Omni Directional movement for tank drive.

[Vikesrock]

Originally Posted by Hawiian Cadder

The goal of this would be to make a robot more difficult to push.

I'm lost. Can you explain how this robot would be more difficult to push?

[Lil' Lavery]

Isn't the rate of "linear" motion related to the rate of rotation in this design? So wouldn't slowing down that rotation, in turn, slow down how quickly you "move" around the field?

I also question the safety of this design on the FRC scale. Even if you keep the design relatively compact (say 18"x18" without bumpers) and rotate at the bottom end of your suggested range (120rpm), the outside corners of your bumpers are already moving faster than 1000 ft/second. Much worse are the hard corners of your frame (which are traveling 800 ft/second). There's a reason that videos like this one give warnings about "melty-bots" being able to kill you if they're out of control. There's a reason why these types of robots are mostly seen in robot fighting, because their very functionality relies on large amount of kinetic energy.

[Grim Tuesday]

Our team has a running joke of inventing "mecanum treads".

[AdamHeard]

The common difficult issue for "melty brain" designs is a reliable heading indicator. If the robot doesn't accurately know where it is at least once per cycle, it can't accurately translate.

Even fully functional melty brain designs achieve rotating translation speeds that are very slow compared to the vehicle purely translating. It would be an incredibly easy robot to just juke around.

[JohnFogarty]

Mauler 5150 v.s. Jabberwocky
Battlebots Televised version.
Watch what happens.
P.S.(I am totally not posting that because my mentor drove the winning robot) noo....why would I do that.)

[AdamHeard]

Originally Posted by John_1102

Mauler 5150 v.s. Jabberwocky
Battlebots Televised version.
Watch what happens.
P.S.(I am totally not posting that because my mentor drove the winning robot) noo....why would I do that.)

I don't see the relevance here. I'm pretty certain Mauler was a shell spinner, and had a traditional skid steer drive inside.

[JesseK]

It's an interesting concept for driving, but I'm pretty sure the mechanisms team would stage a coup after their end effector fell of for the umpteenth time due to excessive stresses on the joints.

[Andrew Remmers]

Originally Posted by Grim Tuesday

Our team has a running joke of inventing "mecanum treads".

Um.... I think we might have done that at the VEX level

[SamM]

Originally Posted by Lil' Lavery

Isn't the rate of "linear" motion related to the rate of rotation in this design? So wouldn't slowing down that rotation, in turn, slow down how quickly you "move" around the field?

I also question the safety of this design on the FRC scale. Even if you keep the design relatively compact (say 18"x18" without bumpers) and rotate at the bottom end of your suggested range (120rpm), the outside corners of your bumpers are already moving faster than 1000 ft/second. Much worse are the hard corners of your frame (which are traveling 800 ft/second). There's a reason that videos like this one give warnings about "melty-bots" being able to kill you if they're out of control. There's a reason why these types of robots are mostly seen in robot fighting, because their very functionality relies on large amount of kinetic energy.

Though your numbers are off by an order of magnitude or two, you are right in theory. It would be much faster to just turn a tank robot and drive in the desired direction than it would be to wait for the robot to "drift" in that direction.

Originally Posted by Grim Tuesday

Our team has a running joke of inventing "mecanum treads".

There's actually a robot with these in one of the labs here at the University of South Florida. I believe a master's student designed it for his thesis a few years back. I'll see if I can get a picture next time I'm there.

[RoboDesigners]

Originally Posted by Grim Tuesday

Our team has a running joke of inventing "mecanum treads".

At VEX level:
http://www.vexforum.com/showpost.php...1&postcount=19
http://polynomic3d.com/user/smith/Mechanum.png <- That's VEX tread wrapped around a sprocket...

[Hawiian Cadder]

the main goal of this is not to make the robot faster, it is to remove traction and torque from the factors that influence how difficult a robot is to push, thus allowing a team with single speed gearboxes to effectively block a team with 2 speed gearboxes.

[Jeffy]

Originally Posted by Hawiian Cadder

the main goal of this is not to make the robot faster, it is to remove traction and torque from the factors that influence how difficult a robot is to push, thus allowing a team with single speed gearboxes to effectively block a team with 2 speed gearboxes.

Curiosity:
How does this eliminate traction and torque as factors?

On traction:
A single speed robot CAN block a 2 speed robot.
Assume:
1. The single speed robot is oriented so that the motors do not backdrive when being pushed.
2. The tractive force between the robot and the surface is larger for the single speed robot than the two speed robot.
3. The two speed robot has enough torque to provide more force than the frictional force provided by the wheels and "spin" the wheels/tires.

The frictional force between the robots contact surface (ussualy wheels/treads) is what keeps it from being pushed. For the most part, in FRC, any robot with AM tread can be an effective "blocker".

[Hawiian Cadder]

in my experience teams that attempt to block sideways are easily "spun" also AM tread is not even close to the grippiest material used, the blue mcmaster tread is much gripper.

[SamM]

If you watch videos of meltys (google: spinning tortoise), you'll note as soon as they contact something they bounce away in the opposite direction. All the offensive robot would have to do is bump into the melty, and the reaction force would move it back and to the side. The offensive robot would move back a little but much less because it has much better traction.

I admit it would be cool to see, but i don't see it being a viable design for FIRST.

[Doug G]

This reminds me of Kingman's (FRC# 60) 2002 robot. It could pick up two 180 lb goals and spin them around a center turret. While they never used it during competition, I saw them demo it for a TV crew at SVR that year. It is one of the most impressive and scariest things I've seen a robot do.