I have a question for the many, many teams that have posted mecanum drives this year. I have no ulterior motive or anything like that.
While it’s only my 1st build season on Chief Delphi, the amount of posted robots with mecanum wheels is a lot higher than I ever expected this game to produce.
What decisions did your team make that motivated you to decide to build a mecanum drivebase? What advantages did you consider important and why? What disadvantages did you not consider important and why not?
Any thoughts on the matter will be appreciated. My team’s drive base is locked in for this year; I am not trying to use this thread in place of my own decision making. I am curious as to how others are thinking when they decide to pick this style of drivetrain. Thanks!
Note: This season, I am only helping one team, 3044. This team is in its second year, and is not using a mecanum or other holonomic drive.
The field is split into three subfields with aspect ratios that are much wider than they are deep. You’d therefore expect that side to side movement would be favored, and non-holonomic drives would spend more time in that axis.
Ball movement is along the other axis, and therefore you’d expect non-holonomic drives to be in that orientation more often.
This disjoint is what favors mecanums. It allows a team to move the robot left to right while moving the ball up and down. It also removes the need to re-orient after capturing a ball.
I expect this is why we see so many mecanums this year.
I think the reason that so many teams found the mecanum drive so alluring is that it has superior maneuverability.
I know that is why we chose it; but instead of buying wheels, we made our own.
Actually, i would like to hear from any other teams that made their own wheels, out of curiosity.
Ours are finished at this point, it is just a matter of assembaly.
if you want to see a finished one, find the thread “wheel envy”.
Thanks for all the responses so far. If possible, if you could elaborate more on your decision making process other than “manuverability” or “agility”, I would very much appreciate it. Especially a comparison to the drivetrain you would have picked if you did not use mecanum. Thanks again!
Mecanum was our backup plan for swerve drive! 1727 started the season looking towards swerve drive because it is awesome. However, we quickly figured out that you should not try swerve for the first time during build season. While we could have built one, it would have put us behind schedule, and with this snowstorm lopping one week off of our build season, I am glad we went with mecanum.
We also built our mecanum wheels hoping for great manuverability. We weren’t sure it would go over a bump, but so many teams showed this is possible we decided in week 3 to go for it. The 10" wheels were so expensive, we decided to build our own 8" wheels. So far we are happy with the result and working on adding some bells and whistles like gyros, serial2CAN position/velocity control to make it better. What about you?
Our team faced heavy debate over our drive train the first week. We would argue about it for a while, but could never really decide what we wanted to actually do.
After a while Sal (our mentor) pulled out a book of past robots, and showed us this bot with awesome custom Mecc wheels. We were WOW’d at first, then started to think, “Hey, we could do that!”
We liked the idea of the rubber adding extra traction. We liked the idea of not being pinned (despite the rules against pinning for too long this year). We liked the idea of being able to accurately manuever around the balls for greater aim, and we liked the idea of being able to easily block the other opponents. We liked the idea of being able to strafe over the bump.
What we really loved about it though, was the thought of making something that bad-$@#$@#$@# cool, and the challenges we would have to figure out doing so. So we did it, and I think we made the best decision.
(If you’re wondering more about our wheels, which we’re totally proud of, check out “Wheel Envy?” in the Robot Showcase forum)
“Take this plastic tote and the ball positioned right here. Now align and ‘kick’ using Mecanum. Now try again using skid steer. Oops, you turned into the ball with skid steer and now it’s rolling away, go chase it!”
We looked at both 4 wheel tank drive and 8" mecanum drive.
We built a kit base during week one, and mounted the toughboxes and kit wheels to create 4 wheel tank drive. We build a quick base out of wood (with similar dimensional properties as the kit base) and mounted the 8" mecanum wheels and BaneBots gearboxes.
After a few days of testing, we decided that the mecanums were the way to go. It was much easier for the robot to climb the hump, especially when starting at low speeds. Also, we found that we could strafe across the top of the hump, giving us a great way to approach the tower and hang. Plus, they look cooler.
I’m not sure if there’s much difference between the sets, but 1982 is using Andymark Omni-wheels. I’ve seen the mechanum wheels, but the only diffrence I’ve noticed are the rollers on the Omni wheels is parallel to the front of the bot, while mecanum wheels are at an angle.
To add on this, you can see that 1727 was focused on omni-directional movement. The obvious downside, lack of power, was why we preferred swerve. Mecanum does take the edge over swerve when it comes to ease of assembly and maintenance, which is why we eventually chose to pursue Mecanum drive.
Omni wheels are used when you want to make part of your drive have reduced friction in the direction the wheels aren’t driven. Mecanum wheels are used to make a drivetrain that can roll in all directions. Omnis can be made to do something similar if mounted at angles, but usually aren’t.
The drive you’re thinking of is Holonomic, which has four omniwheels, one on each corner and each at a 45 degree angle. It was used by Team 417 at the FTC competition this year.
While we are not using Mecanums this year, the thought did come up in our brain storming sessions. A Mecanum Drive theoretically should make gathering balls much easier because you don’t have to do as much rotating to keep the ball in place relative to your robot. Also, Mecanum Drives give you additional maneuverability to move around defenders while maintaining the same heading. (Easier to aim and keep ball)
Why kept us away from Mecanum was CoG issues. Most of the Mecanum Drives here have the majority of their robot’s mass elevated over the wheels because suck a large opening is required between the wheels when climbing the bump which causes CoG to be substantially higher than most conventionally built skid steers. (6+ WD) Also, the added expense of Mecanum Wheels and the Additional Transmissions we would’ve needed were a factor in our decisions…
I agree that mecanum drive is very maneuverable, but the word choice of superior is one that I would like to question. Despite the ability to instantly move laterally, I would argue that a well made and well operated 6 or 8 wheel skid can’t be out-maneuvered by the best of mecanum drives. Last year was a little different because of the surface and the trailer, but if you take a look at some skid steers from 2008: 233, 1114 and 968 come to mind, these team’s maneuverability was mind blowing, and they didn’t have the losses in efficiency that mecanum wheels present. They also weren’t as susceptible to being pushed laterally as a mechanum drive is…
I’m not questioning your decision, I’m just suggesting that mecanum drives maneuverability in reality is not quite what it seems on the drawing board.
