Older blog entries for Nic (starting at number 148)

May 5th, 2005

I got a replacement steering motor in the mail. I also sent an email to DARPA asking if we have the option of sending in videos or other information useful for demonstrating our full capabilities until the date of the last site visit.

May 3rd, 2005

My overall impression of the site visit was that it didn't go very well, but the site visitors made sure to note all the good points they saw. Each team gets three trial runs through their course while avoiding garbage cans for obstacles. The first run of ours the Expeditor drove off course and showed some strange wandering behavior until the last 80 meters of the 275 meter run where it drove down the center of the route. At this point the steering broke. I took a part back home and re-soldered some connections, returned, and we tried to continue the site visit, but, as with any demonstration, it seems, it refused to work; several other parts including the computer unexplainably broke. With only 40 minutes to go there wasn't time to make repairs, so instead of getting our other two runs I explained the software in detail and they asked some questions about the neural network technology, as well as questions about our ability to prepare the Expeditor in time for the Grand Challenge and fund our trip down there and such.

The problem that caused it to wander off course is its inability to determine its heading. Even with a new $400 GPS it didn't update the heading quick enough, and the dead reckoning wasn't accurate enough. I've looked into the problem (a little late) and determined that it needs a dual- antenna GPS in order to give instantaneous heading information - a standard single-antenna GPS averages position data to find heading, and when the GPS is moving forward the average position will be somewhere behind it, and therefor the heading will lag. I would also use some gyros to ensure precise and accurate heading at all times.

As for our chances to getting in the race, my opinion is that they aren't all that good, but I wouldn't count out the possibility - some of the more developed teams from last year's race are pretty intimidating, but I'm guessing only 20 teams or so could run the course hands down, and as 40 teams will be invited to the national qualification event there's room for some others. Maybe our unique-factor will help us out too.

May 1st, 2005

Been workin all day. Time to pull an all-nighter (and then skip school tomorrow).

April 30th, 2005

Today is Saturday. Our site visit is on Tuesday. I've been working non-stop on getting basic waypoint-following down, but it just won't work. I can't get rid of the weaving. The problem is that it doesn't ever know exactly which direction it's pointing. It's all a matter of heading. An artical from Circuit Cellar at http://www.circuitcellar.com/library/print/0404/Miller165/3. htm describes the problem:

"A single-antenna GPS can provide heading information, but it is not instantaneous. It inherently lags the movement of the robot or vehicle because the derived heading requires previous position data. A GPS could not tell you where you are heading if you were to stop and change directions. Like compasses, GPS receivers do not require external reference heading calibration. Once moving, the GPS heading update rate is a maximum of approximately 1 Hz, although some receivers add damping, which increases this time constant even more. A dual-antenna GPS receiver can provide instantaneous heading‧'or yaw‧'information, although the recommended distance between the two antennas is 1 m. This fact, along with its large price tag, can be a limiting factor for many mobile robot applications."

Because of this I have been using dead reckoning unless the Expeditor has been going straight for a few seconds, but it's still not that good. Today I bought a $400 GPS with a built in compass and switched it out, but the compass always thought the computer's harddrives were north. I raised it up on a PVC pipe a few feet, and it gave a good heading, but IT STILL LAGGED. It was better though. A little. It still works at speeds about 2 MPH but not higher. I did a lot of other work today also. I have a lot more work to do in the next two days.

April 27th, 2005

I took the robot out to the site visit field before school, and then remembered that the pull start was broken so I couldn't start the engine. I pushed it down the first waypoint-segment. It had the same weaving behavior as ever. This is extremely frustrating.

UPDATE: I went to Home Depot and got a ratchet socket to open the pull start cover, opened it, took it apart, fixed the spring, and put a new rope on it. Now it works.

April 26th, 2005

This week (except Friday) I start school two hours late, so I've been working in the morning on the robot. Today the pull start rope on the engine ripped and went into the engine. One more thing to do before the site visit... There's one week left.

At about 9 PM I went out to test the robot on the street, but the steering by remote control wouldn't work. After an hour I had fixed the problem. A wire had randomly broken in a connector. This is getting very frustrating.

25 Apr 2005 (updated 13 Aug 2009 at 18:48 UTC) »

April 24th, 2005

This morning I fixed the battery wiring, but accidentally melted a 5V regulator. Afterwards I got some orange buckets at Home Depot to use to mark the waypoints on the site visit route as well as two 32 gallon garbage cans and some free wood for lateral boundary markers. The garbage cans being green, I also bought some white spray paint in case the neural networks can't detect the green garbage cans in the green field.

At the field I marked the lateral boundaries of almost the whole course, and tested the waypoint following some more to observe the robot's behavior. I also recorded data while driving the course, avoiding the waypoint markers and garbage cans on the route.

Once home I modified the software in yet another attempt to perfect the waypoint following.

There are pictures at http://www.craterfish.org/teamprodigies

April 23rd, 2005

The waypoint following only works while driving at speeds under 3 MPH. The GPS position seems to lag behind a certain number of seconds, which makes sense assuming it's averaging many GPS positions every second - if it's moving forwards, of course the average of the locations will be somewhere behind it. The higher the speed goes the crazier it's driving gets, until at speeds above about 6 MPH it just seems random.

I obtained permission to use a new field and sent an email to DARPA about the site visit location change. At the field I used the GPS to mark a route, and then had the Expeditor drive it. I encountered the problem above, until the battery fell off the robot and ripped some wires. Heh.

April 22nd, 2005

I tested it and it finally works. Now I have to perfect the garbage can avoidance.

April 21st, 2005

Tested several new things and discovered and fixed several bugs. Still some problems.

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