pic: 1675's REAL IRI Upgrade

[Ryan Dognaux]

Originally Posted by Jared341

Had 2761 not stopped in their tracks, 1675 doesn't get a clean release into the scoring zone.

After watching the clip about 5 times in a row, I disagree with this statement. 1675's only goal at that point was to get on the other side of the defender and get to the scoring rack. During the two-robot spinning motion, 1675 was on the opposite side and there was really nothing to stop them from translating away from 2761, as shown below -



I think what contributed to this motion was the mecanum wheel rollers being pushed from the side by 2761. The real trick would have been timing the translation correctly.

There's a lot of strong opinions about mecanum drive systems here - which is fine, everyone is entitled to their own opinion. The way I see it now with AndyMark selling mecanum wheels is that this gives teams an opportunity to have an omni-directional drive train with very minimal effort. So you have every team under the sun buying a set and trying them out, even if they aren't necessarily implemented correctly. More often than not, I see teams driving tank style with two sticks, completely ignoring the mecanum's translation capabilities.

So what does this come down to? Mecanum drives are inherently more difficult to control than a standard tank style drive. You can show someone immediately how to operate a tank style drive train and they'll understand it. They won't master it immediately, but I would argue that the amount of time that it takes to 'master' a tank style drive train is less than the time it takes to 'master' a mecanum drive train. No hard evidence to back up that claim either, just something that I've observed.

Most teams don't build second robots and don't have much driver practice time. So when they choose a mecanum drive, they are probably still trying to figure out how to control it out on the field. I think this adds to the perception that mecanum drive systems are a bad choice, when in reality the learning curve is just larger.

I agree that there are inherent disadvantages to using a mecanum drive, and that if your team has the time and resources to build a swerve drive system, then that is the way to go probably. But most teams don't. So they sacrifice some pushing power at the cost of omni-directional maneuverability.

One of our goals this summer has been to get students driving mecanum every week. We will see if it pays off next season - who knows, maybe we will finally be able to produce this fabled mecanum vs. six wheel video.

[Chris is me]

"Healthy" debate about mecanum aside, I think it's ridiculous that we've gotten to the level of directly insulting 1675's machine and design decisions. They clearly had a pretty good robot this year.

[ratdude747]

Originally Posted by Ryan Dognaux

After watching the clip about 5 times in a row, I disagree with this statement. 1675's only goal at that point was to get on the other side of the defender and get to the scoring rack. During the two-robot spinning motion, 1675 was on the opposite side and there was really nothing to stop them from translating away from 2761, as shown below -



I think what contributed to this motion was the mecanum wheel rollers being pushed from the side by 2761. The real trick would have been timing the translation correctly.

There's a lot of strong opinions about mecanum drive systems here - which is fine, everyone is entitled to their own opinion. The way I see it now with AndyMark selling mecanum wheels is that this gives teams an opportunity to have an omni-directional drive train with very minimal effort. So you have every team under the sun buying a set and trying them out, even if they aren't necessarily implemented correctly. More often than not, I see teams driving tank style with two sticks, completely ignoring the mecanum's translation capabilities.

So what does this come down to? Mecanum drives are inherently more difficult to control than a standard tank style drive. You can show someone immediately how to operate a tank style drive train and they'll understand it. They won't master it immediately, but I would argue that the amount of time that it takes to 'master' a tank style drive train is less than the time it takes to 'master' a mecanum drive train. No hard evidence to back up that claim either, just something that I've observed.

Most teams don't build second robots and don't have much driver practice time. So when they choose a mecanum drive, they are probably still trying to figure out how to control it out on the field. I think this adds to the perception that mecanum drive systems are a bad choice, when in reality the learning curve is just larger.

I agree that there are inherent disadvantages to using a mecanum drive, and that if your team has the time and resources to build a swerve drive system, then that is the way to go probably. But most teams don't. So they sacrifice some pushing power at the cost of omni-directional maneuverability.

One of our goals this summer has been to get students driving mecanum every week. We will see if it pays off next season - who knows, maybe we will finally be able to produce this fabled mecanum vs. six wheel video.

it depends on driver setup.

actually, the drivers got the drivetrain part down very quickly, as the way we set it up was just like the controls in video games like halo work. find a halo junkie and they will have mecanum down in a few minutes.

depends on the person i guess.

[Ryan Dognaux]

Originally Posted by ratdude747

depends on the person i guess.

Exactly. You can try to automate and control as much functionality as possible on your robot, but when it really comes down to it, it's up to the driver and operator to control the thing. Some teams just have better drivers than others. Better often means that they've had more practice and have had time to get used to how their machine drives and operates.

Anyway, back on topic - 1675's machine is legit.

[Duke461]

This is why everyone needs to remember correlation does NOT imply causation, as i said earlier. Too many variables are in play. To name a few: Strategy during the match, driver experience, opposition, the game that year, skill of the robot in question outside of drivetrain, teammates, competition location, driver skill, control setup, speed, etc.

[Taylor]

What is it about mecanums that make them so polarizing? The closest analogy I can think of is scissor lifts - they are generally frowned upon for competitive robotics use, but they don't carry nearly as much hatred (or love) as mecanums.
I've yet to see an "I love mecanums they're the best ever" thread; I've seen many "mecanums are the wheels of the devil" threads. Most teams that use them, do so as a bit of a situational compromise - sure, there isn't as much traction or speed as treaded wheels, but there is the gain of lateral maneuverability for minimal mechanical and programming difficulty, compared to swerve/crab drive.

So why the hatred?

[Ankit S.]

Originally Posted by Taylor

So why the hatred?

It might be the way it was implemented. Teams that dislike mechanum drive may have had bad experiences with them, and rather than risk 400$ and try it again (or use those wheels again), they forsake it forever.

My team on the other hand used mechanum this year and we were very pleased with the result. We were able to weave around defense (atleast when our PWM's were connected). Also, the strafing helped us line up with the pegs.

All in all, teams that have had bad experiences w/ mechanum may forsake it, and teams with better experiences will probably stick with it. Due to the complexity and the relative novelty of mechanum, more teams have had bad experiences with mechanum, or better experiences without mechanum.

[ratdude747]

Originally Posted by BeltSanderRocks

It might be the way it was implemented. Teams that dislike mechanum drive may have had bad experiences with them, and rather than risk 400$ and try it again (or use those wheels again), they forsake it forever.

My team on the other hand used mechanum this year and we were very pleased with the result. We were able to weave around defense (atleast when our PWM's were connected). Also, the strafing helped us line up with the pegs.

All in all, teams that have had bad experiences w/ mechanum may forsake it, and teams with better experiences will probably stick with it. Due to the complexity and the relative novelty of mechanum, more teams have had bad experiences with mechanum, or better experiences without mechanum.

This is what I was going to say but you already hit the nail on the head.

[Tom Bottiglieri]

I don't understand this debate. What teams choose to incorporate into their robot is their choice and that choice is made under their value system. Yeah sure, 1114 has never used mecanum, but not every team wants to be 1114.

[Lil' Lavery]

Open-field movement is not the reason to pick a mecanum, or just about any, omni-directional drive. The notable advantage is analagous to how these drive systems are used in the real world. The ability to translate in multiple axes without rotating the entire robot. This is particular useful in small, tightly packed spaces.

Think of how you parallel park in a car. Or, perhaps more of a direct analogy, moving from one normal parking space to the one next to it. That's not a very efficient or easy to execute series of actions in a FRC match. Strafing saves maneuvers like that in tight spaces.

Whether or not this is enough of an advantage to avoid the numerous drawbacks of mecanum systems is up to each particular team. I know that I won't support the selection of a mecanum system for teams that I'm associated with if FRC games continue to have a similar field lay-out and style of play. On the other hand, I probably carry a bias since an alliance partners' mecanum drive was a significant factor in ending my senior season in the Galileo semi-finals in 2007.

Originally Posted by Kevin Kolodziej

Found the video I was looking for. Its not exactly driving circles around the defender, but its certainly a maneuver that would not have been possible without mecanum wheels: http://youtu.be/PDsq1sEVVKs?t=2m28s

Sure it would have. "Bumper-locked spins" happen in FRC all the time. The real key to that maneuver was the open space where it was happening allowing for ~270deg of rotation. This type of maneuver is easily possible with a tank drive in a "side-impact" scenario like that. This isn't a perfect example, but it's one that was readily available and show the same principle being executed by a 6WD being defended by an excellent defensive machine who was on their way to Einstein.
http://www.youtube.com/watch?v=Bzpo3vVeGEY#t=3m45s
e; Another example in the same video.
http://www.youtube.com/watch?v=Bzpo3vVeGEY#t=4m48s

Originally Posted by Ryan Dognaux

After watching the clip about 5 times in a row, I disagree with this statement. 1675's only goal at that point was to get on the other side of the defender and get to the scoring rack. During the two-robot spinning motion, 1675 was on the opposite side and there was really nothing to stop them from translating away from 2761, as shown below -



I think what contributed to this motion was the mecanum wheel rollers being pushed from the side by 2761. The real trick would have been timing the translation correctly.

Notice how they escape from the spin move at the end, they don't translate directly away. They "spin off" the block, similar to how a tank drive would. Everything in that maneuver could have been executed by a tank drive, and similar situations frequently happen.

[ayeckley]

We won Buckeye in 2010 (as alliance captain) using mechanums. During the balance of the season we never felt that we were at any real disadvantage against pusher-bots. In fact, we even successfully stuffed a reasonably-competitive 4WD tank opponent into the goal once. We put a lot of time, effort and $ into the control system to make driving as intuitive as possible however (closed loop on all four wheels, strategic assignment of user I/O, etc.). That, combined with a good driver and a practice bot made us successful, at least at the Regional level which was good enough for us. I don't think we would have been as successful with a traditional drive.

Just another data point...

[Ryan Dognaux]

Originally Posted by Lil' Lavery

Notice how they escape from the spin move at the end, they don't translate directly away. They "spin off" the block, similar to how a tank drive would. Everything in that maneuver could have been executed by a tank drive, and similar situations frequently happen.

Correct - and I guess that would be a question for the driver and operator of 1675's robot, why didn't they translate away? It certainly was possible at that point, but it may have been just a heat of the moment kind of thing. It could also have something to do with they way their controls are set up. I've seen teams using two joysticks with a mecanum drive system, which seems counter-intuitive to me.

[BigJ]

Originally Posted by Ryan Dognaux

Correct - and I guess that would be a question for the driver and operator of 1675's robot, why didn't they translate away? It certainly was possible at that point, but it may have been just a heat of the moment kind of thing. It could also have something to do with they way their controls are set up. I've seen teams using two joysticks with a mecanum drive system, which seems counter-intuitive to me.

We use 2 joysticks. one is translation and the other does rotation on the x axis. Yes, this could be done with a 3-axis joystick but we didn't feel like buying a different joystick. Also tests with team member's personal 3 axis joysticks usually find the twisting in the direction of the arm can be awkward sometimes, especially if you needed to twist while translating in some directions.

[Taylor]

Originally Posted by BigJ

We use 2 joysticks. one is translation and the other does rotation on the x axis. Yes, this could be done with a 3-axis joystick but we didn't feel like buying a different joystick. Also tests with team member's personal 3 axis joysticks usually find the twisting in the direction of the arm can be awkward sometimes, especially if you needed to twist while translating in some directions.

We found the same to be true. We also found that it is very difficult to do a pure forward/backward, left/right, or cw/ccw twist and the driver would often do multiple moves at once unwittingly. For that reason, we have a 2-stick setup - one for forward and turning, one for strafing. Intuitive for laypeople, and workable in competition.

[lemiant]

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