Manipulators: Claws vs rollers?
 

Who has experience using roller type tube manipulators? Like as opposed to a claw, which you have to carefully position to pick up a tube, a design with two rollers seems like it could pick up a tube faster. Thoughts?

Re: Manipulators: Claws vs rollers?
 

Maybe make the claw wide, so you don't have to position it carefully?

http://www.youtube.com/watch?v=EqK_XTSoc1w

We have some experience with a narrow claw from 2007, it didn't work as well as we would have liked

Re: Manipulators: Claws vs rollers?
 

Picking up tubes is all about positioning - So long as your mechanism can be positioned properly, and works quickly, you'll be fine. That can be done with both claws and rollers. Rollers work actively, and if left on automatically - you drive into a tube and the rollers have instant control of it. A claw, on the other hand, needs to be activated when you want to pick up the tube. This can be done by one of your drivers, or if your clever you might be able to come up with some sort of limit switch to automatically activate it. In the end, you can get a claw to close incredibly quickly, using either a motor or a pneumatic piston. Just think about the brakes on your bicycle... you don't need to squeeze them very far in order to get them to move in and grab the wheel.

Re: Manipulators: Claws vs rollers?
 

Same here, http://dulaneyrobotics.com/component...a/Atlanta3.jpg

We're brainstorming better ideas for tube manipulation right now.

Re: Manipulators: Claws vs rollers?
 

Suction cups on servos

Re: Manipulators: Claws vs rollers?
 

Got some Vex? Try a roller claw out in that and play with the geometry. See if you can make it work. If you can, great! If you can't, new design.

The key to a good manipulator is not the kind of manipulator but how much prototyping you put into it.

Re: Manipulators: Claws vs rollers?
 

MAN, this looks familiar :rolleyes:

-Brando

Re: Manipulators: Claws vs rollers?
 

And to give credit where credit is due and obvious - this is directly inspired by a 148 prototype from 2007.

That being said - it's a pretty good prototype! We've learned a lot about tube grip and tube rotation from this prototype, and we'll be able to determine whether or not our final claw needs to be spring loaded in the next few days.

Re: Manipulators: Claws vs rollers?
 

Well said, and I have a video to prove it (link below)!

The kids made 2 proof of concepts Saturday that were both pneumatically-actuated 'dumb' claws, in order to see the feasibilities of chute pickup vs floor pickup. One claw went through the center of the tubes with a 3-pronged approach, the other went for the outer edges of the tubes against 2 pieces of very smooth wooden slats (about 6"x6"). Both worked beautifully from the floor.

We're entertaining the idea of an inner-roller claw since in 2007 that one worked the absolute best* for us and was relatively simple. This year we'd have to modify it, and probably forego the ability to place one of the shapes (gasp!), however that's the tradeoff we'd let our alliances know about.

*look at 45 seconds into the video. We got the idea from Gael Force. In that same video, 340 uses a very simple pneumatic claw as well, adding more anecdotes to Chris's advice.

Re: Manipulators: Claws vs rollers?
 

For a claw, you need a wrist or some other type of mechanism to adjust the position of the ring. With rollers, you can adjust your tube simply by spinning the rollers.

Re: Manipulators: Claws vs rollers?
 

An idea I had for a manipulator, it would be sprung closed with surgical tubing and the wheels spun by banebots motors.

Re: Manipulators: Claws vs rollers?
 

That is, if you need to adjust the position of the ring. ;)

Re: Manipulators: Claws vs rollers?
 

Just to be clear I wasn't trying to call you out for "stealing" a design or anything of the sort. I was just making a comment as to us having pretty much the same exact setup sitting in our lab too.

-Brando

Re: Manipulators: Claws vs rollers?
 

Has anyone thought about making a generic claw design but with extra space in the top part for a roller? That way you could pick up the tube as easily as with a claw and worry about manipulating it with the roller on your way towards the other side of the field

Re: Manipulators: Claws vs rollers?
 

Either one can be very effective but the most effective one is a manipulator on a robot that gives your drivers plenty of time to practice.

You can have the greatest picker-upper-thingy in the world but if you don't get practice with it the team with the uber-simple one that they have spent many hours driving will still kick your butt.

Re: Manipulators: Claws vs rollers?
 

We did pretty good in 2007 so we're gonna try to stick with our claw design as much as possible from that year with some inspiration from our even more successful 2008 bot for the elevator.

Re: Manipulators: Claws vs rollers?
 

This needs to be reiterated. Get those prototypes done fast, get your robot built quickly, and drive it around for a few days before you ship it! Too many teams look as though they're driving their robot for the first time on Thursday morning at competition.

The same concept applies to all the other parts of your robot, too. "Testing" is indeed part of the design process.

Re: Manipulators: Claws vs rollers?
 

We are prototyping several different tube manipulators, including a simple claw and a 'roller claw'...

We are also making our robot modular, so that whatever ends up working best in practice is what ends up on the field!

Re: Manipulators: Claws vs rollers?
 

That's is a great way to go. In fact I seriously doubt we even ship our robot with a picker-up-thingy.

Re: Manipulators: Claws vs rollers?
 

It's a lesson I learned in real-life engineering that I forgot at first in FIRST, and then remembered, and now am getting more and more insistent upon...

Re: Manipulators: Claws vs rollers?
 

Ive found that in essentially every game but 05 rollers are best for picking up an object. With rollers you can have a very active control on the object and pick up the object wthout stopping.

Re: Manipulators: Claws vs rollers?
 

My personal experience with my teams roller gripper from 2007 was this, too much weight. Its very important to keep the weight down on these, its quite easy to get carried away. One other challenge was to design a gripper structure that was light enough to meet our weight goals and work with our wrist actuator design, but at the same time being strong enough to withstand taking a beating on the field and still grab the tubes correctly. We had a match or two where a robot hit us head on with the gripper out, and then it required some 'tweaking' to get the opening size correct. We also prototyped a few different wheel configurations, and tried many different wheel materials, this was very, very useful.

Re: Manipulators: Claws vs rollers?
 

A claw doesn't need to require precise positioning. You can make it wider so the driver only needs to drive into the game piece, and the game piece settles into a position where you can pick it up. (granted, this will probably be much harder this year than it was in 2007)

Whatever you do, make it idiot-proof. Not because your drivers are idiots, but because the fewer precision maneuvers they have to do, the more awesome driving (and scoring!) they have time to do.

Re: Manipulators: Claws vs rollers?
 

One thing we learned whether you use a claw or roller: mount the mechanism on a set of door hinges. That way even if the manipulator takes a hit, it won't deform it will just open the hinge.

Re: Manipulators: Claws vs rollers?
 

With any design remember how high you have to go to reach the highest row. The less mass the better.

Re: Manipulators: Claws vs rollers?
 

sweet idea REX cant wait to see your crazy design this year

Re: Manipulators: Claws vs rollers?
 

Could someone explain the lift in this image? It seems like the ropes simply go from the bottom of one stage to the top of the other, so how does it all go up exactly?

Thanks,
Sunny

Re: Manipulators: Claws vs rollers?
 

You mean the 2008 bot?
Those are slide rails that are designed for use in a copier drawer were used for the elevator.
Just be warned when using them that they can give out (check out 7:52 into the video. Ironically we won the Quality Award after this happened).

Re: Manipulators: Claws vs rollers?
 

I'm more curious about how the actual lift was obtained. Like, it seems that the rope runs from the bottom of one stage to the top of the previous stage. How would you pull that up?

- Sunny

Re: Manipulators: Claws vs rollers?
 

Re: Manipulators: Claws vs rollers?
 

We looked at a claw and a gripper, and made quick ptototypes of each. We are going forward with a claw, but not everyone has full confidence at this point.

A claw is a lot simpler and the parts that are exposed to damage (extended) are easier to fix or replace. It is lighter. A claw can't rotate a tube after picking it up, but this year most or all tubes will essentially be horizontal on the floor. We can do any necessary rotation with the arm. A claw can be made to pick up a tube that is in contact with the robot - and robot/tube contact should orient and locate the tube for pickup. A claw requires fewer wires running out to the tip of the maniplator. It is easier to modify the details of a claw (grip materials, length of the fingers, amount of clamping, etc. Hopefully, our claw will be done soon enough to build a roller claw if it doesn't work!

I expect the tubes to be inflated quite tight. Inflation pressure really changes the dynamics of the pickup. Whatever you use, be sure it can be adjusted for, or is relatively unaffected by tube pressure.

Finish early - then practice, break it, improve it, repeat.

Re: Manipulators: Claws vs rollers?
 

I was convinced with a claw when it was used to pick up a completely uninflated tube with incredible ease... While running.

No such thing as finishing early!

Re: Manipulators: Claws vs rollers?
 

What are peoples thoughts on how fast they think the roller should run to adequitly pick up the tube?

Re: Manipulators: Claws vs rollers?
 

what would you use for a roller or collector that is legal in FRC? i know vex wheels are not legal. And im looking for a collector that is smaller that 4in in diameter? What would work:confused:

Re: Manipulators: Claws vs rollers?
 

...as fast as it needs to...

No, really. Depending on the material surface, diameter, and geometry of your roller claw, that answer is going to have a lot of play.

Design, prototype, test, critique, redesign, re-prototype, test, critique, redesign, re-prototype, test, cry a little, critique... Repeat these steps as necessary!

Re: Manipulators: Claws vs rollers?
 

PVC with tape of some kind (grip tape or electrical tape)?
Pieces of pool tube?

...and why aren't VEX wheels legal for parts of the robot?

Re: Manipulators: Claws vs rollers?
 

I find tank tread riveted to pvc pipe to be an easy solution. we've used it in the past and have never had an issue with not having enough grip on an object.

Re: Manipulators: Claws vs rollers?
 

There is no rule against using Vex wheels on the hostbot.


Drawer liner on a pvc pipe works well also.

Re: Manipulators: Claws vs rollers?
 

The little VEX wheels are almost ideal for a primitive roller claw. Thank goodness they're legal!

We had a very long discussion this weekend about pickup mechanisms. We listed a couple of observations as we acted out retrieval from the opposite side of the field:

• Acquiring from the chute in the wall means the tube will most likely need to be reoriented at some point to prevent it from being inadvertently 'stolen' while crossing the field since it sticks out
• Acquiring from the ground while in that lane is very difficult due to the wall that divides the lane and the opponent's scoring zone. This 12" wall makes it very difficult to accurately line up to a inflated tube that's only 9" high from ~50 feet away
• It's very easy for opponents to 'snipe' a tube that's thrown outside of the lane just by blocking the path to the tube, then going for it (much like blocking out in Ultimate Frisbee)
• It's very difficult to throw a tube in the lane to a place the drivers can see with much consistency

The thought came up that we need some sort of 'garbage chute' that the HP can dump the tube in and our mechanism can retrieve from. Yet we're running out of room and weight on the robot, heh.

So we're going to stick with a simple claw that only picks up from the ground, for the moment. We need to think some more. It was the first time we'd really considered roller claws; however they add an entire layer of complexity in control on top of an already somewhat complex control system (lift + wrist + simple claw will keep a driver very busy as-is).

Re: Manipulators: Claws vs rollers?
 

On the subject of small wheels for Roller Claws and the like, may I suggest looking at the Bane Bots wheels? You can get them with a 3/8" keyed, 1/2" keyed, 1/2" hex, or 3/4" hex center bore, they're relatively cheap, and from our experience more than strong enough for small mechanisms such as a roller claw.

The only reason I would lean towards these over say, a vex wheel, is that they come in some smaller diameters and are much easier to drive than a vex wheel, unless of course you were to put some sort of hub onto the vex wheel.

http://banebots.com/c/WHB-WM

Re: Manipulators: Claws vs rollers?
 

Another vote for BaneBots wheels. I've been using them for a (non-FIRST) robotics project, and they're great. They're lighter than the Vex wheels and have incredible grip. For the orange wheels (40 shore rubber), I measured a static coefficient of friction of 1.06 on a painted wood surface.
As thefro mentioned, you can attach them to just about any shaft with the help of the BaneBots hubs.

Re: Manipulators: Claws vs rollers?
 

Vex wheels work great on FRC robots - you just have to carefully modify them to accept a thicker axle. You won't be able to use them on a Vex bot again, but you'll have a unique, cool robot.