A robust all round robot at a very affordable price
Parallaxs new, bright red, S2 is designed to be a worthy successor to their original blue Scribbler Robot. Powered by Parallaxs Propeller chip, a multicore processor ideal for robotics, the opensource and user hackable S2 should have everyone from beginners to experienced users excited and experimenting right out of the box.
GOODBYE OLD BLUE
In December of 2009, Parallax, Inc. of Rocklin, California, posted an End of Life announcement for the original, $99, Scribbler Robot. The Scribbler got its name from a pen port that let it scribble with a SharpieÂ® marker as it moved. It included so many features for so little money that it was used in academic programs from elementary schools to universities. The last Scribblers were quickly sold and that quiet passing marked the end of the very successful, feature packed, BASIC Stamp 2 based, robot that sold over 10,000 units. How would Parallax follow such a great little robot? The answer is by making an almost completely compatible, but highly improved, Propeller based replacement the new S2.
GOALS FOR THE S2
The S2 was designed by many of the same folks who designed the original Scribbler. The team included Ben Wirz, of Element, Inc., Phil Pilgrim, of Bueno Systems, Parallaxs Asian manufacturing partners and the Parallax staff in Rocklin, Hong Kong and China.
Their main goals were the following:
1 Utilize the Propeller P8X32A-Q44 chip for true robotic multicore processing enabling a variety of robot tasks, sensors and drive routines to be compartmentalized into code objects and processor COGs
2 Provide backward-compatibility with the original Scribbler GUI (Graphical User Interface) Program Maker
3 Provide a wide-access hacker port with many I/Os and a substantial power supply
4 Remain compatible with existing third-party hardware designs, such as the Georgia Tech IPRE Fluke (See description below)
5 Improve the drive system with wheel encoder feedback and stronger motors to create a straight-steering robot
ROBUST AFFORDABLE PACKAGE
As you might imagine, the S2 shares many design features with the original Scribbler. The red S2 has a zero turning radius, differential drive delivered by two DC motors. The simple black wheels use O rings for tires and a plastic tail wheel provides a low friction pivot. One of the legitimate complaints about the blue Scribbler was the lack of wheel encoders. Matching the motors was difficult and this resulted in making the Scribbler difficult to drive in a straight line at times. There was a calibration feature in the Program Maker GUI, but without encoders, it was a bit hit or miss. New to the S2, per the stated goal, are wheel encoders which seamlessly track wheel position and keep the S2 running straight. This function is handled in the S2s code and will not be immediately apparent to a new user. It works amazingly well and there is great consistency of operation between S2s running the same code. Stalls are monitored on the S2 via the tail wheel (idler wheel) with an IR emitter/receiver. A close look at the tail wheel reveals the oddly spaced holes used for this purpose.
The S2 has three forward and upward looking photo transistor light detectors, two forward facing, and side mounted infrared (IR) obstacle detection emitters with a single center mounted receiver and two downward pointing IR line detector pairs for line following or reading bar codes. The original Scribblers line following IR sensors were very sensitive to the properties of black line used. This frustrated some users who could not get consistent results, though when the proper ink was used the sensors functioned well. The S2 provides sensitivity adjustment via software that addresses this problem.
The S2s hacker port is also improved and provides regulated power, ground and I/O pin connections for more advanced hacking. It can supply 1A of current, so it is easy to add devices like servos, wireless cameras, and other hardware having a significant power draw. A quick search of the Parallax Forums will lead you some interesting hacks already underway.
The S2 is powered by 6 – AA cells, which may be standard 1.5 volt or 1.2 volt NiMH rechargeable type. The robot is housed in a tough, molded, bright red plastic case that includes a speaker, microphone, power switch, reset button, a power indicator LED, three user programmable LEDs, a serial programming port and the pen port.
Many basic features of the Scribbler are improved on the S2 and new features abound. The speaker is amplified and volume is adjustable in the software. The microphone is a completely new feature and allows the possibility of voice command and communication between robots. The three, bi-color, user programmable, indicator LEDs are noticeably brighter. These can be set off, red, green, blinking either color or some combination of red and green to provide some variations in shade. The bright blue power LED serves as a power-on indicator as well as displaying the battery condition. When bright blue – the battery is fully charged, when dim blue the battery is partially charged and when blinking blue the cells are low should be replaced. The blue LED is also user programmable. The reset button can be programmed for user input and the number of button presses can be monitored via the LEDs (this function can be seen in the default demonstration program and the code easily adapted to the users programs).
A Serial Cable or USB to Serial Adapter and USB A to Mini B cable is required to program the Scribbler 2. The S2 comes with neither cable. The DB-9 cable is available for $3.99 (for those with a computer that has a serial port!) and the USB to serial adapter and USB cable can be had for $16.99. New users need to be sure to order one or the other. Those who have some experience with the Scribbler have these cables and adaptors already – which is the rationale behind selling them separately. It seems that Parallax worked very hard to keep the S2 at a very reasonable price. The S2 without a cable sells for $129.99 or with the USB adapter and cable included for $139.99 (offering a small savings). The use of the serial programming port allowed backward- compatibility with hardware accessories designed for the Scribbler, like the IPRE Fluke (one of the stated design goals). For more information about the IPRE Fluke, see below.
Toward the end of its life, the Scribblers consumer product safety commission (CPSC) testing, which allowed the Scribbler to be labeled for use by children 8 and up, was dropped because it had expired and to retest the product at the end of its life was considered impractical. The last Scribblers were labeled for users 14 and up. The S2 is listed 14 and up as well. This change allowed the use of the amplified speaker and stronger motors. The S2, in my opinion, is still very appropriate for clubs, classes or in homes with young users working with adult supervision.
PROGRAMMING AND SOFTWARE
The S2 is ready to go out of the box with no assembly required – other than installing the AA cells! Preloaded are eight demonstration programs that are ready to run. This provides instant gratification to new and inexperienced users. The demo programs include: light sensing, light seeking, object detection, object avoidance, line sensing, line following, scribbling a figure 8 and a square, (with amazing precision I might add!) See the illustrations and the ambulance behavior where the S2 runs around with flashing lights and sounds a siren noise at the URL indicated with the QuickResponse Barcode at top. These demo modes can be set by using the light sensors or by pressing the reset button. All of these features are described in a nice start-up guide book which is included.
The S2s default or demonstration program was written by Ben Wirz, of Element, Inc. It provides a wonderful study for users wishing to understand Spin and has a great diagnostic program that can be used to test the S2 using Parallaxs Serial Terminal Software for feedback.
But the real fun comes when the user begins to write his or her own code. The original Scribbler was user programmed with the very powerful and simple Program Maker GUI or with the BASIC Stamp Editor. Users could toggle between the two easily and see how the graphic program related directly to the PBASIC code. This was a truly impressive feature and made the robot accessible to anyone and a great learning tool. Again this feature is retained and improved. The S2s Program Maker GUI allows new users to continue to program graphically. Toggling between the Program Marker and the Propeller Tool (the Propellers IDE), lets a user see the code in Spin, the language of the Propeller Chip. In addition, the Program Maker for the S2 will run programs written on the Program Maker for the Scribbler. This backward-compatibility is great for Scribbler users who have a library GUI programs already written. It is a simple as opening the old file with the S2 Program Maker. All of this is the work of Phil Pilgrim of Bueno Systems and the folks at Parallax. It is one of the best features of the Scribbler Robot Family and is a fantastic learning tool.
The GUI help (accessed from within the GUI) is well written and looks and works very much like the original. But the hidden gem is the S2 Object itself and the very detailed help information provided. The link to this information is found at the very bottom of the left hand sidebar on the GUI help page. Clicking this link opens a world of information about how the S2 Object works. Spin uses objects (basic sections of program code that perform specific functions) that can be combined to form larger programs. The S2 object provides code – available to use and modify that apply to all the S2s various capabilities. This also the work of Phil Pilgrim and is a lesson in programming the S2 in Spin. The value of all this information and example code is hard to explain until youve spent some time studying it. It will be a gateway for many users.
GIVING THE S2 A SPIN
After playing with the S2 demo modes and trying some new and old GUI programs on the S2, I decided to program the robot in Spin. I was familiar with the Propeller, but not with how the S2 Object worked or how it used the S2s specific features. Armed with only the S2 Object help, I set out test the precision of the encoders by scribbling the word Robot, as in Robot Magazine. The help provides examples of the each method (code piece for a specific function) in the S2 Object. I found the Draw method, where there is an example for drawing a capital letter D. By studying that bit of code, modifying it and using some old fashioned trial and error I was scribbling Robot in no time! The only problem was that the letters slowly turned uphill. So I achieved (a special save feature that includes all of the objects used in the final code and saves them together to share with others) and emailed it to Phil Pilgrim. His S2 responded exactly the same. So, he returned a photo and some code which modified the Default Wheel Calibration.
After that slight calibration adjustment in the code, it worked perfectly, as you can see in the picture to the left. Again, the fact that my code produced the exact same conditions on Phils S2, shows the consistency of how these robots perform.
All sorts of documentation including the Start-up Guide, code examples for the Scribbler, line following sheets, electrical diagrams, schematics, photos of the robots innards, along with the Program Maker GUI, the Propeller Tool, Default Program and S2 Object and Serial Terminal Software, The Propeller Manual in pdf are available to download free from Parallaxs website. Parallaxs Propeller Object exchange is library of code written for the Propeller and is open for all to use under a sharing license. It is divided into neat sections for quick reference. The S2 is also part of Parallaxs new open-source design family. That means that customers are free to download S2s PCB layouts, bill of materials, SolidWorks mold designs, mechanical assembly, GUI Perl source code and all the Propeller code. Customers may use any or all of the S2s design for their own commercial products. In addition, Parallaxs user Forums are legendary for their friendly and helpful members who are ready to aid budding roboticists. Already, the Forum community is sharing code and posting hacks along with videos of the S2 in action.
The S2 can also be programmed in PASM (Propeller Assembly Language) and now in variation of PBASIC using PropBASIC. Forum member Bean, a.k.a., Terry Hitt, developed PropBASIC, which is a complier that takes code written in BASIC and produces code in PASM. This compiled code is fast and efficient and may provide an easy entrance to the S2 for programmers used to working in PBASIC.
As a robotics educator, I have used the original Scribbler in clubs and in the classroom with elementary, middle school and high school students. All of them loved it and it gave them all a very friendly introduction to what a robot is and how much fun you can have solving problems. In a demonstration of the new S2 prior to its release, the members of the GatorBots, my schools robotics club, were very impressed and eager to place their orders for the new robot.
About the IPRE Fluke
A very popular third party product was developed by the Institute for Personal Robotics (IPRE) – a joint effort between Georgia Tech and Bryn Mawr College and sponsored by Microsoft Research. The IPRE Fluke attached to the Scribblers serial programming port and featured a camera, three IR emitters, one IR receiver, and a Bluetooth transmitter and receiver. It was directly powered through the programming port. The Fluke was developed for use with the Scribbler and is used to teach programming in computer science departments. The direct feedback of seeing the robot respond to the programming allowed students to learn more easily and made the learning fun. The Fluke made the Scribbler a slave to Python programming running on a PC that was transmitted via Bluetooth through the Fluke to the Scribbler. Sensor and Camera information was transmitted back to the PC the same way. An excellent textbook and software accompanies the Fluke and all is available from Georgia Robotics, Inc. through Amazon.com. Backward-compatibility with the IPRE Fluke was a stated design goal of the S2.
What is there to criticize? Almost nothing – though it might be nice to have direct programming via USB cable (without the adapter). Even this choice was made to allow the continued use of third party products. It is an example of the sort of customer care that Parallax is known for. Exterior access to the hacker port might be nice, but you cant really call it hacking if you dont have to take something apart!
Scribbler owners will find the transition to the S2 very easy. Whats more, all the flaws of the Scribbler have been addressed in the new bot. New users will find the robot immediately accessible because it is fully assembled and ready to go. They will love the GUI Program Maker and can move to Spin as their interest grows. Experienced users will find endless possibilities to experiment with hardware and software. After that the hacking will surely begin¦
It looks like Parallax has a red hot successor for the Scribbler. The Scribbler legacy will certainly continue, and with around four thousand S2s in stock and ready to ship, it looks like Parallax is counting on it. Happy scribbling!
i. The Reverend Whit Stodghill is an Episcopal Priest, teacher, amateur roboticist and a robotics educator. He lives with his wife and children in Northeast Louisiana.
Institute for Personal Robotics
Propeller Object Exchange Library
Terry Hitts (Bean) PropBASIC Thread
Words by T. Whitfield Stodghill