Older blog entries for cschur (starting at number 92)

Just got back from a 3week vacation in southern arizona, we were fossil collecting with our friend that flew in from Australia. Anyway, thanks Steve for posting my article.

We are officially kicking off the next project now. The PicBot 5 program, will extensively detail one of the most important aspects of a household robots existance - Docking. This could be for battery charging, reseting wheel encoders to a known reference point, or simpy navigation of a complex area. Needless to say, if your robot cant dock, it cant "feed" and will cease to do its assigned task.

I will be using a new PIC for this project, the 16F876. It has many powerful features, and enable the docking proceedure to be successful.

Later,

Chris

comets133@yahoo.com

30 Jan 2007 (updated 30 Jan 2007 at 03:59 UTC) »

Hi all,

Well, after a few months of working with our stasis sensor bot, weve got what I feel is a pretty decent write up on what is an often overlooked but extremely important home robotics concept. Here is the new article:

http://www.schursastrophotography.com/robotics/stasislogic.h tml

I would be greatly appreciative if one of you could look the article over, and again, if you think the group can benefit from this article, Id like to ask if you could post it in the robots.net main page. Thanks!

Feedback appreciated,

Chris comets133@yahoo.com

Hi All,

An update on the Stasis project. As you know, the stasis detector is the robots last line of defense on keeping from getting stuck in a household enviornment. In its simplest form, it consists of a drag wheel that is pulled around by the robot, that has an optical sensor to determine if the wheel is moving. So your drive wheels may be turning, but if the drag wheel is not, your stuck. The stasis sensor can either be used as a simple sensor input in your main processor, or even better, when used in a priority arbitration architecture or subsumption type architecture, it is the behavior that overlies the bottom behaviors that continue the robot moving toward its goal.

For example, "Random Wander" maybe the lowest level, overlain by "Seek Goal". Both will always keep the robot moving toward its destination, be it the battery charger or to pick up a can or ball. Overlaying these two behaviors with the "Stasis" behavior will be even better. When the robot gets stuck and the bumpers or IR dont see any problem, then after say 3 seconds or so, the stasis behavior kicks in and attempts an escape maeuver to free the robot from say a lamp cord wrapped around the back wheel.

These three behaviors can be overlain by the ones that actually perform a task when the destination is reached, and will of course subsume over the Stasis behavior so that if we are stopped to pick up a ball, the stasis will not kick in and try to escape.

We have experimented with optical stasis sensors too, and it is amusing to put a phototransistor in a short tube and aim it say at a 45 degree angle from straight ahead. What happens is that when the robot is moving, the output of the transistor is a changing brightness, and thus we know we are moving. IF the variations stop, or are very small, we may be stuck. You can also look straight down at the floor and do the same thing, assuming of course that the floor is not featurless!

Such a simple thing - the stasis sensor, but absoulutely essential for the household robot! Dont skimp on this feature, you wont regret it.

Later.

Chris

Please Write me: comets133@yahoo.com

Hi all,

Weve just started our next project, on robot stasis sensors. As some of you may know, stasis sensors tell the robot when it is stalled, stuck and not moving, or immobile in some other way when its supposed to be moving. A typical sensor might be a wheel that it drags along, and if it stops but the main wheels keep moving, there is a stasis condition.

PicBot IV will explore this concept, and develop a robust stasis sensor system that can be easily incorporated into any home robot. Of course, at the finish of this research project, we will post a very in depth article!

Write me, Id love to hear from you!

Chris comets133@yahoo.com

HI all,

The huge IR Prox Logic article is done and posted. If someone could kindly look it over and if you think its usefull to the robotics community, please post it as an article here, I will be forever in your debt.

http://www.schursastrophotography.com/robotics/irproxlogic.h tml

Chris

Hi All,

We are nearly done with our IR Prox Logic article. Getting a last few graphics done, and It will be ready to post. Some surprises when working in a household enviornment with IR Prox for navigation. We found that tunnel entrapment and small room entrapment to be major issues. With bumpers as you recall, the robots physical diamter is equal to the sensory diameter, and it can usually bounce its way out of a tight space.

Not so with IR prox. The robot is virtually 3x bigger, and can get itself into some fine predicaments in the home. What seems to happen is that a robot will get itself into a small confined area, and then cant get out because the reflectivity in IR on the outgoing trip is higher than the inbound. Thus it cant escape. Long corridor entrapment is also a major issue. A robot can make its way down a narrow hallway then it will at some point start hitting the walls. It can get itself wedged in so that all IR sensors are active at once. That is a difficult one to get out of!

Finally, we did some deep IR photography of a household enviornment at the same wavelength as the robot will see it in IR. The biggest surprise is that wood that is unvarnished is bone white. varnished wood is dark. whew.

Chris

Well, we have finished all the arena testing and evaluation of the PicBot III unit, for exploring the pros and cons of IR Proximity navigation. Now, we are working on the final report, to be shared when it is complete. There were a few surprises with the IR prox sensor array.

First surprise was how much larger the robot becomes when "non contact" IR prox sensors are used. In other words, the virtual size of the robot nearly triples for white walls, and only increases an inch for black obstacles! And to make matters worse, you dont even know what the reflectivity of your obstacle is, so are you a foot, or an inch away? This creates some amusing tunneling entrapment situations. You can get stuck in a confined area that looked dark when you went in, but is white when you turn around to escape - and thus you are quite trapped.

Another surprise was the reflectivity of obstacles in 940nm IR is quite unpredictable. Plants are pure white, so are my black socks! Black poster board is a neutral grey, and black IC foam is totally invisible. To help visualize this, we are adding to the write up an extensive set of images of household objects photographed in deep infrared so you can actually see what the robot will see when it moves about. Pretty cool, ay?

Chris

comets133@yahoo.com

Hi All,

Finally, I can show you what Picbot III looks like. We have been really working hard in the evenings getting it done, and the mechanical and wiring are now as of last night finished. PicBot III is a follow on to the II version, which was to research the bumper logic. Here, the III version is to do the same with IR prox sensors. So Here is the main page:

http://www.schursastrophotography.com/robotics/picbot3main.h tml

and here is the front of my robotics web page, with PicBot III also:

http://www.schursastrophotography.com/roboticsmain.html

Let the programming begin! ;)

Chris

comets133@yahoo.com

HI All,

Were now building our next robotic project, Picbot III, which will be used to gather data for a very in depth project on - you guessed it: IR Prox Logic.

I had some stamp sized circuit boards made by PCBexpress, and they are for the IS417 prox sensors and contain the dual 910nm IR leds. The interesting thing to think about with using this device is 1. The modulation frequency is 50kc, and wont interfere with other IR devices at 38kc, and 2. the wavelength of this IR is MUCH higher than a standard IR like 700 - 800nm. This means my web cam cant see the beams in the dark! This would be to charecterize the beams for an angular resolution analysis. I do however, have one of those edmund phosphor cards which it barely activates. So the quest continues as to how I will veiw the beam directly. (my russian IR night vision scope cant see the beams either!)

Anyone have any ideas for 910nm?

Write me:

comets133@yahoo.com

Chris

HI all,

Just finished a huge project, our article on Bumper Logic. If you have any interest in programming and implementation of a bumper based robot, this article may be of interest:

http://www.schursastrophotography.com/robotics/bumperlogic.h tml

Thanks for looking.

Chris

Let me know what you think: comets133@yahoo.com

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