Beware of R16 your robot design may be too big.

[jgannon]

Originally Posted by 1075guy

I think he perhaps means have the cylinder be angled to the plane of the ground.

<R16> is pretty unambiguous about this. Horizontal dimension, upright cylinder... there's no way to work angles into this at all.

[Paul Copioli]

For those of you that think it is easy based on sketches ... I was there too until we actually prototyped something that is thick enough to be stiff enough and that is when we went "Ohhhhh .....".

If you use any rotational motion at all, be sure to check at the longest pont of projection. Our ball grabbing position is no problem, but the transitions are what are getting us. And no, we are not grabbing all the way around the ball.

Gary,

I guess I just refuse to make my drive geometry more complicated than it should be for a rule that looks like it was meant to prevent the "unfold and block" type defense.

All,

We have done many arms before and this one will absolutely be the most difficult (not complaining) simply due to the 80" rule.

I really just want to make sure everyone is aware of this very restrictive rule. I don't want the tape measure debacle of 2002 to happen again, because that will just irritate me and others who follow the rules from the start.

-Paul

[MrForbes]

Originally Posted by Paul Copioli

For those of you that think it is easy based on sketches ... I was there too until we actually prototyped something that is thick enough to be stiff enough and that is when we went "Ohhhhh .....".

Very good point!

Fortunately the section at the end of the arm need not be very thick, as it is under little load. The section that needs to be thick is near the robot.

[Tom Line]

Squirrel, take a second look at your sketch. As Paul said - it's not actually grabbing the ball that is the problem. It's when you open your gripper that it's going to bite you, depending on where your hinge point is.

[MrForbes]

Yes, I understand the problem, that's why I drew the sketch with the gripper open.

[Paul Copioli]

This is a general warning to all who try to hurdle (we are feverishly designing right now and I have bruises on my head from beating it against the table):

1. EVERY year MOST teams underestimate how hard it is to manipulate the game piece. This year will be no exception.

2. For our team, this is BY FAR the hardest year to manipulate the game piece due to the 80" rule (it is up there without the rule).

3. Please, please make sure you are within the 80" no matter what as I see this rule being strictly enforced all season.

Don't say you weren't warned ...

-Paul

P.S. - Thanks Lavery ... I will be sending you my hospital bill.

[StevenB]

<R16> Once the MATCH has started, the ROBOT may assume a PLAYING CONFIGURATION that exceeds the size dimensions specified in Rule <R11>. While in the PLAYING CONFIGURATION, the ROBOT may expand up to a maximum horizontal dimension of 80 inches (e.g. all parts of the ROBOT must fit within an imaginary 80-inch-diameter upright cylinder).

A maximum horizontal dimension of 80 inches and an 80 inch cylinder don't seem equivalent at all. For example, if my robot is an equilateral triangle with a side 80", then I have a maximum horizontal dimension of 80", but I don't fit into an 80" diameter cylinder.

[Lil' Lavery]

I need to get more sleep...

[StevenB]

If your maximum horizontal dimension is 80", you bet you fit into an 80" cylinder. Maximum horizontal dimension doesn't mean straight down the side of your robot, it means the maximum dimension of your robot parallel to the floor. That is, it's the points with the greatest distance between them parallel to the floor on your robot.
So, in your example, it would be the bisecting line of your equilateral triangle.

I suspect that's what the GDC was thinking, but it's wrong. Note that the bisecting line of the equilateral triangle is 40" * sqrt(3) = 69".

[dbell]

heres a diagram. Maybe it will help clear things up.
DB

[Gary Dillard]

Originally Posted by Lil' Lavery

If your maximum horizontal dimension is 80", you bet you fit into an 80" cylinder. Maximum horizontal dimension doesn't mean straight down the side of your robot, it means the maximum dimension of your robot parallel to the floor. That is, it's the points with the greatest distance between them parallel to the floor on your robot.
So, in your example, it would be the bisecting line of your equilateral triangle.

Uh, I'll take that bet Sean. Better sketch it out and rethink your response. Oops, I see David beat you to it.

I didn't pick up on the discrepancy in the rule StevenB, but you are correct. I just focused on the part in parentheses about fitting inside an 80 inch diameter circle thinking it was a clarification because it is more restrictive; I'll post a question on Q & A if noone else has. That makes a HUGE difference; it's the difference between the back corners being tangent to an 80 inch diameter circle as I've assumed or being the center of an 80 inch radius arc.

I just posted the question; we'll see. I'll be designing to the more restrictive requirement until I hear otherwise.

[Ian Curtis]

Originally Posted by Gary Dillard

That makes a HUGE difference; it's the difference between the back corners being tangent to an 80 inch diameter circle as I've assumed or being the center of an 80 inch radius arc.

I don't have access to CAD (nor am I any good at using it). However, I broke out my handy dandy pen, paper and google (as I left my trusty TI-84 at school), and tried to tackle the size difference. I am notoriously bad at trig, however, so I could be completely off base, becuase I did not get the answer I thought I'd get. I didn't keep track of my work, but essentially, I drew a rectangle inside an 80 inch diameter circle, with the corners being located on the circle. I assumed a fix robot width of 28 inches, and tried to find how far forward once could extend. The answer I got was 74.9ish inches total. Subtracting the robot length (assumed to be 38") this leaves you with about 37" to play with.

If you're extending that far out for any length of time with anything hefty, I can't imagine you'd be very stable.

Can someone else do the math to either confirm or (more likely) tell me I'm way out in left field? It seems to me that if the situation is dire enough to warrant a Thunderchicken bashing his head, then I've probably screwed up my math.

with a cylinder whose center point is tangent to the ground and has a base perpendicular to the ground you can have a robot of INFINITE length! however it would only be able to go 40cm high and thats a semicircular shape

[Schnabel]

Here is something to look at and think about. Even though 80" can get very small very fast, that is a lot of space. Also, the further you go out, the hight center of gravity you will have, thus the ability to be pushed over easier.

[Ian Curtis]

Originally Posted by Schnabel

Here is something to look at and think about. Even though 80" can get very small very fast, that is a lot of space. Also, the further you go out, the hight center of gravity you will have, thus the ability to be pushed over easier.

What I'm gathering from Paul's post is that it is not the grabbing the ball that's the hard part. It's designing the arm to move the grabbed ball up in the air without extending out of your personal cylinder.

In case that doesn't make sense, stand in front of wall and extend your so that it's parallel to the floor, and move up to the wall. Then, move your arm so at a 45 degree angle down, and then to 45 degrees up. While those 45 degree positions may very well be in the cylinder, when the arm is parallel to the floor, it is not. That's where the design gets tricky, and the arm gets complicated to stay within that cylinder.