Older blog entries for Nic (starting at number 153)

May 23rd, 2005

I'm looking at the MIDG II unit in addition to the Trimble GPS. Neither company has contacted me in response to messages I have left.

I experimented with heading determination based on light patterns, and my very basic experiment worked pretty well, but in order for it to be reliable it would have to be much more complex. Maybe I can work something out using the camera image.

May 21st, 2005

I found the perfect GPS - the Trimble MS860.

May 18th, 2005

Workin on some concepts for the new hardware - hopefully it will be coded by the time it arrives. I have new hope for our chances at getting accepted to the NQE - today I found out I got into 10th grade honors english, which I thought was even less likely than getting into the Grand Challenge! ;-)

May 15th, 2005

I ordered a dual axis Phidgets USB Accelerometer and fixed the engine wiring.

May 9th, 2005

I've been busy with school work and baseball - for example last night I stayed up till 5 AM working on an english project. Summer Vacation is in less than a month and a half though, and baseball ends after this week. Next Monday (May 16th) at 8:00 PM PST the Expeditor will be on the Discovery Channel on a show called The Science of Star Wars.

I worked on some microprocessor issues, resoldered a broken connection, and discovered that the only reason the computer had failed during the site visit was that the DC- DC power supply had snapped out of its spot. It wouldn't normally do this except that the lead for the second serial port is right under it so it doesn't fit in place like it's supposed to. I liked a solution suggested to me at the RoboNexus - once everything in the computer is in place, seal the box except for one hole and fill it up entirely with a sealant foam. The foam will harden, securing all the parts, and also absorbs heat.

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.

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