pic: FRC488 Octocanum.

I like the idea. If the execution can be made perfectly reliable, it should be a formidable drivetrain. The trick comes in ensuring theres no problems with throwing chains etc.

Team 1708 actually did something like this last year…

Check it,
http://www.chiefdelphi.com/media/photos/34890

We anticipate using the mecanum wheel set most of the time, so we wanted that to be our most stable configuration. The traction wheels are not really intended to prevent others from turning us in place, but to kindly remove defense from our path when the mecanum wheels can’t get us around it.

Well said. Never know when you’ll need to gently escort someone across the field.

I really like this drive, I feel like it negates the majority of the disadvantages of a Mecanum Drive in a relatively simple and elegant method.

When you guys assembled those mecs, did you do anything special, like grease the washers at the end of each roller and/or replace the washers with nickel plated ones?

**

We checked that each of the rollers is spinning freely, but did not do anything otherwise special to them. As we run the chassis in, we’ll see how they behave and make adjustments as necessary.

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

It’s geared at 8.9:1 right now.

Interesting. That is much faster than I expected.
I look forward to seeing video of it in action so I can recalibrate my mental picture of performance. :slight_smile:

-John

I think it’s a bit faster than I expected, too. We’re going to get a bit more weight onto it soon and test it again under more realistic conditions to get a sense of whether or not it’s something we can handle.

We’ve got rookie drivers this year and haven’t found an area large enough to let it run at full speed for more than about a second, so necessity may require that we slow it down.

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

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!

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.

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

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?

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.

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. :slight_smile:

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?

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.

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