Hello! I have just been wondering what would be the best wheels to use in a 6 wheel tankdrive AM14U5 chassis? We obviously have the HiGrip wheels, we also have some omni and plaction wheels laying around. What would you recommend us to use?
Omnis on the corners will help with turning. For the middle wheels, you either want a lower center or wheels big enough that you’re not riding on the omnis alone. Tread material doesn’t matter that much on tank drives in my experience.
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we’ve generally used 5" Colsons when doing a (drop center) WCD
The correct answer is, whichever wheels give you the effect you desire.
This might be omnis. It might be all higrip. It might be plaction. There’s a lot of flexibility given those options.
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When we’ve done tank drive in recent history, we’ve used either all 6 traction wheels, or 2 omni wheels in the front and 4 traction for the middle and back. We had success with both orientations, and felt that the two omnis in the front gave us enough maneuverability to make up for the loss of traction.
We used similar tread to this but a more beige color. Can’t find where we ordered it from originally but used the same roll of the stuff from 2017-2023.
The AM14U5 is a drop center chassis, so in theory you shouldn’t need to use omnis. HiGrip wheels are pretty decent all around wheels, but the plaction wheels will let you use tread, so you’ll get more grip, but you’ll need to replace the tread periodically. My recommendation would be to use the plaction wheels with black neoprene and plan to replace the tread before every comp.
The reason some teams use Omnis on the front or back of their drive bases is to reduce scrubbing, which is pulling your wheels sideways across the carpet as you turn. Scrubbing can make it very hard to turn if you have high traction wheels, but it is fixed by dropping the center wheel slightly so that the corner wheels have less engagement with the carpet. If you are struggling to turn, make sure you have the proper center drop and gear ratio for your wheel diameter and frame size. If you still can’t turn check through your code for something limiting your torque, and finally you can replace the front or back wheels with omnis. We used black neoprene with a .08” center drop last year and could easily turn in place, so if you’re struggling it’s probably not a wheel problem. Omnis have very low traction in all directions, so avoid them if possible.
It’s been awhile since I’ve used any of those wheels on a drivebase so maybe someone else can comment, but omnis and I believe plactions can break fairly easily when running over field bumps or falling from any significant height. I’d recommend performance wheels instead.
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I’ve never experienced our tractions or omnis breaking, the closest we’ve gotten to that was the plastic versahub cracking on one of our tractions. Swapped to the aluminum ones and haven’t had issues since.
Our team used plaction wheels during an off season competition this year on a KOP chassis and they fell apart after 4-5 matches. The plastic “walls” that contain the tread got worn away causing the tread to fall off. If you want to use tread I would recommend using metal wheels instead.
Robot weight makes a big difference, too. If you tend toward <100lb (45kg) robots, you can definitely get by with six hi grips. If your robots stretch the weight max, at least one pair of omni (or other low-friction) wheels may be in order.
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We definitely ran into scrubbing issues when using 6 hi grips on the KOP in the past, but those years we had really heavy and somewhat long robots. I’d be tempted to go forward with 6 hi grips, but have a few 6" omni’s ready to put onto the robot if you find it “rodeoing” when you turn quickly. In 2020 we replaced our back wheels with these and it drove much better.
However, my number one KOP recommendation is the 4" hi grip wheel 8wd configuration.
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Something to bear in mind with 6-wheel drop-center drive is that you are only resting on 2 sets of wheels at a time and your center of rotation (COR) is determined by the center of whichever wheels are providing grip on the floor as you spin. So, if you are tipped back, your COR will be in the center of your back wheels, whereas if you are tipped forward, your COR will be in the center of your front wheels.
If you add omni-wheels, this changes the COR because the omnis do not contribute to the COR relationship. If you want your COR to be in the center of your robot at all times, having omnis in front and back will keep your COR consistently centered, even as you tip. However, only one set of grip wheels is bad for playing against defense. If you have only one set of omnis, then your COR will change less depending on your tip.
All of that changing of the COR is something your driver has to adapt to. This is why many teams opt for the 8-wheel drive, which has 4 grip wheels in the center of the robot and the outer wheels simply act as balancers and grip for climbing inclines.
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our team had a tank drive with tire wheels in 2022, there were no omnis but it still worked great, and it packed a real punch with 4 falcons powering it
My team has found that a 6 wheel tank drive with HiGrip wheels in the front and middle, and omnis in the back provide a good balance between maneuverability and control.
But it all depends on your driver’s preference on what wheel set up is the best