Rethinking the Low bar

[Boltman]

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.

[Kevin Sevcik]

Originally Posted by themccannman

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).

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.

[marshall]

Originally Posted by themccannman

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).

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.

[mateoland]

Originally Posted by themccannman

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).

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.

[Legator91]

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.

[Trevor1523]

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)

[MechEng83]

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.

[BotDesigner]

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.

[themccannman]

Originally Posted by Kevin Sevcik

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.

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.

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.

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.

Originally Posted by marshall

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.

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

Originally Posted by mateoland

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.

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.

[engunneer]

Originally Posted by Trevor1523

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)

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.

[MaGiC_PiKaChU]

Originally Posted by BotDesigner

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.

let's see if you found what I found

[hardcopi]

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).

[Monochron]

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.

[Cothron Theiss]

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.

[Ryan Dognaux]

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.