The Best Wheel Base: Tread, Omni, Mecanum, or Standard

With the release of this year’s game, our team has come up with many ideas on how to play (score) the game. One issue we are less sure on, is how much pushing (i.e. defense) we plan to encounter. My personal belief is that due to the larger middle console, the drive area is slightly less and therefore we should expect more defenses and more pushing. Although not all of our team is in agreement with this idea, the majority of us are.
Assuming this is true, the more controversial issue is how we go about countering defense. my initial thought was to use a wheel base similar to last year’s, with four motor controlled wheels, giving the robot torque, speed, and the ability to get itself unstuck if it were to bottom out on the ramp. In addition, I would like to place the wheels underneath or inside the robot to keep the majority of the weight directly on the wheel, and not on the motor’s axle. Danny agrees with my idea although is less concerned about where the wheels should be placed, but feels that weight is needed to prevent the other teams from pushing us.
However, some of the newer members are thinking under the idea that we might want to use a lighter weight robot with a versatile wheel base to avoid other robots. I personally don’t think avoiding other robots will be possible given the close quarters, but the idea remains. Others have mentioned tread as an idea, and Danny has even considered the use of Mecanum wheels (although I’m not sure of his current thoughts about them).
So in light of this debate, I’ve decided to line up the prospects and figure out which is best.

Tread: Although we have never tried treads on our robot, it seems note worthy than I have only seen one or two robots use treads in competition. I know for a fact that neither of the teams that did use treads were in the final rounds of any of the qualifiers I was at, and I’m fairly certain no finalists had treads at state either. This may be a relevant issue and it may be something else. Cheryl has told me in the past that treads don’t usually work because they occasionally come off the wheels during a match, and that they’re more likely to break than wheels are. she may have a point, but on the other hand, part of me wonders if the real reason we don’t see treads lies with other issues, such as how much room they take up and the length of the treads made by Vex and Tetrix. as for their general use, I feel it’s important to mention that treads would not necessarily need to use four motors (2 on each side) in order to have decent speed. (This is relevant because FTC limits teams to a total of 8 Tetrix DC motors.) A simple gear system could allow one motor to run and entire side length of the robot; thus freeing up two motors to be used elsewhere on the robot.

This was the robot made by a girl scout team in our area, from last year's competition. It was also the first picture I took during my robotics career.

This was the robot made by a Girl Scout team in our area, from last year’s competition. It was also the first picture I took during my robotics career.

Omni wheels: Although most people outside of robotic engineering have probably never heard of “Omni wheels”, these wheels are an incredibly well known and widely used wheel type in the world of FIRST. Omni wheels are simply wheels with smaller wheels imbedded on their outer edge. This gives a vehicle equipped with these wheels the ability to move in any direction it wishes, by turning specific wheels in a given direction. The wheels are placed rather unconventionally on the corners of the robot at a 45* angle to give the robot the correct vectors (orientation).

Tetrix brand Omni  wheels

Tetrix brand Omni wheels

Despite the obvious benefit of having extreme maneuverability on the field, Omni wheels have one major weakness which deters many teams from using them; that is traction. Because Omni wheels are nothing more than wheels on wheels, they tend to be very easily pushed around by other robots, larger and smaller. For this reason some teams have found that using a mixture of regular wheels and Omni wheels works better than the latter or former on their own. However, even this set up does not fully restore the loss of ground-holding traction one receives with standard wheels.

Mecanum wheels: As I probably should’ve mentioned in the above paragraph, “Omni wheels” are simply any type of traditional-style wheel; that can move in any direction; that is not a spherical Omni-directional wheel (such as a ball roller set or ball transfer unit). So in actuality, Mecanum wheels are just another type of Omni wheel. however, most teams will refer to the Tetrix Omni wheels as the standard “Omni wheels” and will refer to any custom made or Vex Mecanum wheels as “Mecanum wheels”. The main difference between the two is the direction the wheels on the outer edge are facing. instead of being perpendicular to the main wheel, as they are with the Tetrix Omni wheel, Mecanum wheels (designed by Bengt Ilon in 1973) are made of conical shaped wheels that face at a 45* angle from the main.

Vex brand Mecanum wheels

Vex brand Mecanum wheels

Because of this, they do not need to be positioned any differently on the robot itself, and therefore take up less room. They also provide more traction than the Omni wheels; however still less than the traditional wheels do. Many teams who do use Mecanum wheels choose to manufacture their own; either through engineering companies or though 3-D printers, although these tend to be more experienced teams who do so. below is a video of an FRC team testing out the capabilities of their custom Mecanum wheels – it is noteworthy that Omni wheels would more than likely be able to maneuver in the same way.

Although this technology is probably not within the ability of FTC teams to use on their robot, it is neat to see that other companies around the world are toying with the idea of Omni directional travel, as the video below indicates.

Standard wheels: There isn’t anything quite like using wheels that haven’t changed since the roman era. The standard cylindrical shaped wheels with rubber on the outer edge for traction are not high tech nor is it expensive. With the exception of some gold spray paint on the interior, the wheels on our robot are as common and boring as over half of the wheels seen in competition; and that’s ok with me. Because despite the lack of glamorous allure, the standard 4 inch wheels we use work. They have more traction than Omni wheels, Mecanum wheels, and even tread. Not to mention that they are more open to traction upgrades that makes them better yet. Zip-tied wheels are commonly seen among robots that are on the heavy side (>30lbs) as robots go, and is a cheap way to gain extra grip on the field. My favorite wheel upgrade is the Lego Wheel addition, in which a Lego tire is stretched over the standard Tetrix wheels to create an off-road wheel.

The Lego Wheel can be seen on the back wheel of our robot. This picture was taken before we had received all of the tires from Art.

The Lego Wheel can be seen on the back wheel of our robot. This picture was taken before we had received all of the tires from Art.

The Lego Wheel idea is something we learned from team Dark Matter 4150 (shout-out to you guys, thanks for the recommendation).

The Lego Wheel is actually more of an additional tire on a regular wheel. This is the product on Lego Education. Product ID W970047

The Lego Wheel is actually more of an additional tire on a regular wheel. This is the product on Lego Education. Product ID W970047

Although this is another wheel/ movement system that cannot be fully utilized in FTC, it’s just too cool not to put it in this post. This video is something we found last year while trying to learn more about the Mecanum wheel. It’s called the sand flea, and may have some military applications.


3 thoughts on “The Best Wheel Base: Tread, Omni, Mecanum, or Standard

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