Supershifters and Mechanum wheels
 

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)?

thanks! -3734

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

We used 4 AM SuperShifters on our Mecanum prototype base, but we decided it wasn't something we'd ever use in competition unless another game like LogoMotion came about.

Re: Supershifters and Mechanum wheels
 

http://youtu.be/LlSoEfAW47I?t=3m33s

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

Building a competitive drive train is about building an efficient, stiff and robust base with the correct math done regarding gearing. There are resources a-plenty for learning to do this.

At 159, we had such incredible success with our traction drive last year, that it's unlikely we will ever use a drive without traction wheels.

As per lining up...
I build bots with a philosophy that if you can't line it up with a tank drive and a few minutes of practice then your mechanism is broken and not your drive train.

Re: Supershifters and Mechanum wheels
 

Sorry about the "H" :p 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.

thanks so much! -3734

Re: Supershifters and Mechanum wheels
 

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.

Post #254! Go Poofs!

Re: Supershifters and Mechanum wheels
 

Solid philosophy.

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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

Well we got rid of the "h". Now if only we could get rid of that extra "c" :-)

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

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.

EDIT:
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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

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.

Re: Supershifters and Mechanum wheels
 

Hey Frank, did you do that on purpose ? :-)

Re: Supershifters and Mechanum wheels
 

Thank you for the advice! I am pretty sure that you are right, in that our center wheel is not lowered. we are meeting tonight and I will be sure to check it out and grab some pictures.

Also keep in mind that we are only going to make minor changes to our competition bot if any (no major drive train changes) like flipping the frame. In the off-season we intended to experiment with frames (among other things) that are not intended to compete. We have good programmers, tools (mills,cnc,lathe) etc... that if we were optimistic we might attempt to build one of the complex drive trains as a prototype.

Re: Supershifters and Mechanum wheels
 

Thank you for your advice! this answered a lot of questions/concerns that I was having. We are most likely not going to go the shifter/mecanum route in the future as it is expensive,heavy, and not worth it. The reason that I was concerned about being fast and able to deal with pushers was that in our elim rounds we had to defend our teams long range shooter from some of the robots with blockers.

When would you say mecanum is worth it?

Re: Supershifters and Mechanum wheels
 

Ether: A big reason that I am an engineer is that mom knew I would fail miserably as an English major & starve.

For all of you that plan to major in engineering for the same reason.... Being able to communicate is really really important.

Re: Supershifters and Mechanum wheels
 

I think several people her have fallacies with mecanum. Our team decided week one to use them this year, and we did spend a little too much time perfecting it, but in the end it turned out for the better. We were a feeder station/shooter and we found the mecanum great for lining up. This was the problem we had last year. Even with all the summer practice I got with last years bot (hours upon hours) it still was not all that great. So our team debated week one and saw the omindirectional system as very advantageous, versus the challenge last year. Our original intent was to dive under the pyramids and such, but we never got to end up doing that because of the slight variations in pyramids. However, during competition when our shooter failed, we were plenty good at defense. (Youtube video. Not sure how much defense is shown.. http://www.youtube.com/watch?v=3M_YGV9kKP8). We actually pushed several teams with the kitbot around. We did find it easier to drive aroudn them though. We discovered (all too late), that speed would have definitely helped. I think a lot of teams underestimate speed. When are robot can drive around you, or simply quickly out maneuver you with a mecanum, it really makes a lot of things easier. Our teams has nothing bad to say about our mecanum, just make sure that you use a gyro to help with all the subtle problems. We used 6" AM mecs with TB minis

Also forgot to include that when we decided to add a climber, rather than messing with other systems, we were able to mount our climbers on the side and strafe onto the bar

Re: Supershifters and Mechanum wheels
 

Ok, say a team decides to go with a drive base (nothing specific for the sake of helping other teams who view this) for each base, how does one select the "best" gear ratio to be chosen on a bot? Looking at different gearboxes for different drive base types, there are alot of choices and it is quite intimidating to choose considering how expensive they are.

Re: Supershifters and Mechanum wheels
 

There is no single blanket "best ratio" to use. It all depends on your strategy and what you want to do. Do you want to be quick? Do you want to have pushing power, but don't want to be necessarily quick? If you are using a single speed gearbox, you can look between 4.67:1 to 13:1. We ran an 8.46:1 ratio in a Toughbox mini. We got about 9 fps and we had decent pushing power. The toughbox might be a good starting point. The good thing about the toughbox is that you can just buy the gears and change the ratio based on your results. You can also adjust the ratio in the sprockets. Remember, the higher the ratio, the less speed you have, but the more torque you will have behind those wheels. Striking the balance is something you and your team have to figure out. If you search in the CD papers, you can find JVN's drivetrain calculator, which allows you to learn everything you want to about a drivetrain before you build it.

Re: Supershifters and Mechanum wheels
 

We use a two speed and mostly because:
We can set a gear used for acceleration and pushing matches to be traction limited (Torque created at ~40 amps times wheel radius > force of static friction of wheels on carpet)
We can set a gear to get us where we want to go as fast as possible. (balance of acceleration from top speed of gear 1 with top speed)

If you choose a single speed, a balance of top speed and pushing force is ideal. Usually teams set there bot to be right on the edge of traction limited. This is not inherently ideal, but is simple and can give a successful result.

JVN design calc as suggested above is the way to go.

Re: Supershifters and Mechanum wheels
 

As above said, there is no "best ratio". It should be fit into your strategy. So, with a wide open field like this year, you might want a higher ratio if you were going to be running cycles to and from the pyramid, so you can cross the court swiftly. Whereas if you were a team that wished to block a cycler, you might have a much lower ratio, so that you could at least push them around and slow them down. However, with a divided field like last year, you would be looking at a totally different setup, with a lower "speed" ratio (because of acceleration up to your top speed). It all depends on strategy and how you think matches will end up being played out.

Re: Supershifters and Mechanum wheels
 

I would say that mecanum is worth it if and only if:
1) The game requires an extremely high degree of maneuverability.
2) The game does not require the movement of heavy objects, or allows for said heavy objects to be carried in the middle of the robot (not other robots).
3) The team has a good programmer.
4) The team does not have the resources (pick any or all of time, personnel, offseason, money) to pursue swerve, or wants to use a KOP-type frame.

Otherwise, swerve adds extra push to the maneuverability.

Oh, and:
5) The team has already prototyped the system, at some point.

Re: Supershifters and Mechanum wheels
 

We now have 7 regional wins on mecanum wheels so count me in the "likes them" column.

Re: Supershifters and Mechanum wheels
 

Perhaps I'm simply biased, but as a driver I loved driving a robot with mecanum wheels. Our 2011 robot was built on a mecanum drive and won the 2011 Ann Arbor District competition, the 2011 Troy district competition, as well as two local off-season competitions in Michigan. It was definitely a machine to be reckoned with in spite of what many would consider to be a poor choice of drive train.

With that said, there are a few advantages to mecanum drives, but I think they're quite context-based. 2011 seemed to be an excellent year (if there is such a thing) to use the system because of: A) The totally flat field, B) Sizable protected scoring zones C) A shallow protected zone (making the ability to strafe quite useful). For this reason an omnidirectional drivetrain seemed the way to go, but we chose a mecanum drive for its relative simplicity and our previous experience with it, and our year was spectacular because we were able to put lots of effort into our end-effector and other mechanisms besides the drive, and to build a solid mecanum drive there isn't a lot of fancy programming necessary besides speed control.

Mecanums have the advantage of being able to immediately change from forward & backward motion to sideways motion without having to worry about the wheels turning. Driving on mecanums also means that shifting transmissions are sort of irrelevant (as you aren't going to get much pushing power from mecanums and, as such, shouldn't need a significant boost in torque), and because the rollers allow for low-resistance turning.

Surely there are sacrifices made when designing a mecanum drive for a robot, but I still argue that they are a solid option if you want a simple omnidirectional drivetrain and are willing to live with the consequences.

Also, as an aside, the "drunk drive" (as we called it) that comes with mecanums significantly changes the driving experience, and I personally found it a lot more fun than driving the standard tank drive we used in 2012.

Re: Supershifters and Mechanum wheels
 

What was your driver interface? e.g. something this this:

forward/reverse Joystick1 Y axis

strafe left/right Joystick1 X axis

rotate CW/CCW Joystick2 X axis

... or something else?

Re: Supershifters and Mechanum wheels
 

Just to add to this conversation...unless it is a particularly special case (2011 our first pick at north Carolina had them) , any team with mecanum wheels is automatically off our pick list. In fact the only thing our pit scouts do is create a list of all mecanum robots.

Re: Supershifters and Mechanum wheels
 

Why? What is so bad about them?
The only disadvantage I have seen with them is that they are relatively slow strafing versus a swerve.

Our interface was with one joystick (easier and less confusing) with the top two left and right buttons for rotation. We simply put a constant that we were comfortable with.

And they are a simple easy option for relatively new teams for omindirectional movement. Swerve requires a lot of resources, and frankly with a few sacrifices, mecanum is right up there with them...

Re: Supershifters and Mechanum wheels
 

For one, you never want them playing defense. That immediately removes them from being a 2nd pick. To make them viable as a 1st pick, they need to score a lot. Most teams do not run mecanum. That leaves a very select few left who are viable picks. Add in the fact that in elims there is more defense, a team that can get through defense is usually the preferable pick.

Re: Supershifters and Mechanum wheels
 

The strafing speed is one issue. The bigger issue for me is they are worthless against good defense and also cannot provide solid defense either. I have seen too many strong offensive robots be shut down this year in particular as soon as defense is played on them.

Another huge issue I have is that the majority of teams do not program them to be able to take advantage of the few benefits which makes them even less beneficial. Way too many teams drive mecanum robots like a traditional skid-steer robot and only strafe occasionally or never at all. In my opinion, mecanum wheels are a compromise of all things and don't excel at anything.