This is a semi-improved version of the designs posted in these two threads:
It is simpler and smaller than the previous designs. It is very unlikely that my team will ever build it (we would better off learning how to make a WCD chassis) so I put it on GrabCad if anyone wants to take a closer look at it.
Wow this looks neat! My only concern is the CIM motors on the bottom. How will you wire them without the wires being crushed or the insulation melting from the heat of the motors?
I like the form factor a lot, but I’m seconding Ollien’s comment. Expanding it out by 3/4" or so would fix the problem.
The use of 1 wheel for 2 balls is very clever, but you might want to spring load the casters to keep contact with the wheels as they wear down. The issue of “drilling” into the ball with an un-moving wheel is still there, but maybe if you used thinner wheels and something like a metallic ball you might have better luck.
EDIT: What’s the FPS and weight?
I agree with the comment above about the wire spacing, however while were there, on the model posted to grabcad, it appears that the cims themselves are actually interfering with each other. The small round protrusion on the backs of the cims (~1in diameter) are going into the other cims by about 1/8in.
It’s like the decagon wheel, single billet chassis robot… but actually buildable. Props, looks pretty $@#$@#$@#$@# neat.
if someone actually builds this, i will hold you in awe forever
The weight of the robot (excepting the basketballs) is supported by the downward-facing ball casters. Basketballs are typically pressurized to 8psi, so assuming the robot weighs 100 lb, you would need to apply that force over 3+ square inches on each ball. As the casters are not that large, the basketball would significantly deform at this point to bear the load, interfering with the drive-ability (though obviating the need for springs). Deformation would get worse under acceleration. I would consider stiffer balls, perhaps like asid61’s suggestion of metal (or rubber over metal) ones, or at least larger load-bearing ball casters.
Edit: This would be even cooler as a kiwi; I think the forces would add up properly for rotation and translation, though less efficiently at the ball-carpet interface.
In either case, It appears that the inverse kinematic equations are to drive each wheel as though it were an omni, but in the opposite direction. Negative Killough/Mecanum for four-ball, negative kiwi for three-ball.
Could basketballs be replaced by a metalsphere, with some kind of coating for traction? Would a sphere like this work: http://www.kingmetals.com/Catalog/CatalogListing.aspx?CatalogId=c39&CatalogDetailId=204&NSM=Y
If not, how thick would 8-10 in diameter steel spheres need to be to support the weight of a ~100 lb robot?
I think that would be a better way to go. As GeeTwo pointed out, the deformation in the basketballs is going to cause major problems with the driving.
I think the best way to “coat” the basketballs would be to cut some type of grippy material into hexagons and pentagons and glue them on like the ones on a soccer ball.
As for the strength of those steel spheres, I have no idea; you probably have to do some force calculations. They are most likely strong enough; I have played with some garden decoration spheres and they would appear to be able to support this.
While gluing a dozen pentagons and a score of hexagons could possibly work, I was thinking of spraying pickup truck bed-liner or similar material onto a metallic spherical shell.
How would you do the calculations to determine if a hollow metal sphere is strong enough to support the weight of the robot?
I would put omnis instead of whatever wheels you currently have in because the friction is really going to deteorate both the ball(and also the omnis) whilst also causing slow movement