2363 prototype pickup arm
 

This year we decided to focus on scoring high in autonomous, gather disks from the floor when they are available and the feeder when necessary, then hang for 10 points at the end. One key to a high scoring autonomous mode is gathering from the floor. Here is a video of our prototype floor pickup mechanism. While not perfect (it is, after all, a prototype), this has given us the confidence to proceed with final design and fabrication of a competition quality version.

http://www.youtube.com/watch?v=XVD6P...ature=youtu.be

The arm is mounted on our practice bot chassis. The software team has been working with the competition bot drive train for a week and a half (the second key to a high scoring autonomous mode).

Re: 2363 prototype pickup arm
 

Looks great! Hard to tell, will you be inside the 54" cylinder with your bumpers? We were finding it's pretty restrictive.

Re: 2363 prototype pickup arm
 

Where do the frisbees go from there?

Re: 2363 prototype pickup arm
 

Our first prototype (over the front bumper) exceeded the cylinder by quite a bit. This one fits the cylinder exactly with the arm horizontal (maximum extent of the arm) and is a little within the cylinder when down on the floor.

The width of the scooper matches the width of our frame, for maximum disk gathering. The length of the arm is the maximum allowable by the cylinder.

Restrictive is an understatement.

Re: 2363 prototype pickup arm
 

What do you guys plan on doing from there? Conveying them to some sort of shooter or do you plan on dumping the low goal?

Great looking design though, works well too!

Re: 2363 prototype pickup arm
 

If you were to change the pickup funnel so it's not centered, you could hit 2 discs simultaneously and not worry about the first one clearing before the 2nd disc comes in and jams the whole thing. You may also be able to increase the belt speed on that side slightly such that the offset side rollers pull disc #1 in faster, making it clear the intake before the 2nd disc's apex gets in front of it. It's pretty easy to increase the belt linear speed by increasing its drive roller slightly.

Re: 2363 prototype pickup arm
 

This was our original idea. If the "funnel" is offset, it has to go over top of the bumpers. Without going into a bunch of the other constraints (non-interference with the shooter, shallow scoop angle), an arm that was long enough to go over the bumpers broke the 54" cylinder when horizontal. With a couple more weeks to tweak, we probably could have made it work. But, this year we are following the motto: Having a good robot early is better than having a perfect robot late.

This is one of the things we may try, if jamming proves to be a problem. There are many tiny tweaks possible to speed up one side, or slow down the other.

Re: 2363 prototype pickup arm
 

I love it! Nice work! We are hoping to do something similar to this too.

Re: 2363 prototype pickup arm
 

What kind of belts are you using? Where did you get them?

Re: 2363 prototype pickup arm
 

http://www.mcmaster.com/#endless-flat-belts/=l9hqh3

Splicing: https://www.youtube.com/watch?v=auJt...nVjw& index=4

Re: 2363 prototype pickup arm
 

This looks awesome! I've been working on something very similar, only different ;) . Does your bottom plate scrape the ground? If so, how does this affect driving?

Re: 2363 prototype pickup arm
 

Competition pickup arm was assembled last night.

Re: 2363 prototype pickup arm
 

For those of you wondering where the frisbees go after leaving the pickup arm, here's a photo.



The disks go from the pickup arm to a simple conveyer, which drops them in the top of the hopper. The hopper holds four disks. When full, (or anytime, really) the hopper flips up to the shooter, and the disks are rapid fired by the shooter arm.

Re: 2363 prototype pickup arm
 

How are you moving the disks from the hopper to the shooter? I see a cylinder on the top level that I assume is involved, but can't quite tell what it's designed to do.

Re: 2363 prototype pickup arm
 

My guess is that the whole hopper assembly rotates up, a really nice compact way to move frisbees (conveyors take up alot of room). The only negative is it looks like they won't be able to pickup and shoot at the same time, although I am not sure how required that will be this year.

Re: 2363 prototype pickup arm
 

This looks awesome. I can't wait to see the system integration

Re: 2363 prototype pickup arm
 

I gathered that. I was curious how the discs then exited the hopper, but I think I figured it out. The cylinder mounted on top of the wood board seems to be attached to a piece that will rotate and push out the discs.

It looks like the shooter platform can articulate to two angles based on the cylinders of the front of the robot. Can the hopper unload into the shooter at both angles? Or is one configuration simply for starting conditions?

Re: 2363 prototype pickup arm
 

The hopper can load at any angle, we are actually looking to add a 3rd angle to our arsenal.

Re: 2363 prototype pickup arm
 

I assume this robot is going to play heavily on the strategy of picking up missed frisbees around the pyramid and scoring them, which was the other major design philosophy that was discussed on 422.
Are we going to be seeing any vision targeting on the robot this year?

Re: 2363 prototype pickup arm
 

Great idea, but it doesn't look that sturdy. Does it buckle or bend if someone is pushing on the far corners? (imitating a defensive robot)

Re: 2363 prototype pickup arm
 

I believe the piston is attached to a cam.

Re: 2363 prototype pickup arm
 

Well, there is often a difference between what is planned and what actually works. I try not to discuss plans outside the team (much). With the CD community, I'd rather share actual demonstrated results.

Re: 2363 prototype pickup arm
 

Is the pickup arm as robust as we would like? Never. But if you don't expect something to be damaged, you shouldn't stick it out past your bumpers.

So, we plan for easy repair or replacement for when (not if) it gets damaged. That means making things light so we can bring lots of spares within the parts allowance, and designing for quick changeout of replacement parts.

For example, the pickup roller is the most vulnerable part of the arm. The shaft is going to get bent. So, the first line of repair is bending it back. The second is replacing it. We'll have a replacement assembly "on deck", which can be swapped out in about 30 seconds by removing two socket head cap screws. Then the bent shaft can be serviced (or replaced) at our leisure.

Of course, part of the equation is training the drivers not to drive around with the arm down when it's not necessary.

It's very similar to logomotion, in 2011. Then, we had a complete replacement gripper ready and waiting. Our drivers were good at protecting the arm, and we never suffered arm damage until the off season, when rookie drivers left the arm down and drove it into a wall.

Re: 2363 prototype pickup arm
 

Fair enough, I was just trying to casually reference the adventure that was vision targeting in VA last year with the scoreboards.

Re: 2363 prototype pickup arm
 

No kidding! The Jumbotrons of death.

At the beginning of the season, we relied far too much on our vision system for targeting. When we threw out that code and just let the drivers aim, we started doing much, much better. I hope that's a lesson that sticks.

Though I'm mechanical, not software, I've started paying attention to how the top teams use vision processing. The answer seems to be: they don't. My own conclusion is that vision processing in FIRST requires an extreme amount of resources better spent on other things. Then, even if you think you have it right, slight changes in lighting at the venues can flush all that hard work down the drain.

Re: 2363 prototype pickup arm
 

I'm curious if the vision code failed because the code was too simple and made too many assumptions or were the jumbotrons truly misleading? Do you have any images?

Greg McKaskle

Re: 2363 prototype pickup arm
 

Greg,
I think it was both.

The jumbotrons were positioned so they showed up in the camera field of view when the robots were on the key in the normal shooting location. Once we realized what was going on, we could see the turret obviously tracking the jumbotrons rather than the top goal. They were of an aspect ratio and apparent size that mimicked the expected shape and size of the top goal retroreflective tape box. Many teams at the Virginia regional had similar problems. At least one other team requested that the jumbotrons be turned off, but that request was denied. We started taking shots from way off to the side, so the screens were out of the FOV, and our shooting percentage went way up.

That said, I do think that more sophisticated software could have dealt with the problem. Ours tracked only a single square. I heard of others that tracked the three goals as a triangle and disregarded "out of place" boxes as extraneous. That level of sophistication might have helped a lot. Being a mechanical guy, it's just as easy for me to say, "Just make the software better," as it is for the software folks to say, "Just make a shooter that is always consistent." Easier said than done.

My lesson last year was that unless vision systems are developed and tested in something approaching the actual lighting conditions, they will likely be unreliable. Adaptive vision systems, while possible (as demonstrated by the numerous examples of autonomous cars), aren't a task that is easily doable by high school level software programmers in six weeks.

Re: 2363 prototype pickup arm
 

Thanks. I saw a number of teams who decided not to require the rectangle to be hollow and others who decided HSL was not needed, and did much looser color thresholding. While a bit faster, you are trading that for redundancy. I'd like to see how the example code dealt with the jumbotron of doom/death/annoyance.

All of these systems are making heavy assumptions in order to be more approachable by the intended audience, be it the flat carpet covered floor, or the precise dimensions of various elements on the field. Vision is typically not a game-changer, but I do think it can be a student-changer. If you see something that would make it more effective at that goal, please let me know.

Greg McKaskle

Re: 2363 prototype pickup arm
 

Greg,
I just asked our software mentor to stick his head in. Let's see if he has some more authoritative input.

Re: 2363 prototype pickup arm
 

What we did last year was use the JavaCV library to pull out the green channel and then anded that with the inverse of the red and blue channels. After that we did a ratio check on the height and width and did a polygon check to make sure the target was rectangular. We were then able to accurately calculate distances to targets back in the shop. But, unfortunately when we got to the competition the it didn't work as well as we had hoped. We actually had a problem with our software wanting to track the screens on the side of the field also, which actually caused us to burn out a motor at one point early on. On top of the two sets of screens causing us problems, the lighting conditions also changed between practice day and qualifications which caused us problems after having calibrated our camera on practice day. All in all, what we have learned from our experiences is that vision processing is great, when used to assist the driver in aiming and not doing it itself. We just ran into too many outside variables which caused us too many problems.

Re: 2363 prototype pickup arm
 

As you seem to have figured out already, the shooter platform and the disc hopper share a common piano hinge in the rear of the robot. The hopper swings up into the shooter using the pneumatic cylinder in the rear of the robot just above the drive train longeron. The shooter elevation is adjusted by the two pneumatic cylinders in front. The hopper cylinder doesn't have sufficient control authority to push the shooter around, so the hopper will stop moving whenever it engages the bottom of the shooter plate. In our testing so far, this arrangement works well.

Re: 2363 prototype pickup arm
 

The trigger mechanism is an arm that is actuated by the cylinder on top of the shooter plate. It enters a hole in the side of the hopper to push the discs into the shooter wheel.

Re: 2363 prototype pickup arm
 

Thanks for the info. Sorry for the thread-jack about vision.

Greg McKaskle

Re: 2363 prototype pickup arm
 

No problem. We're definitely still in a learning process with vision processing. We'll take any help we can get with ways to improve.

Re: 2363 prototype pickup arm
 

Would that really be a cam? There is indeed a fixed point of rotation, but given that's not really the input or the output of the mechanism, I'm not comfortable calling it a cam. But I'm not an authority on the matter.

Hopefully someone with more expertise can answer definitively.

I gathered the gist of it, but I didn't realize the shared hinge. Makes sense now. Really clever solution to add multiple positions without further articulation.

Re: 2363 prototype pickup arm
 

May I ask how you decided to distribute the allowed frame perimeter length? Are you 28" x 28"?

The machine looks rectangular, but if your collector passes through a gap in your bumpers it'd have to be, at minimum, about 11" + 8" + 8" (or 27") wide.

What am I missing?

Re: 2363 prototype pickup arm
 

It is in fact 28 x 28.

Re: 2363 prototype pickup arm
 

Actually, the dimensions of the frame perimeter are 27 x 27.5 inches (total perimeter length 109 inches). The CAD team has the full up model, but I have a complete enough model that I was able to throw together a quick elevation drawing, since it seems to be of interest.