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View Full Version : Chatter Check out the wheels on this robot chassis.



Martin_H
09-12-2011, 03:35 PM
The wheels on it look like tractor wheels to me:

http://www.ebay.com/itm/360-SERVO-ROBOT-CHASSIS-METAL-CASTOR-STANDOFFS-ABS-PLATES-/250890367125?pt=LH_DefaultDomain_0&hash=item3a6a3b3095#ht_500wt_1203

The result is John Deere meets BOEbot.

erco
09-12-2011, 03:57 PM
YIKES. Whatever mobility gained by those giant tractor wheels is horribly undone by that hideous ball bearing caster. Too much friction, small diameter, affected by every bump it encounters. Never, never, never. Lawyers and those metal casters are most useful on the ocean floor.

Caster wheels need TLC to function properly, especially on small lightweight robots. Bigger is almost always better, low friction, and wide rubber tires are usually best for consistent operation.

@Sam-I-Am: Did I make it clear that I do not like small metal ball casters? Not in the rain, not on a train. Not in a box, not with a fox.

Well, maybe Megan Fox.

Ttailspin
09-12-2011, 05:02 PM
Fear not erco!!, for the end of Casters is nigh...
85014
Ok, Ok, sure, it has wire management issues, and it takes two hands to drive...
Just wait till I figure out what to do with those 10K pots hooked up to the MCP3202...
-Tommy

erco
09-12-2011, 05:30 PM
Molto interressante! Gotta see video of DAT.

Wood? How novel! :)

GordonMcComb
09-12-2011, 07:42 PM
Ball transfers are okay if the robot were heavier, but as it is, there's probably not enough weight on the transfer to make the ball spin, so it's effectively a heavy skid. Might as well just use a skid, like a plastic table leg runner or something. If you're going to add weight it might as well be for something useful.

The 1880's tractor wheels remind me of some Fischertechnik stuff. I wonder if that's where they're from.

-- Gordon

RobotWorkshop
09-12-2011, 08:06 PM
@Erco

You can get the ball transfers with a nylon ball that is quite a bit lighter. They cost quite a bit more than the standard steel ones.

I agree with Gordon that for Heavier robots they can work out quite well. I'm using them on both of the latest robots I built. On of them is almost as tall as I am! One huge advantage for me was the low clearance required for them. If I had to go with castors I would have had to mount them up inside the robot and make large holes in the bottom of the chassis for the castors to come through. Not good for the platforms I built. I still use castors for some robots but ball castors make better sense for others.

Don't rule out the use of ball castors until you've tried them out.

Robert

erco
09-12-2011, 08:55 PM
I speak mainly regarding dead reckoning on medium-sized robots, where large rubber wheel casters are minimally deflected by bumps, doorway thresholds and rug/carpet edges. That's no place for small diameter balls or wheels. If you're just moving randomly from PINGs, you can live with small rollers or even a blunt drawer pull, as the CBA robot does.

IF you call that living...! :)