6 Wheel Drives Without Dropped Centers

[Jared Russell]

Originally Posted by coalhot

Quite interesting, Miss Daisy used the VersaWheels this year, and I witnessed them getting pushed sideways. However, I'm not certain if they dropped the center wheel or not (6wd, 6cim), It would be interesting to hear about their drivetrain.

We had 8 wheel drive with the middle 4 axles 3/32" lower than the outside axles (approximately 26.5" long x 29" wide frame). Note that because of our center of gravity, the rear 6 wheels (and in particular, the 3rd pair from the front) bore most of the load, and wore the fastest. As a result, at various points in the season we had 3/32" +/- 1/8" of effective drop.

It turned like butter (if anything, a little more scrub would have been nice), and it was possible for a high traction robot to push us sideways a little bit. But with fresh-ish wheels our traction in the forward/backward direction was incredible (we inadvertently tore a couple holes in the carpet at the Las Vegas Regional during pushing contests).

[coalhot]

Originally Posted by Jared341

We had 8 wheel drive with the middle 4 axles 3/32" lower than the outside axles (approximately 26.5" long x 29" wide frame). Note that because of our center of gravity, the rear 6 wheels (and in particular, the 3rd pair from the front) bore most of the load, and wore the fastest. As a result, at various points in the season we had 3/32" +/- 1/8" of effective drop.

It turned like butter (if anything, a little more scrub would have been nice), and it was possible for a high traction robot to push us sideways a little bit. But with fresh-ish wheels our traction in the forward/backward direction was incredible (we inadvertently tore a couple holes in the carpet at the Las Vegas Regional during pushing contests).

Ah, thanks for the clarification on the drive. I didn't have too much of a chance to look closely at the robot this season.

Is 8WD a new drivetrain standard with you guys? Just wondering...

[Ether]

Originally Posted by Jared341

tore a couple holes in the carpet

It will be interesting to see what the rules have to say about those wheels in 2014.

[Jared Russell]

Originally Posted by Ether

It will be interesting to see what the rules have to say about those wheels in 2014.

I have also seen roughtop tread tear a hole all the way through the carpet in a similar fashion (1676 attempting to push their whole alliance up a bridge at Brunswick Eruption). In both cases it was a pretty anomalous situation. In our specific case, we were slot loading because our ground loader wasn't working, and the driver didn't realize he was still holding down the sticks when we were against the wall.

[Ether]

So what immediate and post-event remedial action, if any, is taken when a bot tears a hole in the playing surface?

[Gregor]

Originally Posted by Ether

So what immediate and post-event remedial action, if any, is taken when a bot tears a hole in the playing surface?

Black Gaffers tape, lots of it. 2809 got stuck under the pyramid at GTRE, and kept spinning their wheels. They left us 4 nice holes to tape up.

[Ether]

Originally Posted by Gregor

Black Gaffers tape, lots of it.

What about post-event. Any attempt at a more elaborate repair?

[Gregor]

Originally Posted by Ether

What about post-event. Any attempt at a more elaborate repair?

Carpets are not reused event to event. Most are given away to teams.

[AllenGregoryIV]

Originally Posted by Ether

So what immediate and post-event remedial action, if any, is taken when a bot tears a hole in the playing surface?

We tore a few holes at Bayou this year. Lots of gaffers tape is the only fix. The FTA will also normally have a nice talking to with the team telling them to stop damaging their field. (Sorry Eddie)

[cmrnpizzo14]

I am seeing a lot of conflicting posts about versa wheels so could someone clarify a little bit? As far as I know the most defining characteristics are:

1.) Great traction in the standard forward backward drive directions
2.) Poor traction if robot is being pushed sideways while parallel to floor
3.) Great traction if robot is pushed sideways but tips up so that the treads "dig in" to the carpet

If anyone could confirm or deny these that would be very helpful. And if these are true then it appears that these would be perfect for 6wd w/o a dropped center since they should have minimal scrub due to their poor lateral friction.

[T^2]

Originally Posted by cmrnpizzo14

I am seeing a lot of conflicting posts about versa wheels so could someone clarify a little bit? As far as I know the most defining characteristics are:

1.) Great traction in the standard forward backward drive directions
2.) Poor traction if robot is being pushed sideways while parallel to floor
3.) Great traction if robot is pushed sideways but tips up so that the treads "dig in" to the carpet

If anyone could confirm or deny these that would be very helpful. And if these are true then it appears that these would be perfect for 6wd w/o a dropped center since they should have minimal scrub due to their poor lateral friction.

Here's some video evidence. At 0:54, 2834 hits 469, accelerating from about 4 feet away, and shoves 469 about 3 feet. 469 uses VersaWheels. (I got a good look at their drivetrain Saturday evening, about two weeks ago.)

As to your question about their use in the corners of a no-drop drive, I'll reaffirm what I said in the other thread, that I don't think that's a great idea. Consider a 6-wheeled no-drop robot with VersaWheels in the corners. For simplicity, assume the drive base is a perfect square with the horizontal center of mass at the center of the horizontal plane. Thus, the turning circle should touch the contact points of the VersaWheels. Now think about how the tread interacts with the turning circle. The tread looks like this:

-----------
~~~~~~
-----------
~~~~~~
-----------

more or less. And the turning circle at the patch, when superimposed on the tread pattern, looks like this:

-----------/
~~~~~/~
------/-----
~~/~~~~
-/----------

sort of. (Imagine the slashes as being a continuous curve.) When the wheels exert force on the ground, the easiest way for them to slide is sideways. But they instead want to slide along the turning circle! This means a significant portion of the force is wasted trying to turn against the "W" tread.

Of course, this is all theory. The best way to test this kind of drivetrain is to build it. I just don't predict that it'll work out too well.