Poll: Wide or Narrow Chassis?
 

Another day of planning, another poll.

Today, one of our team's main decisions was what kind of chassis we were going to build: a wide or narrow base. While we did mostly agree upon a narrow chassis, we figured it might be worth trying out a quick prototype of each, and see which handles better.

What kind of chassis is your team building? Why? What do you think the pros/cons are?

Re: Poll: Wide or Narrow Chassis?
 

Don't forget that a wide chassis will be more prone to tipping while going over the bump. The upside is that you won't have a problem turning if you decide to use only 4 wheels.

A narrow chassis will be more stable going over the bump, but you'll have to use a 6 or 8 wheeled drive in order to facilitate turning.

Re: Poll: Wide or Narrow Chassis?
 

I think in terms of trade-offs:

Wide gives you a wider acquirer, but it makes it harder to stay upright when you navigate the obstacles.

Narrow limits the acquirer but gives you better balance.

With only 18 balls max on the field, and a three-ball limit, I think the importance of a wide acquirer will be lessened. I doubt teams will have many opportunities to pick up more than one ball at a time.

Answer? Narrow robot.

Re: Poll: Wide or Narrow Chassis?
 

On the pro side for narrow drivetrains, it will be much easier to fit it onto the ramp at the end of the match. During eliminations, these extra 20 points are so very key. That is 7 balls scored on the top hoop, 10 balls scored in the mid hoops and 20 balls on the low hoop. That is literally half of the match making up for the extra time it takes to load 3 onto the ramp. It is IMPOSSIBLE to have 3 "long" robots balanced on the ramp. That is not going to happen.

I disagree with the point of 18 balls being a small enough number that we will only be encountering one at a time. Even if 6 balls had just been scored (1 per team), there are 12 balls on the field. If you give each side 6 balls randomly placed on a 27 by 27 foot section of the court the randomness could allow for even 3 or 4 balls to come together.

- Austin

Re: Poll: Wide or Narrow Chassis?
 

Impossible is such a strong word.

I have 3 robots, all 6-wheel low center drive at 119 pounds:
Bot 1: Heavier in front by 10 pounds, 21" from center wheel to edge of heavy end bumper
Bot 2: Perfectly balanced, 44" long
Bot 3: Heavier in rear by 10 pounds, 21" from center wheel to edge of heavy end bumper.

The bots are lined up on the 88" ramp Bot 1 (heavy end in), Bot 2 (in the middle), Bot 3 (also heavy end in). Bot 1 takes up 21.5", the center wheel is 0.5" from the edge of the ramp. Bot 2 takes up 44 inches. Bot 3 is like Bot 1.

21.5 + 44 + 21.5 = 87 inches. They fit.

Oh, and Bot 2 turned sideways on the ramp before Bots 1 and 3 positioned themselves, now you could fit Andy Baker on there too.

Oh, and all three bots are really 37 inches long, not 38, so there's extra room.

Still Impossible?

Re: Poll: Wide or Narrow Chassis?
 

I'm not sure I understand your math. Are you proposing that Bots 1 and 3 have their lighter side hanging off of the side of the ramp? If Bot 1 and 3 take 21.5 inches, than they can't be 38 inches long and not have some of their chassis over the edge of the bridge. While they would still stay on the bridge I think (the center of gravity is above the bridge), 37 inches per bot would not give any extra space, just some more breathing room. Even if you assume that Bot 2 followed the length restrictions and fits itself in 38 inches, or 28 inches if it turned sideways first, you are still just giving yourself a couple more inches from falling. While I agree that balancing a ramp of three 37" robots is technically possible, the situation you outlined is so specific and difficult to accomplish without pushing a robot off the ramp, that I don't think the possibility holds any probability. I could just be misinterpreting the situation you are outlining, if so, please correct me.

To quote Stephen J Gould, "I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms." While it is possible to balance 3 long robots on a ramp, I would guess that you can safely assume that you have your chances of a three-robot bridge drastically reduced to the point of extreme improbability with three long robots.

That being said, I personally hesitate to support a wide robot chassis for reasons of tippability.

Re: Poll: Wide or Narrow Chassis?
 

It is almost surely not going to happen ;)

Re: Poll: Wide or Narrow Chassis?
 

Bah. Line them up across the edge of the bridge, and I'll push them up sideways with my robot.

Re: Poll: Wide or Narrow Chassis?
 

Of course! And why CAN'T all three robots go on the long way? Part of the two on the ends can hang off and still balance right? Just don't push too much or my robot on the end will bet smashed UP![/sarcasm]

But in all seriousness, it's not very likely that all three robots will fit on the ramp if they all want to get on long-ways. Then again, that's what mecanum wheels are for, right?

Re: Poll: Wide or Narrow Chassis?
 

Our team came to the conclusion that if you ever see three on a ramp that will be the only time you see it. I doubt from calculations we've made that you will ever see 3 robots on at once. I don't think any team will volunteer their robot to be the one hanging off the edge, there's just too much risk involved. To me a wide drive train seems the most logical. After playing many, many matches on Catalyst I can say that there is never a shortage of balls on the ground. Because of that I believe that there is an advantage to having a wider ball collecting zone.
As far as the bump goes, I don't see any major advantage that going over the bump would give you. I can't see a robot crossing the mid field more than twice, and probably more often only once. The only reason to go onto your opponents side would be to guard or to pass balls. If you're doing that then you're probably going to stay at that end most of the game. The only reason you might cross again would be for end game.

I can't see stability being an issue. If all you're doing is going over 1-2 times a game then you can cross the bridge without it being a hindrance to you. On a narrow robot design you have such little space to line up the ball to the collector that it might hurt you more in the long run, than going over the bridge twice would. Catalyst has been very helpful in identifying problems that I hadn't even thought about. I highly suggest anyone trying to decide between a narrow or wide chasis to try out any chasis available on Catalyst. Last time I checked it will only let you use a narrow chasis, but atleast then you may be able to see the difficulty that the narrow collector can cause.

Re: Poll: Wide or Narrow Chassis?
 

My team has Mecanums on our bot this year, so it's kind of irrelevant which end goes first. However, we have a ball intake on one narrow end, so I guess that's the front.

Re: Poll: Wide or Narrow Chassis?
 

To quote one FIRST Senior Mentor:

"If the robot don't fit, you must acquit" (or in this case, not pick that team to be a part of your eliminations alliance)

Re: Poll: Wide or Narrow Chassis?
 

I think we will assuredly see a triple robot balance. what about robots driving onto other robots, I could see a robot designed entirely to hold another robot, and to allow it to climb on with a ramp working very well. If the first robot had a 14 inch wide ball manipulator up front, with a 14 inch extension there is even enough room for a second robot on top while still having a working ball scoring system. A low level of stall against some support on the first robot would enable it to stay on fairly well, and score 2 robots in the footprint (slightly more really) of one.

Re: Poll: Wide or Narrow Chassis?
 

My team, 1511, is heading toward a narrow drive, but I am still in support of a wide drive because it can collect balls faster and can arrange itself on the bridge easier and taking less time.

Re: Poll: Wide or Narrow Chassis?
 

I see no need to pick up balls faster, since you can only hold 3 balls at a time. A narrow chassis will be a lot more sturdier, and will be better to go over the bumps/bridges in the center. A wide chassis can get more balls at a time, however like I said with only 3 balls maximum, picking them up fast won't be very useful.

Re: Poll: Wide or Narrow Chassis?
 

We are going wide

we are somewhat worried about tipping when attempting the bum so we are trying to create some kind of Wheely Bar so we dont tip

Re: Poll: Wide or Narrow Chassis?
 

I'm guessing narrow, but not sure yet. Feels like it would allow for a more convenient placement of the control board as related to ball intake.

Re: Poll: Wide or Narrow Chassis?
 

The speed with which you can collect balls kind of depends on the ease with which you can collect balls. Since there won't be a lot of balls on the field if the Inbounders are playing smart, then you probably want to make ball collection as easy as possible. A narrow robot leaves a very small area to collect balls, if you are using just an opening between the bumpers. Consider that you'll be driving the robot from a long distance away, so it will be hard to see just what you're doing, and getting an 8" ball into a 12" wide opening under those conditions is going to be quite a challenge. An alternative is to make a wide ball collector that hinges out/down, but this presents some different problems.

I like how the trade-offs in this game are so well balanced, it's difficult to decide which is the best way to go. Look at the poll results so far...

Re: Poll: Wide or Narrow Chassis?
 

Yes, that is correct
We are seriously considering just that.
I then conclude your team is not planning on making it to Einstein this year.
Wide doesn't mean fast. Or easy. Do not limit yourself to a gap in your frame for a ball collection device. You can have an arm that swings down, using the same principle used to collect tennis balls quickly, for example. (like this shows starting at 0:19)
Focus very intensely on a low center of gravity. Our 'Breakaway' robot was called Weeble - can you guess why?
Yes, exactly. And teams should realize that most balls will be against a wall, so if your BAD* cannot pick up from against a wall, it will not be very useful. You need a good BAD.

(*BAD = Ball Acquisition Device)

Re: Poll: Wide or Narrow Chassis?
 

Honestly, I have no idea what orientation to call our drive.

The reason is because we're doing something... weird, to say the least. We have decided that we will be using Mecanum drive as the base, with the BAD* situated on the long side. However, assuming that is the front, our wheels will NOT be pointing in that direction. Rather, they will be oriented the long ways, allowing us to have the stability of the long orientation and the ball carrying capacity of the narrow orientation. Best of both worlds really.

Except maybe for having to deal with drifting. But that's a software problem. ;)

*Ball Acquistion Device as dubbed by DonRotolo.

Re: Poll: Wide or Narrow Chassis?
 

i would go narrow... you might have problems getting over the middle with a wide front, unless you have crab/swerve, or some other types of multi-directional drive trains. unless of course you have an low cg, etc. plus you're not really doing mass collection of game pieces

Re: Poll: Wide or Narrow Chassis?
 

I can tell you that my team is leaning towards wide right now and the main point is this: ease of picking up balls. I know you are all arguing that with so few balls on the field we won't need to be able to pick up fast but I believe that fast isn't what the teams going with wide are looking for, we are looking for ease of use. We want something like many of the gatherers last year (33 is a good example) where we can just drive up to a ball full power and pick it up without any fine alignment, almost as if we have some magic vacuum at the front of the robot. Plus there is always fitting on the ramp...

P.S. I love the term BAD and am going to start using it whenever possible.

Re: Poll: Wide or Narrow Chassis?
 

SQUARE. Meccano wheels actually work best with the rollers forming a "perfect" X. That is, the wheels should be in a square, hence square frame (Ether can verify this, I found some white papers of his but I'm too lazy right now to find 'em again.). It doesn't matter which end is front, but one end will have to be the front regardless. You can't swap a hole in the frame halfway through a match!

Re: Poll: Wide or Narrow Chassis?
 

What a difference a day makes.

The last time I looked yesterday, long config was wining the poll ~60% to ~40% but now only ~51% to ~49%.

Interesting.

Re: Poll: Wide or Narrow Chassis?
 

I think that as more experienced teams answer, we see folks who are not afraid to leave their comfort zone.

Re: Poll: Wide or Narrow Chassis?
 

Not on a team currently, but if it was my bot I would go wide with a 14" wheelie bar that was retractable and also function as a bridge tipper.

Re: Poll: Wide or Narrow Chassis?
 

Square where the wheels contact the floor? or square at the outside of the frame?

Re: Poll: Wide or Narrow Chassis?
 

I think it only matters where the wheels contact the frame. One would just build the robot square as well to make it less likely to tip, or to make it look better.

Re: Poll: Wide or Narrow Chassis?
 

DonRotolo, you are a genius :D BAD is so good xD

On a more serious note to the people considering wide chassis for the potential for a wider BAD™, a word of caution. I had a bit of experience with working on a BAD™ and conveyor system a few years back. It is CRUCIAL that if you make your BAD™ wide, you have some way of funneling balls down to a more narrow path for whatever your scoring device is (unless your scoring device is very wide, though I'm not expecting many of those this year). The worse possible feeling in the world is building an excellent BAD™ and the game pieces getting jammed because the robot has no good way to shunt the pieces into single file.

Re: Poll: Wide or Narrow Chassis?
 

Wow, this is a really neck-in-neck poll. :P

Our team is going wide, for the same reasons that have been made. We want to be able to fit 3 robots on the bridge, and decided this just to stay on the safe side. Another factor that has also been said before, is more room for a ball herder. Maybe not so we can pick up more balls at a time, but so we have more room to work with while it's being built/maintained.

Re: Poll: Wide or Narrow Chassis?
 

In my mind, the game lends itself to wide drives.
Wide-
Wider entrance for balls into frame
Ease of use for pickup because of this^
Ease of use of bridge and fitting robots on it

Narrow-
Possibility to be more stable when crossing bump and/or bridge
"Traditional"

If you can make a bot that is "stable enough" in a wide configuration, then I think it is the best option.

Re: Poll: Wide or Narrow Chassis?
 

We're building both wide, narrow, and a third and we'll decide in week 4 which to advance from prototype to the final design. With 70+ students and 15+ mentors, we have the advantage of three full build teams.

Myself, I'm voting for wide. I think going over the bump is overrated in importance, while fitting on the bridge is underrated by most. A wide bot might also be better suited to two shooters, one for scoring and one for inbounding.

With three build teams working, and a ton of great ideas from CD, I'm hoping for a lot of good options down the road. At the worst, it gives us a lot of opportunity to fail faster which is something we've never mastered.

Re: Poll: Wide or Narrow Chassis?
 

Both. But at the moment i'm not totally sure what the mech guys are doing. All I know is that I'm tryng to prevent them from bashing up the encoders on last years bot as we dismantle it.

Re: Poll: Wide or Narrow Chassis?
 

Looking at the earlier calculations on whether three long robots could actually fit on the bridge, one little fact was overlooked. Three 38 inch long robots can fit on the ramp, indeed. But a robot built to its maximum dimensions will not be 38 inches, but rather more like 44 inches. Why? The bumpers are not included in the 38 inch measurement, so when you take into account the extra bumper space, you're going to have a little bit more robot hanging over the edge than you think.

The balance issue with a tall robot can be easily overcome. The simplest solution is to put the center of balance towards the bottom of the robot. With that, it will be much easier to avoid tipping. And a sideways robot can allow all three robots, even if the other two are long ways, to fit comfortably.

With that, long ways will be the best way in my opinion, because as we all know, every little second counts, and that second saved collecting that extra ball can give you those few extra points that you need to win nationals. :D

Re: Poll: Wide or Narrow Chassis?
 

Actually, it looks like basically everyone's calculations (here and elsewhere) do include bumpers, or have been corrected to do so. Here, Don's nailed the 44" from the beginning:
That said, 3 long bots definitely does create a very precarious situation! It's certainly something to think about, though I think you'll find that virtually all teams otherwise likely to be strong elimination contenders will have realized this (and likely the benefit to collecting width-wise) and found a way to compensate. I won't claim this necessarily means driving wide.

Low CG is definitely always something for which to aim. (Unless the GDC ever forgets to specify the height dimension as being perpendicular to the floor.;)) However, I can't claim it's necessarily easy to achieve. It definitely can be if you have a non-existent scoring mechanism, an exceedingly light/low shooter, or Andy Baker. Us tall shooters will being paying very, very close attention to it.

Welcome to ChiefDelphi!

Re: Poll: Wide or Narrow Chassis?
 

Ah, I hadn't read past the first page. But thank you, I've used this site now for a long time, but just now signed up.

Re: Poll: Wide or Narrow Chassis?
 

Well, it has happened: The wide chassis count has surpassed the narrow chassis one. ::rtm::

Re: Poll: Wide or Narrow Chassis?
 

We, the long chassis voters, are now the minority that can, in the end, tell the majority "I told you so". (At least, I hope so. :ahh:)

Re: Poll: Wide or Narrow Chassis?
 

Actually, DonRotolo included this number in his calculations. This does bring up another consideration into the equation though. I believe he had 21.5" of each robot on the bridge. Now, should the wheel on each 6 wheel drive robot be spaced evenly, that would put Bots 1 and 3 leaning on the inside of their center wheel pair. If I am not mistaken, that would make them likely to fall until their is only 20" over the actual bridge. I could be alone in this, but having 24" of my 44" robot and 4 of my 6 wheels hanging over a foot of thin air makes me awful nervous. On top of this, getting both bots 1 and 3 on the bridge without placing them there with a blimp bot (an idea tossed around in our team for a short while:p ) seems to me to be an extremely difficult, if not impossible. I hate to be close-minded, but I tend to side with soxfan269. If we see three long robots on a ramp, it will most likely be a monumentous, if not one-of-a-kind, event.

Re: Poll: Wide or Narrow Chassis?
 

A wide robot on the bridge only partway would likely be a 4 wheel robot, with one pair of wheels hanging off the edge and the frame (or chains?) resting on the edge of the bridge deck, which is a relatively stable configuration

Re: Poll: Wide or Narrow Chassis?
 

Assuming one of them doesn't fold up into a multidimensional space-time warp... (in FRC, you never know):rolleyes:

I didn't say it was likely, just not impossible.

Re: Poll: Wide or Narrow Chassis?
 

We have decided to go with narrow body. We, as a team have decided that is very important to go over the barrier. A wider robot has a higher center of gravity, as compared to a narrow one.

The main point is a wider base means a likely chance of your robot taking a dive.

Re: Poll: Wide or Narrow Chassis?
 

interesting...we decided it's more important to be able to collect and score balls on our side of the field, than to go over to the other side...unless all the balls are gone on our side. And then we'll use one of the two bridges available to us, or carefully cross the barrier if needed.

Re: Poll: Wide or Narrow Chassis?
 

A wide oriented robot does not necessarily have a higher center of gravity than a narrow one, the difference is in the length of the wheel base. As long as you design with an appropriately low CG both should be fine.

Re: Poll: Wide or Narrow Chassis?
 

We understand that, It is just with our current wheel base, a 6 wheel drive, we would have a better wheel base with a narrow chassi, and more likely to go over the barrier without tipping.

Re: Poll: Wide or Narrow Chassis?
 

I agree haha. Grabbing a ball in 11" (I believe thats what we calculated would be the space allotted for bringing in balls according to bumpers being 8" from either end or w.e) space on the narrow end just won't be enough. Using the wide side, you won't have to worry about that. You'll have plenty of space to grab a ball and bring it inside the bot without thinking about it in the heat of the game.

Re: Poll: Wide or Narrow Chassis?
 

Wider does not equal higher CG.

Wider probably does equal larger angle of attack and thus more movement of the CG as it climbs the barrier.

And thats the tradeoff.

Re: Poll: Wide or Narrow Chassis?
 

This is Essentially what I meant, just simply better put. Thanks for making it clearer.

Re: Poll: Wide or Narrow Chassis?
 

The height, length and width are relative. I learned that during our rookie season in 2008. Bomb Squad showed up with a robot that started the match in one orientation but drove around in another. I quickly learned that day what it means to think outside the box. I still think this is the most genious robot I have seen in person.

http://www.youtube.com/watch?v=bI_2UMEUbNw"]http://www.youtube.com/watch?v=bI_2UMEUbNw

Re: Poll: Wide or Narrow Chassis?
 

This was an awesome bot. But is it always legal? In 2008 there was no height limit and only a 80" diameter upright cylinder length/width limit. The bumper zone was also only defined in Playing Configuration. This year the bumper zone is "<R29> Bumpers must be located entirely within the Bumper Zone when the Robot is standing normally on a flat floor", though "normally" could take the "perpendicular" or "standard" definition.

Re: Poll: Wide or Narrow Chassis?
 

On this train of thought: we are planning on 8in pneumatics for traction and barrier travel. If we decide to go to to wide orientation, we could not (comfortably) fit all 6 wheels in the drivetrain. We would therefore take up more space on the bridge in wide orientation because we would have to have both front and back wheels on the bridge to balance. I suppose we could switch wheels size, but I also tipping.

The most dangerous thing i see with wide orientation is the moment you drive up the bridge at it tips from one slant to the other as you cross. I worried the tipping of the bridge will give momentum to the robot to start to tip forward.

Re: Poll: Wide or Narrow Chassis?
 

I feel like that problem comes down to weight distribution and current momentum of the robot. If you are moving the robot at a negligible velocity, I feel like tipping wont be that bad.

We're probably going to play with one of our old wide bots on the bridge today and try to tip it.

Re: Poll: Wide or Narrow Chassis?
 

Have you 'played' the game yet? On the first day, we simulated the game with people being pushed around on dollies, acting like robots. What we found is that if one alliance was able to distribute balls form their defensive end to their offensive end, there would be a serious deficit in the defensive end. In finals, I don't see this as being a large issue because all 6 robots should be evenly matched.

However, in qualification matches, there are times that alliances will NOT be even. Then, you may need to repeatedly traverse back and forth across the bumper to get the balls that you are looking for. If your teammates are useless too, that only adds to what must be done.

I wouldn't underestimate bump travel.

Cheers!

Re: Poll: Wide or Narrow Chassis?
 

Alex.Q the 8" wheels from AM are only (by our measurement) 7.6 in. in diameter and fit 6 nicely in the wide config.

Tipping a wide bot??? Ya if you have a high CG it will probably get more tippy if that is what you mean. Make everything up top LIGHT and everything down low HEAVY. Make your bumpers the full 20 lbs and make them heavy at the BOTTOM and this should help the tippy issue.

Bruce

Re: Poll: Wide or Narrow Chassis?
 

ignore previous response -

[G21]
Robots may extend one appendage up to 14 in. beyond a single edge of their frame perimeter at any time.
Violation: Foul for exceeding size allotments; Technical-Foul for continuous or repeated violations.

"These appendages are intended for use in manipulating Basketballs and/or Bridges. A Robot may have multiple extension devices onboard, but only one may be deployed at a given time."

Re: Poll: Wide or Narrow Chassis?
 

Can I change my answer? We now decided on going wide-ways.

Re: Poll: Wide or Narrow Chassis?
 

The Q & A says different:

Game - The Game » Robot Actions » G21
Q. Can appendages (one at a time) be used for purposes other than manipulating Basketballs and/or Bridges? FRC3005 2012-01-11
Follow
A. Yes, as long as no other rules are violated.

Re: Poll: Wide or Narrow Chassis?
 

Our robot is going to be almost square, 27X30. We have our middle wheels lowered so we have a turning radius of zero.

Re: Poll: Wide or Narrow Chassis?
 

If you use mechanem or other multi-directional drive systems you can always have your intake on the side while your main drive is still forward.