Older blog entries for cschur (starting at number 28)

Were now working on adding the sensors to the bottom of PAAMI to detect edges such as stairways and steep dropoffs. The sharp Gpd12 are being used, in front of and behind the wheels. My setup is to have the nomial 4 inches for the normal running distance. When the distance exceeds 5 - 6 inches, an escape maneuver is executed. Ill have to determine what is the farthest I can fall off an edge without damaging the bot, its certainly less than 3 inches, perhaps initially ill set it for 1.5 inches. Testing will be accomplished by putting an elevated platform on the floor, such that I can vary the height, and letting the bot drive on it. If I slope the edge, such that the lowest point is say an inch off the floor, and the highest point is say 6 inches, it should not drive off untill it finds the 1 inch location. Pretty cool. Im wiring up the 12F675 now which will put out a serial stream to the Impact level 6 subsumption processor of the drop off sensor status.

Ok, enough for now. Anyone out there done drop off sensors on thier bots? Write me!

Chris

comets133@yahoo.com

Hi all,

Here it is - the fruit of our labors for the past few months. Ive uploaded an article on our charging station for PAAMI, and have lots of photos, movies, and descriptive text to show you how we did it.

http://www.schursastrophotography.com/robotics/docking2.html

Ill ask again, if there is anyone out there that has made a self charging robot, Id love to hear from you!

Chris Schur

comets133@yahoo.com

HI all,

We have the PAAMI robot docking and feeding down to a science now. Some key factors we have learned on feeding are run time vs charge time is best optimized for about twice the time charging as running. Putting the feeder (charging station) in a location that is not so obvious - You put it where the robot spends the most time, NOT where it seems logical! For example, I thought the hallway connecting the living room and bedrooms would be central and the robot would spend the most time passing by the charger there. Nope. A robot almost always spends the most time in the largest room or area. So the charger will be there.

We are perfecting the software for the beacon homing as well. This is what gets the robot to the charger every time. The key of course is IF the robot is hungry AND it is in beacon detect range, go dock. Sounds easy, right? The key here is to limit the optical beam width of the beacon such that the docking will be always sucessful. For example setting the beam witdth to say 20 degrees will make sure the robot will only dock when aiming at the charger within a 20 degree angle. This simplifies the contact arrangement. MOre to come on this, I have taken some more movies of the robot docking and will post this soon!

Happy new year! If you have a docking robot - Please write me, Id love to hear from your experiences!

Chris

Hi All,

Another update on the charging station. After trying a lot of different connection schemes, we came up with one that seem quite reliable to use when the robot docks with its charger. At first, I thought we could get away with whiskers that hung down under the robot and skid over copper plates on the charger. But they picked up stuff off the floor, and got tangled. The new method is to put the copper plate on the under side of the robot, and drive over the contacts. They consist of two 2 inch long springs of the type that is fully compressed and you pull to extend it, topped with 3/8 brass balls used in the lamp industry and sold at ACE. The bottom of the springs is connected to the wires that go to the charger. So when the copper plate skids over the balls on the springs, they flex a bit and make great contacts. Ill post some pictures soon...

Chris

Hi All,

Here is the big article I promised you on building a battery charger specifically for robotic applications. It details various types from the basics to more advanced and more importantly describes why we charge batteries the way we do in robotics.

http://www.psiaz.com/schur/astro/robotics/robotchargers1.htm l

Chris

HI all,

Ive got the article finished on basics of building a robotic battery charging system. I have another engineer reviewing it now, and in a day or two Ill be posting it. STay tuned!

Chris

HI all,

The hard work paid off, and we have our Priority Arbitration bot feeding itself. It can now find its charger and dock, charge, separate and move on. I will be detailing in a series of articles our results of how to charge gel cells, find and contact with a charger, and charger location tecniques in the next few weeks. Stay tuned, Ill be posting images very shortly!

Chris

The microcontroller controlled battery charger for Paami is nearly done. What a trip learning on how to best charge lead acid batteries! The dual charger charges both the electronics and motor batteries independently, the voltage from both being sampled with a 12F675 PIC with two 10 bit A/D converters. The same inexpensive pic also turns off the relays from the current sources to stop charging, montors the docking with the charger and sends a signal to the robot on charging and docking status. The scenario goes something like this:

The robot is hungry and heads for the docking beacon. When the charger plates are contacted, the charger micro tests multiple times to make sure were really docked. Then the relays are closed and charging starts. IF the contact is lost during the charge process, the charge controller also reports that so a re attempt can be made. If all goes well, the electronics battery which is smaller will charge first, then the motor batt. When completed, the dock signal flashes at 10hz,a nd the robot knows its done and performs an escape manuever from the charger.

A few notes: The chargers consist of two constant current sources, one 250mA, and the other for the larger battery 400mA. So you can even short them out with no problem. The battery voltage is monitored until it reaches 13.4 v, then the charger turns off that source with the small relays driven directly by the PIC. What I dont know yet is wheather or not Ill need to add an additional time onto the normal charge cycle to get full charge. But the charger is working and Ill evaluate the charge over the next week or so as I cycle the robot from full charge to fully drained.

Write me if your robot automatically charges, Id like to hear your story!

comets133@yahoo.com

chris

I am excited to report we got our robot to successfully dock with the charging beacon. Ive put a write up on the adventure here:

http://www.psiaz.com/schur/astro/robotics/paami7.html

This is a huge step in making our priority arbitration machine self sufficient. We are now working on the charger itself, which will consist of two curved plates that the robot drives over with a set of contacts. If you have the bandwidth, check out the last movie!

comets133@yahoo.com

Write Me!

Greetings all,

An update on our PAAMI project. We have installed the IR beacon sensor on the top center of the robot now. Two guitar string bumpers are in front to protect the dome cover over the assembly from impact. By the way, the E string is great to work with - its a music wire core wrapped in a brass spiral. You can get all the benefits of music wire flexure and be able to solder to it too.

We made the beacon this week too, it consists of five IR LEDs mounted on a small board, with a driving NPN transistor to interface to the processor. Flashing the beacon LEDs on and off at around 38.5 KHz was greatly simplified by using a PIC processor, a 12F629 (less than a buk) with a 10mhz xtal to generate the wave form. I found by using the "Pauseus" command, I could get 39.0 Khz, which is well within the bandpass of the reciever, a panasonic PNA4602. It is very stable, and those PICs really crank out the power.

Detection can be adjusted with a pot in series with the 5v line to the LEDs. at full power, the beacon can be seen head on across the room, but unfortunately, the beacon sensor on the robot can also see the whole room light up with IR energy! Ive cut the power back to 1/3 and get the desired results, about 8 feet head on, and 4 feet on the sides of the PNA detector. This weekend, we will for the first time program the charge subsumption behavior to actually home in on the beacon and see how close we can dock with it. I hope better than 2 inches tolerance!

comets133@yahoo.com

Chris

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