Team 1816 runs the ball into a ball/corner and lifts the forks, but to keep the ball on them and prevent it from moving around we bought bicycle handle grips at target and they fit perfectly on the end of our forks. I have seen other teams use tennis balls on the front. If you just add something with a little grip to the front, as soon as the ball is on, it is on until you let it go. Just make sure you don’t put too much grip or else you will have trouble releasing the ball for a hurdle.
We initially went with tennis balls, but found out that the ball was still rolling out of the side. We’ve got some sort of modification in the works for Javits, I believe it involves a bit of surgical tubing and zipties.
We decided that the ball would come off as we turned the corner, so we added a gripper arm to clamp over the top of the ball. This gives us three point stability. We also added cylinders to the forks so they could open about 30 degrees for easy acquisition of the ball.
When we get the ball - the forks close in from the sides and the gripper comes down from the top. We also have a ball sensor that automatically tells the robot to grab the ball.
We have a fork type picker upper, and to make it work better we put some PVC side arm things on it, they flop down about 45 degrees when we first lower the lifter, and guide the ball to the center and keep it there, seem to work real well especially when driving towards the end wall when picking up the ball. Hopefully I’ll figure out how to get some video off my camera…so you can see them in action…
There’s a lousy video in the LA regional thread, here’s a picture of it with the lifter up, sorry I did not get any with it down, I’ll try tomorrow to do that.
The pvc arms just pivot in some short lengths of 1x1x1/16" square tube that’s riveted to the top of the lifter. They each have a bolt that fits thru a slot cut in the pvc, limiting travel. Easy to make, seems to work well.
We had old strips of toolbox drawer liner material lying around and we added those to the front of our forks and to our gripper. The stuff is lightweight, smooth, and reasonably durable, and it provides a “sticky” (i.e. gripping with very little pressure) behavior without actually being sticky.
Here’s another picture of our modified fork type ball picker upper, the PVC tubing parts flop down as shown when the fork goes down, and guide the ball in for more reliable lifting. They are held on by those short pieces of square tubing, which are riveted on, and there is a bolt going thru the tubing sideways that fits in slots in the PVC. The slots were very easy to make by just holding the PVC in place, and running a drill in the hole in the square tubing, and slowly turning the PVC, so the drill bit mills the slots.
That’s probably not something you should be too proud of.
Our forks pick up the ball very easily no matter where we are, provided we can get the ball in between them. It’s hard to see the other side of the barrier.
We had some trouble with the balls rolling off to the sides. We fixed that by adding “mantis claws” – two protrusions over the top of the ball. When we tip our forks back, the protrusions compress the ball a bit and keep it firmly in place. It works great.
Yeah… it does work great. We got to watch those mantis claws in action just a few more times in the quarters than we really wanted to. :eek:
Our grippers aren’t exactly fork-type (www.youtube.com/dtengineering) but we also found it to be a big problem when we went too far underneath the ball, like we did in Portland.
We swapped the hockey sticks to curve out, not in, and then put a spacer on the gripper pneumatic so it couldn’t close all the way in. We also changed the code to give a quarter second delay between closing the sticks and lifting the sticks. This made a huge difference in our ball grasping ability and we were even able to pick it up “on the roll” once or twice in Seattle.
Our biggest problem was seeing the forks on the other side of the field and smashing them against the wall. I think it may be easier to lift the ball if we make our forks longer and picking up around our home wall.
We have a set of forks that have the same radius as the ball at the height we grab it. A pneumatic cylinder opens them and when the button is released it remains closed around the ball. Our forks are made of carbon fiber and we have had them broken twice so far. (we have spares) Once we ran them into the end wall (in Portland) and another time another team rammed them (I think it was not intentional). They are pretty sturdy and they have a shock absorber of our own design that allows them to flex when hit…
Our third claw (we call it the talon) comes down from the top and traps the ball in a three point grip. It is quite effective at holding the ball.
The entire lift mechanism tilts back when we have the ball and keeps the ball centered on our robot for traveling to the scoring quadrant.
The talon is also powered by a pneumatic cylinder.
The third appendage is our kicker which we affectionately call “the tongue”
which gives the ball a small kick at the top of the overpass allowing us to quickly hurdle.
We had some problems in Portland but re-designed two pieces and now we ar working pretty well.
With the curved claws we can pick up the ball without having to push it against the wall.
team 1086 just uses straight PVC tube, our “twin” 384 put a bend into the end of their forks which prevents the ball from rolling out once they get possesion of it… we did notice 103’s brushes and plan on testing a version of these once we get to championship… but overall we havent had too big of a problem lifting the ball, we just take it nice and slow while lining up with the ball, so we dont bump it out of position.
1885 Used Straight forks and 2 arced “paws” that come down over the ball. The arcs extend over the top crest of the ball to keep it from coming out the front, and they are angled sideways to keep them from coming out the sides. They are actuated to “pounce” on a big ball o’ yarn via a 4" pneumatic piston. (edit) Capturing the ball via this method actually worked very well; we had issues with a weak motor on the lift that prevented us from hurdling well, but that will be fixed in Philly.
We had a huge problem with our forks at VCU because they were, by design, supposed to stick out the front of the bot for the entirety of the match. However whenever we ran into the wall all of the impact force was transferred up to the forlift arm mounts. By the end of Friday, all of the welds on that mount were completely broken and any chance of hurdling was practically gone.
We have plans to upgrade this in Philly with a 2" wide 1/8" thick lexan piece that we bend around to make a semi-circle. Prototyping it suggests that the lexan may wear out in the course of the matches, so we’re going to work on an upgrade for that before Atlanta. The lexan should absorb any wall impact the forklift receives instead of transferring it to the mount points, which is the goal for Philly. The inspiration came from 2106 (Junkyard Dogs) at VCU.