Rethinking the Low bar
 

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

Re: Rethinking 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.

Re: Rethinking the Low bar
 

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.

Re: Rethinking the Low bar
 

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.

Re: Rethinking the Low bar
 

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".

Re: Rethinking the Low bar
 

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.

Re: Rethinking the Low bar
 

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

Re: Rethinking the Low bar
 

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.

Re: Rethinking the Low bar
 

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.

Re: Rethinking the Low bar
 

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...

Re: Rethinking the Low bar
 

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.

Re: Rethinking the Low bar
 

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).

Re: Rethinking the Low bar
 

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

Re: Rethinking the Low bar
 

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.

Re: Rethinking the Low bar
 

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 :D.

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!

Re: Rethinking the Low bar
 

I think everyone should build a smaller bot at some point. We learned a lot in how to efficiently package multiple systems and electronics. It was definitely a learning experience and proved very effective going over obstacles without tipping . I am of the opinion a low bot can do anything as well as larger bots minus better defense. Most of the past world champion captains tended to be low to the ground bots. I think we may continue to go smaller and more compact in the future.

Re: Rethinking the Low bar
 

That's only true in the static case. It's possible to save a situation that would statically be a tip by accelerating or decelerating, which is the equivalent of pushing the CoM one way or another. You can also cause a tip in the same fashion. A heavier robot with more rotational inertia is going to tip less than a lighter one because your motors stay there same. I guarantee you I could build a chassis that flips due to its own wheel force, and fix it by adding weight without changing CoM.

Re: Rethinking the Low bar
 

Yes but I believe the static case for that occurring and the dynamic case are different. When stationary we could pull our robot back to quite a degree without it tipping over but when we attempted to cross defenses the robot turned into a pendulum and it tipped. Adding ankle weights at the four corners prevented it from happening again. Our COM was already low so it wasn't just the COM that needed to be adjusted to fix the tipping issue.

Re: Rethinking the Low bar
 

The problem I saw with the higher robots was not necessarily that they would tip, but that so much time was spent waiting for the teetering to dampen out before being able to drive again. It plagued a couple of teams in Los Angeles. If they hadn't waited a moment to let the back and forth movement settle, they would have most likely driven "under themselves" and tipped backwards. Precious seconds lost multiple times in a match.

Re: Rethinking the Low bar
 

Yes. The low bar is one of the easiest ways to get through the defenses. By designing for it you also build a robot with a low CG. This then makes going over the other obsticles without tipping over much easier. Its worked well for us so far. It did take some extra time to design, but it was worth it.

Re: Rethinking the Low bar
 

Right after we watched the reveal video on the 9th we went to 179's field to see what it looked like. When I saw the height of the low bar I looked at one of my team mates and said "There's no way we're fitting under that". I would probably still have the same reaction.

For me, the low bar is an obstacle that I personally knew most teams would design their robot for because "OOOOHHH WE GOTTA DO EVERTHIN'". So we decided not to. I think we would make that decision again. Even with our #tallbot we still had trouble packaging everything into what we built so kudos to all those low bar robots.

EDIT: I've been wanting to say this for a while and I feel like this is an appropriate place to say it:
The low bar is a defence, yes? Yes. So I looked at the problem as would we design our robot to just be able to damage one defence, say the Portcullis. That Portcullis design is essentially your constraint and you can't remove it, you can't work around it. It has to stay there. So we decided to not let 1 defence constrain us when there are 8 other ones that are available to take down. (I think that makes sense)

Re: Rethinking the Low bar
 

We would definitely take the low bar approach again. We looked at it from a strategy standpoint from district events through worlds. Add to that the design and engineering challenge of getting everything to fit in a tight package. It's a really good lesson in minimalist design. We opted to not have pneumatics this year to save space, and aren't regretting that decision at all.

We typically are crossing the other defenses in teleop, but we still wanted to be able to handle that one, as we might be paired with 2 robots who couldn't do the low bar. From our week 2 event, there were a few times we had to cross the low bar because an alliance partner wasn't able to complete it for one reason or another.

When we are in tower attack mode, it provides a quick path to go back and forth from the neutral zone and/or secret passage. We used it often (though not always) to make that trip.

Low bar isn't for everyone, but it provides a fun challenge.

Re: Rethinking the Low bar
 

My team totally ditched the low-bar Saturday after bag and tag. We are using our withholding allowance to build a mechanism for Colorado that I believe should be able to change the way defense is played in this game.

Re: Rethinking the Low bar
 

Acceleration is a force and therefore would affect the direction of your footprint projection. The footprint is projected in the direction of all forces acting on the robot, I just said gravity because that is always present.

This would prevent the tipping because it would reduce the robot acceleration, and rotational acceleration (which means it would have to undergo lateral acceleration for longer before reaching its tipping point) therefore changing the footprint projection, that's the real reason it wouldn't tip.

As mentioned above, the cases are the same, you just add another vector for robot acceleration.

Very true, the reactionary force when the robot stops makes it like a pendulum, you want to accelerate out of phase with the robot tipping period to not magnify it.

Re: Rethinking the Low bar
 

Counter argument: our design goal was to be able to breach alone, and we picked low bar instead of c class defenses. It means we I ly have to be capable of 7/9 of the defenses instead of 8/9 which would be needed for a solo breaching #tallbot.

I told my students on day two that the game isn't hard per se, but it is a difficult packaging problem, which is very common in engineering.

Re: Rethinking the Low bar
 

let's see if you found what I found :cool:

Re: Rethinking the Low bar
 

We are a tall robot and to be honest I am still alright with that decision. Our biggest problem isn't the robot wanting to tip over it is that our drivers are afraid of breaking the robot so they keep stopping while going over defenses. This makes us "look" like we will tip. We are using the original AM wheels on our tracks and not so much as a crack (we made hubs to take the abuse).

Re: Rethinking the Low bar
 

Without a doubt we would still plan to go under the low bar. We have had multiple matches this year where our ability to do the low bar directly added to our RPs earned in a match (in particular our solo breaching when we are the only robot on our alliance).

Self reliance is something I brought up in the old Low Bar threads and I am very happy to report that it was the right choice for us.

Re: Rethinking the Low bar
 

If my team had the experience and the skill to make a fast, accurate high goal shooter, than we might have. However, we have a track record of building functional but not exceptional shooters, and this year, we just decided we didn't need to shoot high goals.
I am still happy with our decision as it forced us to embrace CAD more in our design process (something the rest of my team had been dragging their feet about) to get everything to fit under that 14" limit. Also, as long as the improvements to our intake we plan on implementing at the Regional work, we should be able to run low goal cycles very quickly, and crossing the Low Bar is critical to that strategy.

Oh, and we inadvertently built a robot that can climb stairs unassisted. That wouldn't have happened if we had gone tall.

Re: Rethinking the Low bar
 

We prioritized breaching and bouldering and that included the low bar. I wouldn't change a thing. Our robot is a breaching machine and could do 3 - 4 low goals a match at our first regional. The low bar allowed us to keep our center of gravity insanely low which made us able to zip over defenses with no worries of tipping.

Re: Rethinking the Low bar
 

Confirmed - we'd still be low-bar capable. The low bar was definitely the easiest defense to breach. The mistakes that held us down at Bayou were mechanical implementation, not strategic decisions. No more #25 chain, at least not for dead-axle drive wheels. We achieved our highest regional seeding yet (#18 of 56), and were the highest seeded 5-5 team due to several breaching RP and a capture RP (we scored a few boulders and carried more into the courtyard). Our post season mods will focus on the drive train and tweaking the pickup and launcher.