Older blog entries for ericzayers (starting at number 27)

19 Oct 2005 (updated 19 Oct 2005 at 16:41 UTC) »

Kudos to the other robots.net webloggers. In particular, Vac Bot 1 and Mr. Stick Legs posted in other robots.net weblogs are quite an inspiration to me.

These past two weeks I've worked on my linefollower project a bit more:

  1. Built some wheels out of Lexan with my Dremel and circle cutter (not a bad job if I do say so myself.)
  2. Getting the Hamamatsu encoders mounted and testing reading them.
  3. Building a little RS-232 to TTL line level converter board w/ a MAX232 chip.
  4. Wired up the first serial port on the Atmel AT MEGA 162 and put in some test code to read and write from the port.

As far as making the rs232 line level converter: A word to the wise, check out Al Williams' web site AWC for a cheap and easy way out. But I was halfway done with my version before I found it. Since I wanted this to be fairly sturdy so I could re-use it for multiple robots, I made a schematic in Eagle and etched a PCB for it. My first board was a flop. Several of the traces had bridges because I didn't scrub all the paper off, and I accidentally mirrored the image to boot. The second board came out of the etching process much better after using a toothbrush to scrub the smaller bits of paper off. But I didn't align the board and the drawing very well for my 2 layer design. And I crossed RX and TX. And I didn't wire up the power pin. And, well, it was pretty much the worst pcb I've ever made, but it does work. Because I didn't plan ahead on putting it in a particular project box, it won't fit in a project box, so I just sprayed the bottom side with clear enamel to prevent shorts and am using it as-is.

Next on my plate for the linefollower is to get it to drive in a straight line. I can work on my motor controller logic (a PID loop, I guess) now that I have the encoders installed and a serial port for debugging.

Tonight I'm off to the AHRC Robot builder's night out. I've got my eye on making a drivetrain for the wiper motors for building some kind of larger size bot.

7 Oct 2005 (updated 11 Oct 2005 at 18:17 UTC) »

My new linefollower project is coming along nicely. Now the family is back, but I've got my project board w/ an ATMEGA162 MCU and HBridge wired up which is controlling both motors now.

I put the robot on the floor for a little test run (no wheel encoders yet.) Overall I was pretty pleased with the flat out speed of the bot and the ability to control speed of the motors w/ locked anti-phase PWM. But I can see that there are some issues:

  1. The wheels quickly lose traction on the painted concrete floor of my basement.
  2. The rear wheel doesn't turn and influences the direction of the robot (especially in reverse!)

The batteries are mounted toward the back of the bot. I probably need to move the over the front wheels to help with differential drive. I may need to replace the wheels with wheels of larger diameter (Currently about 1 1/2" in diameter, maybe go up to 2 1/2".)

The family is out of town, so I am working on robots while not out winning bread. To build a big bot with the wiper motors I'm going to need some more complex mechanics - starting with a coupler for the motor to wheels. I was going to use pulleys, but can't find anything remotely suitable at the local hardware store, so I might just have to make something myself. I can get access to a machine shop at the next AHRC RBNO, or at least some access to some good advice.

I was out and about this weekend and stopped in Hobby Town and picked up a pair of Tamiya gear boxes. Then it hit me - I could quickly build a little robot. So, I decided to go for another stab at a line follower. There was some discussion on the AHRC mailing list regarding locked anti-phase PWM which I put into action.

30 Sep 2005 (updated 30 Sep 2005 at 13:41 UTC) »

I've got my ATTINY26 based hbridge to work with PWM after nutsing around with it for a while. Don't ask me what the PWM rate is. I just kept changing the Timer 1 prescaler value until things work right (too fast, and the motor just makes a whining noise.) Now I'll try to get I2C communication and the encoder wheel working.

I need another chip to be the I2C master to communicate with the hbridges. I purchased a Wright Hobbies DevBoard-M32 for just USD$25. Nathaniel from AHRC brought one of the ATMEGA8 versions of this board to a meeting a few months ago and I really liked it. The board came quickly and I soldered it all up and tested it out in a little over an hour. Eddy Wright was very helpful too. It has a pinout for each pin of the ATMEGA32 and some extra pins for VCC, +5V and Ground for perephrial stuff. I highly recommend it.

Its my birthday today! Its been about a year since I did major work on my website. I did some housekeeping this morning and worked out a few kinks.

21 Sep 2005 (updated 23 Sep 2005 at 11:22 UTC) »

I haven't been doing nothing for all these moths.

- I finished my mini sumo mods and competed again. I won against my competitor from 14 February, but then I went up against delta force and lost. He just scooped me up and pushed me out of the way. I need more weight. I'm only at 350 grams. Something was going wrong with my eye sensors too.

- Built a digital thermometer out of an Atmel microprocessor and some nice freebie high intensity Green LEDs.

- I tried my HBridge again to try to control my 12V wiper motors, this time following a schematic gleaned from the Internet. I got it working for almost 30 minutes before it self destructed. No sparks, but some smoke from one of the MOSFET's

- I went and bought a current regulated power supply at Fry's the next day. That has helped a lot...

- I found that there was a followup schematic to the first one. I created a PCB for it and am now debugging it. I'll update the hbridge page on my website one of these days.

My mini sumo bot is all working now. I had my first Mini Sumo contest on 5 Feb 2005... and I lost big time. The competitor was another MarkIII kit, but when the two robots went head to head, his just pushed mine back and hardly slowed down.

I noticed he had Alkaline cells (1.5 volts) and I was using NiMH cells (1.2 volts), so I think that might have been the big difference.

I ordered the more powerful servos from Junun.org and also got the nice sticky tires. I'm going to add 2 more AA cells to my power supply too.

An issue I'm struggling with now is that I'm a little bit over on the regulation width. I've used my dremmel a bit on the servo and wheel to shave of a bit. I may have to cut off some of the fancy new tires to get them within the 10 cm width. That would be a shame - I want as much traction as possible!

I translated the C sample code for the MarkIII to be compatible with the CCS C compiler. It seems like I fiddled endlessly with getting the servo centering right. Reaming out will a bigger drill bit helped, but did not solve the problem. Then, someone tipped me off that if I shorten the potentiometer shaft on the servo it might help. That fixed the problem!

I broke down and read the CCS C Compiler manual. Now I think I can make the HEX files work with the default boot loader, but first, I want to get back to beating that inanimate block of wood before the AHRC meeting on Saturday.

Just got back to the MarkIII mini sumo kit today. I am using the CCS pic compiler and Linux, and realized I'd have to use another bootloader (Rick Farmer's) than the one that came pre-loaded. I tried to 'reload' the bootloader, but didn't pay very close attention to the instructions and replaced the bootloader with one of my test programs (whoops!). I had to break out the hardware PIC programmer and put the new bootloader on the old fashioned way.

To test the compiler, I used the MarkIII prototyping board. After some head scratching, I realized I'd soldered the headers in the board upside down. After scratching some of the traces and re-routing Vss and Vdd I have a blinking LED on my prototyping board.

After some trying, I realized that my servo mod was not quite right - the left servo wouldn't stay centered, so I had to ream out the gear with a larger drill bit. I can reliably control the servos with my own program, so now I'm cooking with gas. Next step, program it to beat an inanimate block of wood.

The MarkIII wheels didn't fit on the JR racing servo, so I had to drill out the wheels, then mount them on a round servo hub.

The MarkIII kit is all together and after reversing the wiring to the IR sensors, it all tests out properly. I used BotLoader under WINE to get it to program under Linux. A fellow AHRC member (Bob Baxter) loaned me a sumo ring and gave me a blank one to paint. What a guy!

26 Dec 2004 (updated 26 Dec 2004 at 21:56 UTC) »

For Christmas, I gave myself a Mark III mini sumo kit from Junun.org. A nice kit but probably not for the beginner.

The board is compact and looks very flexible, since all 40 pins of th PIC 16F877 are brought out to a header. Make sure you have a small soldering tip! The soldering of the board went quickly. I have yet to test it.

The servos it shipped with were unmodified, so the next step was to modify them. For me, the servo modification didn't go so well. I saw the instruction, "Be careful not to drill out the threads" but then used a large drill bit to be SURE I could get my screwdriver in there and now the screw to attach the servo horn/wheel no longer fits. The second servo I sheared off the moulded axle when trying to remove the servo stop.

Live and learn! I had two other servos lying around and even though they were slightly different (JR Racing instead of Futaba) I was able to modify them without breaking anything.

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