Re: The spread of pinching rollers this year
 

To add a little more to what Scott was saying:

What started out as a front/back single roller after 5 iterations morphed into what we have today. Front and back software clutch variable torque pinch rollers with pneumatic ball gates and a drivers station ball sensor. In theory the ball gates allowed the driver to close a gate so we couldn't intake more than one ball. The gates also centered the ball once captured to our small 3" kicker. The ball sensor allowed the driver to know he had captured a ball even if he could not see it. It took too long to center the ball which is why you didn't see us use our kicker too much. But that's another story.

What made our roller unique was the fact that our rollers are on the front and back of the bot. We use a Jag connected to a CIM and chained up the front and back rollers. We could grab a ball on the front or back of the bot by reversing the rotation of the CIM. We pulsed the speed of the top roller then we sensed current to the roller CIM to change the amount of torque applied once we captured a ball. We also tied in forward/reverse ground speed of the robot to the amount of torque applied and also the torque applied to the ball when we fired the kicker. This gave us our ball loft trajectory. We also used the circuit board in the KOP to add a LED light to the drivers station to sense ball captured. This was helpful when Scott couldn't see the ball.


It took use awhile to figure out how to program the CIM to our control loop. At SVR we found that crashing into a wall would reset the Jags and we would lose the ball and the bot would stall. The Jag has a 3 second default once a fault occurs. That can be changed to .5 sec. We also monitored the amps to the Jag and found out we were hitting a 80 amp spike when we hit hard. Once we figured out the Jags were resetting we changed out the drive train Jags to Victors and wrote in code to prevent the roller CIM to run full power.

The materials we used on the rollers was found by a lot of trial and error. We used tennis grip, duct tape, bicycle hand grip. I think the Poof guys finally showed use what they were using. Water proof electrical tape from Home depot(the magic material) We later changed the top roller material to a polyurethane tube that had a durometer of 30.

So in the end we had over 36 " of ball intake that could pick up a ball going full speed and stuff it into a goal. You will have to ask Scott about learning to drive backwards to stuff a ball in.

Here's a pic of our roller:

http://www.bmf.com/frc%20971/2010%20...s/DSC_7689.htm


Roy

Re: The spread of pinching rollers this year
 

I find that somewhat interesting, because we had an 1/8" drop as well and received penalties as a result. We were told that as we accelerated and decelerated quickly our rock would lift the ball up ever so slightly during gameplay.

I'm not trying to imply the wrong calls were made on either of us, but that's ultimately the reason we removed our center drop and swapped out the rear plaction wheels for slick wheels for MSC on.

I harbor no ill feeling whatsoever towards any ref who may or may not have called incidental carrying penalties such as the ones we experienced, but I do feel that the way it was called at the Championship, i.e. you only received a penalty for carrying a ball an extended period of time, was more within the intent of the rule in my opinion.

Re: The spread of pinching rollers this year
 

It may have also come down to weight distribution. 397 had 1/8" drop and a pinching rollers. There was some concerns with us accelerating hard but because our weight was almost exclusively centered in the back of our robot we only rocked forward when we stopped fast. I don't know 1718's weight distribution but RUSH's looked like it was more centered on the middle wheel (I could be wrong this is just based on my memory of 27's robot) This would cause you to rock forward or backward.

Our pinching rollers were similar to 67's. We also stole the idea of tennis grip from 1718. (And the fact that one of our mentors is a tennis coach)

The only times we got a carrying penalty was when the ball was forcibly inserted into our frame. We had figured that the ball would not compress enough to do this... we were wrong. This was fixed with some steel cable running across the back of our intake. Never had a problem with that.

Re: The spread of pinching rollers this year
 

I agree that that may have been an issue we experienced that teams like yourself or 1718 did not experience. We attempted to distribute weight as evenly as possible, and that could have contributed to us rocking, and/or lifting the ball up, more.

Re: The spread of pinching rollers this year
 

If I remember correctly we calculated ours to be dead center of the bot; it might have been shifted ever so slightly backwards, but no more than an inch.

Re: The spread of pinching rollers this year
 

I don't know about that. It was a piece that many teams copied over from regional to regional. But...

Anyone remember the week 3 video from 121 in 2008? How many teams copied them entirely?

Re: The spread of pinching rollers this year
 

Like...5? Maybe 10?

There were probably 100 or more pinch rollers inspired by 148 and 217's initial video. It's not even close.

Re: The spread of pinching rollers this year
 

I would agree that there were a lot of teams copying the pinch design, but I can't say I'm surprised.

The idea is quite simple, and easy to implement, but it was in the execution of this idea that really made the best systems stand out.

While there may have been 100+ teams that copied the design successfully, there was still a very wide gap in effectiveness between most teams with a pinch roller system and teams like 254, 971, 1114, or 148/217.

Re: The spread of pinching rollers this year
 

One thing to consider is that we were an 8 wheel drive with the center two wheels dropped as opposed to 6 wheel with only one dropped wheel. It's much easier to rock back and forth on 1 wheel obviously. I think we may have had less of a tendancy to rock back because of that. We also had the advantage of not playing in the 1st week when they were really watching for it...it seems the calls on that loosened up a bit as the season progressed.

Re: The spread of pinching rollers this year
 

Ah, the fact that you guys were 8 wheel drive slipped my mind. I would also assume our tendency to rock would be greater than yours.

Re: The spread of pinching rollers this year
 

Our "ball magnet" was inspired by a video posted on CD. We prototyped and shipped with a driven roller wrapped with a high-friction material that contacted the ball above center when it was 3" inside the frame. We had an idler that contacted the ball in the middle to prevent incursion of the ball >3" beyond the frame.

At our first regional in Pittsburgh, we found that we did not have as good possession as we intended and desired. We modified the design to increase the top roller speed, while allowing it to slip on the drive pulley; then we stalled our center mounted roller and coated it with carpet tape.

It was an improvement; however, not as good as we would have liked.

Re: The spread of pinching rollers this year
 

2016 followed suit of the design after our dallas collaboration with 148. we learned a lot from them on their mechanism and seeing its effectiveness we could not resist but to transition for the big stage in Atlanta.

I think we see this every year though, last year we saw teams shoot to dumpers later in the year. So there is always one key mechanism advantage, however for us I noticed that it took a while for our drivers to get used to it and actually use the new system correctly.

That is the biggest disadvantage with changing mechanisms after having gone through one or two regionals.

Re: The spread of pinching rollers this year
 

If my aging memory is correct, Foley had a rocking problem also at Kettering and may have even flattened their drive train there.

I'm guilty as charged for calling a fair amount of carrying penalties, but like all my calls, I call 'em as I see 'em and try to be consistent. :) As all the refs do I believe.

I do think many of the early match calls were very correct because the rules were clear on the definition of carrying and ball magnet designs needed to eliminate that possibility. Without that direction, too much subjectivity is introduced into penalizing a carry. Later in the season, practically every carry I saw was incidental and did not happen consistently because of the design.

Re: The spread of pinching rollers this year
 

I felt you were keeping us honest, and it added a new degree of challenge to Troy. I just hope the Safety Judeges went easy on you guys for being bent over so much of the match. :D

Re: The spread of pinching rollers this year
 

We started off with a vacuum when we shipped. After seeing the 148/217 videos we built a roller assembly and took it to Florida in week 2. We ran UCF with the vacuum. We installed the rollers at Palmetto and struggled all weekend getting it tuned in. We designed a new roller system for Atlanta that floated up and down. Once we dialed it in, we did well with it. One thing that inspired us was seeing the carpet tape on 67. We put double sided tape on the bottom roller and balls were easier to grab. We did notice the ref looking closely at ours one round, so we pointed out to the head ref after the round that it floated. He seemed satisfied.:D