Manipulators: Claws vs rollers?

[IndySam]

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.

[s_forbes]

Originally Posted by IndySam

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.

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.

[pfreivald]

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!

[IndySam]

Originally Posted by pfreivald

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

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

[pfreivald]

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...

[jblay]

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.

[Rob Colatutto]

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.

[Ian Curtis]

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.

[Stephen of REX]

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.

[Gdeaver]

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

[EagleEngineer]

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

[pfreivald]

Originally Posted by EagleEngineer

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

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?

[jblay]

Originally Posted by EagleEngineer

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

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.

[IndySam]

Originally Posted by EagleEngineer

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

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


Drawer liner on a pvc pipe works well also.

[JesseK]

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).