Sideways Hanging - Yes or No

[Daniel_LaFleur]

Originally Posted by coldfusion1279

But if you have 2 robots hanging off your robot in that orientation, your robot's arm will bend way before the steel support (unless your arm is a firmly planted pole of equal size).

Don't be too sure of this. The pole is in bending (shear) while the robot is in compression/tension.

[coldfusion1279]

Originally Posted by Daniel_LaFleur

Don't be too sure of this. The pole is in bending (shear) while the robot is in compression/tension.

Whatever is attached to the bar on your robot (assuming you are hanging next to it) has a moment on the joint attached to the robot.

Think of it this way, force applied to the vertical support is applied parallel to the floor, but the weight of the robots is applied perpendicular to the floor.

This is assuming a design like the original posting.

[Daniel_LaFleur]

Originally Posted by edison

i can only relply to other peoples, can't figure out how to post a new thread, where to go after i sign in??? thanks

On the orange bar at the top of each page is a set of links.

The top left one should say either forums or portal:

If it says portal then click on it and it will take you to the portal anf the top left one will then be forums.

When it says forums, click on it ... that'll take you to the forums list.

Then click on the forum you wish to add your thread to.

Once there there will be a blue button that says new thread (looks like the post button)

[Brandon Holley]

Originally Posted by Ken Leung

The Team Drawings in the document section: http://www.usfirst.org/roboticsprogr....aspx?id=16097, specifically TE-10012.pdf within 2010 Team Field Elements.zip, show a version of the tower using 4X4's as the vertical posts.

If these drawings are official, then it seem the GDC did not intend for robots to attach to the towers using the vertical posts. If they did, then these drawings are invalid for the official game.

Someone need to post a clarifying question in Q&A about this.

I do not believe it is our job to guess what the GDC intends. If there is no rule explicitly stating you cannot hang from it, it would appear you can.

[Chris is me]

Originally Posted by Brandon Holley

I do not believe it is our job to guess what the GDC intends. If there is no rule explicitly stating you cannot hang from it, it would appear you can.

On the other hand, if the tower isn't strong enough to hold a robot hanging sideways (though I personally highly doubt it) than obviously that wasn't an intended part of the game, and if the tower breaks, it's breaking a ton of rules.

[Ken Leung]

Originally Posted by Daniel_LaFleur

Ken,

That drawing is for the low-cost field for teams to practice on and in this case does not accurately portray the official field due to different material (1-1/2" steel tubing vs 4x4) .

Then I would say the low-cost field is an ineffective tool for teams to practice with, no matter how cheap it is.

Originally Posted by Brandon Holley

I do not believe it is our job to guess what the GDC intends. If there is no rule explicitly stating you cannot hang from it, it would appear you can.

I agree we should not guess the GDC's intend. That is why we should ask them to clarify. The bottom line is I am not going to design any robot to hang sideways, nor will I advice anyone else to do so, until the GDC specifically clarify it is allowed.

One thing I learned is never take any strategy for granted, until FIRST specifically say you are allowed to use it. I have seen a few robots too many that were built, shipped, and had to be completely rebuilt at the regionals, many of them with innovative strategies that came as a surprise to the GDC.

[Kevin Sevcik]

A preliminary Inventor model suggests that a 150 lb robot with a CoM 18 inches off the center of the pipe will load a single pipe to 50% of yield.

This is using the cheesy "Stress Analysis" Inventor package we get with the kit, so it's somewhat less trustworthy for the coarse mesh it's limited to. But it's also assuming the pipe is a cantilevered column with support only at the bottom, which is clearly not the case. The rigid connections to the other side of the tower will mean some load will be carried through the top of the pipe as well. So I think one robot per vertical pipe is a reasonable load for the tower.

However.... I was assuming a 12 inch separation between the "hands". The hands generate two equal and opposite forces to create a moment to balance the moment generated by the robot's CoM. The closer the hands, the greater the point force required to generate this moment. At around 6" of separation, this point load starts to become significant. At this point you have to worry about crushing the pipe between your hands in addition to bending the pipe at the base. This crushing type failure will NOT be improved by rigid connections at the top and middle of the platform. The only way to improve it is to increase the separation of your hands.

Something for to think about for teams considering this approach: This normal loading on your hands increases linearly with the weight of your robot(s). And you can customize magnitude of this normal force by choosing the separation between your hands. I wonder how this could be useful.....

[MrForbes]

Originally Posted by Kevin Sevcik

Something for to think about for teams considering this approach: This normal loading on your hands increases linearly with the weight of your robot(s). And you can customize magnitude of this normal force by choosing the separation between your hands. I wonder how this could be useful.....

Interestingly as you reduce the stess on the TOWER by moving the "hands" further apart, you also reduce the force necessary to be able to swing the robot up to it's sideways position.

Definitely something to consider.

[Kevin Sevcik]

Originally Posted by squirrel

Interestingly as you reduce the stess on the TOWER by moving the "hands" further apart, you also reduce the force necessary to be able to swing the robot up to it's sideways position.

Definitely something to consider.

Well okay, I was thinking it was a useful factoid if you're planning on using friction to maintain your Z-level on the pipe. But yes, spreading your hands apart also reduces the stress on the hands, as well.

To address some posts that came up while I was playing with inventor, if you're planning on supporting the entire moment of your robot at one rotary joint... Well good luck to you. 225 ft-lbs is pretty significant for a single joint to support.

Also, as I thought my post made clear, don't assume that the tower is indestructible. It is certainly rather sturdy, but it's not nearly as reinforced as it could be. Front-to-back loads will mostly be carried by the joint at the base, with only a little load carried by the frame at the top. So.... I think it's safe(ish) to hang a robot off the side of the tower, but I don't recommend bouncing or anything when you do it.

[Brandon Holley]

Originally Posted by Swampdude

Pretend he's a robot... This was our first thought on how to hang (due to it's efficiency), so I assume many of you are thinking the same thing. But we're preemptively ditching the idea as I'm sure it will knock the tower over and also point load the vertical member beyond yield. Not to mention if your hanging like this and a couple more bots climb aboard. Actually I haven't studied the footing of the tower but it seems like 3 bots piled up on each others back could get pretty far from center on the tower. Seems like it could go over pretty easy. Perhaps the GDC didn't see this coming, but I recommend a ruling on it soon.

FYI - I'm not planning on asking if this is acceptable on the GDC forum thing.

Have you interacted with the actual field elements? The tower is pretty rigid in my opinion. The steel piping that is used is very rigid. I would make sure you fully explore this option before determining the vertical member will be stressed beyond yield.

-Brando

[Kims Robot]

The tower is very rigid. At one point at the NH kickoff there were three kids hanging on it, and not gingerly.

Its really hard to tell from the photos/drawings, but there are solid metal plates below the tower & the bumps that help keep them solidly in place. They are mentioned in the rules:

The BUMPS are fixed to base plates that are secured to the carpet of the FIELD to keep them from moving. The base plates are covered with the same carpet as the FIELD. Note that this forms a small (approximately ½-inch tall) transition from the FIELD surface onto the base plates.

I dont see it mentioned, but the same style plate is underneath the Tower. You can sort of see it here.

[Swampdude]

I guess my big concern is the column in compression and then a bot hanging sideways as mentioned shock loading that column in bending. Plus if the bot is hanging out like that and maybe sticking out 4', then another bot climbs on the back of bot 1, or even 2 bots. That could put the bots collective cg as much as 4'-6' away from the side of the tower. That's a lot of force on that 1 column that's now in compression and bending. bad.... And if the collective cg gets out past the edge of the floor plate in any direction it could pull it over.

[Brandon Holley]

Originally Posted by Swampdude

I guess my big concern is the column in compression and then a bot hanging sideways as mentioned shock loading that column in bending. Plus if the bot is hanging out like that and maybe sticking out 4', then another bot climbs on the back of bot 1, or even 2 bots. That could put the bots collective cg as much as 4'-6' away from the side of the tower. That's a lot of force on that 1 column that's now in compression and bending. bad.... And if the collective cg gets out past the edge of the floor plate in any direction it could pull it over.

I totally agree that its a valid concern, however there may be ways to avoid that. I think its a creative idea, and I didnt want you to dismiss it quickly thinking the tower was not robust enough to handle the load.

-Brando

[GaryVoshol]

Is whatever mechanism you will use to grab able to be released without power?

[jspatz1]

I would not let concern about the tower post failing or tipping over stop you from pursuing this or any other climbing method. The field apparatus is designed to take whatever methods the challenge has invited. If you are clever enough to do this, go for it.