Let's Make Robots!

Octabot II

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.

Duane S

Wilson, NC  USA


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Hey, what are the size of those wheels? When you add the caster, did it even out the robot?

Hello! I love robots and video games! Check out my blog www.pariahs-guild.com

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.

I'll post again later, when I figure it out.

Duane S

Wilson, North Carolina  USA

Can,t wait to see the video...

I've discovered that Pololu carries several ball casters which could resolve the caster problem.

I may order a couple different ones to experiment with.

PSR_177, you've got to wait until I've got the 'bot working properly before I do a video.  :( 

I'm still concentrating on getting my code working like I want it to.

Duane S

Wilson, North Carolina  USA

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! 



If the ball casters that I ordered from Pololu don't work out, I'll try that.  Thank you. 

Duane S

Wilson, North Carolina  USA

My Pololu order arrived today.  That was quick ! 

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.  :) 

Duane S

Wilson, North Carolina  USA

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...



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.

Thanks !

Duane S

Wilson, NC  USA

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.

Hope this helps.