Older blog entries for svo (starting at number 2)

9 Sep 2005 (updated 9 Sep 2005 at 10:46 UTC) »

smee gain..

Funny, I just discovered that there is (or was??) a robot football team based in the university I graduated from.

It's amazing that they exist in total obscurity. Here's one of a few news articles regarding their success in the long gone 2003. I tried to search for at least some info regarding them and found nothing but news articles.

One would expect higher level of tech-awareness from a winning robot-building team. At least a simple text-only site with contact information would be sufficient. Come on people, come out of the hole, we could benefit from each other.

At least I could :)

Also, there's another robot building community, which is pretty sparse though. Some projects listed are not even robots, more like heavyweight chassis constructions. Interesting nevertheless, check them out (the leftmost bold-font column starting with ATMEL... links to various user projects, some active, some from the distant past).

Re: icechip's accelerometer tutorial - that's a great one! Thank you for sharing. BTW, I see that most articles and reviews somehow miss Motorola/Freescale family of MEMS accelerometers. This may vary with supplier, but here I could buy their MMA6260Q (dual-axis, +/- 1.5G) for about 10e. That's at least twice cheaper than similar devices from Analog. The outputs of MMA6260 are voltages proportional to acceleration (or axis angle relative to g, if in g-sensing mode), which may happen to be very convenient if there's a multi-channel ADC on board already. I could whip up a quick description of my application just in case anyone's interested.

Assembled Akipaki again last night. The new construction is much sturdier and easier to disassemble/assemble than previous duct-tape-and-wire one. Pics are on the project page.

Decided to think about batteries later and focus on the PID control loop instead, while using external power. The RC servos seem to brilliantly withstand +12V without much trouble. The current was limited during the test though, so I'm still not sure yet. But anyway it's very nice to see that L6204 bridge is not heating, fully lobotomized servos spin and the controller is getting its +5V well refined and without spikes.

I wonder why it's next to impossible to buy raw gearhead motors, at least here? I have to buy a servo and rip it apart. Weird. Don't RC models of some kind need motors too?

Now I can get back to the firmware. That's the part I've been avoiding for quite a while.


The reason is the crippled PIC16 architecture. Strange use of flags coupled with anti-intuitive skip-instead-of-branch conditionals make arithmetics a little complicated. And those banks.. did they really have to spread all registers across all 4 available banks? Could not they just stay in one bank? The code on a multipage PIC (like the 16F873A i'm using) consists mostly of BANKSEL instructions, each of which is translating into 2 bit set instructions.. And since it's barely possible to know which bank was selected beforehand, it makes it 3 cycles per instruction (user register file is banked too), so where's the advantage of RISC??? Microchip, tell me? It's great that I haven't yet crossed the first program page boundary - the day when my code spans across 2 pages is the day of doom - all calls would have to become long-calls. And it's not really surprising that there's not a single decent C compiler for this abomination of computing, let alone freeware one.

The only thing that's great about PIC's is documentation though. I guess that's how they get people hooked. At least that's how it happened to me - first one's free.



Currently my 2-wheeler is a disassembled set of parts and boards (which used to be assembled once but had too much problems that screamed for hardware solution).

Originally I wanted to control RC servos modified for continuous rotation, but this proved to be a very bad idea. Balancing works, but overshooting in control is inevitable and it's nearly impossible to implement fine control. Basically I have "full throttle back" and "full throttle forth", without anything in between. Thus i decided to build another board with H-bridges that would replace RC servo electronics. With it I can implement PID control of the motors.

The real problem #1 now is the power though. The logic board needs good and stable +5V (well, more than +4V anyway, the stability is more important that absolute value). The motors can run at +5, but the H-bridge chip I'm using needs about +7..+8V or more to boot.

It looks like having 2x 4-piece AA battery holders onboard is inevitable. Thus I could get 9.6V when using rechargeables. Any ideas regarding power/batteries are welcome! And just out of couriousity, for how long a typical "standard RC servo" would stand 10V DC? 10V with 50% duty cycle?

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