pic: FRC488 Octocanum.

[Racer26]

Originally Posted by JVN

Hi Madison,
Looks good. The Robowranglers built an octocanum platform this fall. Do you mind my asking -- what are you geared at for the mecanum drive?

-John

Robowranglers building more non-conventional drivetrains? 2010 was Nonadrive, I wonder what 2011 holds. Eep!

[Jonathan Norris]

Nice to see someone try this, I've been thinking about this kinda of drive system for a year or so. We developed a CAD of this system ourselves during the offseason, but never got the time to build it. The main concern that I had with this system was the side loading of the 'swing arms' that the traction wheels are mounted on. I would be concerned with the loading on the swing arm when trying to turn with the traction wheels down. We had designed for delrin blocks on either side of the 'swing arm' to transfer those loads to the frame. From my understanding 148 had similar problems with this last year, I'm sure JVN could elaborate more on that. Good luck with it!

[Madison]

A new picture of the entire drive is pending in the gallery, but here's a video of our first test of the articulation mechanism. Our cylinders finally arrived, so we were able to get this hooked up and tested today.

http://www.youtube.com/watch?v=nQgri...e_gdata_player

[JVN]

Originally Posted by Madison

A new picture of the entire drive is pending in the gallery, but here's a video of our first test of the articulation mechanism. Our cylinders finally arrived, so we were able to get this hooked up and tested today.

http://www.youtube.com/watch?v=nQgri...e_gdata_player

I really like your articulation setup. I'm admiring the elegance and simplicity of the long connecting link between the two up on top (using the height of the module as your torque arm).

I struggled with something similar in the pre-season, and just ended up using 2 cylinders (I got too caught up in using the cylinder without a connecting link somewhere inbetween the modules, but the force vectors never worked out. This is a much better way to solve the problem!

Kudos!
-John

[coldfusion1279]

Looks like a great mechanism for raising and lowering the wheels. May I ask, with such a short traction wheel base, are you worried about the front wheels 'rearing' off the ground in a pushing match? Maybe the center of gravity is low enough that this wont be much of a problem?

[Madison]

Thanks for the compliments on how we've arranged drive articulation.

In the interest of keeping everything in one place, here's another brief video of the drive. The programming team has implemented field-oriented drive reliably enough to drive the robot freely.

http://www.youtube.com/watch?v=sM8cixsE5fo

I believe this is still at some fraction of top speed, but I'm not sure how it's being scaled. I also believe, but am not sure, that we're using two gyros to determine orientation. This stuff isn't my department.

[thefro526]

That is the most impressive Mecanum Demonstration I've ever seen.

Wow.

I'm assuming a movement like that would be incredibly difficult to do without field oriented control?

[Chris is me]

Hey look, a mecanum drive doing what it's supposed to. Cool!

I'm willing to bet you'll have one of the top 10 mecanum robots this year.

[robodude03]

Originally Posted by Chris is me

Hey look, a mecanum drive doing what it's supposed to. Cool!

I'm willing to bet you'll have one of the top 10 mecanum robots this year.

Absolutely agree with you Chris. This is an amazing system and I love the simplicity in design (referring to the actuation of the drive wheels.

[Arjun Namineni]

Originally Posted by Madison

The wheels are going to be actuated by two pistons -- one along each side of the robot.

Why did you guys decide for two pistons? Wouldn't one work just the same, but with less weight and less air loss?

[Madison]

Originally Posted by Arjun Namineni

Why did you guys decide for two pistons? Wouldn't one work just the same, but with less weight and less air loss?

One cylinder provides enough force at 60 psi to lift the entire robot, but we imagined that added complexity of the mechanical system needs to actuate all four wheels with a single piston offset any weight saved by eliminating the second piston. The second piston is only about 2 lbs. and it means that our actuation system can operate reliably with as little as 30 psi or so.

[PaW]

I'm going to sneak over to the "Seattle Cascade" field from the "Seattle Olympic" field just to watch this.



Your new drive team is gonna have some fun this year...

[Madison]

More video: http://www.youtube.com/user/teamxbot.../1/5_wZ58rzxg4

This time, we were testing to see how the robot would behave if we deployed the traction wheels while strafing. We wanted to test side-loading on our wheel pods and stability of the entire robot. It looks like things will be fine.

The most confusing aspect of the change is that the robot, right now, automatically shifts from field-oriented drive to standard two-stick tank drive. That's why, whenever the wheels are shifted on the fly, the robot immediately starts to move "sideways." We're looking at options for making the switch more intuitive, but it's probably something that a bit of practice could overcome well enough.

[Madison]

This is kinda like blogging my season, right?

Last night, our programming team brought our "follow wheels" on line. These are non-powered wheels with encoders attached that relay actual distance traveled back to cRio. We use three on this robot because of its holonomic capabilities.
You can then do neat things like this: http://www.youtube.com/watch?v=Jr-eglZBAHQ