Older blog entries for cschur (starting at number 75)

11 Jul 2006 (updated 11 Jul 2006 at 18:28 UTC) »

Hi all,

Just got back from 2 weeks in Queensland Australia, diggin dinosaurs and doing some astronomy. Time to get back to the Geobot. I finally found a brush to use for my rock scoop. Its a ceramic core, with stiff nylon fibers used for a hair brush. I cut a 2 inch wide section out of it, and am currently mounting the motor to it. This will be lowered by the new arm we installed 2 weeks ago to the ground, and turned on when it touches the ground. A wire mesh cup will catch the spray of material that comes from the brush, including small rocks and pebbles.

So we have the new arm working fine, the robot is turning around at its destination which is 100 feet for now, and returns very nearly to where it started just fine. The brush collection assembly is the last part to put on, but its not so easy to make!

I keep asking myself where Im going to store this huge robot after we accomplish our goal of rock collection...

Write me,

Chris comets133@yahoo.com

Here is a progress report on the Geobot. The devantech compass is finally working, the unit we got simply would not calibrate for blood or money. We rotated it in the cal mode over and over, but the cal done lamp would not change. Finally, in desparation, we calibrated it using the old style previous rev software version method. It worked. Apparently, we got an unmarked chip, which was not the newest version.

Anyway, The robot now goes out a preset distance, rotates 180, and returns very near the start position. We are ready to add the arm now, that will collect the rock samples from the remote location and return with them.

So two problems we encountered this week are first, the tank base I used (Stuart M5) doesnt have the power to rotate in place on 3 inch deep grass. We stick to rocky flats for now. Second, the motors genrate a horrendous magnetic field from the magnets inside them, which cause up to 20 degree offsets at certain angles from the real bearing!

WEll, other than mount the darn compass on a six foot pole, Im going to try to keep missions on the NS - EW line for now, thats where the compass is calibrated to be dead on. Alternately, I can make some sort of look up table for each angle as to what angle really is 180 degrees so It turns around at its destination for the return trip.

The final goal of course will be to send the robot on a rocky gravely plain (common here in Arizona) out to 100 foot distance, collect surface specimens with a motorized scoop with a rotating brush on the end, and return them to the start point.

The project page for the Geobot is at:

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

Write me if you have time! chris


Hi all,

After three grueling weeks of testing, design and calibration, we have finished the first phase of compass integration into the Geobot. I have put an article together complete with photos, diagrams, schematics, and mpg movies with sound of our recent efforts. We are one step away from getting the robot to go to a destination and return to home autonomously. Here is our latest article:



Chris comets133@yahoo.com

I got our compass working now on the Geobot. Its a bit tricky to deal with the numerical roll over from 359 to 1 degrees but I found a simple solution. Anyway, the robot takes a bearing upon turn on, and maintains it within about 2 degrees tolerance as it pounds its way across the rocks in our testing area. Its the damndest thing - I set the robot down, and it swerves around avoiding rocks and such, then turns toward the original bearing when its not hitting something! Very cool to watch.

I did run into one issue with the Devantech compass, it would not calibrate per instructions. I kept on rotating it and the done line never went high. I finall in desparation used the old cal proceedure with 4 points at 90d, and that worked. Id be intersted if anyone had a similar problem with thier compass?

Write me: comets133@yahoo.com


HI All,

Well, here it is as promised, the write up on shaping and final testing of our quadrate sonar array on the Geobot. I think we have learned more about sonar in the past few weeks than in my entire life:

http://www.schursastrophotography.com/robotics/sonarshld1.ht ml

Write me!

Chris comets133@yahoo.com

More on Outdoor Sonar....

We have spent many more hours this week on getting our quad sonar array to work outdoors. I have discovered a very useful fact about doing this, Id like to share. With a sonar mounted just above ground level, say six inches or so, you will be detecting the ground at some point a few feet away, and it will change rapidly in some cases from a foot to over four feet in a heartbeat.

We tried aiming the sonar upward about 25 degrees which pushed the ground detect point outward only slightly, but now it was picking up beams on the overhanging roof! So dont point your sonar upward.

This "ground effect" requires you to do one of two things to make the sonar useful for obstacle detection. First, you can always jack it up a foot or so off the ground. Then youll miss some pretty major obstacles, but your ground detect point will move out to past the detection limit of about 8 feet for the SR04 sonar.

Alternately, we can try to reshape the beam. Research into this on the web has shown mainly failed attempts, the general consensus is you CANT change it. Well, we found thats not entirely true!

You cant add like tubes or cones in front of the beam or over the emitter/detector because it just sees the tube and its signal overwhelms the detector. BUT you can modify the pattern by reflection. Here we put a smooth surface for the beam to deflect off of, exactly like a mirror. By intelligently putting a flat piece of lexan under the sonar xmitter, we can deflect the sound waves that would hit the ground up into the air. so now we are determinng the shape of that flat plate, and how big it should be. Im guess ing it will be D shaped, and about four to six inches radius.

More to come, working with a sensor system that literally sprays signal all over the place outdoors is quite the challenge!

Write me if you have any suggestions.



27 Mar 2006 (updated 27 Mar 2006 at 17:51 UTC) »

Sonars in the Outdoors

We made more big progress on our quadrate sonar array on the Geobot this weekend. Last I posted, we had just mounted the array on the front of the robot, and started testing a new sonar PIC to do all the dirty work to take the load off the main processor. Well now we have finished the sonar processor, and it puts out both serial and paralell data to indicate both the distances for each sonar, and which zone the closest danger is in. And now, last night late we wired that processor into the main 16F877a controller.

I next set up the priority arbitration architecture in the program for the sonar, which takes second place only to the bumper. And a quick run indoors at some targets on the floor, and its veering and banking away proportionally from the obstruction!

So whats next? We found that in an outdoor enviornment, the sonar is picking up the rough ground about 2 feet in front of the bot, even with no rocks around. In the house with the flat plywood work table we have it on, it did not do this. So heres the catch - If you aim the sonar straight ahead, it will still see the ground intermittently and think there is a giant rock out there its heading for. IF I tilt the sonar up, I miss the ground, but also miss close by rocks that are too tall.

Sonar is very broad beam, and very sloppy of course and is quite a challenge to use out of doors! Also, there is the problem of a slope. When the robot sees a bottom of an easy to climb hill in front of it, it still sees it as an obstacle to avoid.

So for small rocks and the ground, a low lying sonar will not always see the comming impact. But It will see many feet straight ahead so it doesnt encounter a huge boulder or more commonly a tree trunk. So there is a small zone Ill have to cover between the bumper and bottom of the sonar beams with another set of some sort of sensors.

Our next step is to take the bot outdoors and run it through an array of obstacles such as rocks, branches, logs and ditches to get the sonar tilt set to optimal.

Its the wierdest thing to see a tank tread vehicle with differential PWM drives running figure 8's all over the yard!

Write me: comets133@yahoo.com


HI all,

Finally a new article on our Geobots systems to post, Here we go into our 4 quadrant sonar zonal system, and how we are implementing it in the new robot:



Chris comets133@yahoo.com

Ok, I havent posted in a while, so heres whats up. The design for the layout of the mutli beam synthetic aperture sonar for our Geobot has been killing me for the past two weeks. Finally its done. Its going to be a 4 channel Devontech array on the front lower bumper, and armored incase of impact with a giant rock. It will work this way: Each sonar will be read in succession, then the distances will be binned into four zones. The sonar processor chip will then determine based on these numbers the maxium danger. This is reported both parallell and seriall to the main processor (Running priority arb.) for the appropriate escape response. This way I can use the new dual PWM tank tread drive to bank, veer, or rotate away from potential obstacles. Its going to look very cool when its done! So back to chopping more lexan...


Hi all,

A very busy week for the Geobot, we added two pwm processors to the drive train and can now do something other than full on and full off on the track drive. Our test was to do a S curve, something not easy with a tank tread drive! Anyway it works fine, and now we can do any type of turn we wish to avoid large trees and rocks or home in on a distant target by simply veering one way or the other.

Our PWM drive was done this way: Both motors are driven with the dual L298 motor driver from Solarbotics. the Enable line is the PWM input, and the other two inputs provide the direction for the H bridge.

What we did was drove these inputs with a 16F628 PIC we programmed to accept a serial data stream at 9700kb on its input containing the two direction bits, and a 0 - 255 pwm percent bit. So to go straight for example, I blast off a single serial command from the main processor to this motor driver PIC and it changes and stays that way until we send off another serial command to change it. Set and forget control. If anyone is interested in the hex file for the PWM driver, and want to make thier own free serial to PWM chip, email me.

Were moving on now to the 4 channel matrix sonar array, and have a unique approach to obstacle avoidance tied right to the PWM for each motor, youll like it...



66 older entries...

Share this page