Wheel size poll

I seem to recall having asked this before but I searched and did not find, so here we go. What size wheels did you use this year on your robot? Please round to the nearest size. If you care to elaborate on anything, feel free to post below.

862 used 2 8" Skyway and 2 8" IFI wheels (2" wide).

2 8" AM Omni (trick wheels) for the front.
2 8" 2" wide IFI wheels for the back.

We used 8" so we’d have enough ground clearance for that ramp.

Two 8" IFI wheels combined with four 8" Skyways (used for cost purposes).

Four of these. Effective diameter 4.8 inch.

We used these http://www.andymark.biz/products/omni/6in-omni/6-omni-pic.jpg

6" o.d. wheel, with 14 rollers
Weight 0.75 pounds
Hardware Body Material is molded black glass-filled polycarbonate plastic
1.125" id bore (sized for 1/2" id bearing)

Worked well at the Lone Star regional. Heavy hitting and pushing on Archi in Atlanta resulted in at least four wheels cracking apart from hard hits. AM reports that they are going to look at a softer plastic that can bend but not break verses the strong yet brittle material used this year. It made for a very cool holonomic drive with four of these mounted at 45 degrees. :cool:

Looking into mecanum options for next year with hopes of someday being able to crab steer. :yikes:

8" IFI traction wheels x 4

As a rule of thumb, bigger wheels mean you can traverse more uneven terrain. Yes, this can be acheived other ways, but bigger wheels tend to save weight and complexity (think of the 2004 stairs for a perfect example).
Smallers wheels are lighter and take up less space (duh!), which leaves more space/weight for the rest of your robot.

Simple trade-off.

Maybe not that simple.

Assuming equal motors, faster robots don’t push as hard. So no matter what wheel diameter you choose, you still have the basic speed vs. force trade-off to consider. You find your own optimum solution by selecting your gear ratio (or ratios in the case of a shifting system) and your wheels.

8" IFI traction wheels will need about twice the gear ratio that 4" IFI traction wheels need, to get to the same speed and force. If your speed reduction system gets larger or heavier, or less efficient, because of the higher ratio, then you’ll need to consider that trade-off against the benefit of larger wheels.

As always, the right answer depends on the game.

I was assuming that you’d adjust the drive shaft rpm to match speeds, as I was purely comparing wheels, not entire drivetrains. Yes, wheels essentially act as the final gearing on the shaft, and you must adjust the shafts rpm to match your desired speed/torque. But you have to do that no matter what wheel size you chose.

6" wheels all around. 4 skyway pneumatic tires, one on each corner of the robot and 2 A/M traction wheels. 6 wheel drive.

We actually used tracks but one of the reasons is to give more stability. Large wheels reduce stance. Points of contact are closer to the outer edges of the robot with smaller wheels making it less likel to tip. The “wheels” we use with the track are about 3 inches.

We used four 6" AndyMark plastic omniwheels (like those in Andrew Schuetze’s picture). We only had one break, on our practice robot right before Nationals. We were in a heated battle with 469’s practice robot at their field, and we got jammed up against the ramp and broke off one roller. Other than that, they worked great. A perfect balance of price and performance, IMO.

On a side note, in my experience, 6" wheels have usually been the “sweet spot” for most games that didn’t involve large variations in terrain. They usually seem to be about the right balance of speed and power, without requiring excessive gear reduction. Also, I’ve used bigger wheels before, and they tend to take up too much space, and can sometimes make for awkward turning. They’re great for games with ramps and stairs, but for a flat-field game, I always choose 6".

Four 6" custom aluminum wheels with Nitrile tread, 3/4" width. Check them out.

Last year custom wheels with conveyor belt tread ruled the field. This year cheaper, simpler IFI and AM wheels ruled the field with their extremely wide tread (1" and over). This year 604 got pushed around because so many people had these wheels.

Darn IFI and AndyMark for making quality products! :slight_smile:

Where do you guys get wheels that are easy to machine out like in the post above. I’m looking for some plain 4" wheels that i can machine out some of it and im not having any luck. Any rocomendations or anything to search for? Thanks.

Sorry A little off topic there, but this year my team used 6" AM omnis and 6"/1.5" Ifi’s.

6x 8" Skyway non-pneumatic wheels (KOP) ground flat with SBR Roughtop inclined conveyor belting from McMaster-Carr on them, attached with small wood screws. We ended up using ginormous 54-tooth AndyMark aluminum sprockets on them. Next year, I’d really like to downsize to 6", (Somewhere I have math that backs up what Jeff said about those being a sweet spot, at least in terms of gearing) although one of the mentors wants bigger wheels. (I really have no clue why)

We used 6" Skyway wheels from the Kit, turned down to 5.75", in a 6WD arrangement with custom-built omniwheels at the corners. This was all attached to the standard kitbot gearing of 17:1 and performed respectably. I wouldn’t hesitate to use the setup again.