New lower price for Axon II ($78) and Axon Mote ($58).
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> Cesar wrote> Thanx Peter, for that link. I've seen those robots, I> just didn't know the names. They look like fun robots.They're advertised in quite a lot of the e-shops. I don't know how many arebeing sold though - I only get royalties at the end of each year. I suspectit's not as many as I would like and certainly not enough to pay for thedevelopment time. Yes, they _ought_ to be fun robots. I designed them for children, newbiesand people who buy things in "gadget shops" and throw them away after amonth. They have a very simple programming language that (I hope) anyonecan use immediately just by clicking buttons but that allows full use ofthe various sensors. They're designed to use very few, very cheapcomponents and they're produced at very reasonable prices in China. So they ought to be half the price of any other robot you can buy. Why thenare they so overpriced? I could rant for hours about the iniquities ofretailers. Am I advertising here? Not really. I'm saying I don't think they're goodvalue for money. Buy some components and built your own from scratch. Maybethe same gripe applies to any other robot you can buy.The only retailer who has understood the philosophy is Rapid who sellBrainibots for about £6.75 ($13) if you buy an "educational pack" of 20.They're used by educators who run "introduction to electronics/robotics"aftenoons and the like. $13 is an excellent price. But you try buying aBrainibot from any other retailer for less than $45.Someone is making money but it's not me. And don't get me started on thebully-boy tactics of the chain stores ...What I have enjoyed is trying to understand what makes a good small robotprogramming language. It's a deceptively difficult problem. You have arobot with some subset of: two or three motors, antennae, one or two IRobstacles detectors, one or two light-level sensors, a speaker, a linefollower, a microphone and a time-out timer. The processor has just 128byes EEPROM to hold the user's program. What's the best programminglanguage? It sure isn't Basic or C.My "target" program is something like: head towards light; if you detect anobstacle, reverse away from it; if, after 1 min, the light is no brighter,reverse away and spin around looking for the brightest light then startagain. Or: follow the wall on the left until you meet a wall in front; thenturn 90deg right and head towards the light until you hear a loud noisethen stop.That's the sort of complexity of program that schoolchildren can attempt.But in 128 bytes of user memory? What should the instruction word size be? For the Programmable Brainibot, Ichose 4-bits (two instructions per byte but some instructions are 8-bit).For the other robots, it's 5-bits (three instructions per two bytes). What control structures should it have? Each robot has turned out differentas my ideas have changed. The Brainibot uses a traditional block-structuredlanguage with If-Then-Else, While, For and Begin-End but no variables. ButI found it was hard to write useful programs in the limited user-memory -you need too many if-sensor-then blocks. The Picobotz and Quadrabotz haveif/while/for/repeat plus procedures and "Events". Events are likeinterrupts. Each Event has a "guard" condition that triggers it. I thinkthat's how the original Mindstorm "stacks" worked. You need a lot fewerif-then's because you know that the bot will respond instantly to sensorinput. The Quadrabotz is the only robot to have variables. It has a traditionalstack-based instruction set compiled from a language close to Basic.Although that makes the language more "powerful" it takes more instructionsto do anything so you can get less into the 128 bytes. It's those sorts oftrade-offs that make this an interesting problem.I'm now re-designing the Brainibot (because the CdS cell is not RoHScompliant; it will have IR obstable sensors not antennae but should stillcost the same). I've got a new language that I'm very pleased with. It hasno traditional control structures: no if, while, for, gosub, variables,etc. It only has Events and "Behaviours": a Behaviour is a completelyseparate program that you can swap to. (As you can imagine, it's inspiredby subsumption.) At first sight, it seems odd to program using only"interrupts" but it works really well. Even complicated programs are small- I've not yet used more than 25% of my "user memory" and the robotresponds much more quickly.As I say, it's a deceptively difficult problem. I've not seen anyliterature on it and I haven't found anyone who is working on it. Doesanyone know of anything? If anyone wants to try designing their ownlanguage, just choose an instruction set (what's the optimum mix?) andstart writing programs. How complicated a program can you fit in 128 bytes?> If I remember right, I saw a walking robot liket that,> but much larger, made of PVC pipe.Great. Do you have a link.Peter
> What processor are you using now, if you don't mind me being nosy?For the Picobotz and Quadrabotz, the PIC16F627. I find that it has themixture of features that I need and is pretty cheap. I could go to thePIC16F628 if I needed more code space but that's not been neccessary sofar. I don't need an 8-bit ADC - the 4-bit one in the PIC16F627 is fine formeasuring the motor current in the Quadrabotz. For measuring light-level,I've found that a linear ADC can't give good resolution over the wholelight range of a typical room; you really need a logarithmic response. So Iuse the discharge time of a cap and then do a log/lin conversion.The original Brainibot uses a 12C508 or 12C509. That was the cheapest chipavailable at the time (8-pin flash PICs weren't around). It has the hugedisadvantage of no EEPROM which means that the user's program is held inRAM and is cleared when the PIC is turned off. Yuk. The new Brainibot usesa 12F629 which has 128 bytes of EEPROM for the user's program. Using 8-pin PICs is an enjoyable challenge. The new Brainibot uses just 5I/O pins to control two light-level sensors, two IR obstacle detectors, abeeper, serial comms to a PC and the the H-bridges for 2 motors. That's alot of multiplexing. It left an extra input pin so I have it as an"external" input for the customer to add their own sensor.I've designed robots with bigger chips but never persauded anyone toproduce them. Cost is everything. The new Brainibot's electronics and pcbcost around £3.50 in 100off. Presumably in China, they'd be half that.So far, the limit of 1024 instructions hasn't been a problem. The originalBrainibot was a bit of a squeeze but it has both comms from the PC (but notto it) and a built-in editor so you can "type" your program in via theantennae. The other robots can only be programmed from a PC so their codeis smaller.A larger EEPROM would be nice but I don't want the extra cost of anexternal chip. With a good interpreted language you can do a fair amountwith 128 bytes.Comms with a PC can be tricky. To reduce costs, I always use the PIC'sinternal oscillator but, in theory, it isn't quite good enough for reliablecomms. RS232 requires the clock to be accurate to about 5%. But a PIC'sinternal oscillator can only manage 9%. So I use a system of long and shortpulses: the PC sends $80, $F0 or $FE via RS232 to send "Start", "1" and "0"bits. Self-clocking codes like that are more tolerant of noise andclock-frequency mismatches. But maybe it's not necessary. The Picobotz usesstraight RS232 and no-one has ever returned a Picobotz because the commsdoesn't work. Maybe Microchip's worst-case figures are unduly pessimistic.In future, I might look at using the 16C745 USB PIC. Adding USB is a "big"expense in terms of the socket, cable, etc. but serial ports are bcomingmore scarce. I'll also have to learn how to do USB comms ports. I don'twant the cost of a separate USB-serial convertor chip, especally as a PICcan already do it. I've already done USB-keyboard on a 16C745 butUSB-keyboard has the advantage that the drivers are already built into XP. I don't understand the driver situation for USB comms ports. Is the driveralready in XP? Or do I have to write a PC driver? I think it's built-in:serial comms, like HID, uses a standard protocol. But, if it's built-in,why do USB-serial convertors come with a CD? Does XP just need an INF fileto describe the connection? Does anyone here know? Has anyone here done aUSB comms port on a 16C745?Peter
> If I remember right, I saw a walking robot liket that,> but much larger, made of PVC pipe.