Recent blog entries for earlwb

I thought I'd post something for the beginning of the new year.
I bought myself a Parallax M-Sortr M&M Sorting machine for my Christmas present. It sure beats the typical "Old Spice" gift packages I always get.
Anyway, sorting M&M's by color isn't as easy as it looks on the surface. But I got it working Ok and the unit is on my desk at work as a nifty conversation piece. It helps to intimidate my fellow programmers and impress the boss too.
It is a lot of fun as it sort of gets people to watch it like they watch fish aquariums and such. It tends to mesmerize them as they watch it sort the M&M's by color and drop them in the correct tubes.

It's been a while. DPRG's Roborama just finished, and I won the Quick Trip First Place Award with my Autonomous Mini-Cooper Bot. I had originally planned to use it for Autonomous Robot Road Racing, but I ran into the problem where at speed the robot couldn't react fast enough to make the turns properly. In real life we can "anticipate" a turn coming up and take action before we get there, but with robots, the robot can only "react" as things happen. I think I'll have to build a more robust road racing robot to test things on as the front end parts on the Mini-Cooper Bot are too expensive to break or make up if it hits something. It can go over 30mph so it does break things when it crashes. Anyway, now that I won first place I stop competing in Quick Trip and do on to better things like Can Can. I just recently had a need for a Function Generator, so after checking around, I felt it best to make my own. One gets to learn plus it costs about $100 or so versus several hundred plus. Anyway, after getting all the parts and PCB made, I built it up and it worked OK right from the start. I still have to tweak the three range capacitors a little, but it's time to put it into a case. before tweaking and tuning I am getting 5hertz to 18megahertz in three ranges, with a 0 to 4v AC output. I also did a layout for a Atmel 8535 MCU to have a digital frequency counter built in too, along with a Peak AC voltage level DMM too. I am just now building up the PCB for that now. I am waiting for some nifty rub on letter transfers to arrive so I can make the knobs and switches look good, or it would all be almost done by now. It was also fun to turn my own knobs out of some aluminum bar stock too. I did have trouble getting the knurling to work out OK though. What was amazing was that I had to use all DIP package IC's as the surface mount IC's were all simply not available. So the PCB's were laid out using DIP's for the IC's with surface mount parts for the resistors and such. Normally you can't get DIP's but surface mounts are available.

I haven't put anything up here in a long time so... I almost have a new version chassis for my nano-sumo bot. I only need to do some more dremeling out of the chassis to get the width under 1 inch. Then I'll have to work on my brushless-coreless DC electric motor some more. It should make for a interesting locomotive source for a small robot. But then I have about a dozen different things I want to do. Too many things and not enough time, and if I have enough time I probably can't afford it.

Tomorrow, Thursday 20th of March, I am driving up to Illinois from the Dallas Area to pick up a steel Sumo ring from on behalf of the DPRG club. This ought to be very interesting as I get to see the top secret Lynxmotion facilities, where they make all those great robots. The new Japanese Sumo rules have us using a 1/8" thick ring of steel as the sumo ring for the matches. This allows the use of magnetics and vaccum assist to improve the traction of the robots. Of course you can't just stick a robot in the ring, it still has to move around and attempt to push the other robot out of the ring. This is for the 1 or 3kg 22cmx22cm class of robots. Also supports autonomous robotics thus radio control isn't used.

My nano-sumo bot project is still going. I've had a number of attempts at getting under the 1 cubic inch size barrier. And it looks a lot closer now. I just discovered some 402 sized SMD LED's from LUMEX. So I did a Atmega8 (MLF formfactor) PCB using 402 sized parts on it as well. It eeks out a little bit more space on the PCB. I still have a 603 sized component PCB just in case.

Now if I can only find some small rechargable Lithium-ion battery cells small enough to work. using non-rechargable cells sort of sucks as they are very expensive. I see tantalizing pictures, but no one selling them yet. Or at least selling in small quantities.

I can't beleive it is so hard to get two identical speed controls.

I wanted to get two ESC's for a firefighting robot I am trying to build. So I ordered two ESC's from a nice supplier. They both arrived, except one was DOA. So I sent that one back to the manufacturer for warranty repair/replacement (that's what the instructions say to do). So they send me a even better one that the one I sent them (heck what do you do?, they did really good on the warranty DOA). Big difference too, a 140 amp (.012 ohm) ESC replaced with a 162 amp ESC (.004 ohm). Doesn't exactly allow for a robot to track straight. Anyway, I order another 140 amp ESC from the supplier and they accidentally send me the wrong one a 65amp one. I ordered two of a different model ESC from a different dealer, and I wind up with them accidentally only shipping one instead of two.

I've called them all and they are all correcting the orders and sending the stuff out. So everyone is bending over backwards to correct the problems. But it's just the bad karma of it all. Jeeshhh. Only four weeks trying to get two matching ESC's. Besides all the time lost waiting. I have to sort of squish everything into the robot and build up on top of that in the robot, so there isn't a lot of room to go trying to disassemble everything.

I should have known better and just built the stupid things myself. But I haven't been able to get the 140-160 amp motor controllers that small yet. Mine are too big.

But before anyone says anything. A set of motors needs maybe 20 amps max to work. But a 140 amp motor controller doesn't need neat sinks as the transistors have such low on resistance (PWMing them) that they don't even get warm. Thus you can cram them into a small, tight, low to little air circulation place, and they don't get hot.

Definitely going to be hard to build a firefighting robot at this rate. Maybe for next year's firefighting contest, I'll be ready. Don't know about this year.

I got some Atmega8 MLF's and some Atmega128 MLF's in last Friday. The Atmega8's are really small in the MLF package format. Basically, it sort of looks like the old PLCC packages, except the little pads are about .020" wide and about .015" apart. Plus they have a center square pad that serves as a solderdown and holddown point. The pads are also arranged around the bottom edge or lip of the chip case, and don't extend up the side. The pads are also plated with a gold like substance and not tinned with solder like you would typically expect.

Now all I have to do is come up with a PCB that has the Atmega8 and two 3v motor hbridges on one PCB that is less than 1 inch square, and still have a place to put in a IR object detector or two and a line detector as well. What would be really neat is to get a small LM2621 or MAX1621 DC- DC 1.2v tp 3.3 ot 5v step up converter to work on that same size as well. The MAX DC-DC converter can handle up to 1 amp max, so I could run the two tiny swiss gear motors off the converter via the motor controllers too maybe.

I am thinking about whether backing up is really important or not. The nano-sumo bot can go forward and turn easily enough, one or the other motor off. Or maybe only use one hbridge for reversing one motor and run the other forward only. In this case, if the robot detects a line, it can do a reverse turn to the left and turnaround to the right and continue on it's way. Forward only saves a lot of space, only one small SMD transistor per motor, the other nethod uses one transistor and one hbridge.

Atmel Atmega8 and Atmega128 MLF package MCU's from digikey or Pioneer are finally available in some small quantities. A Atmega8 MLF chip is about 5mm square, really small. I ordered some, I hope to shrink my nano-sumo robot PCB's down to one PCB with the MCU, dual hbridge motor controllers, and really hopefully maybe even the 1.2v to 5v DC-DC converter all onto one under 1 inch PCB. Currently, my nano-sumo PCB has a MCU board, two motor controller boards, and a DC-DC converter board. I actually use a LM2621 DC-DC converter that puts out about 1 amp max, so I use it to drive all the electronics including the two tiny motors as well. Then I can use one nicad or nmh battery cell just like the little Microsizer RC cars.

Bad luck building up my Can Can DPRG contest robot. One of the ESC's appears to program but not drive the motors. One ESC works and one doesn't. So I have to send it off to get fixed and wait forever for them to send it back. I hate it when that happens. New right out of the box. I guess I should just stick to building my own motor controllers, at least I can fix them myself.

Last week I was successful at building a second Gyro/Accelerometer combo board. And it works as well. It was a little scary at first, as I accidentally caused a short on the gyro chip and had to remove the chip, clean up the chip and the PCB and resolder it back down. In this case I used a ADXRS300 chip with 300 gegress per second performance versus the earlier PCB using a 150 degree per second chip. Those hot air SMD rework stations are worth their weight in gold.

It was a busy week, I got most of my new balancing robot built up. I made up a PCB co-processor board using a Atmel ATiny26 MCU to use with the gyro combo board, and I also got the Atmel ATMega128 MCP main PCB built up and tested as well. Now comes the fun part, wiring in all the stuff and getting it all programmed. I am using two of the new Hbridge motor controllers from NewMicros and I'll be running the motors using 16 NMH AA cells for about 19.2v. The plan is to have the ATiny26 read the Gyro and accelerometer chips and keep the robot in balance. The Atiny26 will also monitor the serial port for commands from the main MCU. The main MCU will tell it to go forward, reverse, slow, faster or turn left or right as needed. I've mounted a couple of encoder discs to the wheels with encoders so I can get distance traveled information or RPM indications as well. Lots of little things to do now.

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