Long vs Short Drive Train

[Ideal_Nerd]

During the off season our team is testing different dive trains. Is there any major difference between a long and short setups?

[Ether]

Originally Posted by Ideal_Nerd

During the off season our team is testing different dive trains. Is there any major difference between a long and short setups?

Yes. Long skid-steer bots can have trouble turning smoothly.

[styxracer97]

I recommend a long bot. When done right you will not run into steering issues and you can drive the bot harder because it is not as easy to do wheelies like a fat bot.

[MechEng83]

Originally Posted by styxracer97

I recommend a long bot. When done right you will not run into steering issues and you can drive the bot harder because it is not as easy to do wheelies like a fat bot.

Emphasis mine.

Seems a little biased. Each has their advantages. I am also in the long-bot camp, although with the reduced frame perimeter from the last few years, square is not a bad option if you want to maximize space.

Our last wide bot was 2009. We've gone for nearly-square long configs the last 2 years.

[Jon Stratis]

The biggest difference is with tipability (if i may create a new word). Basically, most long robots are difficult to tip over, while many wide robots are easier to tip over. You can go to extremes, of course - a very long and narrow robot might be easy to tip over sideways, for example... but usually that's not something people worry about much.

Tipping, or popping wheelies, is all about center of gravity. If your center of gravity is too high, then any robot can tip over easily. On the other hand, if you can design your robot so half the weight is within the bumper zone, it's going to be hard to tip over no matter what you do.

Thinking back to Rebound Rumble, I can't even count the number of teams I saw tip over from the bridge - a lot of tall, boxy robots with their center of gravity too high. They would get half on the bridge, their alliance member would back up tipping the bridge, and they would fall right over. Robots with a proper center of balance didn't have that issue - with our robot, if the alliance member tipped the bridge too early we would lean back and everyone would gasp, but then the alliance member just tipped the bridge back, we landed on our wheels, and completed the balance. With that robot, we had 60+ lbs within the bumper zone, and had to be tipped greater than 85 degrees before we would fall onto our back.

With wide robots, you might be able to get away with 2 wheels, while long robots need at least a third drop center if you want to be able to turn.

[Pretzel]

I will second the notion that your robot's center of gravity is a major player in how easily your robot will tip over, and can play a role in how you design your drivetrain.

In 2013 our team opted for a climbing design (http://i.imgur.com/mUfHf6L.jpg) that ended up having a high center of gravity because of the hooks. Even with a "long" style drivetrain and belts, I would end up using the hooks like skids when I rapidly switched from forwards to backwards. While the hooks prevented us from fully tipping over (I could right it by accelerating forwards again) we would have been in trouble without those hooks. The weight was very high up and wasn't centered in the robot, making it easy to tip that direction even with a long-style drivetrain.

Fast forward to 2014, where one of our design focuses was a low center of gravity after last years robot. Our current robot (http://www.chiefdelphi.com/media/img...02d42d06_l.jpg) has a very low center of gravity with only the collector extending above the lifting handles that are a part of the side panels. The collector is made of box aluminum tubing, meaning the whole collector arm assembly weighs under 15 pounds. With a total robot weight of 110 pounds, that means only 13% of the robot weight is more than 3" above the bumper zone. This robot, which has a square drivebase and frame, was impossible for me as a driver to tip even with other robots "assisting" me in my acceleration.

You do have to design with turning in mind when you have a long style drivetrain. You need to remember that your center wheel will likely need to be dropped more (assuming you use 6 traction wheels or tank treads like we do) than it would be in a wide style drivetrain just to allow your robot to turn more easily. Otherwise you can actually get into a situation where you cause a Jaguar to draw more than it's rated 60a of current and have it reset on you just by turning the robot.

Just a couple things you might want to keep in mind when designing if you're worried about the tipping aspect. As far as turning goes, a long style drivetrain will generally not turn quite as well depending on a large number of factors (how far is the wheel dropped, how "long" is it, how heavy is it etc.). Our team has found that a dropped center gives us the mobility we need, but different teams have different needs.

[pmangels17]

The Long Vs Wide Debate basically comes down to what you want your robot to do. Using this year as an example, a long bot had a better ability to put mechanisms in front of and behind the ball, so if the shooter/launcher you had in mind needed such spaces, then a long bot might be the better option. If you wanted space left and right of the ball for an intake or other mechanisms, then a wide bot was your best bet.

Up until the last two years, frame perimeter rules made it less than advantageous to build a square or almost square robot, but now more and more teams are taking advantage of the more flexible rules to facilitate mechanisms all around the game pieces.

Obviously this year was special with the game pieces as big as they are, finding real estate around them was tricky. Sometimes, it is simply preference, I know some teams that have always and will always build one style of base, and if that works for them because they have a design style that they have perfected, then props to them.

Personally, I tend to favor long and square bases over wide bases because in all the matches I've seen, the long and square bots have done better at pushing other robots, and not being pushed around, but that is not to say that all wide bots cannot push, it is just a trend I've noticed.

[cadandcookies]

The theoretical "wide" vs "long" debate is, in my opinion, one with very little meaning outside of the context of a game. It gets caught up in all sorts of what-ifs and assumptions.

The fact is, you can design an effective competitive robot with a wide or long robot. One of the things that stands out to me in this case is Karthik's strategy presentation at Champs in 2012-- I recall him saying to the effect of "no team should have built a long robot this year, because of the bridge and triple balance"-- but, come Saturday night, and look at who's playing: 25 with a long drive train was part of the winning alliance!

I don't think it's worth getting caught up in.

Personally, I lean towards square robots with wide drive trains-- more difficult to tip than pure wide robots, maximizes your area for a rectangle, easier to make turn than a wide robot. But that's just like, my opinion man, so take it as you will.

[Paul Richardson]

Also consider that a long robot can fit through a narrower gap than a wide robot. Getting past typical FRC defense is a matter of fitting through gaps (disregard pushing, if you're an offensive robot in a pushing match, the defender has already won because you're wasting time even if you "win" the pushing match).

[NWChen]

Originally Posted by Paul Richardson

Also consider that a long robot can fit through a narrower gap than a wide robot. Getting past typical FRC defense is a matter of fitting through gaps

At the same time, typical FRC defense also consists of T-bones/pinning, in which case a long robot (which requires more torque to turn) could be a disadvantage.