21-02-2003 15:34

Matt Reiland

F.Y.I. It's never good to use the rod of a cylinder for lateral support

I think you will also be suprised by the force of some of your opponents, in fact I know you will

21-02-2003 15:41

Jeremy_Mc

i really hope you're not using the ability of a human to push your robot as grounds for these claims.

a robot can hit with much harder force than any human. you should take another robot and hit yours with it to test these things.

no one person could move a robot at our exhibition, but then another team's bot rammed it and it slid 2 feet.

plus, i don't think suction cups are going to be very effective due to the nature of the HDPE.

*jeremy

21-02-2003 16:00

Duke 13370

those aren't jsut any suction cups, those are sheet metal holders, and they don't slide, and are tested for about 300 lbs. Yeah, the pnematic might bend, but at that point, our robot will have fallen to pieces and we'll be out for good (that wouldn't be fun )

Oh, and they actually work best on smooth materials like the HDPE.

<edit> We are more worried about this monster bending our robot's frame than we are of anyone else doing that.</edit>

21-02-2003 16:17

DanLevin247

Nice looking bot...but wouldn't it be wise to somehow protect that cylinder? It would really suck if you guys got hit or ran into someone, and fubar'ed your suction system in the process.

21-02-2003 16:19

MarcusF

They do work on smooth surfaces, but the HDPE will become very worn and will not be a flat surface after a few dozen matches, it will have pits in it. Just my opinion

21-02-2003 23:33

comet22

i would add a lateral support beam, it wouldnt be too difficult, but i do believe you will be slideable... you aren't drawing vacuum which will make your suction less effective.

22-02-2003 00:36

Clark Gilbert

those aren't jsut any suction cups, those are sheet metal holders, and they don't slide, and are tested for about 300 lbs. Yeah, the pnematic might bend, but at that point, our robot will have fallen to pieces and we'll be out for good (that wouldn't be fun )

That's odd, because we had those (MSC right?) and they slid pretty bad, i can also tell you they didnt make it on our robot.

22-02-2003 04:05

Eric Bareiss

They look like Anver suction cups to me, and if they are then yes they do slide. They don't slide very easily, but if someone like team 60 or 45 comes up the ramp at full speed, off the ramp you go.

FYI - The 300lb tested force is lifting force, the shear force (sliding) is probably going to be less that 50lbs.

22-02-2003 04:12

sevisehda

Nice hatch for the controls.

I'm not sure if that cylinder will that very long. I can almost gaurantee the shaft will bend after 1 good hit.

Even that bracket that holds the cylinder looks weak, you may want to put it on the end of the cylinder where the shaft comes out. So as not to crease the wall.

The HDPE isn't a very hard surface and will start to get scratched and pitted very fast. If you take into acount all the collisons and action on the ramp it won't stay smooth very long.

I'm not saying you wont be able to stay on but I don't think you stay on for long.

22-02-2003 08:58

RobDeCotiis

try this: flip the piston upside down. make a mounting bracket to connect it to a piece of extruded aluminum so the aluminum is flush with the back of the piston when the piston is extended. have the piston retract to pull the extruded alumiinum bar down, pushing the suction cups onto the ground. that way, the piston rod is inside your bot when you're taking the force, and wont bend nearly as easily if you take a hit. other than that, not too shabby.

22-02-2003 10:03

Duke 13370

I get the vaugest feeling we prolly won't want to take to many hits on this thing, but it is very cool to watch it lift the opposite side of the bot.

22-02-2003 11:46

Dave_222

You just better hope you dont meet us cuz we push at well over 300 lbs and um suction cups arent stoping us.

22-02-2003 12:32

Duke 13370

do you have any images up?

<edit> nevermind, I found it. It doesn't look like you have enough traction to do that, are you sure you can push 300lbs.?</edit>

22-02-2003 13:13

Madison

It's next to impossible to make any judgements about tractive effort by looking at a picture. Big tires doesn't equate to big traction. Cool belts don't equate to big traction, either.

In fact, this season, I expect many people are going to have to relearn all they though they learned about traction - especially where the HDPE is concerned.

As someone already mentioned, the 300 lbf. figure you have is probably for tension, not shear. Suction cups don't really resist shear all that well, and there are robots out there that can exert well in excess of 300 lbf., anyway.

Against some robots, you'll likely be fine. . . .well, assuming that your drivetrain has the oomph to move other robots with similar ideas out of the way. Against others, you won't stand a chance. There's always someone who does it better, or differently, or some way you never even considered.

It's a bad idea to assume you're immovable, or unbeatable, or that much more clever than the rest of us.

Edit: Grammar. Also, do you understand the difference between pushing something that weighs 300 lbs. along a surface and exerting 300 lbf.?

22-02-2003 14:00

soezgg

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.

22-02-2003 14:10

Duke 13370

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.

22-02-2003 14:13

Andy Baker

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.

22-02-2003 14:14

soezgg

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

22-02-2003 14:21

Duke 13370

HUH!?!?!?

22-02-2003 14:26

kevin.li.rit

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.

22-02-2003 14:38

Jeff_Rice

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.

22-02-2003 14:45

comet22

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

22-02-2003 14:52

Duke 13370

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.

22-02-2003 14:59

Madison

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

22-02-2003 15:14

team222badbrad

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.....

22-02-2003 15:47

Duke 13370

none of you links work

22-02-2003 16:10

Jeremy_Mc

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

22-02-2003 16:29

Duke 13370

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.

22-02-2003 17:37

Dave_222

if you knew what they were made of you would under stand. there are more factors than diamiter or width.

22-02-2003 17:58

team222badbrad

Highlight the whole link for some reason CD didnt like the () in the link.

If you copy and paste the link into your address box they will work!

22-02-2003 21:00

sevisehda

Personnaly I don't know why the majority of teams make claims this early. Minus the few teams who have scrimaged how how your bot will fair is almost impossible to determine.

Suction cups are too finiky. HDPE gets scratched way to easy and will let air into the vacuum. If a team wants to impress me with there suction power they'd have to take 50 grit sand paper to some HDPE(to simulate playing field after a few rounds). Then suction on to it and have the bot hold on to it for 30 seconds.

Saying your bot can push 300lbs isn't accurate either, teams have pulled cars. It isn't the wieght of the object there pulling it the amount of force there pushing/pulling with. Get a spring-scale attach it to a wall and the bot then drive forward take a reading and post that.

Wheel size, tank treads, pnematic tires all act differently on different surafce areas. More surface contact isn't always better, especailly for manueverablilty. It also depends on the wheel material, and this year if you want good traction on all the surfaces then you need more than 1 wheels type.