What is T-boning?

[Andy A.]

Originally Posted by BBray_T1296

So like a normal omni-tank drive, but with 4 wheel independent gear-trains. Sounds expensive.

I doubt many such configurations are planned. It's probably more a case of not getting the software (and/or hardware) working correctly, and tank steering being a contingency plan.

[JVN]

Originally Posted by Karthik

There are a surprising number of mecanum robots that are not actually programmed to go sideways; they simply use mecanum wheels in a tank drive setup...

Just because they don't EVER move sideways, doesn't mean they're not programmed to do so. It is bad scouting to make an assumption like this...

[techtiger1]

Originally Posted by JVN

Just because they don't EVER move sideways, doesn't mean they're not programmed to do so. It is bad scouting to make an assumption like this...

*Or that the driver can use this capability effectively.

[Michael Hill]

Originally Posted by Karthik

There are a surprising number of mecanum robots that are not actually programmed to go sideways; they simply use mecanum wheels in a tank drive setup...

This blows my mind. With code available online that does the work for you, how do teams let this happen to them?

[zinthorne]

Originally Posted by tickspe15

If you have your mecanum programmed properly and your drivers know how to take advantage of its holonomic capabilities i dont understand how you can possibly get t-boned. When somebody comes along side you all you need to do is translate away.

While this is possible, our Mecanems couldnot strafe or go fast enough sideways to get out of it.

[cjl2625]

Originally Posted by Karthik

There are a surprising number of mecanum robots that are not actually programmed to go sideways; they simply use mecanum wheels in a tank drive setup...

Why would any team put mecanum wheels on their robot and not implement strafing code? You lose your pushing power and don't even get the added maneuverability. Might as well just go with normal tank drive...

Originally Posted by safiq10

...some examples of how team get out of these situation...

We rotate our wheels 90 degrees and move away.
Or perhaps we might pivot around a wheel and roll out of it.
hehehe... #swerve

[Mark Sheridan]

Originally Posted by Michael Hill

This blows my mind. With code available online that does the work for you, how do teams let this happen to them?

Having done mecanum and octocanum successfully (or not) for about 4 seasons with 3309. I had to debug a lot of other teams's mecanum drives. The number one reason I saw was not implementing a gyro. With inadequate practice, drivers just revert tank. Some just avoid strafing, others just use the tank code instead. I think most teams I met did not know the gyro was important, the remainder could not get their gyro to work. I speculate the later was due to a lack of time for the programmers to work on their robot.
the second issue I have seen is that teams over tighten the Andy-Mark mecanums, locking the rollers preventing the strafe. this issue can very from all the rollers to just one. Even with one roller jammed, strafing is awful with every rotation of the wheel.

I had lot of fun with mecanum, its a cool off season project but I am having 3309 go back to tank. To explain I will steer this conversation back to the t-bone topic. There are defensive analogues for mecanum. 3309 and 3476 have practiced a fair bit together. 3309 ran a octocanum this year. 3476 had a west coast tank that were slightly faster than 3309.

Two moves that tanks can do against mecanum are:
1. Plowing: Essentially a T-Bone but you carry through with your hit. this was common tactic in the wedge robot era. 3476 would ram the side of 3309. 3309 would attempt to roll dodge. then its a battle of skill , 3309 would try to roll off and continue but if 3476 turns with 3309, 3476 would keep pushing or rather chasing 3309. So its essentially looks like a high speed t-bone. If 3309 stops moving, 3476 will push them or if 3476 lets off, 3309 would escape. If 3309 can't escape, eventually the robot will wither run out of room to roll dodge and get pinned into a wall (with pining rules being applied) or attempt to straighten out to shoot where the pushing force 3476 will start shoving 3309 off course. typically, 3309 would roll to the goal and thus 3476 would shove 3309 into the wall forcing 3309 to low goal score.
2. Wall defense (I know this as crossing the T): i think this is the best against mecanum. 3476 would drive back a forth perpendicular to 3309. We tried having 3309 strafing to get around but the drive was not quick enough. Mecanum could not push through, so 3309 dropping to tank mode to push 3476, it would work but wasted a lot of time. So it forced 3309 to adopt V turns and fake outs to get around. This was when 3309 decided to not do mecanum again because the bulk of the moves that would work were tank drive moves that 3476 uses. We just started running out of uses for the strafe.

I think these are the terms that are colloquial to FRC. It would be interesting if anyone know the history of these driving techniques and how they evolved over time. Personally I feel mecanum is safe from the 20 second long t-bone but they are not immune to defense. More importantly, mecanum can't excecute a t-bone without being a octocanum. finally with ballistic nylon and sail cloth bumper material options, any team can build a very t-bone resistant tank drive.

[Gregor]

Originally Posted by cjl2625

Why would any team put mecanum wheels on their robot and not implement strafing code?

It's less a question of intention, and more a question of capability.

[Pat Fairbank]

Originally Posted by Michael Hill

This blows my mind. With code available online that does the work for you, how do teams let this happen to them?

I've seen worse -- teams that chain both mecanum wheels on each side to the same gearbox.

[Michael Hill]

Originally Posted by Pat Fairbank

I've seen worse -- teams that chain both mecanum wheels on each side to the same gearbox.

Again, that blows my mind. Why buy mecanum wheels?

Also, when are the Poofs going to use mecanum to show us how to do it right? :-P

[AdamHeard]

Originally Posted by Pat Fairbank

I've seen worse -- teams that chain both mecanum wheels on each side to the same gearbox.

I've seen worse.

4wd Swerve. Each module had a super shifter in it (it actually rotated the 360* with the wheels).

Steering motors were removed, Andymark mecanum wheels installed. Shifters locked in high gear. Never saw them strafe

I called it Andy Baker's daughter's college fund.

[EricH]

I can think of one possible reason to use mecanums in a 4WD tank configuration. ONE.

And it's not even a good one--there are a number of other possible tricks to use to get the same result without loosing traction.

The reason? Better turning (this is on a 4WD long bot with a long wheelbase--say about 36" or so).

The other alternatives? Omnis on either one end or opposite corners. Play with the tread materials to get some better slippage. Use Lunacy wheels (). Stick a wheel in the middle with a slight drop (OK, so that's called a 6WD). Monkey with the wheelbase/trackwidth to get a shorter wheelbase and thus better turning (this is best done in the design stage, but if you're desperate...). Drop-down wheels. You get the picture. And guess how many of them are most likely better than the mecanum option?

[PayneTrain]

Originally Posted by cjl2625

Why would any team put mecanum wheels on their robot

Great question. (Really can't believe no one's done that yet.)

The general reasoning you can find relating the implementation of mecanum drive and a successful robot are as follows

1) The teams that DO implement it do poorly because they may find themselves spending inordinate amounts of time working on the drive base alone, only to maybe not even have it work. Teams with more experience have better success with the system, BUT
2) The teams you would consider to be successful don't implement it for reasons you can say boil down to finding a better way for them to implement omnidirectional drive (148) or them mastering a simple (not easy necessarily, but simple) concept like the WCD on 254.

(can't stress enough this is a sweeping generalization on mecanum and quote-replies of anecdotes about your team's success with mecanum drive will be met with thunderous indifference)

[Karthik]

Originally Posted by JVN

Just because they don't EVER move sideways, doesn't mean they're not programmed to do so. It is bad scouting to make an assumption like this...

It is bad scouting of scouting to make an assumption of an assumption in regards to another team's scouting...

Originally Posted by Pat Fairbank

I've seen worse -- teams that chain both mecanum wheels on each side to the same gearbox.

Yup, seen this one before.

Mecanum drives fascinate me, so when I see a mecanum team that doesn't go sideways, I'll try and make time to go ask the team why they aren't going sideways. The most common answers are:

1. We just wanted to use Mecanum wheels. We didn't know they needed special programming.
2. The robot moves much faster in tank mode.
3. The robot wouldn't drive straight with mecanum mode.

[Taylor]

It's amazing to me how many threads devolve into mecanum-bashing.

Our FRC team used them once in 2011, and once again in offseason versions of our 2013 robot; we liked them for our strategy and for that game, and have no ill feelings toward them. They were rock-solid and worked perfectly well for what we wanted. But we never got t-boned - in fact we actively avoided contact because that's what mecanum wheels are designed to do.