6 wheel swerves

FIRST General Forum
1

Does anyone know anything about 6 wheel swerves? Has it been done?

Is it possible to do a 6 wheel drop center swerve? Where the center 2 wheels are dropped the normal 1/8 of an inch, enabling easier turning with the same swerve capabilities? Is that bad? Do you not need it to turn easier?

Any pics/vids would be great! Gonna go look at CD Media some more and see what I get. ::rtm::

Thanks!

2

I believe 1625’s 2010 robot was a 6 wheel swerve. Heres a vid: http://www.youtube.com/watch?v=U7sXWhHfULs

Wouldnt it just be easier to program the robot for turning in a “wide” orientation?

3

Team 1625 built a 6WD swerve in 2010. It ended up playing on Einstein.

If you search through Aren Hill’s recent posts, he’s got some solid information and pictures out there. Or PM directly if he doesn’t post in this thread.

I believe that 1625’s 6WD swerve is the first and only 6WD Swerve.

Good picture in this post: http://www.chiefdelphi.com/forums/showpost.php?p=1086307&postcount=21

4

Like everyone has stated, 1625 has done it. (I believe that they are the only ones so far.)

Here are some pics that I got from CD-Media. I’m sure that 1625 has many more on their website.

http://www.chiefdelphi.com/media/photos/35824

http://www.chiefdelphi.com/media/photos/35087

http://www.chiefdelphi.com/media/photos/35854

Also, here is a great whitepaper that 1625 published about their swerve drives throughout the teams history.

http://www.chiefdelphi.com/media/papers/2578

5

1625 also posted this paper that references the 6 wheel drive swerve.

http://www.chiefdelphi.com/media/papers/2578

6

Thanks all! Just finished watching their video on youtube from 2010. Seems nice. The only real implementation I can see is extra pushing power in all directions, which is in itself useful, depending on the robot.

7

If you want to know more about that message Dillon Carey, he’s the one who made the thing

8

People tend to forget that 1625 isn’t solely Aren Hill. :rolleyes:

9

See the litany of other threads on the issue, but more wheels does not mean more “pushing power.”

10

This is not always true, especially with small rough-top tread wheels. I believe someone posted Data on the subject that showed a ~20% increase in Pushing Power/Tractive Force/Force of Friction when a 4" wheel was widened from 1" to 2". (For all intents and purposes, the same as adding another 1" wide wheel to the DT.)

This seems to be caused, at least in part, by the way rough-top tread interfaces with carpet.

11

^ What Dustin said.

12

Please provide a link.

13

234 has not posted the Data online, as it is their choice. But Chris graciously sent me the info and test setup they used to determine traction differences. They compared 4",6", and 8" wheels, 1" and 2" wide. 4x2 wheels won out by a very significant margin

14

I don’t have a direct link to the data as it was given to me second hand.

If all goes well, I will have some data soon on the relation between pushing force and contact patch once we complete testing with our prototype chassis.

15

I think that the principal is sound from a real-world physics standpoint. I think that it is very possible to see significant traction gains from wider wheels.

From my race car experience (both designing, setting up, and driving) I have learned that polymers’ coefficient of friction is related to their contact pressure. A larger contact area therefore leads to a higher coefficient of friction.

They way it was explained to me is that as a polymer, i.e. roughtop or a tire tread, is pushed onto a surface small parts of the two surfaces become interlocked. As normal force between the two surfaces increases, the two surfaces interlock less and less per unit normal force. At some point the polymer/material interfaces are completely saturated and there is not much more grip to be had.

16

Quick aside – if 234’s data is true then wider treads also make turning more difficult due to extra skid traction (if implemented across all 6 wheels).

17

The six wheel swerve actually had basically no extra pushing power past that which a four wheel swerve would have supplied. This is because it was a dropped center 6 wheel. Therefore it effectively only had four wheels on the ground at any given time.

The main plus to the 6wd swerve was maneuverability.

Our team has done a few 4 wheel “swerves” (people call different wheel configurations different names, so I will just group them all under the term “swerve”). We had always done 4 wheel swerves before, but didn’t have the programming capability to create a swerve with independent steering and power for each module. without doing this a four wheel swerve will almost always lack the ability to rotate about itself well. (a notable exception is 1717’s steering configuration)

In order to get past this dilemma without using programming, we decided to solve it mechanically, with the 6wd swerve.

18

*For any math-oriented students who might be curious, here’s1 the inverse kinematics for 6-wheel swerve.

I can’t imagine any team actually wanting to build one like that, but who knows :slight_smile:

1look for “swerveN.pdf” near bottom of list

**

19

While I’m not certain of the exact testing setup 234 has created and tested, we setup our own system.

I can verify that 4X2 won out in our setup as well.

-Brando

20

Brandon/234/Aren,

Did you use a flat plate of tread of varying sizes or use actual wheels and some kind of load cell? Did you do both? It probably doesn’t matter for the final result, I’m just curious how much of that increase is due to straight up surface area or if you get “bonus traction” due to the changing radius and interactions of the wheel/carpet interface under different loads.