Swerve and Swivel Too

FIRST General Forum
1

Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 2/28/2000 9:15 AM MST

This is really great, being able to look at all these amazing creations in the Photo Gallery this year. I think it’s terrific the way so many teams are posting pics of their bots. I’m just stunned by the quality of engineering design and construction that shows through. Cruising the pits is my favorite part of the Competition, and these pics really whet my appetite to stick my head into some bots to figure out what you can’t QUITE see.

The changes that FIRST made this year in the additional materials list have unleashed a quantum jump in sophistication of construction. Complementing that, the new control systems from Innovation First make for a monumental improvement in the technical aspects of the Competitions. I wonder how we all, as a national community of teams, can correspondingly upgrade our side of the show?

About the message title, JOE, I can’t wait to see how your drivers handle CDV’s steering capabilities. PCHS has always fielded supreme drivers, but how on earth do you drive with 2 steerable powered wheels and 2 casters? Isn’t that a little ‘loose’ on the corners? Tell me the caster swivels are constrained, or at least torsionally sprung against free swiveling??? It should be fun to watch!

Dodd

2

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]

Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 2/28/2000 9:41 AM MST

In Reply to: Swerve and Swivel Too posted by Dodd Stacy on 2/28/2000 9:15 AM MST:

Dodd,

Have you never been to the big tent?

Haven’t you seen the magic that circus performers can make look easy?

Then why do you doubt the ability of our drivers to close the loop on any unstable system we care to design for them?!

Actually, it has taken hours and hours for our drivers to be able to exploit the capabilities of the drive system, but they are there.

Look for new levels of mobility from Chief Delphi V.

Can you say ‘arbitrary instant center positioning’? :wink:

Joe J.

3

Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 2/28/2000 10:01 AM MST

In Reply to: Circus performers at PCH… posted by Joe Johnson on 2/28/2000 9:41 AM MST:

: Actually, it has taken hours and hours for our drivers to be able to exploit the capabilities of the drive system, but they are there.

What is this new and alien concept? Where do drivers find hours and hours of practice? Was this something I missed on the Addl Matls List? Is this even allowed? I thought we were required to put the bot in the box BEFORE driving it.

I just can’t wait to watch these guys go! I’ll have an admiring eye on CDV for sure.

Dodd

ps: ‘Circus Performers’ The Chief CAN’T really loop the bar, can he?

4

Posted by Keith Liadis.   [PICTURE: SAME | NEW | HELP]

Student on team #131, C.H.A.O.S., from Central High School Central and Osram Sylvania and Fleet Bank.

Posted on 2/28/2000 6:40 PM MST

In Reply to: Circus performers at PCH… posted by Joe Johnson on 2/28/2000 9:41 AM MST:

Arbitrary instant center positioning?? Can you… elaborate??

5

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]

Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 2/29/2000 5:10 AM MST

In Reply to: Excuse me?? posted by Keith Liadis on 2/28/2000 6:40 PM MST:

As a rigid object travels through space, it always has an ‘instant center,’ a theoretical point about which it is rotating.

For instance, if a machine is traveling straight ahead, its instance center is at infinity to the left (or right – same point in instant center math).

Another example, if a machine is traveling in a curved path to the right, then the instant center is somewhere to the right of the machine.

Yet another example, if a machine is spinning about its center, then the instant center is in the center of the machine.

The important thing for this discussion is that if a machine has two non-steerable wheels whose axles are in a straight line and the tires do not slip with respect to the ground, then the instant center of a machine is always on the line passing through the two wheels.

This is what I will call ‘non-arbitrary’ instant center positioning, in that the instant center can ONLY be on the line described by the two wheels.

What if, for example, a machine wanted to pivot about a point 5 feet in front if the machine? Not possible with 2 wheels with parallel axles.

But… suppose the wheels were independently steerable. In this case, the wheels could be adjusted so that the lines through the axles of the wheels intersect anywhere on the playing field, for instance, 5 feet in front of the robot. This intersection point is the instant center for the robot.

This is what I will call ‘arbitrary instant center positioning.’

Anyway, with such a drive/steering system, improved mobility should result.

Joe J.

6

Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 2/29/2000 12:33 PM MST

In Reply to: Instant centers posted by Joe Johnson on 2/29/2000 5:10 AM MST:

So then, in photo 047CDV7, the instant center is just about under the left front(?) wheel? Or are you messing with young minds here?

I really want to see the driver control interface for this amazing machine. Do you use any software ‘transforms’ between the driver’s raw ‘stick’ inputs and the steering motors on the robot, to coordinate the steering of the two wheels at all? Or does the driver directly control each individual drive wheel’s direction and speed?

Dodd

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Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]

Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 2/29/2000 2:03 PM MST

In Reply to: Toe Stubber posted by Dodd Stacy on 2/29/2000 12:33 PM MST:

Dodd,

We were afraid that nobody would notice how clever we were so we exaggerated the amount of steering angle difference from side to side in order to get someone’s attention :wink:

Yes, of course you are right, when one wheel points toward the other, the instance center had better be under that wheel or else some very nasty groaning sounds start to emanate from the area of the robot!

As to driver skill and what control schemes we use, you will be surprised at how innovative our approach has been: We have simply we have flown in circus performers on winter break in Florida. It took some heavy duty arm twisting with the school district to get them officially enrolled at Pontiac Central, but hey, did we want to win or not? :wink:

Joe J.

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Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 2/29/2000 2:27 PM MST

In Reply to: Exaggeration for effect posted by Joe Johnson on 2/29/2000 2:03 PM MST:

: As to driver skill and what control schemes we use, you will be surprised at how innovative our approach has been: We have simply we have flown in circus performers on winter break in Florida. It took some heavy duty arm twisting with the school district to get them officially enrolled at Pontiac Central, but hey, did we want to win or not? :wink:

: Joe J.

From what I have seen of the PCHS kids over the last 4 years, you have no need for ringers. Your kids have made a huge impression on me since the first day I saw them in Manchester, all decked out in uniform and just great to interact with.

Dodd

9

Posted by Daniel.

Coach on team #483, BORG, from Berkeley High School and NASA Ames & UC Berkeley.

Posted on 2/29/2000 7:27 PM MST

In Reply to: Instant centers posted by Joe Johnson on 2/29/2000 5:10 AM MST:

Ahhh…

So it begins to make sense. Now the case you provided exists while the wheels are positioned tangentially along the circumfrence of a circle who’s center is your ‘instant center’.

So…

What is the result when the two wheels, as tangents, don’t create a circle? Of course any two tangent lines determine a set of circles…and one point determines the radius; but what if the other tangent point doesn’t lie on that circle? Namely, what if the ‘instant center’ isn’t in line with the center of the 'bot? Wouldn’t you get a lot of drag there? Or maybe you just don’t move in a circular path…

…hmmmm

-D

10

Posted by Raul.   [PICTURE: SAME | NEW | HELP]

Engineer on team #111, Wildstang, from Rolling Meadows & Wheeling HS and Motorola.

Posted on 3/2/2000 6:13 AM MST

In Reply to: Instant centers posted by Joe Johnson on 2/29/2000 5:10 AM MST:

Hey Joe,

I guess your 4-wheel steering, was the shape of things
to come (check out sites below). I guess maybe you had to deal with Instant centers in your real job? I would love to hear your story on this.

It just makes me wonder if there will also be large rotating arms with gas springs on cars in the future. :slight_smile:

http://www.delphiauto.com/index.cfm?location=1672

or equivalently,

http://www.delphiauto.com/ and follow the link to ‘Delphi Introduces
Innovative Four-Wheel-Steering System at SAE 2000’.

Raul

11

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]

Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 3/2/2000 8:39 AM MST

In Reply to: Hey Joe, how about automobiles?? ;), posted by Raul on 3/2/2000 6:13 AM MST:

I have watched with wonder the 4 wheel steering system Delphi supplies to GM. A very cool system.

Alas, I can not yet be in all places at once (at present I can only manage to be in several places at once :wink: so sadly, I had nothing to do with Delphi Chassis’ & Delphi Saginaw Steering’s 4 wheel steer project.

But, as to FIRST mechanisms ending up on the floor of a car dealership near you, be patient. Soon and very soon we will have such products to brag about.

Joe J.

12

Posted by “MOE”.   [PICTURE: SAME | NEW | HELP]

Coach on team #88, TJ2, from Bridgewater-Raynham Reg. High School and Johnson & Johnson .

Posted on 2/29/2000 8:58 PM MST

In Reply to: Circus performers at PCH… posted by Joe Johnson on 2/28/2000 9:41 AM MST:

:HELLOOOoooo
Joe I think I can do that, Maybe CD5 and TJ2 can get together
and show the real deal. till we meet in NJ good luck to all.
See YA Team #88 and MOE