Tips for Understanding the Bill of Materials (BOM) Rules

FIRST General Forum
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The BOM (BIll of Materials) is a very complicated part of the FRC robotics competition. There are many rules and dozens of Q&As to read and understand to get a full grasp of how to fully document the cost of your robot.

Teams that are not close to the $5000 Cap

For many teams, the most reasonable thing is to document all of the things you purchased that were put on your robot. You can exclude items that cost less than $5 or that were in the KOP(R11), such as items in the kickoff kit (including the rookie tote that not everyone received), you got from FIRST Choice, or you used a product donation voucher to completely purchase. Make sure that no one item costs more than $500 (R12).
Most teams will not get near the budget limit of $5000 as defined in R11. Have your BOM ready(paper or digital) for your inspector and you will likely not have any issues with the BOM during inspection.

Teams that are close or possibly over the $5000 Cap

For those teams that may get near the total, there are a lot of rules to understand to know if you are actually over that limit or not. I believe a lot of teams are very close or over the BOM if they properly account for all the items that they need to for their robot. I believe that the number of teams that are close or over the cap has dramatically increased after the rule changes implemented in the 2019 season.

Disclaimers

Below is my attempt at explaining some of the BOM rules. This is just my understanding based on reading the rules, asking Q&A questions, and far far too many (like way too many) discussions about the BOM with other members of the community. I am not an authority so an LRI/inspector at your event may have a different understanding and there are countless corner cases that if you believe your team encounters should be resolved by asking a Q&A question. Read the rules and the Q&A for yourself to build your understanding of the rules.

If you haven’t read any of my other opinions on the BOM, you should know that I don’t like the current implementation of the BOM at all, but these are the rules we have for this year, so we should all follow them to the best of our abilities.

Items many teams forget to include on their BOM

  • Bumper materials

    • Plywood and fabric (if not IFR to what is in the rookie kits)
    • Material for the numbers may also need to be on your BOM, if they are not purchasable for less than $5.
    • Bumper Noodles if you paid $5 or more for each
    • Must include the materials for all the bumpers you bring to inspection.

  • Snap Action breakers more than in the kit.

    • $7 - 40A (6 in the KOP, up to 2 more on your robot)
    • $6 - 5A-30A (2x 30A & 2x 20A in the kit, possibly 4-6 more on your robot)

  • Any wire not in the kit of parts or IFR to KOP wire.
    If you specifically choose more flexible or different gauge or color wire and can’t purchase the lengths needed for your robot for under $5 all those wires need to be on the BOM in a purchasable quantity.

  • 3d printer filament per roll you can buy it, if you use 1.23 KG and you buy it per KG list 2 KGs.

  • Paint or powder coat - if you can’t purchase it in a usable qty under $5 it goes on the BOM

    • We used a can of Aluminum Primer Spray paint, I haven’t found a source for it under $5 and we specifically wanted that spray paint and not a can of cheaper paint so it’s not IFR to other paint. That $5.98 will be on our BOM.

  • One battery and assembly. Assuming your battery is IFR (if you specifically used a different brand than MK for some specific performance reason you may need to account your battery) and the connectors and wire can be had under <$5 per item are probably true. But if you use special wire or heat shrink it may need to be on the BOM. Q258

  • Tape - each type(possibly color if not IFR) of tape should be on the BOM unless you can buy it in a usable qty for under $5. Gaffer’s Tape, Duck Tape, special tapes for intakes, etc often cost more than $5 Q260

  • Any Lubricants, glues, Loctite, etc should be on the BOM unless you can buy it in a usable qty under $5.

  • Extra PCMs or VRMs (more than the 1 of each included in the rookie kickoff KOP totes)

Are there other items that you think teams forget to put on their BOM?

How to calculate raw material

Please read the full blue box under R13. It is the most helpful in understanding how to account for raw materials. This is one of the places I see many teams making mistakes when I inspect their BOMs or when they ask me questions about their BOMs.

“The Fair Market Value of raw material used to construct FABRICATED parts may be accounted for in one of two ways:
• The cost of any purchasable quantity that can be used to make the individual part (i.e. the purchasable raw material is larger than the FABRICATED part).
• Grouping parts made from the same raw material and accounting for the cost of a single quantity that can produce all of those parts.”

Example 7 is very important to most teams trying to document their BOM totals.

“Example 7: A team purchases a 4 ft. by 4 ft. (~122 cm by 122 cm) sheet of aluminum, but only uses a piece 10 in. by 10 in. (~25 cm by 25 cm) on their ROBOT. The team identifies a source that sells aluminum sheet in 1 by 1 ft. (~30 cm by 30 cm) pieces. The team may cost their part based on a 1 by 1 ft. (~30 cm by 30 cm) piece, even though they cut the piece from a larger bulk purchase. They do not have to account for the entire 4 by 4 ft. (~122 cm by 122 cm) bulk purchase item.”

This means you only need to find a purchasable size for any item that is on your robot and you can combine items on your robot in a way that they could be made from purchasable quantities. This explicitly does not mean that you can just calculate every square inch of the aluminum sheet on your robot and just account for the square inches of aluminum that you use. You must be able to actually cut the items on your robot from the sheets/quantities that are listed on your BOM.

There are three reasonable ways to do this.

  1. Account for way more than you actually used.
  • If you printed several parts out of a roll of PLA, cost account for the entire 1 kg roll of PLA.
  • If you have a few custom gussets that you cut from ⅛” 6061 aluminum and you account for the cost of a 2’x4’ sheet of ⅛” aluminum and you know you could cut all those gussets from that sheet, then you are probably good.
  1. Bounding box
  • If you need to go into more detail to reduce your BOM total. You could also figure out the bounding box of each part made of a material on your robot and account for a sheet/rod/length that you could purchase of a size that fits all those bounding boxes.
  • For example if you have 2x 1ftx2ft polycarbonate panels, and also 4 parts that each fit on a 1ftx1ft polycarbonate sheet. You could account for a 2ft x 4ft sheet of polycarbonate.
  1. Nesting
  • If you really need to account for the least amount of material. You could figure out optimal nesting patterns for all your parts of the same material on to the smallest possible purchasable sheet of that material that would fit all of your parts.

It’s important to understand the difference between items that are accounted for as a raw material and items that are purchased in bulk quantities.

Items that are purchased in qty (such as bolts, nuts, connectors, etc) have a FMV of the total cost divided by the quantity (Q60). This means that most of these small items are going to have a cost of under $5 which means they are exempt from your BOM. This is good. To be clear length of aluminum tube, sheets of raw material, 3D printer filament, wire, tape, fabric, etc are not considered to be solid in-unit quantities (in most cases). Also, some items may be solid in bulk quantities but shipped as a single unit but these items are still accounted for as a bulk quantity item. (Q100)

Identical Functional Replacement

What are Identical Functional Replacements(IFR).

From the blue box under R11 IFR is defined as

“An “identical functional replacement” is an item which, to any reasonably astute observer, has the same form, fit, feature set, and function as the original component. “

We have several Q&As that give us clarification on what this means. (I’m going to quote relevant parts of the answers if you want the full question and answers click the links.)

Expensive Chain vs Cheap Chain - FIRST FRC Q&A System

A: “While we cannot rule definitely on a particular component, it is likely that a chain that sells for ten times the cost has differences in “form, fit, feature set, and function” such as material strength, wear life, etc. The reasonably astute observer test in R11 is intended to be a guideline and not a purely visual test as many parts with wildly different price and performance may be visually indistinguishable.”

This is critical because it’s not just a visual test but it is understood that the reasonably astute observer has information about the product and its production/brand/specifications.

1x2x1/16” Aluminum Tube - https://frc-qa.firstinspires.org/qa/140
A: “No, aluminum in the same profile is not necessarily an identical functional replacement.

Rounded corners are not considered a critical part of the profile for an Identical Functional Replacement provided the use on the ROBOT does not depend on the alternate feature (sharp corners).

The mechanical properties of the material are important, and an Identical Functional Replacement must have similar mechanical properties (in this case, the supplier indicates that 6061-T6, 6005-T5, and 6105-T5 aluminum have similar mechanical properties).”

This answer leads us to understand that it’s not just how an item looks or it’s specifications but also how it behaves or is used specifically on the robot.

How is a team or inspector supposed to know what parts of a COTS item or material are “critical”- https://frc-qa.firstinspires.org/qa/148
A: “We encourage teams to use parts as close as possible, within reason, and we believe the answer to 140 provides enough guidance to teams and inspectors to know which parts work as an Identical Functional Replacement.”

This was answered in a way that says there is no set standard, it is up to the teams and inspector to know what is IFR. I don’t mind this answer, they have set a line where they are going to trust their volunteers and teams, I believe this is good.

We do get some more clarification in future Q&As.

Does Tape color matter for IFR? - https://frc-qa.firstinspires.org/qa/260
A: “We cannot rule on if a different color tape is a functional equivalent - if the tape’s color matters (for sensing, aesthetics, marking, etc.), then a different color is not a functional equivalent.”

Does wire colors that are specified by the rules cause two wires to be non-IFR? - FIRST FRC Q&A System - “A wire color that’s identical except for color may or may not be a functional equivalent. For example, a blue wire of the same gauge, etc. may be considered functionally equivalent to the original black wire even though it’s a different color - it has the same functional purpose electrically and they both communicate negative leads. If the color change communicates something different (e.g. a red wire being swapped in for a black wire), it’s not functionally identical.”

So if you care about the color for any reason then the two items are not IFR of each other.

So to sum up here is my current understanding of IFR.

Two items are IFR to each other if when you are assembling your robot if you could in good faith grab either of the two items and put them on your robot such that you’d have no reason to choose between the different items. This means to me if you’d choose one item over the other for any reason other than true cost or convenience to you (examples of reasons that don’t effect IFR: already have one, shipping costs, shipping time, donations, etc) then they are not IFR. This may not be the same understanding of IFR as other inspectors or teams have and I think we are all learning how HQ wants us to understand IFR.

Why Does IFR Matter to the BOM

IFRs come up in two rules important to the BOM.

R11 - “Exceptions are as follows: B. items from the team’s current year’s KOP (identical functional replacements may be used to meet this criteria),”

&

R13 (blue box) - “The Fair Market Value of a COTS item is its price defined by a VENDOR for the part or an identical functional replacement.“

This means that you can exempt any IFR items from the KOP(in the KOP quantity) from the BOM and you can price any item on your robot based on IFRs of that item. Some of which may be under $5 which would mean they are exempt as well.

Fair Market Value

R13 Blue Box - “This price must be generally available to all FIRST Robotics Competition teams throughout the build and competition season (i.e. short-term sale prices or coupons do not reflect Fair Market Value), however teams are only expected to make a good faith effort at determining the item price and are not expected to monitor prices of ROBOT items throughout the season in response to price fluctuations. The Fair Market Value is the cost of the item itself and does not include any duties, taxes, tariffs, shipping, or other costs that may vary by locality. If COTS parts were sourced in bulk, the cost may be scaled proportionally to assess the Fair Market Value of one unit.”

FMV can be from any Country based on Q119.

FMV can be of Identical Functional Replacements as stated above as well as based on Q236

Teams should make a good faith effort if they need to account for an exchange rate based on Q111

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Before reading this post, we had few issues with the BOM (and are usually way under). However I have a few questions after reading that may change at least my mind if not the team’s about it.

They are mostly around cable.

So, we do use silicone wire for aome of our mecanisms (drivetrain and shooter). We also use Neos for these mecanisms. So let´s say we have a five foot motor run, and we bought the cable for 25’ for 25 dollars.

We have to say that one cable run (let’s say black) is 25 dollars in value and not 5? It gets more conplicated too. If we wire up that motor, we will use not one but three cables (black red white). In that event, it is not 15 dollars, but 75. So, what happens when we account for the next motor? Since we can (and do) use the same cables, does that still count as 1 line item (75 dollars not 30)?

Also, as far as IFR, not all of our motors use the good cable, we use regular 12AWG cable for that. When we account for it, can we not count it as IFR because the two cables (black and red) are in a sleeve? In addition, some of those motors are also neos. For the third cable, we could use black or red, but use white for safety. Since this is a different color for a function, it is also not IFR correct?
Finally, we bulk buy all of our non silicone cable. Do we need to put the price of the 500 feet of control cable and 100 feet of 12Awg, or not include it at all because a roll the size we use on the bot could be purchased for 5 bucks or less (I think).

Electrics is always our most exspensive category on our robot (Sylvania a sponsor of ours is able to provide us with 8020 for our framing). This could make it even more so.

Thank you for posting. The BOM is both confusing and scary.

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Allen Gregory, distinguished BOM scholar

What is the meaning of Q148’s statement…

We encourage teams to use parts as close as possible, within reason

Our robot’s parts are really close together but there is still some clearance.

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Not sure I agree with this perspective. Here’s where I am at:

  1. Per Q236, IFR price can always stand in for FMV. Is the reverse also true? Let’s assume that it is.
  2. Per Q119, FMV does not need to include “other costs that may vary by locality” and therefore teams “may list a cost from a VENDOR that would not provide a part to their locality.”
  3. Therefore, access/availability is NOT a consideration when accounting for IFR price in lieu of FMV.

Q305 asked.

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Thanks to @AllenGregoryIV for highlighting the many issues with the current BOM rules.

The most unfortunate part of the status quo is that the teams that follow the rules more closely are punished more than teams that pay less attention. That seems very wrong to me.

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Thanks for staying up (very) late to write such a comprehensive guide for the community.

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Thanks for doing this @AllenGregoryIV, it is a very thorough exploration of the BOM rules. What this all tells me is that this is going to be an even worse headache than I thought it was. Compared to the old CAW rules, much of this just doesn’t seem to make sense. It’s inflating the accounted cost of the robot in a way that’s going to make many of the innovations teams have come to rely on too expensive to use, in my estimation. We’ll probably come in just under, even following the rules carefully, but it’s going to be a lot of late nights working through all this to get the thing right.

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The BOM cost generally has little relation to what you actually paid for the material. :thinking: Or I feel your pain. Most of our wire is on 500 ft spools. Raw aluminum is bought in quantity with a fair amount of carry over year to year. I have no idea what we actually paid for a specific piece. My supplier sales by the pound unless I remember to ask for a different accounting. (They are still thinking in pounds though.) I try not to dump this on the kids because I rather them be designing and creating. They can deal with reality later. :slight_smile:

Anyway, You can reference the cost for the lowest commercially available quantity. IE Some places sale the silicone wire by the foot. For easy math say $1/ft. Lengths less than [edit 4] feet don’t have to be accounted for (<$5.00 commercially available).

Edit Fixed that for you Allen:

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I think my wording was poor there, I was listing examples of things I considered convenience. I probably should have said true cost or convenience but I assumed people aren’t listing the more expensive IFR items on their BOM so convenience made more sense at the time.

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Yes, I realize now that I misread it. Thanks! The nonanswer to Q305 supports this direction.

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Be careful there, the rule is items less than $5, not less than or equal to $5. If you can get 5ft of wire for $4.99 it’s exempt but if it’s $5.00 it’s not.

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Seems kinda crazy that it takes 13,500 characters to present these rules in a way that makes some sense. That’s longer than the Chairmans award essay we spent weeks writing!

I’m very supportive of moving the BOM over to a submitted document that factors into a judged award.

This 100%. Although we have a lot of student involvement on our business side of things: including budgeting, ordering, and inventory tracking, the amount of effort and knowledge needed to exercise every exemption is unreasonable. They could tell you how much we spent and what we spent it on from a google sheet on their phone, but I’m fairly certain that number would be greater than $5,000 without the exemptions. It’s crazy, and not a very inspiring task for a student. Unless we’re trying to get them excited about filing taxes, which making the bom always reminds me of.

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I had a question…

Does the KOP drivetrain opt out voucher count as a voucher that you can take off you BOM? Ex - If you purchase $400 of parts from andymark with the voucher, do those parts count as $0 on your BOM?

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Answered a couple of time in the Q&A. It is a voucher and is treated like all voucher. Anything complete covered by the voucher is $0 cost on the BOM. You buy a $451 gear box with it: it is not covered. $451 on the BOM

Q188 Has the clearest answer on this

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I am very much against that. It will create major CD threads on mentor vs student authored BOMs.

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Hmm. This is a non issue for us. Also, it’s weird to think that white glovers would be more upset about mentor-built BOMs submitted for the purposes of an optional judged award, than about mentor-built BOMs submitted for the purposes of competing on the playing field in the robotics competition.

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@AllenGregoryIV is not the hero we deserve. He’s the hero we need. Thanks for this awesome resource!

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You see! It has already started. :slight_smile: Anyway. Currently the BOM just has to exist. It doesn’t have to be pretty. If was part of a judged award we would have to spend a lot more time on it. (Also I already have esteem issues. I don’t want my work judged as part of a high school competition so I wouldl make a student do it.) You can search CD for mentor built verses student built robots and judged awards. (Or create your own, but please wait to off season.

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This has been a very interesting read. We tend to do the BOM last thing and I tend to take a “spirit of the game” approach as our robots are pretty clearly way under the limit. I’ve never seen a BOM scrutinized at an event, it seems to be pretty much a formality. Is it examined closely and questioned at other events? I can see where it might be looked at more closely for regional winners or teams moving on. What are others experiences?

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No it is not examined closely at most events. However some inspectors take it on themselves to scrutinize some teams for their BOM more than others. I don’t want inspectors looking for documented costs for wire, paint, tape, bumper fabric, etc. However teams should be aware they are supposed to be included in their BOMs and totals so they build a legal robot.

Just because it is not scrutinized does not mean teams should not attempt to follow the rules. At the end of the inspection process a mentor and a student most sign the document stating they have followed all the rules, I wouldn’t feel comfortable signing that unless I believed for sure my team was following all the rules. Prior to 2019 I could do that with student getting a respectable BOM togerher and knowing we were well under the limit(FC and KOP exemptions were much broader). With the 2019 and 2020 BOM rules I no longer feel comfortable (and believe many teams shouldn’t as well) just assuming we are under the total. It is very easy for a robot with ~13-16 motors/controllers and many COTS gearboxes to approach or exceed that total very quickly and without the team even realizing.

I hope that no teams are prevented from playing the game with the robot that they want because of BOM cost however finding exemptions and IFR parts that are cheaper for your BOM accounting is a complicated process. It is a practice that I will not be leaving up to my students. I hope these tips help teams get closer to actually meeting the rules and not just assuming that they meet the rules or relying on inspectors to notice that they haven’t and then be scrambling to update their BOMs at their events.

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