Underestimating the Trailer [Archive]

Enigma's puzzle

05-01-2009, 10:46

I have a feeling the everyone is going to underestimate the trailer. Everyone to a different degree but i believe that everyone will. This severely limits the ability to backup. And it makes an easy pinning target.

Dean and Woody never went backwards with their robots, most likely not to throw their hand to a major complication to our robots.

Avoiding a jack knife will be a major strategy, as will pinning a robot by the trailer as you are less likely to slip off and you can keep your goal close to the center of the crater.

My Thought: Teams that don't build trailers to practice with will be surprised at completion by these Tricky Trailers. And only the quickest adapting of these teams will be successful.

I'm thinking of taking the drives out to the farm and putting them in one of these freezing rain puddles with a tractor and trailer, and see who can handle it.

Dominicano0519

05-01-2009, 11:01

yeah the trailer is gonna be a pain
if youve ever driven in the snow or icy roads with a trailer in the back

trust me no fun

the trailer basically drives you , if you go right the trailer goes left

lbl1731

05-01-2009, 11:11

MrForbes

05-01-2009, 11:15

The problem is that if the published wheel friction specs are accurate, then it's going to be very slow going backing up with the trailer jacknifed.

Ali Ahmed

05-01-2009, 11:20

I think that will be underestimated now but once teams have finished drive trains and once they build a trailer they'll get used to it. So i say in about 10 days we will see threads like, "Driving Is Impossible!". Hopefully not.

Maybe talking to truck drivers might be helpful.

Enigma's puzzle

05-01-2009, 11:55

I agree that it will hurt your manuevering, but I really don't think jack knife will be a problem. Think about it. The wheels on it are the same as are on the robot. It'll slide easy. I say jack knife it. You'll just push it backwards and sideways. Don't worry about backing it up staight or anything.

But you are pushing the wheels the way they don't want to roll, I heard somewhere on CD that the transverse friction is twice that of the normal forward travel friction. There probably not enough friction to catch the ground to cause the trailer to flip but you will be fighting it the entire way.

You the kind of person i'm talking about, that is going to underestimate the potential problems.

I know that we are building a trailer tonight and the next coupe of days so we can test it to foresee possible problems.

dani190

05-01-2009, 21:21

really good point, tomorrow i am starting to build our trailer, and hopefully we can have it up and on last years robot or something that way we can see how driving is...

Petey

05-01-2009, 22:17

Something to think about:

Can you build a robot in such a way that the trailer's wheels are always oriented like the robot's?

R.C.

05-01-2009, 22:30

The trailer is gonna be tricky but the best way to deal with it is simply to have practice. Also learning how to drift would be nice!:yikes:

EricH

05-01-2009, 22:31

Something to think about:

Can you build a robot in such a way that the trailer's wheels are always oriented like the robot's?I don't think so. The contact is to be bumper-bumper instead of bumper-tongue (<R18>E) and the hitch is to be on the outside edge of the robot (<R18>D) and the the trailer must be easily removed after the match by removing its pin (<G36> and <R18>C).

It's possible, but it'll be pretty hard. You also have <R08> to consider, which includes the bumper perimeter.

Petey

05-01-2009, 22:37

I don't think so. The contact is to be bumper-bumper instead of bumper-tongue (<R18>E) and the hitch is to be on the outside edge of the robot (<R18>D) and the the trailer must be easily removed after the match by removing its pin (<G36> and <R18>C).

It's possible, but it'll be pretty hard. You also have <R08> to consider, which includes the bumper perimeter.

I bet it'd be hard, but I'm pretty sure it's possible. You don't need a square chassis, all you need is a way to construct your back end in such a way that the sides of the hexagon abut the back end of your bot while the trailer tongue is pulled pretty far in while also observing the other rules about attaching easily and not hitting the walls before bumpers.

e: what's the shear strength of the bolt?

EricH

05-01-2009, 22:39

menace101

05-01-2009, 22:40

It's definitely possible. I think if you have your normal chassis but at the back, you leave some sort of indent that pulls the tongue in so that the trailers bumpers will rest on your bots bumpers. It's not that hard, Petey, is it?

Petey

05-01-2009, 22:45

Enigma's puzzle

07-01-2009, 09:14

We had been thinking about butting up to the trailer to, but now that out of the question with the update, but what about a way to make your wheels point the same as the trailers? HMMMM...........Ideating

kirtar

07-01-2009, 11:19

I bet it'd be hard, but I'm pretty sure it's possible. You don't need a square chassis, all you need is a way to construct your back end in such a way that the sides of the hexagon abut the back end of your bot while the trailer tongue is pulled pretty far in while also observing the other rules about attaching easily and not hitting the walls before bumpers.

e: what's the shear strength of the bolt?

Just remember that the hitch has to be on the bumper perimeter. Even if you put an indentation, the outer vertices would still define a polygon which would put your hitch not on the bumper perimeter.

Also, to EricH, you only need bumpers on 2/3 of the bumper perimetier. The entire bumper perimeter exists whether on not there are bumpers on the robot.

=Martin=Taylor=

07-01-2009, 11:28

Something to think about:

Can you build a robot in such a way that the trailer's wheels are always oriented like the robot's?

Whats the advantage?

If you're dragging the trailer wheels sideways while you turn your gonna make steering much harder.

We've found that jacknifing the robot/trailer back and forth quickly is a great way to steer. Seems to work better than just plain tank steering.

Anna B.

07-01-2009, 11:55

We've found that jacknifing the robot/trailer back and forth quickly is a great way to steer. Seems to work better than just plain tank steering.

Exactly. Instead of fighting it, why not work with it?

pfreivald

07-01-2009, 12:26

We've found that jacknifing the robot/trailer back and forth quickly is a great way to steer. Seems to work better than just plain tank steering.

What kind of drive train did you use when you were jacknifing to steer? Tank? 4WD?

Thanks,

Patrick

Swerting

07-01-2009, 12:38

My team made a basic tank drive chasis from VeX kits, hooked up a trailer (also made of VeX) and drove it on a smooth table (the wheels being gears) and while it did seem to jacknife(?) quite a bit it didn't seem to matter too much since the wheels also slid fairly easily.

of course, it's just VeX on a smooth table, and it may be entirely different in competition

eschanz

07-01-2009, 12:51

I dont think it will be as hard as people are saying, because with less friction it will be close to impossible to get jack-knifed. This is because when you slide, the force from hitting a wall or another bot will send the trailer flying past or hit the wall (or bot) too.

JesseK

07-01-2009, 12:53

FYI, unless there's something that I missed you cannot move the hitch location once the match has started. The rule regarding the trailer hitch says a rigid, fixed location which has been interpreted by most to mean that the hitch cannot be actuated.

As for detecting the trailer location, you could have ultrasonic sensors pointed out the back of the bot to where the tongue meets the trailer. If the trailer swings to one side, the range finder on that side will get shorter and the range finder on the other side will report a longer range or just noise. Of course, this assumes you already have a crab drive system and there's an actual benefit to keeping your robot wheels oriented with the trailer wheels.

EricH

07-01-2009, 15:04

Also, to EricH, you only need bumpers on 2/3 of the bumper perimetier. The entire bumper perimeter exists whether on not there are bumpers on the robot.That's what I said. You only need 2/3 of it (the perimeter). Though maybe I should have added "covered" to the end.

Also note, though this is not official by any means: the trailer hitch will (most likely) take up 7" of the 1/3 uncovered. I don't think the GDC will rule that it's a bumper...

=Martin=Taylor=

07-01-2009, 19:42

What kind of drive train did you use when you were jacknifing to steer? Tank? 4WD?

Thanks,

Patrick

4WD "long" configuration.

Tank steering.

pfreivald

07-01-2009, 20:01

4WD "long" configuration.

Tank steering.

That's nice to know. We only have a single 4x8 sheet of the FRP so far, and we were looking at 4WD tank steering, probably wide configuration... As a team that experiences a lot of ice and snow on a regular basis, we've been thinking about 'using the slipperiness' instead of somehow trying to fight it since day one.

Patrick

rees2001

07-01-2009, 20:12

As a team that experiences a lot of ice and snow on a regular basis, we've been thinking about 'using the slipperiness' instead of somehow trying to fight it since day one.

Patrick

Wouldn't today be one of those ice & snow days?

Booksy

07-01-2009, 22:04

What if you designed the robot to be mainly driven backwards?

Have the trailer be like the "skis". When you want to turn, just jackknife the trailer and drive straight. The wheels would that way aid in turning.

Or else maybe drive forward, turn backwards.

I honestly didn't think turning would be an issue... until we tried to turn today on linoleum. If you start off spinning you're fine, if you try to turn while driving straight, you better be prepared to wait. And that's without a trailer BTW.

I think the trailer could be used advantageously, if used properly. Just some testing is needed to figure out how that would work. Hopefully we'll have a trailer by Monday. I am thinking of taking some video of it and recommend other teams to do the same, that way we can all examine it and try and figure out how to drive with this thing.

Enigma's puzzle

07-01-2009, 22:27

If i planned on building to utilize the trailer for steering i would get practicing now.

silicon_ghoti

07-01-2009, 23:02

I bet it'd be hard, but I'm pretty sure it's possible. You don't need a square chassis, all you need is a way to construct your back end in such a way that the sides of the hexagon abut the back end of your bot while the trailer tongue is pulled pretty far in while also observing the other rules about attaching easily and not hitting the walls before bumpers.

We were looking into that too, but our team came to the general consensus that FIRST was trying to articulate that the trailer hook-up was to be attached to the "outer-edge" created by the bumper polygon. For those curious about the bumper polygon it is shape created by the outermost points/corners of the robot. (Note, by definition polygons cannot have indentations, or in other words internal angles greater than 180 degrees.) But I would love for someone to prove us wrong.

Team 2811

07-01-2009, 23:07

I think that if you have enough speed when you are backing up the jack-knife problem won't be a problem since the wheels on the trailer have no more traction than the robot wheels so they will slip and slide even going sideways when jack-knifed. As long as you keep some speed when going either backwards or forwards you cann still keep going into a possible orientation spot.

Team 2811

07-01-2009, 23:18

I also think that the idea about asking a professional truck driver or accomplished person in terms of backing up with a trailer. I luckily have my very own Dad for that but unfortunatly for me my dad is very busy right now being Scoutmaster owning his own business and with the recent snow storm neither of those are going well but I still appreciate the idea.

pfreivald

08-01-2009, 23:05

Wouldn't today be one of those ice & snow days?

Sure 'nuff. We had about 1/2" of ice on EVERYTHING in Naples, so we had the day off from school. By eleven it had all melted, so I spent the day going from hardware store to hardware store to get everything needed to build the field elements.

Well, except for FRP.

But anyway, back on topic, I think that freaking out too much over the slipperiness and trailer, instead of some level of 'going with the flow', will be at least as harmful to a team. Of course, figuring out what the appropriate level of freaking out about *anything* is always the main challenge of FIRST, isn't it?

Patrick

meastman

08-01-2009, 23:21

It shouldn't really matter, underestimating the trailer, because we are all at the same disadvantage.

usbcd36

08-01-2009, 23:43

How many teams have built a trailer (or trailer analog) and practiced with it?

BrAAndon

09-01-2009, 02:08

How many teams have built a trailer (or trailer analog) and practiced with it?

Quite a few I suppose, we made a makeshift one, but it is quite easy to make if you don't get to technical.

GaryVoshol

09-01-2009, 06:55

Also note, though this is not official by any means: the trailer hitch will (most likely) take up 7" of the 1/3 uncovered. I don't think the GDC will rule that it's a bumper...More than that - you've got to have a big enough gap in your rear bumper so that the trailer tongue doesn't hit the edge side of your bumper.

Brandon Holley

09-01-2009, 08:46

How many teams have built a trailer (or trailer analog) and practiced with it?

We have 2 trailers built. One identical to a competition one (bumpers, wheels everything). The other a slightly dumbed down version (no bumpers, older wheels).

We took our 2007 bot and modified it for the rover wheels. That is our current practice setup.

Ziaholic

09-01-2009, 12:38

More than that - you've got to have a big enough gap in your rear bumper so that the trailer tongue doesn't hit the edge side of your bumper.

According to some "back of a napkin" math we performed, the 7" is an adequate bumper gap if you are in the "wide" formation and have the remainder of the 38" covered in bumpers.

The trailer/bot bumpers should contact before the trailer tongue touches.