Picking Up Upside-down Totes?
 

For the past couple of days I have been hearing mutterings from my team (STEMpunk 4531), as well as from many here on Chief Delphi concerning the difficulty of picking up an upside-down tote as compared to one found rightside-up. So to put the speculation to rest I ran a few experiments ::ouch:: 10-12 times each, and determined quite reliably that at a contact pressure of no less than 6 pounds, any arbitrary end-effector should be able to grip the sides of an upside-down tote so long as the friction coefficient between the surface of said end-effector and the plastic walls of the tote is made equal to or greater than the coefficient between plastic and a pair of sweaty boy hands.

I didn't even need a calculator for this one, but if anyone else has a spread sheet or a graph or something showing exactly what it takes to grip a plastic bin at varying distances and with different materials, I would certainly like to see it, even if I wouldn't necessarily make one myself.

Now, of course there are other problems involved with upside-down totes aside from simply picking them up. For example; How do we flip them right side up for stacking quickly and efficiently, why not stack them all upside down, and how do we get our robot to recognize and accept both orientations in auto or even tele-op are all tricky issues and I would love to hear what you guys have to say about them!

Re: Picking Up Upside-down Totes?
 

We figured that a tote-flipper would be more sensible, since a right-side-up tote is a lot easier to deal with in the robot. An arm that grabs the far top edge of the tote and pulls it towards the bot while driving backwards would achieve the job.

Actually, we figured that it's probably not necessary for playing the game pretty well. It might be needed to win CMP, though.

Re: Picking Up Upside-down Totes?
 

Thanks for testing and making your first post to Chief Delphi a good one :)

Could you describe how you measured the 6 pounds of force?

Re: Picking Up Upside-down Totes?
 

Do you really need to? There's enough that are right side up. Perhaps it would be easier to just move the upside down ones out of the way.

Re: Picking Up Upside-down Totes?
 

If there were only 2 possible orientations of the Tote, then only stacking like totes is an easy solution.

But, you still need to figure out what to do with totes laying on their side.

Re: Picking Up Upside-down Totes?
 

Honestly, it was a complete guess and the although I did actually run the "experiments" 3 different ways 10-12 times, the entire post was laden with dry humor and mild sarcasm. Really, that was just what it felt like to me as I picked them up and set them down, BUT I did go and check the friction coefficient between skin and plastic, and it looks to be ~0.98 as described here -> http://hypertextbook.com/facts/2005/skin.shtml for dry skin. Given this and the weight of the totes at 7.8 pounds you can deduce that to grip the sides with dry hands you would need about 7.9 pounds of contact pressure, maybe a bit less with sweaty hands, so I wasn't too far off the first time when I said "no less than 6 pounds"!

Re: Picking Up Upside-down Totes?
 

If only we could find a COTS source for human skin! :p

(looks like we'll have to settle for phone grippy things)

Re: Picking Up Upside-down Totes?
 

A tote flipper is not at all a complex or challenging thing to make. Look at Stack attack for ideas ;)

Re: Picking Up Upside-down Totes?
 

Stack Attack was more about knocking totes down than stacking them up. The human players did most of the stacking.

Re: Picking Up Upside-down Totes?
 

Oh, and what about picking up the recycling bins, if you ask me, anything that can pick up one of those should also be able to deal with the totes pretty easily.

Re: Picking Up Upside-down Totes?
 

What I would do is have two pads (possibly rubber or something else that can grip plastic well) that are built off of arms with motors on them. This way, you can grab the tote and flip it right side up by using the motors. You could even do this in testing and have it automatically rotate the motors (and as a result the container) only a certain number of degrees.

Re: Picking Up Upside-down Totes?
 

'Snow Problem spoke a little bit about upside-down totes in this video. We made a couple of observations about how they move on the ground with zip ties.

Re: Picking Up Upside-down Totes?
 

That's not true for all teams, but we'll focus on this game. ;)

Re: Picking Up Upside-down Totes?
 

You could just have a little arm with a spatula-like thingie on the end of it.

Here; I made a picture:
PICTURE
(yes, I am a bit bored. How did you know?)

Re: Picking Up Upside-down Totes?
 

The only robot I saw in 2003 who's sole focus was making stacks of bins was FRC 73 (a very ideal robot design for this year) and they got quickly figured out by having a bot assigned to stay close by and either force them to hold onto their stack of boxes or slap it down soon as it was released.
Teams realized it was much more worthwhile being King of the Hill than it was making easily destroyed stacks unless you brokered a deal to have them left alone.

Re: Picking Up Upside-down Totes?
 

It should be reasonably easy to flip totes. While this (http://youtu.be/qfu9l_OF_gw?t=2m4s) is definitely not an FRC link, I feel like it effectively shows a possible (albeit massively overpowered) system for flipping totes. If you compacted it you could probably just bolt it to the back of your bot. It's not like it requires anywhere as much force to flip a tote.

I don't think it's reasonable to stack totes on top of an upside down tote that's being held with friction. Then again, your robot design and experiences may vary from ours.

Re: Picking Up Upside-down Totes?
 

Wait, couldn't you make basically a flapjack flipper? Yknow, to flip over the disoriented totes? Just a thought, not really sure HOW to accomplish this, but just wondering. :confused:

Re: Picking Up Upside-down Totes?
 

My fear for building a device that flips totes is flipping them onto, or over, the step.

Re: Picking Up Upside-down Totes?
 

Your pic is for flipping over an upside down tote. My question was for a tote laying on its side.

Also, your design assumes enough friction to keep the tote from sliding, and that there is room behind the tote.

Re: Picking Up Upside-down Totes?
 

We prototyped this, but we decided passive pads on bearings would be simpler. (Our new designs being considered at the moment don't involve this system yet, since we are still speculating if flipping is necessary.)

If you pick up a tote off the ground with the pads within the area that is the bottom half of the tote, whether it is right side up or upside down, it inverts since the point of contact is off center and near bottom, and the object wants to find a point of rest with minimal potential energy. That point of rest is met when the point of contact is now above the middle of the tote. i.e. When the tote flips when held at the bottom, it rotates down so then it is being held at the top half. So this works for flipping totes that are upside down, right side up, and it can also be possible to use it for the containers. The only thing that needs to be powered is the pinching and lifting so the tote or container can get off the ground to swing to its natural position due to gravity and the off center contact points. I recommend playing with that idea.

Re: Picking Up Upside-down Totes?
 

The only strategy I found with trying to deal with the upside down totes was to get to the extra containers on the step if your reach was short range, when the human players have plenty more totes in the Alliance Station available to the robots.

Re: Picking Up Upside-down Totes?
 

My team decided to go with a pincer style grabbing mechanism, and we decided to use a material similar to the grippy stuff on tennid rackets with a bearing on the "hand" part so no matter which way grabbed, it will turn right side up because of how the weight is distributed.

Re: Picking Up Upside-down Totes?
 

Yeah, that's what my team was saying. One of the people on my team did the math and he said the max points you could make not including time is 408, and those upside totes only count for like 20 or something like that, so it probably won't be significant when you have more than enough right side up totes. They may become more relevant in Nationals, and by then you'd have more time to make changes so that you could deal with the upside down bins. I'd say they aren't very relevant unless you're with a team that can quickly and efficiently stack all totes and bins so that you'd actually need the upside down ones. 10 out of the 64 totes are upside down, I don't think they'll really need to come into play till nationals, or if you really need points on your average (since you don't win individual matches till eliminations) or wanna go try hard mode.

Re: Picking Up Upside-down Totes?
 

Ah! The gravity flip certainly is a fine idea, I must say. The only trick here is implementing it on the fly.