I just wanted to post this out there as I have seen other teams doing it recently as well.
We will be updating a blog throughout the competition season with our team’s ideas, designs, prototypes, successes, failures, etc. You can watch us go through the design process and see weekly updates from our students here: http://vrc357.blogspot.com/
Click on the link and see our team’s first CAD study using a prototype gripper.
The gripper looks familiar! 
Familiar as in close to what you guys have come up with or similar to the design we used last season? Just curious!
We still need to see how this will work with barrels that are on their side, and with the balls by themselves as well. The other issue is the lip on the barrel when it is standing vertical - the curved edge is very small this year. It seemed that even a 1/16" lexan thickness wasn’t immediately sliding under it, but after filing the edge down some to give it a gradual slope, this seemed to help quite a bit.
We posted an update from tonight’s meeting, feel free to check it out!
Well It looks like what you used last year! Ours is a bit… different for sure (not cadded yet) 
Get back to you on that one! 
P.S. Might want to center the picture (just looks better on the post)
Good eye! This design worked pretty well for us last year and it was simple to construct. The game objects are a little more complex this year, but we wanted to start with something that worked last year and build off of it - at least for this idea.
We also posted a video from the Alex’s Lemonade charity event, lots of young students got to drive a VEX robot for the first time (some of these young people were absolute ringers, we need to start recruiting in elementary school!) - VRC357 Royal Assault Build Blog: Video from Alex's Lemonade
So I was thinking about your gripper for a second. I did a slight mobility study in my head comparing my iteration of your concept and the concept shown on your CAD.
What you have shown is basically two different kinds of grippers inside of one, This is nice because you can pick up stacked objects very easily!!! However, what happens when all of your stacked objects are gone?
The obvious answer is picking up random single objects (this is where the problem is… I think at least) The trouble would be created by the ball (unless you already designed for this, then the entire rant/criticism is pretty much useless)
Nonetheless!
If you were to make the bottom part of the gripper a “universal gripper” where it could capture and lift both kind of elements this would remove your problem as you could efficiently pick up and transfer both objects while they are locked in your gripper. I would just do what you did with the ball on the top grip from the “edges” of the ball not the center
This design would require 4 lexan pieces on the bottom part of the gripper while the top would remain as 2 (unless you plan on somehow picking up a cylinder with the top half of your gripper) I’ll make a sketch what the bottom should optimally look like with this design later However for now I must do chores.
This would be awesome, we’re very interested in improving this idea further.
We posted an update tonight - VRC357 Royal Assault Build Blog: Lesson on Torque and More Brainstorming - we went over some of the other mechanism concepts and have very rough sketches of them right now. We are going to prototype a few of them up to see what works and what doesn’t.
Stay tuned for further updates. We have a long meeting this Saturday and should be able to get a few things running which means you’ll see some video soon!
The team was busy over the weekend, but mostly with things outside of the VEX competition, check out the blog for more information: VRC357 Royal Assault Build Blog: Carpet Day & Lego Camp
That’s not to say that a few things didn’t get done, manufacturing has begun on the claw and it is looking promising. The image shown below is a little rough, the claw pieces still need to be cleaned up:
Check the blog to see an additional image of the claw. It currently looks like it should be able to pick up both barrels and balls individually as well as when they are stacked.
Looks like I didn’t have to draw a sketch, looks like about half of what I was talking about! Just mirror that to the top hemisphere of the ball and then you can grab both the ball and the cylinder with the bottom portion, It would be up to you if you wanted to do that a second time on the top part. I personally don’t see many cylinders to be grabbed with the top but it would be nice to have if you had to.
We have posted an update over on the build blog: VRC357 Royal Assault Build Blog: Drives Nearly Finished and Conveyor Mechanism Prototype (with video)
There’s a video of one of our first prototype mechanisms that uses two conveyor belts to manipulate the objects.
Check out the blog for lots of images as well -
That video indirectly reveals something I otherwise would have had to find out in prototyping. Thanks for posting!
Glad it helped!
Check out a video of one of our potential drives for this season: http://youtu.be/jrythsWcdF0 I’m not sure what people usually call it but our students have been calling it the C-drive base.
It’s great to watch videos of your design process, and that you have released them to everyone – keep up the good work!
As for your drivetrain type; I usually call it a T-drive, for the same reason that X holonomic is called X holonomic, and + holonomic is called + holonomic.
~Jordan
I like C-Drive Granted is an x holo without one wheel. But still cool Nonetheless Maybe you should try to make a kiwi… 
Thanks for watching! It should be interesting to see what we come up with between now and later on in the season. As long as people are interested, we will keep posting video segments and pictures throughout the entire season.
Not the greatest picture, but here’s an update on the claw. Hopefully we will get some footage of it working on Thursday.
Awesome pretty close to what I envisioned!
One thing you might want to add is something to secure the ball from an offcenter location so it grasps it from the “top” and “bottom” of the ball
Originally the claw was going to do this, but we found it wasn’t really necessary during assembly. You probably noticed there are less lexan pieces than in the original CAD design.
I’ll get a few better pictures to show this, but basically a small part of the ball sticks out of the top of the claw and this secures it in place when it is sitting on top of the barrel. You could turn the claw upside down and the game pieces would stay in place.
Happy 4th of July everybody! Check out our blog for four videos of prototypes, most of them testing of the claw - http://www.youtube.com/watch?v=28kb7E2h87Q
Just a few more photos from the weekend, the 4-bar is coming along nicely, still trying to figure out a way to integrate extending linear slides to connect to the claw -
And here’s the table of concepts and drives so far. Getting to the point of just integrating everything together -
Lots of tweaks and changes still happening though. Most likely these robots will still look different in the coming weeks ahead. Don’t expect much of an update this week, the students are helping run a VEX summer camp for incoming freshmen students. This will serve as a fun summer learning experience for the incoming students, and possibly a way to drum up interest for the team once the school year starts.