FRC T-bone-ing and Hexagonal drive

[Chris is me]

Originally Posted by Ty Tremblay

I don't think you understand my point. 1678 is a team that has the organization and resources to devote effort into properly testing and designing a hexagonal drivetrain.

I don't want this post to leave teams thinking that if they build a hexagonal drivetrain they'll miraculously be better robots when they still can't handle the game object efficiently.

A drivetrain won't win you an event, what you mount on top will.

Originally Posted by Ty Tremblay

Game breaking strategies like 2002 are not an accurate example in this era of FRC. 3rd robots aren't going to get picked for their hexagonal drivetrains. They're going to get picked for having solid, well driven drivetrains. If a team has to sacrifice either of those two in the least then they are not a team that should build a hexagonal drivetrain. My team, 319, is one of those teams.

Originally Posted by Lil' Lavery

Sure, there are exceptions, but I don't think Ty's assertion is incorrect. You're generally not going to win an event because you have a stellar drive train alone. A bad drivetrain can certainly lose you an event, but a good one isn't going to win without a functioning manipulator, drive team, and strategy.

Bumper profiles and bumper fabrics are things that are important for the 90th percentile teams trying to become the 95th or 99th percentile teams. They are far less important for the 50th percentile team. Rather than spending time, money, and manpower into researching bumper shape/material, it's probably better to invest that into, say, intake shape/material.

I agree with these two, but also want to add something. Making your drivetrain shaped like a hexagon isn't even the best way (in terms of effort to reward) to beat T-Bone pins! Drop down casters, smooth bumper fabric + solid core noodles, etc. all seem to produce a higher reward without having to change how you design drivetrains in the first place. Don't reinvent the wheel when you could just add one that drops down if you really need it.

Plus, how many times have you been a great scoring robot with a fast drivetrain that performs well, only to be beaten by T-bone pins? The teams that need to beat T-bones to become competitive already know this, and the teams who are reading this thread who hadn't really considered the problem before probably have bigger things to worry about than this defensive edge case.

[jijiglobe]

Can any teams that have used sailcloth for their bumpers give recommendations? There are a lot of options for materials. Which materials are best? Is there one that's clearly optimal for use on bumpers?

[nuclearnerd]

Originally Posted by Ty Tremblay

I don't want this post to leave teams thinking that if they build a hexagonal drivetrain they'll miraculously be better robots when they still can't handle the game object efficiently.

Not to mention that if a hexagonal drive base proves to have a huge advantage (I haven't worked the numbers, but I'm not convinced), teams will develop "anti-anti-t-boning" features. A gap in the front bumper for instance would allow any defensive robot to T-bone a hexagonal robot nearly as well as a square robot.

[Lil' Lavery]

Originally Posted by nuclearnerd

Not to mention that if a hexagonal drive base proves to have a huge advantage (I haven't worked the numbers, but I'm not convinced), teams will develop "anti-anti-t-boning" features. A gap in the front bumper for instance would allow any defensive robot to T-bone a hexagonal robot nearly as well as a square robot.

Only if they hit it right on.

[GeeTwo]

Originally Posted by nuclearnerd

Not to mention that if a hexagonal drive base proves to have a huge advantage (I haven't worked the numbers, but I'm not convinced), teams will develop "anti-anti-t-boning" features. A gap in the front bumper for instance would allow any defensive robot to T-bone a hexagonal robot nearly as well as a square robot.

Originally Posted by Lil' Lavery

Only if they hit it right on.

Putting these two together and reaching a bit farther, I'm imagining a defensive robot with an enormous crescent wrench head.

[nuclearnerd]

Originally Posted by Lil' Lavery

Only if they hit it right on.

If I understand it correctly, one of the effective things about T-Bone pins is that they are "self-engaging". Check out the attached sketch (in stunning powerpoint CAD!) When the defensive robot on the left (yellow) hits the offensive robot on the side (blue), the contact force is angled to the right of the Blue robot's turning center. This creates a torque (green arrow) that turns the blue robot into the front bumper of the yellow robot. Since the other corner of the yellow robot is on the left side of the turning center, contact there will try to turn the blue robot back the other way. The result is as long as the yellow bot pushes, the blue robot can't exert a turning torque greater than the one caused by the contact, so the two robots become locked together at a 90 degree T (not shown).

A hexagonal robot (shown in blue on the right) changes the contact location and angle in an attempt to move that contact force closer towards (or completely across) the blue robot's turning center, reducing the leverage and producing less "T-Bone torque". But this can be subverted by notching the front bumper of the defensive robot (shown in yellow on the right). The notched bumper contacts the blue robot at almost exactly the same place, and with as much T-Bone torque as the scenario on the left. (although it might be a little reduced if the hex angle is sharp enough).

An easier way to reduce the chance of getting T-boned is to move the turning center closer to the front or back of the offensive robot. If you moved the turning center on the blue robot all the way to the right of the diagram for instance, the yellow robot would produce almost no T-Bone torque (or even reverse or helpful) T-Bone torque. The turning center can be repositioned using permanent or drop-down omni wheels (as suggested earlier), or with swerve drives. Those features allow an offensive robot to "pick and roll" off a T-Bone pin.

That's my understanding of things anyway. I'd be interested to hear if other people of different theories or data.

[GeeTwo]

Originally Posted by nuclearnerd

An easier way to reduce the chance of getting T-boned is to move the turning center closer to the front or back of the offensive robot.... using permanent or drop-down omni wheels (as suggested earlier), or with swerve drives. Those features allow an offensive robot to "pick and roll" off a T-Bone pin.

That's my understanding of things anyway. I'd be interested to hear if other people of different theories or data.

Using permanent omni wheels to allow you to roll off of a T-bone pin may be jumping out of the frying pan into the fire. If you move your center of rotation very far towards one end of the robot, you are making yourself more susceptible to being steered from the other end by an opposing robot.

[JVN]

Originally Posted by GeeTwo

Using permanent omni wheels to allow you to roll off of a T-bone pin may be jumping out of the frying pan into the fire. If you move your center of rotation very far towards one end of the robot, you are making yourself more susceptible to being steered from the other end by an opposing robot.

This is entirely game dependent. Several teams were successful in 2014 using a 2+2 setup. Similarly safe zones in 2011, 2012, 2013 would have lent themselves well to this setup.

"Beat the defender, get into position and score."

In 2014, the secret was to score quick enough that a safe zone wasn't needed.

[GeeTwo]

Originally Posted by GeeTwo

Using permanent omni wheels to allow you to roll off of a T-bone pin may be jumping out of the frying pan into the fire. If you move your center of rotation very far towards one end of the robot, you are making yourself more susceptible to being steered from the other end by an opposing robot.

Originally Posted by JVN

This is entirely game dependent. Several teams were successful in 2014 using a 2+2 setup. Similarly safe zones in 2011, 2012, 2013 would have lent themselves well to this setup.

"Beat the defender, get into position and score."

In 2014, the secret was to score quick enough that a safe zone wasn't needed.

Exactly what I meant by "may be". If a defender can steer you away from where you want to be, that might be as effective as stopping you where you are. Note also that you may be opening yourself up to being effectively defended via steering by robots which cannot generate enough force and drivers who do not have quite enough skill to effect a T-bone against you.

[AdamHeard]

Too many people in this thread are speculating. That puts a lot of noise out there for teams looking for good information.

[EricH]

Originally Posted by AdamHeard

Too many people in this thread are speculating. That puts a lot of noise out there for teams looking for good information.

Question (somewhat rhetorical): As it relates to being the victim of a T-bone pin, does swerve (or mecanum, or other omnidirectional drives) help you get out, or make the problem worse? What about if you're trying to place the T-bone?

[Ari423]

Originally Posted by EricH

Question (somewhat rhetorical): As it relates to being the victim of a T-bone pin, does swerve (or mecanum, or other omnidirectional drives) help you get out, or make the problem worse? What about if you're trying to place the T-bone?

Wheels with rollers (mecanum, omni) don't get T-boned, they just get pushed. This could be a positive or a negative depending on your team's strategy. Swerve also can't get T-boned because you can turn the wheels 90* and drive away from the T-boner.

Wheels with rollers also can't cause a T-bone, since they can't push with any substantial force. Swerve drive can place a T-bone.

[AdamHeard]

Originally Posted by EricH

Question (somewhat rhetorical): As it relates to being the victim of a T-bone pin, does swerve (or mecanum, or other omnidirectional drives) help you get out, or make the problem worse? What about if you're trying to place the T-bone?

In regards to swerve, we didn't do enough testing with this in mind to make scientific statements. That being said based on the three we've run, I would think it would make it easier to get out of T-bones in a perfect world. I'd highly recommend not investigating swerve as a t-bone solution. There are so many points in a swerve drive where the increased load from being t-boned could cause your gearing to experience increased friction and make the situation worse.

Our experience running butterfly in 2013 offseason made it seem well suited for that style of safe zone to safe zone sprinting, but we also ran a normal 6wd that year and had similar performance.

It's hard to say for sure, there are many variables involved with the implementation (and how its' driven) that matter a great deal, so it's not as simple as X drive versus Y drive.



The best thing to do is to proto and test what you want to run if this is a performance advantage you are going for. Designing your setup to be a modification of the AndyMark or Vex kit drives would make this iteration easier for most teams.

[Andrew Schreiber]

Originally Posted by Ari423

Swerve also can't get T-boned because you can turn the wheels 90* and drive away from the T-boner.

Source? You're operating under the assumption that the wheels can under the extra pinning load (which for some swerves isn't true) and that the wheels all retain normal loading making driving it sane. And that the driver thinks of that.

I've seen swerves get TBoned.


I've also seen mecanum wheeled robots shove 6wd robots sideways.. Physics is weird sometimes, this is why we prototype.

[notmattlythgoe]

Originally Posted by AdamHeard

In regards to swerve, we didn't do enough testing with this in mind to make scientific statements. That being said based on the three we've run, I would think it would make it easier to get out of T-bones in a perfect world. I'd highly recommend not investigating swerve as a t-bone solution. There are so many points in a swerve drive where the increased load from being t-boned could cause your gearing to experience increased friction and make the situation worse.

Our experience running butterfly in 2013 offseason made it seem well suited for that style of safe zone to safe zone sprinting, but we also ran a normal 6wd that year and had similar performance.

It's hard to say for sure, there are many variables involved with the implementation (and how its' driven) that matter a great deal, so it's not as simple as X drive versus Y drive.



The best thing to do is to proto and test what you want to run if this is a performance advantage you are going for. Designing your setup to be a modification of the AndyMark or Vex kit drives would make this iteration easier for most teams.

Curious. What kind of butterfly did you run? This style? How did you have the controls set up? Were the front and rear wheels able to actuate independently?