Hi. I’m on a second-year team and we’ve changed out the front and rear wheels on our kit chassis for 6in omni wheels. Since the omni wheels have a greater width than the kit wheels, when we follow the instructions to build the chassis, the spacers are too large + the omni wheels hit the ledge on the outer plate. We’re thinking of dremel-ing out that part of the ledge. Is there a better solution?
Do you have smaller spacers that will work?
The base kit comes with smaller spacers that work on the rear wheels, but for the front, the pully has to be right up against the plate to make sure the wheel doesn’t hit the ledge. We’re also looking at using a band saw to cut some thinner spacers.
We did the same thing last year and tried the bandsaw method, but didn’t have good results. I’d suggest trying to 3D print some spacers out of Nylon or ABS that are closer to the size you need. We measured the gap with calipers and 3D printed three sets. We only used two sets between two regionals and Houston Champs.
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Our team change front wheels for Omni afterseason, and we make spacers with 3/8"+ metallic tube before we measured and aligned the Omni.
We made it because we want to have as option the original wheel again without any further change.
VEXPRO sells 3/8" hex spacers that would work. They should fit on the 3/8" bolts. Getting a pack each of the 1/2" through 1/16" should give you enough variety to get the results you need.
If you are using the omni wheels from Vex, we have had great success in the past by bolting a pulley either side of the wheel (not just one per wheel as per AM instructions). This also allows you to use the non flanged 3/8" ID bearings that you get in the kit and saves you needing new bearings. In our experience the spacing is worked out just right. Also be weary of the belt rubbing on the rollers of the omni wheel or on the flanges of the drivebase structure. These will cause uncharacteristically high wheel wear and belt wear respectively.
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I’m sorry if I’m missing something critical here. Why are you changing the wheels out for omnis? I haven’t ever been on a team that used the KOP drive train as it was intended(the explanation is hugely off topic), but my understanding was that the drop center was sufficient to enable all 6 wheels to be traction.
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Another concern to keep in mind would be the potential of damaging the omni wheel rollers while crossing the steel rendezvous boundaries.
For the last two seasons 614 has made some minor modifications to the drive wheels in order to make things more sturdy and reduce the drop. At first we tried to shave down the center wheel to reduce the tipping back and forth. When we did so, we found that we couldn’t turn as well, so we replaced one set of wheels (in 2017 we changed the front wheels, in 2018 we changed the back wheels) with omni wheels. This allowed us to eliminate the drop, but still have the maneuverability that we were used to having.
We found that we could turn better with the omni wheels in place of a set of traction wheels when even using the standard drop of the KOP. For reference, here’s a video to show how we lined up to place a hatch last year. Without the omni wheels on the back of the robot, this wouldn’t be possible.
Back to the OP’s point though. The last two seasons we have used the old Andymark omni wheels that are about the same profile if not a bit smaller than the traction wheels. This season we are swapping to the Duraomni wheels, and they are wider. We made our own spacers to make sure that the wheels don’t rub on the frame. On some of the wheels that spacer was just a couple of washers.
We have used nonmetalic conduit, it fairly easily cut straight with the rings. You maybe able to get a small piece from a local electrician. https://www.homedepot.com/p/Carlon-3-4-in-x-100-ft-Electrical-Nonmetallic-Tubing-Conduit-Coil-Blue-12007-100/100404116
We thought about using washers but were worried that it would metal would rub against the frame and end up poorly. Has using washers worked out well for you guys?
It’s worked fine for us. Truly you just need enough space so that the bolt heads from the pulley don’t run against the frame. The washers haven’t really caused any sort of wear or problems so far.
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