CMU Mechatronics Project: Multi-shot Cannon

The challenge
Design and build a machine that fires Nerf foam balls and hits static and moving targets with great accuracy and speed.

The team
Four engineers joined forces to accept the challenge.


Justin Farrell (firing), Melvin Rayappa (vision, coding), Jason Atwood (system integration), and Rachel Jackson (loading, aiming)

The machine


Figure 1. Depiction of overall mechatronic system with key components highlighted.

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Contract Electromechanical Engineer

For the last ten months, I’ve been contracting as an electromechanical engineer at a research chemistry firm in Atlanta. They specialize in commercializing several patented processes and they have hired me to automate the processes for several applications. I have used this opportunity to refine and expand my electronics and process controls skill sets. They work with several Fortune 500 companies producing quick market solutions. In the interest of all of this privacy I am bound to a pretty strict confidentiality agreement. Unfortunately I can’t talk about details, however, I am working on some really cool projects so I’ll stick to the how’s and leave out the what-for’s.

I had this really long post in the works and was completing it piece-meal as I had time. Sad to say though, I’ve been so busy doing work that I haven’t had time to write about work. So in the interest of brevity and to start a format where I can easily add new posts as I finish projects, I’m going to limit my writing and let some pictures do most of the talking.

I am spending a lot of time working with LabView and I have become quite efficient at writing programs and designing process control systems. One of our processes requires monitoring and controlling seven gas flows, monitoring the pressure in two liquid lines, monitoring the temperature in ten locations, and moving a two axis robot to various positions and repeating several paths. The program can also export all of this data to an Excel file of the user’s choosing.

The motion hardware at ____ is antiquated ValueMotion driver and nuDrive amplifier hardware, which took me a bit of time to setup and get working properly. I’ve implemented both a mechanical and software emergency stop. The thermocouple and pressure transducer monitoring is accomplished with National Instrument’s FieldPoint modules, which while also legacy technology, are quite ubiquitous at ____.

I wrote a program that incorporated all of these features. I’ve removed any confidential information but here is a overview of the program and the necessary files.. I am in the process of upgrading all of ____’s Labview to LV2009 from the much older 7.1 (and even 5.0 on some machines). So this program is written in 7.1.

Front Panel

Block Diagram

LabVIEW 7.1 (files zipped)

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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