Supershifters and Mechanum wheels

[Anupam Goli]

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.

[bs7280]

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.

[ablatner]

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.

[JohnFogarty]

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.

[MichaelBick]

Originally Posted by ablatner

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.

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.

[Bruceb]

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.

[FrankJ]

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.

[Ether]

Originally Posted by FrankJ

Since mechanum needs...

A well driven mechanum...

...big plus for mechanum.

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

[bs7280]

Originally Posted by FrankJ

Since mecanum 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 mecanum with good drivers & a plan can drive around pushing matches. In this game, lining up on the feeder & aiming is a big plus for mecanum.

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?

[EricH]

Originally Posted by bs7280

When would you say mecanum is worth it?

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.

[Tom Ore]

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

[J_Miles]

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.

[Ether]

Originally Posted by J_Miles

I loved driving a robot with mecanum 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?

[sdcantrell56]

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.

[jbsmithtx]

Originally Posted by sdcantrell56

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.

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...