Older blog entries for ericzayers (starting at number 22)

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.

The good news is that there are 364 days left to plan for next Halloween.

I got the H Bridge working, but then my control circuit went all flaky on me and I couldn't get it working in time for trick-or-treating. We put out a blacklight shining on a black board with the message "Happy Halloween" instead.

I am now building a UV light table to use for circuit board printing.

Now the relay based HBridge is working. Now to work on the mechanical parts (a rope with a pulley to move the ghost along.)

27 Oct 2004 (updated 27 Oct 2004 at 13:32 UTC) »

I'm experimenting with building a little HBridge. I let the smoke out of some MOSFETs trying build the HBridge. It was exciting, but not the kind of excitement I like.

Someone suggested I try using a current limited power supply while testing. Sounds like a good idea. I'm switching the circuit over to using relays since I have a tight deadline (Halloween is this weekend!), I don't have a current limited power supply at the moment, and I don't really need to use PWM at the moment.

As an offshoot, I'm going to try to help a friend with a rig to help him automate some sandblasting he does if I can ever get this #!$@$@ HBridge to work!

The billy bass audio circuit is still to be done. There is an AHRC Robot Builder's night Out tomorrow that I hope to use as an opportunity to debug the audio circuitry issues.

The current project on the bench is an H Bridge to use for a Halloween gag. I am going to put a rope up that runs along the path of our sidewalk. A "ghost" will then move along the rope via remote control.

I am using a PIC16F684 for the motor controller and MOSFETs to build an H-Bridge. It is my first H-Bridge project. I added 2 leds to show which direction the H Bridge is enabled for. With just these 2 LEDs and holding one line or the other as "high" the MOSFETs heat up pretty quickly (within about 15 seconds) and the power cuts off. I guess you really do need PWM...

25 Sep 2004 (updated 25 Sep 2004 at 10:55 UTC) »

Today is the AHRC meeting AND the CTK church carnival where the modified bass is to be put on display. I'm not sure I can make both. On top of that, I am feeling sick.

My audio circuit woes are that:

  1. There is a lot of hiss in the background when I record.
  2. There is noise caused by motors (I have mitigated against this somewhat)
  3. There is distortion.
  4. The volume isn't loud enough.

There is every indication that the LM386 isn't powerful enough to cut the mustard. I bumped up the power to 9V on the amp and that helped some. I built a "Better" amp circuit based on the LM386 that had less distortion, but it still wasn't loud enough and it is still on the breadboard. I don' t know that I have time to solder it up for the festival (starts at 10am)

The end result is that the hack "worked" but isn't quite as impressive as I had hoped. I acquired another fish robotic toy called "Rocking Fish" which is a really bad knockoff of Billy Bass which is a bad knockoff of "Boogie Bass". So what I did is made a little umbilical cord and now the control circuit moves *both* fish. I hope that kind of makes up for the lame sound quality I am getting.

I will try to update my webpage tomorrow.

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