the reason our team didnt want to use suction cups is that they are very finiky about their attatching surface...

dust, scratches, oils, moisture in the air all have an effect on how well they grip (or dont grip) the surface.

also: for a suction cup to operate properly the force on them has to be perpendicular to the surface in 2 directions.

when a robot hits it, it will be from the side.
we didnt think they would be a focused subsystem for our bot...



but good luck.

my 2 cents.

Oh, i wish we were, but i know better. we spent mabye $20 dollars on the robot afte the kit and donations. Actually i think the zip ties were only $8, so we prolly spent more like $10.

Any way, I find the power that thing has very ammusing just because we've been testing this on dented, scratched tile, and it was very immpressive to see this thing pull us down.

Good idea
 

This is a good idea and your robot will hold it's position over MANY other robots.

Let's look at this design and evaluate the impact:

It appears that the suction cups are being actuated up and down on a 2" dia cylinder (at 60psi, pulls at 170 lbs, pushes with 180 lbs).

Also, let's assume that they have the same mechanism on the other side of their robot.

From our team's experience, you can pull up on these suction cups with about 100-120 lbs of force before they let go (it depends on the cleanliness of the surface).

So... the cylinders push down, suction cups stick, and the cylinders try to pull up. They probably regulate the cylinder down to 40-50 psi in order to not pull the cups off of the floor. All of the force that they are pulling up on is being transferred to their wheels, and their robot essentially weighs much more than the actual weight of the robot. The downforce on the wheels is shown below in an equation:

Downforce on wheels = robot weight + left side cylinder/cup pulling force + right side cylinder/cup pulling force

Downforce on wheels = 130 + 100 + 100 = 330 lbs.

So... essentially, with both suction cups engaged and the cylinders pulling up, their robot weighs 330 lbs. Although it's not best design practice to simply let the cylinder shaft support the side loads on the vacuum cups, it's the wheels that are exerting the downforce, not the cups. An opposing team not only has to slide the suction cups, but also 330 lbs. of downforce applied to their wheels.

In order to push this robot, an opposing robot has to push with more force than this robot's holding force (at least that's what I call it). Their holding force = 330 lbs. x mu (their wheel's coefficient of friction).

Now, with regard to scratches, these cups still do pretty well. If they had a lower durometer, they may even be more resistent to scratches.

Great 'bot... good luck!

Andy B.

not to complain...but i thought id help you out by telling you that your light shield is illegal...not that you can fix it now or anythign

HUH!?!?!?

Your pistons are gonna get bent especially if a robot hits it directly, I hope you BOUGHT SPARES cause it takes a while to fix a bent piston.

Yes, it is illegal, duke.
Won't hurt ya to get rid of the shield, unless there are moving parts near your light that aren't shown.

I see your robot as being difficult to move... but by no means impossible... suction can gain you an advantage but most of that advantage will be as said before in downforce. To really gain an advantage being pushed from the side you need to draw vacuum. Also dont underestimate suction on scratched surfaces. It will take a pretty deep scratch depending on the material the suction cups are made out of

No big deal, we can fix that easily, but what about the rule that said "keep it protected", all that is is chicken wire.

Yeah, we can move it, but a lot of teams will really have their work cut out for them.

Your light isn't illegal. Don't worry about it. It's upright, it's visible, and it's protected.

You want a pic HUH?

Pushing a 300+ kid on our team.

http://www.tahsroboticsteam.org/new/2003-02%20(Feb)-15c/HPIM0162.JPG

Pushing old robot up and over ramp....

http://www.tahsroboticsteam.org/new/2003-02%20(Feb)-15c/HPIM0170.JPG

Aftermath of pushing old robot up and over....

http://www.tahsroboticsteam.org/new/2003-02%20(Feb)-15c/HPIM0174.JPG

P.S. Our wheels are made of (insert words here), they are 6 inches in diameter and are 2 inches wide.....

none of you links work

Re: Good idea
 

again this all relates to the orientation of the robot...sheer vs. tension. it also relates to how fast the other robot is going and how concentrated the force is (remember, force and pressure are not the same thing).

6 x 2 is wide, but you have a small wheel compared to many teams...we have some wheels made out of err...rubber? that are 8" x 2". not that it gives you more traction, just faster speeds.

*jeremy

Our wheel are 8.5*2 (apx, we shaved a little off), but that doesnt matter mch when we are being held to the floor.

6*2 really doesn't give you any more traction, just a little more of torque.