Everyone knows that you should never go to the grocery store when you are hungry. If you fail to follow that truism, then more often than not you'll end up coming home with bag after bag of stuff that looked good enough to eat as you pushed your cart down the aisles. I should have kept that in mind when we visited the San Francisco area just before Christmas...
As it turned out, we flew into SFO late Monday morning and were shuttled up to our hotel near Union Square. We caught a quick bite to eat for a late lunch, then I took my wife around to some of the department stores. It was after 3:00 pm when we finished, and I knew that the Hobby Engineering store in Milbrae, miles away, would be closing that evening at 5:00 pm. Still, the rest of our visit schedule was already packed to the brim, and I wasn't going to have another chance to go shopping for robot or electronics stuff.
So, I took a chance that I could make it there before closing time, and started off on my journey. It was amazingly simple and straight forward. I walked down the hill from the hotel for a few blocks, then ducked into the local BART station. Luckily I only had to wait for about 10 minutes until the next train arrived for SFO/Milbrae. The only surprise during the BART ride was when the train pulled into the SFO terminal and just sat there for a while. I kept peeking at my watch, but eventually the doors closed, the train reversed itself out of the station, and headed for the end of the line. It arrived at the Milbrae station right around 4:20 pm - which didn't give me much time, but still might be workable.
Then I ran into a major problem. The signage at the BART/CalTrain station, like almost all stations, seems to assume that everyone already knows where to go... At first there didn't seem to be any way out of the station! All the signs pointed to either a BART or CalTrain platform, when all I wanted to do is exit the station on the El Camino side. And there didn't seem to be any station staff in sight. After a minute or so of confusion, I decided to take the escalator down to the CalTrain platform to see if I could find anyone to ask. Once I got down to the platform level it was obvious that the CalTrain platform is completely open. All I had to do was walk across the street and I was out of the station. Simple, but not obvious to someone who has never been there before.
From the station it was only about a block up to El Camino. About that time I realized that I had spent most of my US cash earlier in the day, so I stopped at a bank ATM to withdraw some spending money. From there it was less than a 3 minute walk to the Hobby Engineering store. My watch, which is often wrong, said it was going on 4:42 pm...
I made it! I have to say that I wasn't disappointed at all. I was like a kid in a candy store. All the robotics stuff I had seen and drooled over on the Internet was right there, ready and waiting for me to pick it up, play with it, and debate over which goodies I just couldn't live with out. And, the clock was running. I only had about 15 minutes to look at everything, pick out what I wanted, and pay for it...
I found IR photo-sensor kits that would give my robot some 'eyes', whisker feelers so that it could sense and avoid running into walls, a magnetic compass module, a 2 axis accelerometer module, servo wheel encoders, assortment packs of resistors, ... the list goes on and on. There was a whole bookcase full of books on robotics and electronics experimentation, and display cases with lots of different robot kits. Under other circumstances I could have spent a whole afternoon there just picking through the parts. I guess the fact that my time was so short ended up saving me quite a bit of money in the end. I rapidly put together my 'shopping cart' of stuff, and asked the store clerk to tell me what the damages were going to be.
She was extremely helpful and knowledgeable. Unfortunately there was one item in my cart, I think it was the wheel encoders, that wouldn't come up on her computer.... I had visions of her asking me to come back tomorrow.... Then, much to my surprise, she asked me to wait for a moment then reached up and pounded on the wall right behind her!
About two minutes later, Al, the owner of Hobby Engineering, came rushing through the front door of the store to help. He had been back in the warehouse (behind the wall) preparing some mail order shipments, and didn't have a cell phone with him - which is why she resorted to the bang on the wall message technique. Al quickly updated the database, completed my order, and stuck around for a friendly chat. It was great to meet him face to face after having exchanged emails from half way across the world.
I'm happy to report that the service and support I've received from Hobby Engineering has been excellent - both via mail order, and in person at their Milbrae store. I highly recommend stopping by their store if you happen to be in the area.
Here's a link to an excellent article covering the equations and model for steering a robot. It requires an initial familiarity with calculus, but goes to great lengths to keep the examples and equations simple and easy to follow.
"The differential steering system is familiar from ordinary life because it is the arrangement used in a wheelchair. Two wheels mounted on a single axis are independently powered and controlled, thus providing both drive and steering. Additional passive wheels (usually casters) are provided for support. Most of us have an intuitive grasp of the basic behavior of a differential steering system. If both drive wheels turn in tandem, the robot moves in a straight line. If one wheel turns faster than the other, the robot follows a curved path. If the wheels turn at equal speed, but in opposite directions, the robot pivots. So steering the robot is just a matter of varying the speeds of the drive wheels. But how exactly do we choose the speeds so that the robot will move where we want it to go? In these notes, we will try to refine this intuitive understanding into mathematical expressions that can be used for implementing robot control software."
I firmly believe that there no totally new and unique problems that present themselves. Every problem we face has been faced by others before us, and they have met with various levels of success and failure. That being said, it would be beneficial to invest a little time and effort to learn what they learned - to profit from their success, and avoid repeating their mistakes.
With that in mind, some research into robot drive and positioning problems uncovered a wonderful 1996 report entitled "Where am I?" - Systems and Methods for Mobile Robot Positioning. It includes 282 pages, 200 illustrations, and 400 references. Best of all - it's totally free and available online in pdf format.
Link: Where am I?.
Sometimes you start off looking for one thing, and totally by accident or extreme good fortune you end up finding something entirely different. That's exactly what happened to me this morning. As I mentioned in some previous posts, I bought the original components/kit for my first robot from Hobby Engineering in California. I was cleaning up my home office to make room to start my robotic adventure, and after a couple of hours took a short break for a diet coke and a quick surf of the internet. I decided to see what other websites mention Hobby Engineering. While I was scanning down through the Google results I noticed this entry-
The Hobby Electronics from Japan - Menu
Updated on 7 November 2004. Welcome to the Hobby of Electronic Circuit Engineering. If you are in the USA or if this site is not ...
Of course, the 'Japan' word immediately drew my attention and I had to click on the link. What I found was totally amazing. "The Hobby Electronics from Japan" website is a personal project of Seiichi Inoue, a systems engineer that lives in the Tokyo area. His site includes a wealth of information on microcontrollers, circuit design, applications, software, website design, and even some pages covering language. That wouldn't be too unusual, except for the fact that he also publishes his website in English, and has a mirror site in the U.S.
I've lived in Japan, off and on, for over twenty years, and I've always been addicted to all things electronic. My idea of a great Saturday field trip is to spend the whole day exploring all the shops in the Akihabara area, poking around in parts bins, trying out the latest gadgets, and meeting people with a similar addiction. That being said, my general approach to exploring Akihabara is totally random. There are some stores I always visit - like Laox Computer Kaikan, but usually I just wonder up and down the streets browsing as if I was touring a huge museum.
The result is that if you asked me where to buy something specific - like a transformer, resistor, or a particular brand item - I couldn't tell you. I could certainly go to Akihabara and find it for you, and I would enjoy the search immensely. But I couldn't give you the name and location of a specific store where you could locate what you need.
Inoue-san, on the other hand, seems to have documented everything! His site as detailed, clickable maps of the stores he frequents. Not only does he tell you what stores he shops at for different components, he also gives you a lot of background on the stores. In his writeup for a small arcade parts shop he mentions that you better use tweezers to pick up the small parts otherwise the shop owner will get angry.
The amount of detail is totally amazing. For example, under the station train tracks there is a two story electronic parts arcade whose origins date back to the black market right after World War II. It's jam packed, elbow to elbow, with tiny shops and frequently a crush of customers. The ceilings are so low that I have to duck my head. If you're in love with electronics, as I am, it's like a mini-version of hog heaven. But there is so much going on that after a while it all becomes chaos - at least to my simple brain. I quickly reach a state of sensory overload and forget where I saw what.
Inoue, bless his heart, has gone to the trouble of mapping it all out. His site has detailed maps showing each shop, what they specialize in, and the shop name.
If you plan on visiting Akihabara, and you're interested in electronics from an engineering perspective, you owe it to yourself to check out his site. I plan on printing out his maps and carrying them with me on my next trip to Akihabara. If you do stop by his site, make sure to use his contact form to tell him how much you like his site.