Searching For Swerve / Holonomic Drive Idea

[CalTran]

Originally Posted by asid61

Would not mecanums be easier to implement than a swerve drive and a ball drive? As an offseason project I like swerve drives more if you have the resources to do it, or mecanum if not.

Depends on the ultimate goal of the project - if you're strictly trying to develop some omnidirectional drivetrain, than yes, mecanum would be far cheaper. But if you're looking into it from a learning standpoint and wanting to push the envelope, than developing some sort of ball drive would probably teach a lot more than a "conventional" drive.

[pwnageNick]

Also a traditional mecanum drive isn't much of a mechanical or design challenge. It is slightly harder than a standard tank, purely because of the 2 extra gearboxes.

Also I think we can all agree swerve is a more advantageous drive if the resources available to you allow you to use it.

[ctt956]

What about a robot that's just one ball, like an oversized Sphero?

[RyanShoff]

I thought this would make a good bot:
http://www.gizmag.com/spherical-driv...orcycle/24095/

[lark95]

Originally Posted by ctt956

I would think rotating while driving straight with any drivetrain would be fairly difficult...

If i understand what you guys are talking about correctly it really doesn't take that much coordination at all.

All the driver has to do input the the desired direction of rotation and then match that speed of rotation with the rotating of whatever control axis controls the forward/backwards, and strafing.

For example, a driver controlling the robot with 2 joy sticks one of which controls rotation by moving left and right, and the other controls all of the strafing commands. If the driver wants to move the robot in a straight line all the while rotating to the left, all he must do is move the rotation joystick to the left, while at the same time rotating the strafing joystick in a clockwise direction with the same rotation speed as the robot itself. By slowing down the speed that the strafing stick is being rotated the robot will veer to the left and by speeding it up the robot will veer to the right.

[CalTran]

Originally Posted by lark95

If i understand what you guys are talking about correctly it really doesn't take that much coordination at all.

All the driver has to do input the the desired direction of rotation and then match that speed of rotation with the rotating of whatever control axis controls the forward/backwards, and strafing.

For example, a driver controlling the robot with 2 joy sticks one of which controls rotation by moving left and right, and the other controls all of the strafing commands. If the driver wants to move the robot in a straight line all the while rotating to the left, all he must do is move the rotation joystick to the left, while at the same time rotating the strafing joystick in a clockwise direction with the same rotation speed as the robot itself. By slowing down the speed that the strafing stick is being rotated the robot will veer to the left and by speeding it up the robot will veer to the right.

Something akin to this basically. It's certainly do able, just takes a lot of work and a change in how you would intuitively drive.

[asid61]

Originally Posted by CalTran

Something akin to this basically. It's certainly do able, just takes a lot of work and a change in how you would intuitively drive.

I would have the operator control the rotation, and use field-centric control for the driver. That simplifies the controls greatly.

[Alan Anderson]

Originally Posted by Ari423

...with this configuration, the drivetrain cannot travel in all three dimensions (x, y, r) at the same time.

Why not?



Each ball is independently driven in the forward/backward direction, which yields control of y and r. They are driven sideways together, which would happen anyway since they're in the same line in that direction, and that controls x. The omniwheels just go along for the ride in x, and give the same forces as the balls in the y direction (and, by extension, r).

I've driven it. It spins in place. It drives and strafes. It moves diagonally very well. It can go in nice arcs whichever direction it is traveling or facing. With extreme care and very slow and halting motions, it has even made its way in a nearly straight line while doing a full rotation. It acts very much like a four-wheel Mecanum or angled-omniwheel drivebase.

[Ari423]

Originally Posted by Alan Anderson

Why not?

Each ball is independently driven in the forward/backward direction, which yields control of y and r. They are driven sideways together, which would happen anyway since they're in the same line in that direction, and that controls x. The omniwheels just go along for the ride in x, and give the same forces as the balls in the y direction (and, by extension, r).

I've driven it. It spins in place. It drives and strafes. It moves diagonally very well. It can go in nice arcs whichever direction it is traveling or facing. With extreme care and very slow and halting motions, it has even made its way in a nearly straight line while doing a full rotation. It acts very much like a four-wheel Mecanum or angled-omniwheel drivebase.

Having driven it, you probably know better than I do. I would have imagined that if you only get a sideways force from the back two wheels, you would rotate rather than strafe (the same way you would turn if your horizontal wheel in an H-drive was all the way at the back), but I could be wrong. If it drives like you are saying, then I guess it is fully omnidirectional.

[Peyton Yeung]

Originally Posted by Ari423

Having driven it, you probably know better than I do. I would have imagined that if you only get a sideways force from the back two wheels, you would rotate rather than strafe (the same way you would turn if your horizontal wheel in an H-drive was all the way at the back), but I could be wrong. If it drives like you are saying, then I guess it is fully omnidirectional.

If you look at the video I posted about it, all the strafing done is just done by the ball. I don't recall correcting the rotation as I strafed. The rotation while strafing is pretty minimal at worst.

[Alan Anderson]

Originally Posted by Ari423

I would have imagined that if you only get a sideways force from the back two wheels, you would rotate rather than strafe (the same way you would turn if your horizontal wheel in an H-drive was all the way at the back), but I could be wrong.

I don't know why you would imagine that. The pair of drive balls doesn't simply apply a fixed-orientation thrust. Each of them moves at a specific speed in a specific direction. When strafing directly to the side, that velocity is exactly sideways. There is no forward or backward motion of either ball. Unless they slip on the carpet, the robot simply does not rotate. Since the omniwheels are also not turning during a pure sideways strafe, they too act to keep the robot direction constant.

I think you're failing to recognize that the balls are completely controlled in both x and y directions. Unlike omniwheels or Killough cagewheels or Mecanum wheels, there is no direction in which they "slip".