Poll: Wide or Narrow Chassis?

[Hallry]

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?

[aheg1220]

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.

[Ninja_Bait]

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.

[biancs15]

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

[DonRotolo]

Originally Posted by biancs15

It is IMPOSSIBLE to have 3 "long" robots balanced on the ramp. That is not going to happen.

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?

[Sconrad]

Originally Posted by DonRotolo

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?

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.

[TheOtherGuy]

Originally Posted by DonRotolo

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?

It is almost surely not going to happen

[Tristan Lall]

Originally Posted by TheOtherGuy

It is almost surely not going to happen

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

[3v3rnoob]

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?

[soxfan269]

Originally Posted by 3v3rnoob

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?

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.

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.

[Jared Russell]

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)

[Polaris395]

Originally Posted by soxfan269

*snip*
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.
*snip*

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!

[Bruceb]

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

[Alex.q]

Originally Posted by DonRotolo

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?

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.