... is publishing an article on Sunday, July 1, about the NASA Centenial Challenge program. They will be focusing on the latest three challenges, including the regolith challenge that I participated in.

A photographer from the magazine spent a day at my house a couple of weeks ago, so I am eagerly waiting to see how it looks, what they said.

Check it out... NY Times Magazine online

Jim

It has been a very busy 30 days, but well worth the effort...

There were 4 teams at the competition on May 12th, and my machine was the only one to run the entire 30 minutes. It also moved about 75 kg of JSC-1A, 65 of it going into the collector, 10 on the ground. It also ran exactly at the specified limit of 30 watts average. Rob Mueller of NASA made the point that is the power used by a refrigerator light bulb, and it is amazing that any real work can be done with it. Even though it didn't move the minimum 150 kg to win a cash award this time, I think that it can be done.

This is one of the cases where simple was better. The machine can be described as an inverted bucket, continuous chain driven drag. The buckets are moved to the end of a 4 foot horizontal boom where they flip over and contact the soil, and drag it back towards the delivery ramp at the root of the pivot. The machine uses 3 motors driving the bucket chain mechanism, and one to pan the boom from side to side. The boom pivots vertically as the hole it digs becomes deeper. I'll have some pictures posted on a web site soon, but I'm still recovering from the last couple of weeks...

In the meantime, here are links to a couple of small avi files that show an earlier version in action during a test on some clay soil:
Front View
Back View

Read More...

Well, I decided to take the plunge and enter this contest with only one month until the competition... Here is a link to the information site.

This is a NASA sponsored contest to create a machine that can excavate lunar soil to be processed, one process being removing breathable oxygen from the soil.

One key reason that I decided to enter is that the competition takes place about 15 miles from my house; I couldn't pass up the opportunity! It doesn't hurt to have a total purse of $250,000 available, but in reality, the most value will be from all of the people that I will meet at that time.

This particular challenge involves moving simulated lunar soil from a 4 meter square sandbox into a 1 meter square collection box. The machine that moves the most material, over 150kg, wins first place. Oh yea, did I mention that you get 30 watts of power for 30 minutes to do this?

I don't want to say much yet about my design approach, but I will say that I have a prototype machine that already digs pretty well, and there is plenty of time to work out the details.

More later...

Over the past few years I have been reading about UML Statecharts and state machines in general, but never found a construct that I liked for small embedded systems. Most designs have some events being fired from outside processes, but in most of the stuff I do the event processing belongs inside of the state machine itself!

I created some macros in C that make it very easy to create a state machine that supports entry actions, transaction testing, and exit actions, all living inside the same case statement, making it very simple to understand and maintain.

It will be very clear what is going by viewing this example . However, I should explain the meaning of the "_EXCLUSIVE" macros...

With the entry action, transition test, and exit actions all inside the same case statement, the default is to execute them in order, potentially finishing all three in a single call. This might be good in some cases, but causes problems when expecting predictable timing through the state machine.

The "Exclusive" versions of the macros only allow one of the three parts of a state to be performed each time in. This means it will always take at least three calls to the state machine to pass through a state.

Try it out, and have fun...

I stumbled upon a very good book about robotics called Robot Modeling and Kinematics , by Rachid Manseur. It is completly about modeling robot arms, and nothing about navigation, etc.

One of the neatest things is that it comes with a bunch of programs that create VRML files to simulate robot arms according to parameters you specify. You run the program, type in some specifications for an arm design, and you can view the resulting animated simulation in your web browser. It uses tons of matrix math, which I don't know much about, but it actually is a fun way to learn about matrix math...;-)

For the FIRST Robotics competition this year, my team used a very simple, one joint robot arm. It worked well, and I don't think I would change it, except perhaps to add a single-axis wrist. I was able to model our arm very easily using the programs that came with the book, and this will help with future designs of robot arms...

I'm actually glad that I didn't find this book until after the FIRST build season; no telling what I would have suggested for out robot after seeing the cool ideas in the book.

One more thing, there are a number of mistakes in the book, but you can download an errata file from the publisher's web site here.

I will post more as I get into modeling robot arms...