Slack in the Overpass

[Wayne C.]

"Team 25 posted something last Thursday indicating the overpass was an inch or so lower than it should have been, so if you're counting on having 1/4" clearance, you might want to rethink your design!'

good advice but the design stage was last January and it may be too late......


More on sagging overpass-

By the time NJ was finished yesterday the overpass was visibly torsioned. Numerous robots would hang up on it and try to pull away when they were hurdling and I am sure that was messing up the metal.

Our measurement in the field on Friday night had the overpass by the control side at 76" height midfield and 76.5 right at the wall (atop the wall support). Neither was the 78" assumed height (+- 1 inch). Yesterday it was getting lower in spots to the degree that we would pass cleanly under one side and tip the other on our IR guided round. Our robot height was set for 75". I measured it personally with a tape before the round.

In one round we popped the ball up slightly and it rolled down the overpass in slow motion like the marble in one of those games with the holes. It was obvious that the materials of the overpass were getting beat up and the height was nowhere near 78" as per specs.

As stated previously- we had more issues with the field related nonsense than with dealings with the other robots.

I would like to see teams allowed onto the field at the beginning or the rounds and at downtimes to take measurements so they can adjust their machines(in the same manner we had camera calibration times in prior years). We designed to the specs in the manual. If the field can't maintain that there is a problem.

WC

And one other thing-

we built our bumpers to the exact specs in the manual. We only covered 3 of 4 sides of the robot. Why would they weigh 16.5 lbs? The only way anyone's bumpers seemed to be passing inspection and making weight was to remove the angle aluminum that the manual tells us to put on them. We did so and had a half pound to spare.

If we had 4 bumpers and built them exactly as the manual prescribes they would never be able to pass the weight test. Maybe our experts who write the manual should reexamine their weights and measures or give a more realistic range.

[MrForbes]

Originally Posted by Wayne C.

"Team 25 posted something last Thursday indicating the overpass was an inch or so lower than it should have been, so if you're counting on having 1/4" clearance, you might want to rethink your design!'

good advice but the design stage was last January and it may be too late......

Yes, it's too late to start over, but not too late to make some minor changes that might allow for the field elements to be as they really are. I guess that's just one more game challenge...trying to second guess how the actual field will compare to the drawings.

I think our 4 bumpers weighed right around 12 lbs, 26" for the ends and 36" for the sides, 5" high, no angles. Quick calculation of the weight of angle shows that adding 1/16" thick 3/4" angle would put them just over 15 lbs. Perhaps they had 1/2" angle in mind? Not much room for screws then....yes, the prescribed design seems to be questionable.

[IndySam]

Originally Posted by Wayne C.

And one other thing-

we built our bumpers to the exact specs in the manual. We only covered 3 of 4 sides of the robot. Why would they weigh 16.5 lbs? The only way anyone's bumpers seemed to be passing inspection and making weight was to remove the angle aluminum that the manual tells us to put on them. We did so and had a half pound to spare.

If we had 4 bumpers and built them exactly as the manual prescribes they would never be able to pass the weight test. Maybe our experts who write the manual should reexamine their weights and measures or give a more realistic range.

Our bumpers are built to spec and cover three sides of our robot, they weigh exactly 10lbs. We have used full bumpers the last two years and have never been anywhere near the max bumper weight.

What size aluminum are you guys using? What size bolts? What kind of plywood?

Originally Posted by squirrel

I think our 4 bumpers weighed right around 12 lbs, 26" for the ends and 36" for the sides, 5" high, no angles. Quick calculation of the weight of angle shows that adding 1/16" thick 3/4" angle would put them just over 15 lbs. Perhaps they had 1/2" angle in mind? Not much room for screws then....yes, the prescribed design seems to be questionable.

We use 1/2" and there is plenty of room for the screws.

[Paul Copioli]

Wayne,

Were you measuring to the top of the overpass or the bottom? The specs clearly state the height of 78" is to the top of the overpass. With the pipe at approximately 1.25", the bottom should measure nominal 76.75". With the +/- 1" that would make the range 75.75" to 77.75".

Paul

[Bruce Newendorp]

We measured the Saint Louis Regional overpass height first thing Thursday since we needed to be pretty close to knock the ball off in hybrid. It was 76" to the bottom of the overpass tubing.

[Jeremiah Johnson]

Looking at the MWR field I definitely saw some sagging, but nothing that was getting in the teams' way.

[Raul]

Originally Posted by Jeremiah Johnson

Looking at the MWR field I definitely saw some sagging, but nothing that was getting in the teams' way.

Well, you must have missed seeing us get hung up half the time we went under the middle of the overpass.

[ALIBI]

If the crossover drops two inches, you are going to hear a very loud crash when we go around. Luckily we can easily adjust our height, however, do both sides of the overpass drop the same amount? We will be fine if the crossover is held to +/- an inch, much more than that could cause trouble. We designed according to the specifications, if it looks like it ends up having more of a +/- 1.5 inches for a three inch range from one side to the other, that may cause problems for us and I am guessing several other teams. We would be fine if each side is kept within an inch or two of eachother to even +/- six or seven inches of the stated 78 inch height. How many flags are hitting the overpass? Will we be able to measure the overpass or could the field administration take measurements several times during the day and annouce/post the actual high and low points to the bottom of the tubing for clearance?

[Wayne C.]

Originally Posted by Paul Copioli

Wayne,

Were you measuring to the top of the overpass or the bottom? The specs clearly state the height of 78" is to the top of the overpass. With the pipe at approximately 1.25", the bottom should measure nominal 76.75". With the +/- 1" that would make the range 75.75" to 77.75".

Paul

Paul- you are right- the 78" would be to the top but the bottom spec says approx. 76.5. A 75" robot should have cleared. Not to dwell on this- we will and did adapt.

Next time we'll just have the robot leap the overpass and knock the balls off on the way......

[wilsonmw04]

Originally Posted by Wayne C.

"And one other thing-

we built our bumpers to the exact specs in the manual. We only covered 3 of 4 sides of the robot. Why would they weigh 16.5 lbs? The only way anyone's bumpers seemed to be passing inspection and making weight was to remove the angle aluminum that the manual tells us to put on them. We did so and had a half pound to spare.

If we had 4 bumpers and built them exactly as the manual prescribes they would never be able to pass the weight test. Maybe our experts who write the manual should reexamine their weights and measures or give a more realistic range.

We ran into the same problem. we switched from a 1/8" thick angle to a 1/16" and we lost the weight

[JesseK]

Watching the webcasts of NJ & MidWest, there was noticable flex in the overpass when a bot would hit it. There was a ~2" 'bounce' at one point in the elims just from a launcher bot shooting the ball at it from underneath and hitting it.

This is a huge issue for us as we planned on setting our autonomous for a specific height -- if the overpass is too low we'll probably have the most hilarious high-speed flip-over in FIRST history -- 15ft/sec in hybrid . With the fatigue from the flexing, I wouldn't be surprised if we saw an overpass crack towards the end of the season -- hopefully the mounts for the overpass are replaced in between regionals.

[mtaman02]

Trust me robots hit that overpass all week b/c they forgot to lower themselves before going under. That overpass is not going anywhere unless the regional assembles it wrong. Shockingly enough I didn't see really any extra spare pieces of the field like I did last year. I saw one piece of spare driver station plexi but that was it. I guess FIRST also feels confident the field won't break.