Swerve Drive vs Mecanum Wheel drive?

[Alan Anderson]

Originally Posted by Citrus Dad

From a scouting perspective, we heavily discount robots with mecanum drive because they don't have the same defensive abilities as tank drive.

Prejudice like that shouldn't be part of scouting. I think the appropriate thing would be to make your assessment based on what each robot actually does, and how well, rather than what you think its design is capable of.

[Monochron]

Originally Posted by Citrus Dad

From a scouting perspective, we heavily discount robots with mecanum drive because they don't have the same defensive abilities as tank drive. To be honest, we haven't see a high-scoring mecanum drive robot, even at Worlds, so I don't have an opinion about the use there.

This is an incorrect assessment of mecanum wheels. See the RoboBees this year:
https://www.youtube.com/user/TheHive836

They were easily the top performing robot at the NC Regional, had the highest OPR by nearly 20 points, and missed out on taking the whole thing due solely to a Tech foul that their alliance got in the last match of finals. Yes, there were absolutely robots out there with more pushing power, but letting another team snatch up the robobees in selections would be a bad idea.
https://www.youtube.com/watch?v=A3dKBW8dbOI

[Keegbot]

Originally Posted by Citrus Dad

From a scouting perspective, we heavily discount robots with mecanum drive because they don't have the same defensive abilities as tank drive. To be honest, we haven't see a high-scoring mecanum drive robot, even at Worlds, so I don't have an opinion about the use there.

Mecanum can play defense, but it is a different style than defense with tank. While tank can dish out hits and stop an opponent in their tracks, mecanum can maneuver around the opponent and get in their way when when they shoot or try to pick up the ball. I know mecanum can play defense because I have done it.

As for the high-scoring part, I think that has more to do with type of shooter and intake that the robot has, not the drive.

[Tyler2517]

On the other side swerve drives can play some really mean defense too. The ability to lock your wheels in to a X or O. This way you cant get pushed but maintain a very high gear ratio. We played some mean defense by just out maneuvering robots and out running them then locking the wheels and that's a nice 1/2-1 foot a second across the field no matter how much pushing power you got.

[Abhishek R]

In my opinion only, I feel there will always be exceptions, but mecanum just doesn't have any appealing aspects. Whenever I see a competitive team with mecanum I just wonder what they could have done with tank, butterfly/nonadrive (I've heard this is called TexCoast Drive now...) or swerve. The idea of using rollers on wheels is very unappealing to me.

[Tyler2517]

I think that a drive should be chosen for what it's robots goal is. Yes you can push a mecanum drive. But a good mecanum driver would not be being pushed for to long.
On a different note mecanum is much funner to enplane with people then a tank drive is. Cool maths and some programming a a long talk on vector math beats explaining a tank drive. At least for marketing stuff.

[Joe Ross]

Originally Posted by Alan Anderson

Prejudice like that shouldn't be part of scouting. I think the appropriate thing would be to make your assessment based on what each robot actually does, and how well, rather than what you think its design is capable of.

I think 1678 probably has the scouting thing figured out pretty well. They won Curie last year, after 4 teams declined them.

While I wouldn't recommend going beyond objective evidence for most teams, it's clear that additional information in the hands of informed individuals can make for better decisions. If a team passes over picking a awesome robot with mecanum drive, it's their potential loss.

[Joe Ross]

Originally Posted by ekapalka

I've been tentatively skimming through this code for around half an hour and can't seem to find where the magic happens... I'm not particularly accustomed to the command based model Could someone point me in the right direction? Thanks!

src/org/usfirst/frc2084/CMonster2014/commands/FieldCentricMecanumDriveCommand.java

[EDesbiens]

I think its all about the drivers... I never drove a robot on swerves but I know how mecanums feel... If you are able to drive correctly, you don't need power. You only need to know your robot and how to counter the other team.

It's all about strategy and logic, it's not material...

[Michael Corsetto]

Originally Posted by Joe Ross

I think 1678 probably has the scouting thing figured out pretty well. They won Curie last year, after 4 teams declined them.

Thanks Joe.

Obviously, there will always be good robots with a whole spectrum of drivetrain configurations (great example is 1425 this year, what a machine!)

In many cases, selecting a first pick robot is a straightforward offensive scouting exercise. Keep in mind, we picked 368 at SVR, a fantastic offensive machine, which also happened to feature one of the meanest swerve drives I've ever seen. Seriously, check it out at Champs, it may surprise you to see how many COTS components play a key role in that design.

However, our second pick preferences are very specific, and mecanum does not fit our desired robot configuration for our second pick. This is obviously our team bias, and is shaped by how we want to build our alliance, but it is a guideline we have followed with decent success over the past few years.

I won't say mecanum robots aren't good, because that's not true, there are plenty of great robots with mecanum drivetrains. However, they probably won't make our 2nd pick list.

But that's just us, we're still figuring this whole scouting thing out. I'd like to think we're making progress, but there's still so much we can be doing better!

-Mike

[Chadfrom308]

For defense, I say we are no slouch this year.

Yes we do have mecanums, but as said above, its a different style of defense. It is turning and ramming that will get the opponent annoyed. We have played defense quite effectively, even against tank. We can normally stop tanks in their track when we go up against them. I have played better defense than some teams do with the kit of parts.

Defense is not about drive train, it's about the driver skill

[Keegbot]

Originally Posted by Chadfrom308

Defense is not about drive train, it's about the driver skill

I agree. Different drive trains can all play effective defense (the style will vary), but a good driver makes all the difference. If the driver doesn't know how to use his/her drive to the best of its abilities, the robot will be less effective regardless of the type of drive train.

[fox46]

I like mechanum, Omni and swerve drives- it makes it real easy to bulldoze through them and get to where you want to go on the field!

Keep in mind, this is coming from someone who helped pioneer the design and iteration of several omnidirectional drives back in my days with 854 so it's not that I don't like them, I'm just honest-

Unless you have an awesome driver- preferably one who has experience with RC helicopters, don't even bother with omnidirectional drive unless you're building a practice machine and can allow piles of stick time and endless drills to get their skill level up. Far too many teams build omnidirectional drives and just don't use them to their full capability and if you aren't using them to their full capability then you WILL be outgunned by a skid steer/tank drive.

Secondly, don't even bother with Omni if you aren't using a gyro and accelerometer to take some of the work away from the driver. DC motors always run better in one direction than another and to try and pull off one of these drivetrains without some sort of logic to make sure it is doing what the driver tells it is just setting yourself up for an extremely difficult to drive robot.

Swerve drive- People think that with a swerve drive you have the tractive capabilities of a tank with the maneuverability of Omni- you do not. Each wheel has (at least) one motor. When you start pushing against something, all your weight transfers to your rear wheels leaving your front wheels spinning in the air. Hence, in a shoving match, typically you are only using half your available drive power. Furthermore, the lag time associated with steering your modules is painful. Any lag time slows down your ability to utilize your maneuverability to its maximum advantage and if you don't utilize it to its maximum advantage you WILL be outgunned by a skid steer/tank.

[Jefferson]

Well... I've successfully avoided this thread until now, but I'm not going to walk away from this one...

Originally Posted by fox46

I like mechanum, Omni and swerve drives- it makes it real easy to bulldoze through them and get to where you want to go on the field!

We've not been buldozed much this season, even by very well built 6 CIM tank drives.

Originally Posted by fox46

Keep in mind, this is coming from someone who helped pioneer the design and iteration of several omnidirectional drives back in my days with 854 so it's not that I don't like them, I'm just honest-

For someone who doesn't not like omnidirectional drives, your post has a very different tone. Everything you say in here is stated as absolutes, and it's just not that clear cut.

Originally Posted by fox46

Unless you have an awesome driver- preferably one who has experience with RC helicopters, don't even bother with omnidirectional drive unless you're building a practice machine and can allow piles of stick time and endless drills to get their skill level up. Far too many teams build omnidirectional drives and just don't use them to their full capability and if you aren't using them to their full capability then you WILL be outgunned by a skid steer/tank drive.

This is true of any drivebase, not just omni drives. A well built drivebase does nothing if the drivers don't have practice time on the sticks.

Originally Posted by fox46

Secondly, don't even bother with Omni if you aren't using a gyro and accelerometer to take some of the work away from the driver. DC motors always run better in one direction than another and to try and pull off one of these drivetrains without some sort of logic to make sure it is doing what the driver tells it is just setting yourself up for an extremely difficult to drive robot.

We've never used an accelerometer in our drive code and only late last year incorporated a gyro into the driver-controlled code. The gyro improved the performance of the robot, not the ease of driving.

Originally Posted by fox46

Swerve drive- People think that with a swerve drive you have the tractive capabilities of a tank with the maneuverability of Omni- you do not. Each wheel has (at least) one motor. When you start pushing against something, all your weight transfers to your rear wheels leaving your front wheels spinning in the air. Hence, in a shoving match, typically you are only using half your available drive power. Furthermore, the lag time associated with steering your modules is painful. Any lag time slows down your ability to utilize your maneuverability to its maximum advantage and if you don't utilize it to its maximum advantage you WILL be outgunned by a skid steer/tank.

Pushing doesn't make the wheels leave the ground, getting under the robot (bumper) does. ANY robot that has weight taken away will have less traction and lack pushing force.

[Ether]

Originally Posted by Jefferson

Pushing doesn't make the wheels leave the ground

Horizontal pushing "transfers some of the weight" to the rear wheels, even if the front wheels do not leave the ground.

ANY robot that has weight taken away will have less traction and lack pushing force.

I believe the point being made was that with a chained drive, all motors on each side are still providing force... And that force will be distributed to the wheels with the greater traction (the rear wheels), once the wheels with the lesser traction (the front wheels) have reached their traction limit.