Cats, Caps, and Contests

Ultracap Update

After prototyping a cell-balancing circuit for my robot power supply based on Maxwell 350F Ultracaps, I discovered the original choice of the TI TLC25L4CN low-voltage op-amp was not a good one. The little chip just couldn’t deliver enough current to balance the cap voltages in any reasonable amount of time. The peak output of the prototype was about 4 ma. So after spending a couple of hours searching for an op-amp that could operate at low voltage and put out a substantial amount current, I came up with the TI TLV4112IP high-output-drive op-amp. At last week’s RBNO, I built a second prototype and… it works! The new op-amp outputs up to 300 ma easily. Using the test circuit, I set it up with one Ultracap at 1v and the other at 2v. In little over a minute, the system balanced with both caps at about 1.6v. Next Tuesday, I’ll put together a more complete prototype with four Ultracaps and three cell balancers.

The cell-balancer has also proven to be a good way of trying out the GPL Electronic Design Automation (GEDA) package. I’ve been using the schematic capture program gschem primarily (screenshots) and have been asking lots of stupid, new-user type questions on the mailing list. They’ve been very patient with me so far and I’m begining to get the hang of it. It turns out good-looking schematics. Once I finalize the power supply, I’ll post a link to the GEDA files for anyone who might want them.

Cats in the garage

The abandoned mother cat and two kittens we brought home a few weeks ago are still with us. We know a lot more about them now. The kittens were much younger than we first thought. We’ll probably hang on to them until the kittens are a bit older. Susan has settled on names. The half-siamese mother cat is Sophie, the black kitten with the missing toe is Zippy (though she insists on spelling it “zippie”), and the tailless calico kitten is Callie. No luck finding a home for any of them yet. Callie is probably too emotionally disturbed to make a good pet but we have located a group called Barn Cats International that assists with finding homes for problem cats on farms and ranches where they can live with minimal contact with humans. Hopefully we’ll be able to find good homes for the other two. If anyone in the Dallas/Ft. Worth area needs a cat, let me know!

Nigritude Ultramarine contest outcome

The contest ended on July 8th. Thanks to everyone who linked to my site, especially, Bram. His link resulted in more hits on my site during the contest period than anything except Google itself. Feel free to remove those links now. I’ll probably leave the page up until the domain expires. I ended up in position 6 in the final results. The winner was a blogger who apparently won primarily through old fashioned Google bombing. Oh well, my site received a sort of honorable mention prize, the Judge’s Choice Award. My prize is one of those teeny, tiny “James Bond Stealth digital cameras” like you see on ThinkGeek. I’ll post a photo as soon as I get it talking to my Linux box (it only comes with Windows software but it has a USB cable so I’m hoping I can just mount it like a little USB drive).

We’ve been pretty busy at the office doing website design jobs. The lease on our office space is up soon and we’re deciding whether to stay put or move to new space. Even if we move, we’ll stay in Dallas and probably in the same general area.

Intermediate Robot Building by David Cook

This review was originally written for the blog

David Cook is webmaster of the popular website, a collector of bizarre safety signs, and author of Robot Building for Beginners. His new book, titled Intermediate Robot Building, explores more advanced issues than his previous book. This one is aimed at the reader ready to move from building robot kits to designing and building a robot from scratch. If you’ve been wondering how to control a motor, build an H-Bridge, or how to attach wheels to your motors in a precise and reliable way, this book is for you. Read on for a more detailed review.

Intermediate Robot Building assumes you understand the basics and have built at least one robot from a kit. The book delves into some of the common problems that face robot builders working on more complex robots built entirely from scratch.

The book focuses primarily on hardware issues such as machining metal parts, connecting wheels to motors, controlling motors, and building robot power supplies, briefly covering microcontrollers and sensors as well. This book provides far more detail on the hardware aspects of robot building than any other I have seen to date and is worth picking up if you want to learn more about hardware.

If you’ve browsed the table of contents above, you may wonder why four chapters of the book are spent on connecting wheels to motors. To quote David, “Until people actually try to build a robot themselves, they don’t realize that one of the more difficult tasks is finding a precise and reliable way to connect a motor to a wheel”. Speaking as someone who is primarily a software hacker, I can certainly vouch for the difficulty of solving seemingly simple hardware problems like mounting wheels, especially without proper tools or experience. The book offers several solutions and describes each in a detailed, step-by-step way with plenty of diagrams and photos.

I particularly liked this book’s promotion of standard SI (metric) units, which are used everywhere else in the world, instead of the medieval system still favored in the US. So you won’t have to measure your robot’s speed in furlongs per fortnight while using this book!

The book also promotes the use of modular robotics. By creating drive modules, motor control modules, power modules, logic control modules, you can assemble your robot from the modules rather than having to build the entire robot as a single project. The modules you build can be improved or re-used to create other robots. The modules described in the book are used to create a robot, called Roundabout, that avoids walls and obstacles using IR sensors.

One convention adopted in the book may seem a bit strange at first. All the schematics in the book use a mix of normal schematic symbols for some components (e.g. capacitors, zener-diodes, transistors) but represent other components iconically (e.g. resistors, photo-diodes). This can be a bit confusing initially. The author explains his reasons early on for this and another exception to modern schematic technique, the old-style use of a “jog” to represent crossed wires that do not connect. David’s experience is that beginners find these wiring diagrams easier to understand, hobby robot builders often prefer them to formal schematics, and he believes his diagrams reduce the chance of mistakes. It’s really a minor issue and experienced builders used to contemporary schematics should be able to adapt easily enough.

Overall, the book provides lots of practical information to help the reader over the difficult areas of building a homebrew robot. Recommended!