furthermore, I am relying on a tremendous effort from MacField Young to perform most of the German to English translations. The sole purposes of this blog entry are to communicate with my contractor, to document my progress, and relay certain concerns. In other words, this entry is a work in progress finished!.

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