the team I was on had some trouble with driving this year (it wasn’t great but it did the job). Having mecanum wheels would have helped greatly in lining up our robot to grab/shoot frisbees and we also had some trouble with speed and getting blocked.
How well does a set of four mecanum wheels deal against being blocked? and how fast could a set of mecanum wheels get a robot up to compared to standard wheels?
Are supershifters worth it? and how would a supershifter on each mecanum wheel do (assuming the money didn’t matter)?
What were the details of your team’s drive train this year? Also, what are the details of where you had trouble lining up? If you had trouble lining up with the feeder station slots, it could be that having a wider target for your human players to feed the discs into would be the solution rather than altering your drive system, for example.
Before you pursue an entirely new drivetrain, let’s break down your current one. What setup were you using? (Gearboxes, number of wheels, which wheels, wide configuration or long configuration, etc). Could you also provide us some video of the robot driving? There’s more you need to look at before making a decision such as moving towards an omnidirectional drivetrain. The kit drivetrain is one of the easiest and most powerful drivetrains out there.
Please keep into consideration that our season is over (we had a good run, first time getting picked) and we are currently working on a new frame from scratch (preserving this years bot) in order to test drive trains. We also have a good amount of money left in this years budget that we can most likely buy the gear boxes (we already had the wheels) especially considering that they are reusable.
This years drivetrain was a 6 wheel tank drive on the andy park standard KOP frame using the long formation with omni wheels in the front and back of the bot, and kit standard wheels from andymark (highgrip) in the middle, all 6 inch. we had 4 cim motors on two cimple boxes. We added the omni wheels because it could not turn for its life on carpet. It worked well in competition, as it could run very well when it was just going back and forth collecting and shooting frisbees. I was pleased with it because last year we were basically a sitting duck with our 6 highgrip wheels powered by 2 cims.
The problems came up when we had two line up our bot to shoot/load frisbees. Unfortunately our bot could not change the firing angle at all, and had no sensor, so the shooting had to be lined up by shooting very specifically at the bottom of the pyramid. It worked great in auto mode, but telop was tricky because with tank drive it was impossible to make slight adjustments to alignment. Especially with lateral movement.
The feeding was the same thing, but easier because we could communicate, still took way too long. I will admit our feeder could have been much better designed. On the optimistic side, lining up on the pyramid was easy and took no moving parts at all for climbing.
I don’t have any great videos, but we have some O.K. ones on our website with more elsewhere that need to be uploaded. there really are not any obvious problems at first glance, but it is defiantly not fast, and it does not block/handle blocking well.
Shifters are great, but I’d have to recommend against Mecanum wheels for the usual reasons. You can find many threads on the subject. Many of the top teams use 6 or 8 performance wheels. I know 254 almost always uses the same drive train with eight 4" wheels (this year maybe six because of reduced size). Many other teams have the same setup too, unless they have a good swerve drive like 1717 last year.
Rather than looking at a new drivetrain, let’s analyze what was going on with your setup. You said the standard kitbot drivetrain was not turning on carpet. Where was your center of gravity in this setup, and are you sure you dropped the center wheels in the 6 wheel drive by 1/8"? Make sure your center of mass is low and over the center two wheels. If this still does not remedy your issues, look into going to Toughbox gearboxes, or something with a higher ratio. I think the CIMple boxes house a 4.3:1. This ratio is meant to give you a lot of speed, but not much torque. You might need to drop down to 8 or 9:1 in your gearboxes. The toughboxes should be enough, even with high traction wheels, to allow your robot to turn smoothly, given that the center wheels are dropped 1/8" and the center of mass is low and over the center wheels. This is in fact what the kitbot on steroids project by Team 1114 is based on.
Alignment issues are a pure driver practice thing. It’s much easier to get your driver to practice lining up in one sweet spot (and with the goal this year being so wide, you don’t need to exactly have only one sweet spot) than it is to invest time and resources into an omnidirectional drive, only to use it just to strafe a couple of inches every match. Try expanding your feeding are on the robot. My team’s loading mechanism on the robot is the length of 2 frisbees. We had very rare issues with lining up to the feeder slot, and we ran a standard 4 wheel wide drivebase.
Sorry about the “H” I though that I had fixed all of them.
What was wrong with the mecanum super shifter combo? or what was wrong with just the mecanum wheels?
if one were to make a swerve drive, what ratio would be best for the speed/power combo (as I saw a lot of options on andymark)? I feel like part of our shoving problems came from our omni wheels (so that takes care of its self). I am tempted to try and make one as a summer project.
could you please go into team 254’s drive-train, or at least just something to use as a search query.
Don’t underestimate the power of the kitbot. 2013’s new and improved kitbot performs better than many, if not most, custom drivetrains and, possibly most importantly, is quick and cheap, so you have more time to spend on developing other systems for the robot.
Additionally, with simple modifications, such as building 1114’s kitbot on steroids, adding higher traction wheels or perhaps shifting transmissions.
Personally, I haven’t played enough with Mecanums enough to give a verdict on their performance, but from what I’ve seen, a decently constructed, well driven tank drive can often outperform all but the best Mecanum drives in everything but going sideways. When considering Mecanum, you have to decide if going sideways is worth being slower and having less traction.
In the past few years we have used both AWD robots with traction wheels and robots with mecanum drives. The team has tended to favor mecanum for its alleged maneuverability strengths. I think this is a bit of a fallacy, as we haven’t been able to drive or align the mecanum robot any better than the AWD versions.
Building a mecanum robot is a great learning experience from a build and a programming standpoint but don’t expect a huge boost in driver performance. It isn’t as maneuverable as it looks on paper.
I personally have something against mecanum wheels (insert dead horse to be beaten), but what I’m really trying to get at is to start simple and learn from your mistakes. It’s easy to jump around ideas and only implement them halfway, but you learn more about engineering and gain more experience when you iterate your design to the best possible iteration. Do the changes I mentioned with your kit drive before exploring swerve and mecanum. If a team can’t master the kit base and the standard 6 wheel drive base, they certainly don’t have the resources or time to master an omnidirectional mecanum or swerve drive. If you want to learn more, A simple search in the whitepapers for a drivetrain design can help.
Mecanum is good for when you need an omnidirectional drive system but don’t have the time/resources/money/programming team to devote to swerve or butterfly drive. For example, we didn’t make the decision to go mecanum until just before the start of week 2 during the build season, after realizing that an omnidirectional drive could be very advantageous.
I’d take a mecanum kitbot with basic WPI code over a hacked together and poorly programmed swerve drive any day.
If you really, and truly need an omnidirectional drive train, I’d start with mecanum and plan to go to swerve or butterfly later.
If you don’t, look at some of the tank drives with traction (and sometimes omni) wheels around FRC, such as Team Titanium’s Tremendous Turning Twinspeed Tank Transportation in use on this year’s robot.
I will admit that our loaded could have been much better for sure. it was about as wide as a frisbee, not very helpful. We made some changes at competition that allowed us to have a “flapper” that would allow us more surface area to collect frisbees, but anyways, lesson learned there (practice more).
We could try making those changes (as well as checking which need to be fixed) once we meet again. I definatly will push for the gearbox change. If it helps, it could turn its self way better than any human could (on carpet) without us lifting it up.
I like that philosophy. Next year we are going to drive and make some competition pieces so we can get a better idea of what problems we are having.
Almost forgot to mention. Our center of gravity is centered very well (climber is in the middle) and the main problem from driving is that the front and back wheels of the tank drive where having a lot of lateral resistance on the carpet. enough so that no person could push it. So when it tried to turn, that was what it was fighting.
Could you possible provide some pictures of the drivetrain? Ideally, there should be a lot of resistance in the direction perpendicular to the forward-backward motion. The key to being able to turn a long robot is to have that drop in the center wheels. This way, the robot is on the front 2 and mid 2 or the back 2 and mid 2 wheels, never on all 6. This reduces the length of the drivebase effectively in half, requiring less torque for the robot to turn in place.
Also, make sure you look at all of the other issues before putting in a new transmission in the drivetrain.
254 almost always uses 6wd, not 8wd because you have a lot less parts to make. They also usually vary their wheel size based on the game, but usually stay very small. If I remember correctly in the past few years they’ve been using wheels that range from 3.5" - 4.5" in diameter.
The kitbot on steroids is a very good drivetrain. It’s very easy to make and will give you a drive that is better than 90% of teams. Having a reliable, easy to make drivetrain will give you more time to build a reliable manipulator, tune your programming, and get drive practice.
I find that omnidirectional movement is usually overrated. Mecanum and holonomic drives tend to have a lot of problems, especially when you want to try to get around or play defense. Swerve drives take up a lot of resources. First of all, they are complex, hard to design right, and take a lot of time to machine. Also, code is very complex, and if you don’t do your code right you will be a sitting duck.
One of my favorite examples of the complexities of doing swerve right is 973’s 2012 robot, Encore. 973, being a powerhouse and the 2011 World Champions, they had the resources to build a very good independent swerve drive. However this took up a lot of their resources, and ended up detracting from the other parts of the robot. This year, 973 decided to revert back to a west coast drive. In my opinion, this decision benefitted them tremendously. With more time and resources to divert to their manipulator, 973 was able to spend more time tuning and practicing with their robot. I feel 973 had by far the best robot at the LA regional, leading them to their 2nd regional win.
That said, I think you should work with building the kitbot on steroids during the offseason. With so many good new products from many new vendors, you may eventually want to spend time improving the kitbot on steroids(i.e. add shifters) and even creating your own custom drive. However the kitbot on steroids will put you on the right path.
I dont get it. If you used the kitbot chassis then you have the same chassis we did. Long orientation, 6 kitbot traction wheels, 4 CIM’s on toughbox minis as provided in the KOP. Perhaps you didnt notice that the middle hole on the chassis material is off center and you assembled it with the middle axle up? We used, for the first time the entire kitbot chassis and it was strong, reasonably fast and turned on a dime. We seeded 11 in both Wisconsin and Buckeye and made it to finals in Buckeye after being first pick by the first seed. This was, with the belt drive, the MOST BULLETPROOF chassis we have ever used. I am never going back to chains and using onmi’s on the ends is just wasting traction.
We had no trouble pushing people around most of the time and having 6 traction wheels made it almost impossible to push us around. The only thing I would change in the future would be to go back to super shifters to give us more speed and power when needed.
Check out you chassis assembly, I bet you have the center axle raised instead of lowered.
Since mechanum needs four gear boxes, shifters add bit of weight & complexity. you would want to gear them fast & faster since you are not going to win pushing matches against well built pushers anyway. I don’t think shifters would be worth it. They really don’t do as bad as most think against the average drive train. Once again I am not talking about winning pushing matches as much as avoiding them. A well driven mechanum with good drivers & a plan can drive around pushing matches. In this game, lining up on the feeder & aiming is a big plus for mechanum.