Here is my first attempt at building a hobby robot. I'm using an Octobot II platform from Budget Robotics. The MCU is a PICAXE 090 experimentor's board with a PICAXE 28X1 chip.
The Octabot II platform uses 2 R/C servos that have been modified for continuous rotation.
There is a Parrallax Ping))) ultrasonic sensor mounted on the turret. The turret has 180 degrees of movement via an unmodified R/C servo.
I've installed an IR receiver so that I can operate it by remote control, or let it operate autonomously.
I'm at the point now where I have all of the hardware operational, and am in the process of debugging my code.
Thank you everyone at LMR for the inspiration and advice.
Videos are to be uploaded on Videos are to be uploaded on Youtube or google or similar, and then embedded in here. Edit your project and see the options for more. Comon, we wanna see
I’ve never uploaded anything to Youtube, and do not even have an account. I’ll get there before long, but for now I’m concentrating on making the bot work. I have limited “hobby time”, and I’d like my first video to be something that I’m happy to bring to “show and tell”. After that, I’ll show the failed first attempt. I promise.
I’ve learned at lot in this effort. One mistake that I made was to use 4 D cell batteries for my servo power. (I was trying to save myself from constantly changing batteries). Even though they are mounted “almost centered” over the axles, the weight on the rear caster seems to be too much for it to move freely. As a result, it’s impossible to move in anything close to a straight line on carpet. (It works O.K. on tile though.) I guess I’ll go with 4 AA’s instead.
nifty, same chassis nifty, that’s the same chassis I used for Igor! I mounted a 8xAA 12v battery underneath the lowest deck, between the drive servos. It’s convenient, but honestly Igor does not drive straight either, even though the weight is all on the drive wheels. My impression is that it’s more the fault of the caster wheel used on this chassis. if I tap the caster straight while he’s in motion he drives straight, but it has too much friction to straighten out by itself
One Idea I have to to give the caster a little more traction by putting a tire of some sort on the wheel, then maybe it will straighten itself out. I looked at my local home depot for a better quality caster of the same size and had no luck. THe ones they had were even worse than the one it came with. Still looking for something that will work as a tire, if that works ill try to let you know…
If you’re having problems with friction, especially things like castors, use a minute amount of high quality machine oil to lubricate all the moving parts. An even better choice, so good it’s practically a legend in many countries, is WD40 which is a spray on lubricant.
It’s also worth getting a tube of molybdenum grease for the insides of gear boxes. You should be able to buy it from just about anywhere that sells servomotors or Tamiya gear (in fact the brand that I’m using is from Tamiya).
Be aware that once you start using lubricants, you’ll be wanting to keep your floors clean because any traces of dirt and dust will stick to the lubricated parts.
Thanks for the WD40 advice. I’m very familiar with WD40. Tried it in fact, with little or no improvement. It’s just a small, cheap caster, with no swivel bearing.
I may try helping it out with a little lapping compound when I get a chance. I’m hoping that changing from D cells to AA cells wil help in the meantime.
omniwheel A free running omniwheel makes a very good castor. Just put it on a fixed axle so it can turn and the rollers around its perimeter take care of the sideways motion.
I’ve thought about that, but haven’t tried it yet.
I have a 40 mm double row omni-wheel that would “just” barely fit. I’ll have to fab up a bracket of some kind first, but that’s do-able.
I do not doubt that it would work very well on a hard surface, but I do wonder about how it’d work on carpet. Heck, the castor works fine on a hard surface, but 95% of my home is carpeted.
Hmmm… I guess that it would never be “sideways” to the carpet during forward travel, so it shouldn’t “steer” the 'bot wrong, but I wonder how it’d work when I WANT the 'bot to spin around. (like in a Zero Turn Radius move).
Have you ever tried using an omniwheel as a castor on carpet?
Yeah, I was struggling with why it would sometimes curve to the left, and then later to the right unitl I noticed that the caster was not properly centering itself. I’d tweak speeds, thought I had them matched, and later the symptom would be completely different. I went thru thru same caster tapping experiment before I realized that it was the caster causing the problem.
I also looked for a better caster, with no luck so far. I found a ball caster that had promise, but it was way too tall.
I like the idea of mounting the batteries under the lower deck. It wasn’t an option with the 4 pack of D cells. It’d sure make changing batteries easier.
not so far I haven’t used an omniwheel as a castor myself, but I’ve seen photos and videos of small robots where it is done. You should be able to verify very easily for yourself if it will work on your carpet by putting your omniwheels on a suitable axle and holding them there while you drag them sideways across your carpet. That way you’ll be able to tell if they will still move freely or not. I have the same kind of omniwheels as you I believe and mine work fine on my carpet.
Actually, I modded my octobot to use an RC airplane tail wheel, it rotates much smoother, and doesn’t bind up like the stock caster does. The fit was a little odd tho, cuz I got sort of a bigger one than I should have perhaps, it sorta hangs off the back, but all the same, works great!
The # 956 1" plastic ball caster is SO smooth, I have confidence that it will resolve my caster issue. ( It’s even smoother than my 70’s pickup lines were ). This caster changes directions as easily as I could back then.
No, it does not even up the robot, in fact it makes it worst. But I’m working on that.
The original Octabot II wheels are pretty big, 2 1/2 " ( approx. 62 mm ) in diameter.
The original crappy caster is about 42 mm tall.
The Pololu ball caster is about 27 mm tall.
Hmmm… I’m still thinking about this. I have some 40 mm omnirollers that I could replace the original wheels with, and that could make up a lot of the difference… Or I may keep the original wheels, and add 19 mm spacers to the ball caster.
