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CD47-Bot
03-03-2003, 07:08 PM
[cdm-description=photo]15200[/cdm-description]

Duke 13370
03-03-2003, 07:10 PM
Is it just a lightning trick or are you really powering the sideways movement of those balls with the cims? It's kinda hard to tell if those are for that or extra drivettrain omph.

Jnadke
03-03-2003, 07:14 PM
Originally posted by Duke 13370
Is it just a lighting trick or are you really powering the sideways movement of those balls with the cims? It's kinda hard to tell if those are for that or extra drivettrain omph.
Yes, if you look the chiaphua motors engage the balls. This is what gives the balls their sideways motion so their robot can go sideways.



Essentially, this is a true omnidirectional drivetrain. They can go forward, backward, left, and right at will. They can also change the direction their robot points at will. I haven't seen anything this great since the Kiwi Drive (http://stuweb.ee.mtu.edu/~alkrajew/FIRST/). Unfortuantely, you can't really do this without problems because of no 3rd drill motor this year.

With the exception of the Kiwi Drive last year, I've yet to see a team that has a truly omni-directional drivetrain. Now the TechnoKats are added to this 2 team list. Many teams can create the illusion of an omnidirectional drive but they really can only move in 2 directions in any given instant. Swerve drives have to wait for the wheels to re-align. Teams with a 2nd drivetrain that drops down still can't move in a diagonal path, and have to wait for the drivetrain to lower.


I suggest some people read this:


Originally posted by patrickd (http://www.chiefdelphi.com/forums/showthread.php?s=&threadid=16990&perpage=15&highlight=Kiwi%20Drive&pagenumber=2)

I think there is some confusion about drive systems... and locomotion in general.

On a plane (i.e. the surface of the playing field), describing an object's position at any instant in time requires three coordinates. For example, a robot can have an x-location, y-location, and direction (angle) which the robot is pointing. You can not describe the robot's position correctly with less than three coordinates. It is also possible to describe position with polar coordinates and other coordinate systems.

Now, over time, a robot can alter these coordinates. Typically, a robot can move forward and backwards. In other words, it can translate along one axis (move in the direction of the front of the robot). Most robots can also turn at the same time (adjust the angle which their robot is pointing). These two "degrees of freedom" are what you get out of a tank-drive system, which most teams choose to use. The number of degrees of freedom your robot has is defined as the number of coordinates (x-translation, y-translation, and z-rotation) that your robot can adjust simultaneously. A tank drive might be able to turn and translate in another direction, but it can not translate sideways, thus it does not have the third degree of freedom.

Typically, an omni-directional drive system is defined as a drive system with three degrees of freedom. Very few (I can only think of one last year) teams ever have three degrees of freedom. Tank drive only has two. In fact, even if you can turn all your wheels in any direction you like (i.e. swerve drive) you still have only two degrees of freedom, because at any instant in time your wheels are pointed in a given direction, and your robot is restricted to that linear and angular movement, giving you only two degrees of freedom. However, the advantage of the swerve is that you have the ability to change the direction of your prismatic (translational) degree of freedom with respect to your robot. If you can change wheel angles almost instantaneously, your robot is almost as good as one that can go accelerate in any direction at any angle, thus you virtually have three degrees of freedom. Robots that have a set of wheels that drop down perpendicular to your main set also only have two degrees of freedom, since at a given instant in time they can only move in one translational direction and rotate.

Now, a crab-walking robot could be built such that it has three degrees of freedom, but it would be difficult and almost certainly very very slow. The efficiency of an electric motor is far better than the efficiency of a crab-walking mechanism.

There only two mechanical ways I know of to get three degrees of freedom... meaning at any time, you can have any x-acceleration, any y-acceleration, and any angular acceleration. One of these I have posted a brief paper on how to get started on applying it to a FIRST robot (in the white papers) and the other is a little bit abstract and not too likely to work on a FIRST robot. One team had omnidirectional last year, and I forget the number, but I think it was a first or second year team. Basically it entails having three or four omniwheels perpendicular to the center of the robot. With three wheels, each unique combination of independent torques to the three wheels results in a unique direction and angular velocity of the robot.



Challenge for next year: Try to improve upon this drive such that the traction between the ball and the drive wheels can be improved to the point where it rivals a tank-drive robot. If anyone can do this, they would have the supreme advantage.

yangotang
03-03-2003, 07:15 PM
That's pretty sweet. But i still think the odd-colored ball must go. make it one unform color :P

good work

WakeZero
03-03-2003, 09:19 PM
Somebody has been looking at a mouse too long, lol. Nice job... I actually had a similiar idea for something I was working on outside of robotics, glad to see it works :D

FotoPlasma
03-03-2003, 09:52 PM
Looking at the previous posted picture, I had no idea that the ball was powered (I didn't look too hard, sue me :p), but at this point, I am impressed to the point of being unable to walk.

Mad props go to 45, and the engineer who came up with this innovative and inventive (read: crazy as heck) idea.

/me gives double thumbs-up.

:D

sanddrag
03-03-2003, 10:04 PM
It's wierd; we've got an engineer named Mark who comes up with really crazy stuff too.

<edit> From the pic, it looks like your broke (or bent) the radio port on your controller. We did the same thing to ours and had to solder in a new port. I would check on that because ours still worked after breaking but after opening it up we found some pins were broken. I would change the mounting location or orientation (raise it?) of your controller so there's no force from the plugs on those fragile ports.</edit>

Dan Richardson
03-03-2003, 11:29 PM
Omg I want video?

So cool

Duke 13370
03-04-2003, 04:56 AM
very, very cool.

D.J. Fluck
03-04-2003, 08:17 AM
Originally posted by sanddrag
<edit> From the pic, it looks like your broke (or bent) the radio port on your controller. We did the same thing to ours and had to solder in a new port. I would check on that because ours still worked after breaking but after opening it up we found some pins were broken. I would change the mounting location or orientation (raise it?) of your controller so there's no force from the plugs on those fragile ports.</edit>


No, the controller and radio port are ok. When making space for electronics they didnt estimate how much space they would need for the robot controller. The robot contoller is just at an angle and the bent look is not real. At the first regional, I planned to get that fixed when I had time.

Greg Perkins
03-04-2003, 08:38 AM
do you know where you get a set of those omni wheels?
and how much they cost, i see some potential for my own personal use...



Bad

Joe Matt
03-04-2003, 09:12 AM
My question is this, how can it more sideways if it attached to the frame. Or am I seeing things wrong. Anyway, great idea. I'm going to try and improve on the idea this summer.

I want to see the program too.

Clark Gilbert
03-04-2003, 10:09 AM
Originally posted by badjokeguy
do you know where you get a set of those omni wheels?
and how much they cost, i see some potential for my own personal use...



Bad


You wont be able to buy any like this, unless we build some for you and sell them, or give you prints so you can buy the parts and construct them yourself.

Steven Carmain
03-04-2003, 12:14 PM
Originally posted by JosephM
My question is this, how can it more sideways if it attached to the frame. Or am I seeing things wrong. Anyway, great idea. I'm going to try and improve on the idea this summer.

I want to see the program too.

First, if I think I know what you are talking about, it is just like having a ball on a caster, it can spin in any way. You can get diagonal movement by powering 2 motors in different ways. Like to go NE, you just power the forward-backwards motor forward, and the sideways motor to the right. So, in theory, there is no limitation in movement.

Second, the program was thrown together at the last minute. The program is just a simple tank drive code with 2 sticks, and if you move the right stick left and right, it gives you sideways movement.

Joe Matt
03-04-2003, 01:17 PM
I get it now, but I thought there was a point where the ball was attached to the frame using a bolt (on the left side of the ball, there is a thing touching and possably in the ball, but I guess not)

How do you keep the ball in there without it flying out going over the ramp?

soezgg
03-04-2003, 01:31 PM
i have to say: that is so $@#$@#$@#$@# cool VERY VERY VERY COOL.

i didnt think anyone would do anything like that

my questions are:

what is the ball made out of?

how fast are the motors geared to the ball?

do they ever slip?

how strong is the drive itself?


all in all: VERY VERY VERY COOL.

Gretchen
03-04-2003, 01:36 PM
yo- the ball drive is awesome....but is it really an asset for this years game? what kind of traction are you getting?

Steven Carmain
03-04-2003, 02:23 PM
There are a lot of duplicate questions answered here. (http://www.chiefdelphi.com/forums/showthread.php?s=&threadid=18772)