Swerve Drivetrain.

[EricH]

Originally Posted by Mk.32

And what rule exactly is it that dis-allows slip rings?

This year, there is not one. In fact, they are explicitly allowed.

In past years, rules varied on legality. In future years, the rules may or may not allow them. Hopefully, they will be allowed. But, we can't be certain.

[Mk.32]

k that makes sense.
Thanks for the clear up.

[Mk.32]

Also another question,
with the wild swerve drive modules
http://www.andymark.com/ProductDetai...ctCode=am-0496
do we need to blot both the top and bottom plates down?
or would just blotting the top plate be enough?

[cire]

Originally Posted by Mk.32

Also another question,
with the wild swerve drive modules
http://www.andymark.com/ProductDetai...ctCode=am-0496
do we need to blot both the top and bottom plates down?
or would just blotting the top plate be enough?

You need to bolt both the top and bottom plate, otherwise it will just bend the top bracket.

[Ether]

Originally Posted by GGCO

The hardest part though is the code base. Make sure you have a TON of time and good programmers to do this.

There are a couple of short papers here which explain the kinematics of, and give example code for, 4-wheel-independent steering and speed control.

[PAR_WIG1350]

Originally Posted by Joe G.

The revolution module that you linked is what is known as a coaxial swerve module, meaning that the motors are mounted vertically, parallel to the module's rotation axis. The wild swerve module contains the CIM motor, and gear reduction, within the swerve module itself. The primary advantage of coaxial modules is infinite rotation, as there are no electrical components within the modules. Wild swerve style modules are limited by the wires running to the motors, and must use sensors to limit their rotation. This limited rotation can also cause changing orientation to take more time than it might otherwise.

Non-coaxial modules, by nature, are independently powered, which can open up some flexibility in how the swerve is operated. For example, tank style turning will be much easier to accomplish in any orientation on a non-coaxial setup.

Finally, here are some teams that have produced quality crab and swerve drives over the years. Look into some of their past robots, its a great way to learn!

16 (most years)
71 (most years)
111 (most years)
118 (most years, but not the past couple)
148 (2008)
1114 (2004)
1640
1717

I was under the impression that coaxial module swerve was (usually*) the more flexible of the two due to the deletion of electrical connections to the module thus allowing the module to rotate directly to the desired position (for example, a 10 degree rotation in a coaxial setup could translate into a 350 degree rotation in a MOM (motor on module) setup). I am currently working independently on coaxial swerve and how to unlock it's full potential. Technically, due to the allowance of slip rings this year, MOM swerve is superior due to the greater efficiency that can be gained by eliminating the 90 degree transmission necessary for coaxial modules and the removal of MOM's limitations by the slip rings allowing unlimited rotation of the modules. One key design feature to fully utilize the abilities that swerve can give you is the independent steering and drive of all modules. After venturing into the 'branch' of swerve that I have, It is difficult to look at front/back // left/right linked swerve and say that it is even approaching all of the benefits that a fully functional swerve drive train has to offer. (NOTE: I plan on releasing that white paper I promised eventually).

[buchanan]

Originally Posted by PAR_WIG1350

:After venturing into the 'branch' of swerve that I have, It is difficult to look at front/back // left/right linked swerve and say that it is even approaching all of the benefits that a fully functional swerve drive train has to offer.

A good point. While it's unlikely anyone would build a tank/skid steer drivetrain without a software/control system capable of exploiting all its physical capabilities, the same cannot be said of fancier systems like swerve and omni/meccanum. It's entirely possible to build one of these that exploits some, but not all, of what's physically possible with its hardware.

You can look at a 6wd, tank, etc machine and know pretty well what kind of maneuvers it's going to be able to make (speed aside). You can't make the same assessment of a swerve or meccanum platform without knowing what's in the software.

[apalrd]

Originally Posted by buchanan

...While it's unlikely anyone would build a tank/skid steer drivetrain without a software/control system capable of exploiting all its physical capabilities...

I disagree.

Including the ride height automation, I have almost as much code in the drivetrain of our robot as I do in the elevator.

Ignoring the ride height automation, I still have a lot of code. The driver inputs come in, are run through filters if certain conditions are met (to provide better response and less oversteer), can be flipped if the driver requests invert, and are fed through a special algorithm that handles turning and arcing better (to fix some issues we found where the driver requests a (1,0) but really means (1,coast). We then run the commands to the closed-loop speed control (which in itself has automation of coasting to stops and holding position), and then run the shift scheduler.

The simple way of programming a skid steer would be to set the motors to the joysticks.

[Joe G.]

Originally Posted by PAR_WIG1350

I was under the impression that coaxial module swerve was (usually*) the more flexible of the two due to the deletion of electrical connections to the module thus allowing the module to rotate directly to the desired position (for example, a 10 degree rotation in a coaxial setup could translate into a 350 degree rotation in a MOM (motor on module) setup). I am currently working independently on coaxial swerve and how to unlock it's full potential. Technically, due to the allowance of slip rings this year, MOM swerve is superior due to the greater efficiency that can be gained by eliminating the 90 degree transmission necessary for coaxial modules and the removal of MOM's limitations by the slip rings allowing unlimited rotation of the modules. One key design feature to fully utilize the abilities that swerve can give you is the independent steering and drive of all modules. After venturing into the 'branch' of swerve that I have, It is difficult to look at front/back // left/right linked swerve and say that it is even approaching all of the benefits that a fully functional swerve drive train has to offer. (NOTE: I plan on releasing that white paper I promised eventually).

My statement is based around the fact that non-coaxial modules are, by nature, independently powered, while many coaxial swerves power the modules in pairs, or even from a single "power plant" swerve, as 118 often does. Putting multiple modules on a single power source limits some of the motions you can make.

For example, say you have your modules steered in front/back pairs, and powered in left/right pairs, as many (most?) coaxial swerves do. This setup excels at akerman-style steering. But tank style steering is impossible in any module orientation other than "forward," and in long orientation, with four traction wheels, may even be difficult there. Motor-in-module setups, however, would allow tank-steering in any orientation; forward, sideways, and probably diagonally to some degree.

This downside of coaxial is considerably more apparent in a 118 style setup. With all wheels tied to the same motor, there can be no variance in their speed. This makes any kind of tank steering just about impossible, and for this reason, all robots that I know of built this way have been either turreted, or had no real "front" (think 148 in overdrive). Which is something that a team may or may not be able to fit into their design.

Admittedly, it's not a huge downside. And you're correct, ignoring the possibility of slip rings, having infinite rotation of the modules is a big plus for coaxial. If you can do a independently powered, independently steered "pivot drive," more power to you, but that's not an easy undertaking. Which system is right? It depends on your robot, what you have experience making, and which set of pros and cons you think is best.

[The Analog]

this year we (Team 79 KRUNCH) went with swerve drive again after a few years away from it. We are using a coaxial system with all 4 wheels driven independently and the front and rear wheels are steered separately (fronts steer together and rear steer together). So far this year, this has proved to be a very versatile drivetrain.