The World After VEXVEX Robotics posted this on it's Omni-Directional Wheels web page: "New for the 2019 FTC / FRC season, we've redesigned the 4” Omni-Directional Wheel to have a similar construction style to our 3.25” Omni-Directional Wheel. We decreased the number of rollers, to reinforce the body and improve the strength during sideways impacts. Don’t worry, it’s only a little wider than the current 4” Omni-Directional Wheel, and should still fit anywhere you were currently using a 4” wheel before". [emphasis mine]. Well, that's not quite true!!! The V1 Omni Wheel was 1.344 wide or 2.688 for the pair (not allowing for the spacer between them) while the V2 Omni Wheel is 1.53 wide or 3.06 for the pair (also not allowing for the spacer between them) and will be an impossibly tight fit in the 3.1 space of the SAK Center foot. [follow the links above for copies of the original VEX drawings]. There are several options. First, if you like the V2 version of the VEX Omni Wheel, you can use just a single wheel set front & back. You'll need to revise the spacers on the bolt/axle to center the single wheel in the SAK mounting. It won't provide the same stability or smoothness that a 4 wheel center foot would have. The other alternative is to find another Omni Wheel supplier. What follows is the list of suppliers that I've researched. If you just want to see the "solution" jump here.
||This is a pair of the ServoCity Omni Wheels.
the image links to a 3d .pdf file so you can see the other side.
It's been modified - the 1/2 inch center bore has been expanded to 7/8 inch to accept the balance of the bearing.
Flat head 6/32 screws hold the bearing mounts in place.
(Use Nylon Locking nuts on the other side.)
The details of the modifications follow.
|This is 8 of the modified wheels mounted in the VEX wheel holder of the SAK center foot.|
The flat head screws go towards the center with a 1/16 inch space between them. Spacers (washers) on the outside are used to center the wheels in the wheel holder [spacers not shown].
The assortment of parts we're starting with. The CNC panel of
bearing mounts is version 1 and will be updated. (It's parts for only 4
wheels, Version 2 will have twice as many parts.)|
Above: remove the parts from the panel & trim off the tabs. Not shown in this version, one spacer of each set of 3 will have countersunk holes, another one will have a recess for the hex nut. The third one is used as a spacer between the two wheels.
|Left: The bearing , most likely, will not fit in the bearing mount. It's intended to be a tight fit.|
Below: To enlarge the hole roll a sheet of fine sandpaper with the grit out.
Slide the roll into the bearing mount and let it unroll. Then
slide it back and forth a few times - check the fit. It won't take much
sanding. Don't over do it!|
Below: Bearings in the bearing mounts
|In order for the bearing to fit you have to enlarge the center bore of the Servo City Wheels from 1/2 in to 7/8 in. The easiest way to do that is with a Step Drill. I got mine from Amazon (see parts list ) You only have to enlarge to a depth of 1/8 inch. I've marked my drill with a marker so I know where to stop.|
Wheel after bore is enlarged.
Above: I put a block of wood under the wheel because the Step Drill extends through the wheel body. (yes, I've drilled into the table of my drill press. avoid that if you can - it dulls the drill bits!)
Right: The swarf will obscure your progress - Turn off the Drill, wait for it to stop spinning, and clean it off! Then continue...
Bring one of the bearing mounts with you when you are drilling so you can check the depth of the bore.
We're ready to begin assembly. They are hard to see, but I added countersinks to the holes in one of the mounts. The shop didn't do them in Version 1.
Use the screws to align the holes in the bearing mount with the holes in the wheel. (there are 10 holes in the wheel.). Don't bother doing the 2nd wheel, the bearing mount will pop out while you align the first wheel with the second one. Note: the screws shown here are actually too long. You'll have a choice of using 1.5 in screws or 3.0 in screws. (more later)
Turn the first wheel over and slide the space (3rd bearing mount) on over the screws.
Align the second wheel so that' it's Omni Bearing are centered between the ones of the first wheel.
Modify and Assemble a second set of wheels (Actually 3 more sets!) Install on your axle with the flat head screws in the center.
to come: Version 2 of the Bearing Mount panel will have a set of 3
spacer rings to be used between the two sets of omni wheels and
on either side of the pair of wheels. As mentioned above one bearing
mount will have CNC cut countersinks for the flat head screws, the
other one will have a hex recess for the Nylon Lock Nuts. I'll also be
experimenting with using 3 in screws so you can lock all 4 wheels into
alignment if you want to. For right now we at least have a workable
Click Here for the Parts List