Al's Annual Inspection Thread 2015

[Al Skierkiewicz]

Alex,
You are correct, the email telling me that a new inspection checklist was being published came while I was writing the above entry. The difference is the firmware version for the RoboRio. We have been informed by NI that all RoboRios shipped with one of the only two available firmware versions both of which are legal. It is suggested that if you have not updated your RoboRio, do not attempt to install a later version. The installed version will be legal.

[Al Skierkiewicz]

OK, This is going to be a short list for now as I respond to a post elsewhere and some of the reports coming in from regionals this weekend. I know I have said this before but please make sure everyone you know sees this.

Materials that are not safe or cannot be used on FRC robots.
1. Uncoated lead used for ballast. Even if your build location allows lead in it's raw form, if you plan on traveling, the lead needs to be sealed. You can paint it, dip it in tool handle coatings, you can even injection mold plastic around it. Many locations and venues list it as hazardous in it's raw form. If you are using sealed lead, it may not be machined, drilled, cut, etc. while at an event.
2. Mercury in any form. It is hazardous in this country and many other countries. Just shipping it requires specific methods and documentation. Small quantities may be handled differently depending on locale. R8 specifically disallows any switches or contacts that use mercury. If a team happens to spill mercury onto the field, it becomes a hazardous materials site.
3. Any ballast attached using duct tape, ty-wraps, or adhesives. Please think about what you are doing. If the ballast comes loose, your robot, other robots and people near your robot will receive the consequence of your actions. Ballast must be attached with known good fasteners, to the frame of your robot. Use of 1/4" hardware or larger, through the ballast and into the frame, is ideal. In some cases, stainless steel hose clamps may be sufficient but it is up to the LRI at your event to make that call. If the Head Ref or FTA see an issue, they may alert the LRI to check your installation again.
4. Anything that can spill onto the field is also not allowed. This means sand, ball bearings, shot, pebbles, or water or anything else that you can think of.

[IndySam]

Al are you saying a small dumbbell weight (2-5lbs) attached to the frame of a robot with zip ties is some kind of a hazard and would not be allowed?

[Alan Anderson]

Originally Posted by IndySam

Al are you saying a small dumbbell weight (2-5lbs) attached to the frame of a robot with zip ties is some kind of a hazard and would not be allowed?

He has said before that zip ties are not a structural fastener. That's what I told the team in Kokomo using them to hold on their hand-weight ballast. One student suggested that they could attach the weights with duct tape instead...

I did a quick tug test and didn't think they were a problem in that case, so I didn't ask an inspector to review it. In a more collision-prone game, I definitely would have done so.

[Thad House]

I get the zip tie thing, but at the same time I don't. The field is held together with zip ties and Velcro, and it seems to work just fine. As long as you buy good quality zipties, they could easily hold a robot together.

[Alan Anderson]

Originally Posted by Thad House

The field is held together with zip ties and Velcro, and it seems to work just fine.

Velcro holds the field to the carpet, and there's quite a lot of square yards of the stuff doing it. Good luck getting that much holding area on a robot.

Zip ties on the field are used for wire management, not structure. Unless you're talking about the lexan side panels on the original field design, in which case you might be interested to find out that several of them do break on average every event, and they have been replaced with rivets in the new design.

[Jon Stratis]

Originally Posted by Thad House

I get the zip tie thing, but at the same time I don't. The field is held together with zip ties and Velcro, and it seems to work just fine. As long as you buy good quality zipties, they could easily hold a robot together.

The only parts being held together on the field by zip ties are the Lexan covers (NOT structural, these are intended for shielding and to provide a smooth playing surface). In those cases, the physics are well understood - most of the force against those covers will come from head-on collisions with robots, in which case they are pushed against the pipes supporting them. Sliding force has been known to break zip ties on the field, and they are replaced as needed. Additionally, if those zip ties break and the Lexan comes lose, it's not exactly moving - it just flops to the ground. The structural elements to the field (all the aluminum piping) is held together by slotting pieces inside of each other and locking them in place with pins. There is a firm mechanical joint between every part of the field structure, and it's designed so it can only come apart in a very specific way.

Contrast that to a weight attached to a robot. The weight is constantly experiencing acceleration and deceleration as the robot moves around. It can take an impact from another robot, in which case this is two robots hitting each other, not one robot hitting a stationary target. If the robot is spinning in a circle full speed when the zip tie lets go, the weight isn't just going to fall to the floor - it's going to be thrown across the field (and possibly outside of it). This is a much more dangerous situation.

[Al Skierkiewicz]

Scott,
Yes.
Anyone who does not think high speed collisions are not possible should have been at a friendly scrimmage/practice I attended yesterday. One of the robots had a "software" glitch and drove across the field at full speed into the player station.
Thad, I can assure you that zip ties are not rated for dynamic loads and are known to fracture under a variety of conditions, most of which are present during FRC matches. If you watch the field as closely as some of us, you will have noticed the FTA or FTAA running back to the field box and pulling out ties to replace those broken by robots every day, every event.

[Mr V]

Originally Posted by Alan Anderson

Velcro holds the field to the carpet, and there's quite a lot of square yards of the stuff doing it. Good luck getting that much holding area on a robot.

Zip ties on the field are used for wire management, not structure. Unless you're talking about the lexan side panels on the original field design, in which case you might be interested to find out that several of them do break on average every event, and they have been replaced with rivets in the new design.

In last year's field zip ties and gravity were the only things holding the high goal and its support structure above the heads of the drive team. This year the tote chute's ramp and cover are held together by zip ties and gravity. From my understanding the original AndyMark fields did ocassionally break the rivets that held the polycarb panels which are a structural element in the AM field. I believe that they uprated the rivets used in the production versions because of this.

Originally Posted by Jon Stratis

The only parts being held together on the field by zip ties are the Lexan covers (NOT structural, these are intended for shielding and to provide a smooth playing surface). In those cases, the physics are well understood - most of the force against those covers will come from head-on collisions with robots, in which case they are pushed against the pipes supporting them. Sliding force has been known to break zip ties on the field, and they are replaced as needed. Additionally, if those zip ties break and the Lexan comes lose, it's not exactly moving - it just flops to the ground. The structural elements to the field (all the aluminum piping) is held together by slotting pieces inside of each other and locking them in place with pins. There is a firm mechanical joint between every part of the field structure, and it's designed so it can only come apart in a very specific way.

Contrast that to a weight attached to a robot. The weight is constantly experiencing acceleration and deceleration as the robot moves around. It can take an impact from another robot, in which case this is two robots hitting each other, not one robot hitting a stationary target. If the robot is spinning in a circle full speed when the zip tie lets go, the weight isn't just going to fall to the floor - it's going to be thrown across the field (and possibly outside of it). This is a much more dangerous situation.

There are zero pins holding the traditional field together this season. Last season there were a hand full of pins used to keep the high goal together but not to keep it supported above the driver's head. The shelf that the high goal structure sat on was attached to the driver's station uprights by zip ties. Yes the shelf had semi circle notches that kept them centered on the upright and served to transfer the load, however without the zip tie it would have been very possible to bump it in a manner that could send the entire structure crashing down. Yes those zip ties were heavy duty, rated for 150lb load IIRC and there were several, but still zip ties were an integral structural element in last year's design. With the impacts the driver's station wall saw last season I was always a little afraid of what could happen during one of those sever impacts. It was normal for the field to grow a couple of inches over the course of an event due to those impacts. I saw many cases where a substantial lump formed in the carpet behind the driver's station due to the impacts stretching the carpet.

I do not know for certain if there are any pins in the AndyMark field because I have only seen the flyer and not seen one in the flesh.

[FrankJ]

Another Q&A A welcomed clarification of the solenoid pressure rating rule. Pretty much any industrial valve with a rated working pressure over 100 psi should meet this.
R446

Q. R66(D), a solenoid valve "rated for a maximum working pressure that is less than 125 psi" versus a relief valve "set to a lower pressure than the maximum pressure rating". According to the manufacturers we have contacted and NFPA definitions MWP and MPR are 2 unrelated requirements. A valve is safe up to its MPR but only rated to "work" (the solenoid would actuate the valve normally) at it's MWP. If the MPR is >125 (ours is 215) is it acceptable without additional relief? Our MWP is 115.
2015-03-04 by FRC2973
A. Thank you for the question. This is legal, and the language will be updated in the Game Manual in Team Update 2015-03-17 to be consistent with this answer.

[IKE]

Originally Posted by Thad House

I get the zip tie thing, but at the same time I don't. The field is held together with zip ties and Velcro, and it seems to work just fine. As long as you buy good quality zipties, they could easily hold a robot together.

Emphasis was mine. Often when writing a rules for any sort of sanctioning, the ruless have to written in such a way that if to prevent something dangerous from happening, it is inspectable. For example, in amatuer racing, roll cages are often specified at Steel, of a particular diameter and wall thickness with an inspection hole. While not all steel is created equal, the lowest common denominator is used and specified to ensure that at a minimum the cage should be safe.

As most of us know, Zip-ties vary in quality and strength by a very large range. Do I think you can find Zip-ties that could handle impact loading... Yes. Do I think I can tell the difference between those and "junk ones"... NO (or at least not easily).
A simple McMaster Carr search shows 15 varieties of cable ties with a wide range of ratings. It is also worth noting that with plastics, just because it was originally rated at 100 lbs strength does not mean it will always be that strong. Some plastics degrade with humidity. Other plastic degrade with UV light exposure.
At the end of the day, there is just too high of variation which is why you get the pushback.

Does this mean you will never see a robot with a dumbell ziptied to the back? Doubtfull. It does mean though that once it gets noticed, it will likely be asked to be correctly anchored.

I would still be very impressed if a team showed me the calculations for the resultant G loading of a 10 feet per second robot hitting the wall, the documents that show the cable tie rating, and the calculations and safety factors that make them believe it is OK.*

*for a 10 FPS robot with bumpers that compress 2" ideally it is around 10G. If you assume about 0.25" of deflection it is nearly 100G. Thus a 10 lb dumbell might exert 100 to 1,000 lbs. of force on those restraints.

[Paul Boehringer]

Hi Al,

Three questions. My team is considering a tethered ramp.

1.) Is the q & a still open for questions? (If so I would like to ask the following there for official confirmation)

2.) Would it be legal to put some velcro or something similar on the bottom of the ramp so it will stay in place?

3.) Would it be legal to use a passive suction cup (just stick it on before a match) to stick to the wall by the chute door?

Thanks for this thread.

[notmattlythgoe]

Originally Posted by Paul Boehringer

Hi Al,

Three questions. My team is considering a tethered ramp.

1.) Is the q & a still open for questions? (If so I would like to ask the following there for official confirmation)

2.) Would it be legal to put some velcro or something similar on the bottom of the ramp so it will stay in place?

3.) Would it be legal to use a passive suction cup (just stick it on before a match) to stick to the wall by the chute door?

Thanks for this thread.

Yes to #1.

Probably not legal for #2.

R5 Traction devices may not have surface features such as metal, sandpaper, hard plastic studs, cleats, hook-loop fasteners
or similar attachments. Traction devices include all parts

Richard beat me to the rule #.

You might want to look at this for #3.

[Richard Wallace]

2) see R5 and G16 (blue box item a.)

3) see G16(d)

[Alan Anderson]

Originally Posted by Mr V

From my understanding the original AndyMark fields did ocassionally break the rivets that held the polycarb panels which are a structural element in the AM field. I believe that they uprated the rivets used in the production versions because of this.

Some of the riveted connections on the single original prototype field failed during a FIRST-supervised stress test, when a robot was intentionally and repeatedly slammed into the field wall after it had survived an off-season competition. That's the kind of thing prototypes and stress tests help find. The production field design addresses that weakness and others (plus a few small cosmetic/convenience features).

There are zero pins holding the traditional field together this season.

The connections between the year-specific corner walls and the rest of the field are still the same sort of drop-in tubing "pin" that has always been used on this size field. That interface isn't likely to change as long as the old welded fields are still in regular use.

There are also indeed still zip ties holding things together on the year-specific parts. That too is unlikely to change unless a catastrophic event occurs because of them...or unless the Robot Inspectors get authority over the field. ;-)

I do not know for certain if there are any pins in the AndyMark field because I have only seen the flyer and not seen one in the flesh.

In addition to the structural pins I already mentioned, very small pins are used to help keep the alliance wall polycarb panels from flexing or vibrating out of their slots.