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.