# Older blog entries for cschur (starting at number 65)

HI all,

Our write up on the Geobots tilt sensor is up, and as usual weve covered this subject with great detail in case you would like to try to make one yourself. It was fun testing the sensor outdoors, on steep hills and large piles of dirt.

http://www.schursastrophotography.com/robotics/geobot3.html

Chris comets133@yahoo.com

HI all,

We made some great progress this weekend on the Geobot. I installed a tilt sensor, made from a damped potentiometer with a six inch weighted pendulum. Reading it with the 10 bit A/d in the 16F877, we set it for a 12 degree uptilt for the limit forward, and a 22 degree down tilt when going down the hills. There is a lot of pea gravel sized rocks in our area, so thats why the relatively shallow uptilt. Its like driving on ball bearings! When a uptilt limit is reached, the architecture considers it as a top priority impact, and stops, reverses for 2 seconds (pendulum time constant) and turns 90d right. Then resumes. In this manner, it tends to skirt a hill to get around it.

Downtilt is another matter. Since reversing wont work since it slips too much, I cut the speed in half for up to 22 degrees , and after that a full stop is in order.

We did get the sonars and Devontech compass from Mark III robotic store very promptly. As soon as we are through with the tilt sensor algorithm, then its on to the exciting world of sonar navigation amongs giant rocks!

Ill post a page on the tilt sensor soon...

Chris

HI all,

as promised, here is the latest write up on our tank tread odometry technique and a hint on the new architecture for programming we will be using:

http://www.schursastrophotography.com/robotics/geobot2.html

Thanks for looking!

Chris comets133@yahoo.com

Hi all,

We have devised a hybrid method of programming our Geobot, that combines the best of Finite State Machines and Priority Arbitration, which we are calling "Finite State Priority Arbitration". With a single processor (16F877a) it is not practical to implement a true multithreaded program, so we have limited the subsumption portion to just when the robot travels from the starting point to the destination.

So far, we have bumpers on the front, and now a daylight readable (and I mean DIRECT Sun) optical wheel spoke encoder on the tank tread. We accomplished this with the IS417 chip, which detects only self modulated IR.

Anyway, our next write up on the tank tread wheel encoder for outdoor use is comming along. Ill let all of you know when its posted!

Chris

HI all,

Great progress this holiday weekend on the Geobot. We added the IS417 based infrared wheel encoder to one side of the tracked base. The rear "cog" has seven holes in it, an gives 2.7 inches per hole on the ground. I made up my own circuit boards for these cool parts, they not only provide the modulated drive source for the twin IR leds, they also filter the IR with a built in filter, and also only look for the 38khz frequency. What a killer part. Anyway, we took it out into the sun today, and with the sunlight shining right at the sensor, and I mean right ON it, it easily picked up the single LED trasmitter on the outside of the hub about 4 inche out. Next, we set the software to count to 45 spokes on the hub and stop. Thats 120 inches, and after 10 feet on hideously rocky ground, it stopped.

Here is my feel for outdoor robot odometry, two wheel odometric navigation is almost impossible unless the ground is pefectly and unrealisticly smooth. What you CAN do is get a single wheel to give you the approximate distance youve traveled, despite the rocks and bumps to get you close enough to your target (via compass navigation) to see it with your other sensors. We have base ball sized and larger rocks in our test course (my backyard) and there was no way we could get a dual wheel odometric system to give you some sort of x-y coordinate of where you were. So we are opting for a digital compass, and a cucam, to spot the target area, probably a orange cone, to start its distant work. Well, thats all for now, I will post some images soon of our IR setup on the wheel - er tank hub.

Chris

18 Dec 2005 (updated 18 Dec 2005 at 23:32 UTC) »

Hi all,

We have been very busy designing our new bumper system for the Geobot, and I am proud to present to you our first images and movies of the outdoor rock drive, with a description of the new instrumented bumper design. We were pleasantly surprised at how well it avoided large rocks, and actually made it through the torture course we had planned for later when we add the sonar. Youll like the results:

http://www.schursastrophotography.com/robotics/geobot1.html

Chris comets133@yahoo.com

Hi All,

Bought all the parts and pieces for Geobots front and rear bumper system. After I built the prototype mechanical sytem in Lego, I then did a CAD layout of the real one. For an outdoor robot, which has grippy tank treads the problem of ramming rocks and destroying any traditional bumper is quite real! My design, which I will post as soon as I get a bit furthur along uses one single metal bar, with two 1/4 inch metal rods about two inches apart in the center sticking out. These slide in and out a set of holes thus making the bumper not only go in and out, but the close proximity of the two rods also allows a rocking motion so each side can press a protected lever switch.

Once Geobot has this bumper, I can say it is a robot, and not a motorized cart. The plan is to add sonar next, and use that plus the sun itself to navigate to the collecting field. Geobot will be designed if you remember to autonomously collect rocks and fossils.

Chris

Hi All,

Ive just uploaded the first main page of our new GeoBot project, a larger heavy robot designed specifically for outdoor use. Its eventual goal will be to autonomously collect rock and soil samples and return them to a starting point or home base. Here is what I have so far:

http://www.schursastrophotography.com/robotics/geobot_mainpa ge.html

Chris comets133@yahoo.com

HI All,

I want to let you in on a secret - The LM298 motor driver from Solarbotics. This kit is available for a ridiculously low price of \$17, and includes all parts, connectors, and PCB, and a very well written manual for assembly and testing. I got 4 of them last week, and the first one I have put together so far worked great. You cant even buy the parts yourself for that cheap. And If you havent noticed yet, the L298 is 3- 6amps and up to 30v motor H bridge driver thats the hottest thing for robotics. I use them extensively at work, and now with the solarbotics kits, everyone can use this fine part.

The Geobot project is in full roll now, Ive put the big 16F877a processor and L298 driver board together, and am ready to mount it on a top board for the motor base, a 3 foot long dual tank tread drive, that is allready finished.

More to come...

Chris comets133@yahoo.com

Hi All,

While were waiting for some of the parts to come in for the new GeoBot project, I was trying out a prototype 4 wheel skid drive system in the house last night. The concept sounds simple enough - two close wheels per side, and drive them like a tank. When going straight, the traction is awsome, and it will climb over anything. But try to turn on a carpet and your in for a surprise! It shakes, shimmys and is very jerky and uncontrolled. Fine for a smooth tile floor or maybe outside in the sand. But on a grippy carpeted surface or maybe in your lawn it makes a mess when it turns. Just like tank treads but worse, in that the wheels are trying to drag sideways while turning. I need to try some more outside tests before condemning it.

Chris

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