pic: 1675's REAL IRI Upgrade

[ratdude747]

Originally Posted by EagleEngineer

So crab drive and swerve drive are the same thing right?

pretty much unless you get to the nitty gritty, where if you use your terms right, there is a difference.

[Kevin Kolodziej]

Originally Posted by Andrew Schreiber

Thanks for reminding me what year 47 ran its second crab. I kept thinking 99 for some reason.

47 did have a crab drive in 1999. There was a match at Great Lakes where they and 111 (on opposite alliances) both grabbed the puck and started going round and round. It was quite fun to watch!

[Andrew Schreiber]

Originally Posted by Kevin Kolodziej

47 did have a crab drive in 1999. There was a match at Great Lakes where they and 111 (on opposite alliances) both grabbed the puck and started going round and round. It was quite fun to watch!

TIL...

[Tristan Lall]

Originally Posted by Andrew Schreiber

47 - 1998, 2000 - 0 Championships(to my knowledge they were the first crab in FRC)

47 in 2001 was a crab too—except with treads. Each module was independently driven and steered.

http://www.chiefdelphi.com/media/photos/12374
http://www.chiefdelphi.com/media/photos/12290
http://www.chiefdelphi.com/media/photos/12291
http://www.chiefdelphi.com/media/photos/12292
http://www.chiefdelphi.com/media/photos/12293
http://www.chiefdelphi.com/media/photos/12736

[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.

[Duke461]

Originally Posted by Taylor

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.

Also agree. Our joysticks at BMR got screwed up and i was forced to use a 3-axis joystick. granted, i had no experience with one and it was still a little screwy (shavings in jaguars we assume), but i absolutely hated it. I would love to hear as to why 2 joysticks is "counter intuitive"; i see no reason as to why it would/should be. In fact, i find a 3-axis counter intuitive.
Eventually we switched back, after much pleading, to using controllers like we did in 2010. Way better.

P.S. Although i prefer one for turning, one for strafing and forward/backward.

[ratdude747]

Originally Posted by Duke461

P.S. Although i prefer one for turning, one for strafing and forward/backward.

sounds like halo style controls... left does all of your translations, right rotates. pretty standard.

3 axis style mecanum/crab is a mistake waiting to happen... when you try to translate left or right, you often rotate yourself as well...

some teams use tank-style controls where to strafe, you have to move both sticks left or right... never made sense to me... I am bad enough at tank controls, let alone that kind of horror.

[Molten]

Since nobody has commented on this yet, what if they tried to strafe with the wheels like this? What would happen? Would they slowly drive out of the treads? or would it just sit there and put tension on the drive? Anyone know?

Just curious,
Jason

[Laaba 80]

Originally Posted by ratdude747

sounds like halo style controls... left does all of your translations, right rotates. pretty standard.

3 axis style mecanum/crab is a mistake waiting to happen... when you try to translate left or right, you often rotate yourself as well...

some teams use tank-style controls where to strafe, you have to move both sticks left or right... never made sense to me... I am bad enough at tank controls, let alone that kind of horror.

Its all about what the driver is comfortable with, it doesnt matter what anyone else thinks about it.

[Duke461]

Originally Posted by Molten

Since nobody has commented on this yet, what if they tried to strafe with the wheels like this? What would happen? Would they slowly drive out of the treads? or would it just sit there and put tension on the drive? Anyone know?

Just curious,
Jason

Well first off, the treads would probably slide off because they're not secured too well....but ignoring that, i would guess that it would barely strafe, and skip around like popcorn popping. What i want to try is to individually wrap each roller with tread. Nobody steal my idea unless 461 doesn't do that in 2012

[BigJ]

Originally Posted by Molten

Since nobody has commented on this yet, what if they tried to strafe with the wheels like this? What would happen? Would they slowly drive out of the treads? or would it just sit there and put tension on the drive? Anyone know?

Just curious,
Jason

Like I said, the kids didn't test it on the practice field like I wanted them to!

My guess is that without securing the treads to the mecanum hubs the diagonal force of the rollers would pop the treads off or tangle them in the wheel if it popped off diagonally.

If secured to the wheel it would just act like a lumpy traction wheel.

If secured to the wheel AND strafing was tried, the robot would be trying to pull itself apart and go nowhere.

[Dave Scheck]

Originally Posted by Laaba 80

I believe wildstang used a 3 axis joystick in 2009, I think it worked out pretty well for them. Its all about what the driver is comfortable with, it doesnt matter what anyone else thinks about it.

Nope, not us. 2009 was a Logitech gamepad. The left stick was the crab strick. You could think of it as a top view of the crab modules. Which ever way you deflected the stick, the module would go there. If you let go of the stick, the module would center. The right stick had multiple purposes. When the crab stick was deflected, only the Y axis was used, and it acted as the throttle. When the crab stick was not deflected, the right stick acted as a single stick tank drive. There were also a few gimmicks that we used such as having a button to angle the crab slightly (helped with picking up against the wall) and some special logic to tank turn while the crab wheels were not centered (standard tank turn logic doesn't hold true when the wheels are turned because the robot will try to pull itself apart )

[Laaba 80]

Originally Posted by Dave Scheck

Nope, not us. 2009 was a Logitech gamepad. The left stick was the crab strick. You could think of it as a top view of the crab modules. Which ever way you deflected the stick, the module would go there. If you let go of the stick, the module would center. The right stick had multiple purposes. When the crab stick was deflected, only the Y axis was used, and it acted as the throttle. When the crab stick was not deflected, the right stick acted as a single stick tank drive. There were also a few gimmicks that we used such as having a button to angle the crab slightly (helped with picking up against the wall) and some special logic to tank turn while the crab wheels were not centered (standard tank turn logic doesn't hold true when the wheels are turned because the robot will try to pull itself apart )

Sorry about that. One of our mentors spoke with someone on your team about your crab drive, to get information about building our crab drive. Have you guys ever used, or tested out a 3 axis joystick for your crab drive? He was pretty convinced that a 3 axis joystick was the way to go after talking to you guys. The way he told us, the twist did the function that your left stick on the game pad did. Either he talked to the wrong person, or he confused himself.