What size & type wheels do your team(s) use, and why? Also, if you use drop center, how much and why?

Title pretty much explains it. Please feel free to be as detailed as possible.

We use a variety of wheels with the choice determined by the needs of the particular game. The part that has not changed for us has been the use of the AndyMark sheet metal drive base. We’ve been using the AM14Ux since it came out.

We’ve used the 6" and 4" AndyMark HiGrip wheels in 6WD tank configurations. We’ve mixed 6" HiGrip wheels with 6" VEX Omni-Directional Wheels in a 6WD tank drive configuration. We’ve used the 8" AndyMark Pneumatic Wheels with the polycarbonate hubs in an 6WD tank drive configuration. We’ve even used eight of the VEX omnis in an H-drive configuration.

Since we’ve been using the AM14Ux base, we’ve mostly been running 1/8" center drop on our 6WD, since that’s the way that sheet metal is drilled. That has been fine for us in terms of ease of turning and the slight rocking of the drive base has not been an issue. With the 8" pneumatics, we probably would have been better off with 1/4" center drop and would probably experiment with that using a custom frame if we felt we needed pneumatic in a future game.

We’ve never broken any of these wheels. The Hi-Grips and VEX omnis were totally fine this past year playing Deep Space with flying starts from hab level 2. The polycarb hubs with pneumatic wheels held up fine through the abuse of Stronghold a few years back.

Our philosophy has been to spend our time on manipulators, sensors, and software and to go with simple, stout drive bases with common wheels.

Just to answer yiur question about why the enter wheels are dropped. If all 6 wheels on a tank steered drivetrain are level there is quite a bit of friction between the wheels and the field carpet when trying to turn the robot. This results in a higher current draw from the motors along with added stress on the drivetrain components. In addition robots tend to bounce or hop when turning when turning creating an unstable machine. A dropped center wheel of around 1/8" is a simple cure.

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We typically go with 6 inch wheels as we aren’t able to design super drivetrains and still be able to go over all sides of the platform.
148 Overhang-

2017, 2018, 2019 all had the White AM Hi-Grips.
17- 4WD | tall bot (broke quite a few wheels from getting rammed into)
18- 6WD drop center i think it was 1/8 or 1/4…
19- 4WD | 2x 6" VexPro Omni | 2x AM
20- Hoping for some blue nitrile or colsons… but depending on the field elements…

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Are you asking what the purpose of a drop center is, or why did we choose the number that we chose?

Usually drop center drivetrains range somewhere between 1/8" and 3/16". I’ve personally only ever run a drop center using Vex’s clamping bearing blocks, which are 1/8", and the kit chassis, which has a drop of 0.14" (if I’m reading their very complicated drawing correctly). The other tank drives I’ve been involved with have had no drop and used omni wheels in the front or back to allow for better turning.

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This thread is from just a week or two ago:

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It depends on the year. in 2016 my team used a 6 wheel 8 inch pneumatic wheel drivetrain to reduce shock of defenses and make traversing them easier.

2017 and 2018 our drivetrain was almost exactly the same being an 8 wheel 4 inch colson drivetrain with a 1/8 drop on the center 4 wheels. This is my personal favorite drivetrain (although i am biased because i was driver these 2 years)

2019 we had a 10 wheel 6 inch pneumatic drivetrain with a 1/4 raise on the center and outer 6 wheels effectively making it a 8 wheel drivetrain until we drove over the corner of the platform for our climb (which was initially the only purpose of the center wheels). We discovered later in the season that due to the nature of the wheels when inflated to 20 psi all 10 wheels would be on the ground when pushing against another robot more than doubling the amount of wheels on the ground giving us much more pushing power.

I personally don’t like omnis as they break easily and are not needed if you do your center drop(s) properly. pneumatic are great fro shock absorption or traversing non-flat surfaces while colsons have a high surface are and coefficient of friction.

When it comes to your center drop/ outer raise it depends on your wheel type, your wheel number and your wheel spacing. but for a safe bet i would recommend 3/16-1/4 inch for pneumatic wheels or other compliant wheels and 1/8-3/16 for solid wheels.