Saturday, March 22, 2008

Rockhopper v1.5

As usual I have been bad about updating my blog. I have started on a new version of Rockhopper for this years Trinity College Fire Fighting contest. I certainly can't take 8 weeks off like I did last year but honestly the majority of that time was spent figuring out how to do things so by taking what I learned from that I should be able to do this one much more quickly. There won't be any major new ground broken with this one (which is why I call it v1.5 instead of v2.0) but it will be a "refined" version of last years design. Much of the code will be re-used from last year with some updates. I am using the same linux kernel as before also so that is a lot of time saved not having to re-do that.

The highlights:

It is smaller. Rockhopper was just barely within the maximum allowed size of 30cm (in all dimensions). Rockhopper 1.5 is about 22cm wide and long. This should make it able to maneuver past obstacles more easily.

Cleaner wiring. Since much of how I am doing things is the same as last year I know ahead of time what is going in. The problem with Rockhopper is I was a lot of it was designed as I went.

New ARM board. Ok, mostly this is because I accidently fried a not-so cheap piece of hardware :( but it gave me a good reason to update to an TS7400 board from Nice features of this are that it is smaller and has an SD slot so I can easily have 2G of flash space. I also can boot from the SD card so I can have a full linux distro installed. I am using debian right now since an ARM image of debian was already available. I am normally a Fedora user and I hear some people are working on an ARM port of Fedora so I might go with that later on.

New Flame sensors!!! This is something I have been planning on designing for a long time and should make things much cleaner and more reliable. The picture here isn't so good. I will see about uploading a better pic later on. This is a small board with an i2c A/D converter on it and 4 IR phototransistors. I have used the phototransistors on my last few robots and they are simply _by_far_ the best way I have found to find the candle. Perhaps I am giving away one of my competitive advantages but I believe in sharing of info :)

The IR phototransistors can be bought from digikey for something like $0.75 each and are part number op599a. You don't need a fancy board like I designed. Use a 47k pull up resistor on one side and put the other side to ground. Connect one of your microcontroller's A/D ports between the resistor and the phototransistor. Works perfectly. It can be fooled a little by incandescent light bulbs or bright sunlight but if it is shaded from above I have found that isn't a problem. Also, does not get fooled at all by florescent lights or the sodum vapor lights used in the gym at Trinity.

I am considering starting a small (very small) home business and selling these boards. Probably not for any real profit but hopefully enough to offset my robot building costs. If people have an interest please post a comment here. I am guessing I could sell them in kit form for probably $25 each. However since the chip is a surface mount I imagine that would scare off many hobbyists. I might sell assembled boards for probably $45 each (need to figure out how much it is worth to me to solder a bunch of these myself).

For those of you going to the contest at Trinity come check them out and we can all see how well they really work.

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