Rethinking the Low bar

[Drew_trak]

Just wondering.... If you had the chance to travel back to kickoff, would you still design to travel under the low bar?

[Oblarg]

Originally Posted by Drew_trak

Just wondering.... If you had the chance to travel back to kickoff, would you still design to travel under the low bar?

Yes.

It hasn't caused any major problems for us yet, and it has the benefit of forcing you to keep a low center of mass which is essential for not flipping over when traversing the other defenses.

[serenagh]

Yes. Our strategy was pretty low-bar centric, and it payed off for us. We were the only low bar robot on our elimination alliance, and all of our partners in quals let us play under the low bar. It forced a strong focus on our strategy and design, and was good for our team as a whole. It also allowed us to have consistent auton.

For context: we played at CVR this weekend-- our robot shot high + low goals successfully, and we crossed the B and D defenses.

[marshall]

Originally Posted by Oblarg

Yes.

It hasn't caused any major problems for us yet, and it has the benefit of forcing you to keep a low center of mass which is essential for not flipping over when traversing the other defenses.

Actually, a low COM is not the only key to not flipping over. As crazy as it may sound, our originally tall robot (1 inch shy of max height) that we had in Palmetto could tip over crossing defenses despite having a COM that was only 5~6 inches above the ground.

The second key is not the COM in the static case but the overall location of weight in the dynamic case which can be aided by distributing weight out to the edges of the robot.

Granted, I'm not a physics whiz and I'd love to have someone like Ether comment on this but I believe it to be true based on our experience with adding ankle weights to our robot in Palmetto and seeing the same thing work for another team here at the last NC District event.

[Michael Hill]

Not at all. In fact, I wish we would have come to the conclusion to ditch the low bar sooner. There are so many low-bar capable robots out there, it's not worth the design challenge to fit everything in 13".

[Richard Wallace]

If you can cross it, the low bar is the easiest route to the secret passage. So yes, we would do it again, knowing what we learned at our first event.

Getting boulders quickly and shooting them accurately is the key to high scores. In Week 2, we were able to seed high and win by running about six scoring cycles (crossing plus boulder shot) per match; we think the competitive number of cycles will keep getting higher.

[Boltman]

Absolutely..its basically a "give me" in breaching we saved it for the end in many matches.

[Kevin Sevcik]

Originally Posted by marshall

Actually, a low COM is not the only key to not flipping over. As crazy as it may sound, our originally tall robot (1 inch shy of max height) that we had in Palmetto could tip over crossing defenses despite having a COM that was only 5~6 inches above the ground.

The second key is not the COM in the static case but the overall location of weight in the dynamic case which can be aided by distributing weight out to the edges of the robot.

Granted, I'm not a physics whiz and I'd love to have someone like Ether comment on this but I believe it to be true based on our experience with adding ankle weights to our robot in Palmetto and seeing the same thing work for another team here at the last NC District event.

Adding weight to the edges would greatly increase the rotational inertia of your robot. So you'd rotate slower and less for a given input of rotational energy. Also, more weight means a stronger gravity vector to resist any torque from motors or defenses that are trying to turn you over.

[Anthony Galea]

Honestly, I would stay as a tallbot, because I love our shooter the way it is, and I am fully behind our design. However, I would have us build our drivetrain differently. A 6WD makes life terrible for going over category B, and a properly designed 8wd would be able to tackle the B/D with a lot less stress.

[Joe Johnson]

I think this is an interesting question. I go back and forth on the answer. One thing that I have come to believe is that the low bar saved this game.

I'm serious. I shudder to think of the bedlam that would have ensued had it not been the case that 90% of the teams decided to try to be a low bar robot (forget if they actually CAN limbo, they TRIED, and that saved a lot of them).

I have seen more upside down and tipped over robots this year than in any year I can remember*. Had 90% of teams built 4ft tall robots the highlight reel would have been filled with tipped robots.

Again, the GDC saved this game by making the low bar be the one permanent defense.

Dr. Joe J.

*well, excepting 1997 when when Naval Undersea Warfare went after the other two robots on the field at the opening trumpet blast, tipped them with a spatula type thingy and scored at their leisure once they were the only upright robot left but let us never speak of such things. The horror, the horror...

[GeeTwo]

Caveat: this is the eve of our first competition.

No way - I think we made all the right to-level choices. Things really came together tonight - we're driving and (manually) aiming with a camera now, and We have the driving (low bar, B, or D) if not aiming and shooting parts of auto working. We can make high goals more than half the time, with a fairly high arch, and low goals more consistently. The only real concern about making a solid run at the banner is the beating that the robots (and field) are taking this year, and building a tall robot would only have made those worse.

I'll try to remember to post a follow-up on Sunday.

[themccannman]

Originally Posted by marshall

Actually, a low COM is not the only key to not flipping over. As crazy as it may sound, our originally tall robot (1 inch shy of max height) that we had in Palmetto could tip over crossing defenses despite having a COM that was only 5~6 inches above the ground.

The second key is not the COM in the static case but the overall location of weight in the dynamic case which can be aided by distributing weight out to the edges of the robot.

Granted, I'm not a physics whiz and I'd love to have someone like Ether comment on this but I believe it to be true based on our experience with adding ankle weights to our robot in Palmetto and seeing the same thing work for another team here at the last NC District event.

The only thing that determines when an object tips over is when it's COM passes outside of it's footprint projected in the direction of gravity (downward).

[Boltman]

Originally Posted by GeeTwo

Caveat: this is the eve of our first competition.

No way - I think we made all the right to-level choices. Things really came together tonight - we're driving and (manually) aiming with a camera now, and We have the driving (low bar, B, or D) if not aiming and shooting parts of auto working. We can make high goals more than half the time, with a fairly high arch, and low goals more consistently. The only real concern about making a solid run at the banner is the beating that the robots (and field) are taking this year, and building a tall robot would only have made those worse.

I'll try to remember to post a follow-up on Sunday.

Go for breaches in every match.... get those 3 RP and keep practicing HG shots for eliminations. LG is A-Ok. Good Luck GeeTwo

[MetaEngineer]

Even as I am presented with ever more ways the electronic and pneumatic systems must shrink or move to accommodate additions to the bot, I still think it was the correct choice for us. As much as my grouching under time pressure would suggest otherwise, I have come to enjoy sharing an exercise in compact and rugged design with the students.

There are plenty of things I would love to change if I could rewind to kickoff, but all of those would simply be time, resource, and frustration savers for our design and not abandoning the low bar.

[Tom Line]

We'd keep it.

Like many lower numbered teams, we've had a lot of experience shooting balls. We took those lessons learned and incorporated them since day 1 and we were confident we could make it work.

It was a huge challenge for us to package everything. I hate some of the compromises we made in the wiring of this robot. We had no dedicated electronics area so everything ended up where it fit. That doesn't make for the cleanest layout.

We are still working on some of the trade offs. We have far too few pneumatic tanks and our compressor runs too much. At this point we have no more space, so we're going to live with that. That was the result of a late design decision after we had already calculated and committed to our tank capacity and mounting points - we were shocked to find the robot goes over the obstacles much easier with our arm in the up position (a higher center of gravity). Moving our large arm takes a lot of air.

We went with a near-sheet metal chassis (our first) to maximize space on the inside of the robot. That was a compromise that resulted in a chassis that is far more flexible than we expected. But as long as the welds hold we don't care .

It's resulted in the moving of our camera twice, our flashlight twice, and numerous rewiring jobs as we look for that extra inch of space.

We've gone from long cylinders to pancake cylinders on our AM PTO, and that's caused us a couple headaches re-engineering the connection points twice so that they don't unscrew themselves.

It's been fun!