Design → Machining → Assembly
I wanted to detail how 3512 produces the parts for our robots, and the process and tools that make that job more manageable.
Part Numbers
Like many teams, we use unique part numbers to identify every part our team designs. I’ve written a detailed guide on part naming schemes on our CAD Training site, but here are a few examples:
21-000-000
- 21 – The first two digits represent the last two digits of the year in which the assembly was created.
- 000 – The next three digits are the higher level assembly identifier. When this is 000 it specifies the highest level assembly (which is the entire robot assembly).
- 000 – All assemblies end in “000” to denote it as an assembly.
In this example, the part number denotes an assembly created in 2021 and is the highest level assembly containing the entire robot.
21-DRT-102
- 21 – The first two digits represent the last two digits of the year in which the assembly was created.
- DRT – The next three digits are the higher level assembly identifier. DRT in this case is an abbreviation of drivetrain.
- 1 – **The next digit is the lower level assembly identifier. This denotes a sub assembly within the drivetrain such as a gearbox.
- 02 – The final two digits indicate the Part Identifier of the part. This is the second part in the DRT-100 sub assembly.
In this example, the part number denotes a part created in 2021, the part belongs to a lower level sub assembly within the high level drivetrain assembly. An example would be a drivetrain gearbox plate.
It doesn’t really matter what naming scheme you use, but be consistent and use one!
Part Tracking Spreadsheet
We use a part tracking spreadsheet called the PBS (Product Breakdown Structure) to track the custody of a part from design all the way through manufacturing and assembly. Our spreadsheet is modeled off the one described in this Wintergatan video.
Our PBS tracks custody of any given part by capturing 2 pieces of information (among other things) to establish which subteam “owns” the part:
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Build Type: Mill, Lathe, CNC, Subassembly, ect.
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Status: Designed, Printed, Assmebled, ect.
Different combinations of Build Type and Status are entered on the DATA tab allowing for parts to have different workflows throughout the design process. As an example, here’s some workflows for different types of parts/assemblies:
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Mill Part
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Plate CNC’d part
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Subassembly
Intuitively, It makes sense that a CNC part would have a different workflow than a Lathed part; the former needs CAM, while the later needs a printed drawing.
Here are some other useful features of the PBS:
- Build que tabs to see a snap shot of what parts any given subteam needs to work on itemized by machine
- Material
- List of all common materials we use, entered on the DATA tab
- Assigned Team Member
- List of all students on the team, entered on the DATA tab
- Automatic Cell colors to represent higher and lower level subassemblies
- Achieved via conditional formatting
- Flagging parts with issues causes the entire row to highlight red
- Achieved via conditional formatting
- Deprecated parts automatically crossed out
- Achieved via conditional formatting
Kitting Assemblies
While we wait for parts to produced for any given subassembly, we kit out that assembly by gathering all the necessary COTS and Custom parts into a staging area. Some tips to make this easier:
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Labeled Plastic totes to store all parts for a given subassembly
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Where possible, keep COTS parts that come in individual labeled bags (like gears and sprockets) in their original packaging
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Set aside a place in your build room to place COTS orders as they come in, and add parts to their relevant assembly totes as soon as possible
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Part Bags to keep multiples of the same part together
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Masking tape + sharpie, again to keep multiples of the same part together
Exploded View Assembly Drawings + BOM
We mandate that the CAD team produce Exploded Assembly View Drawings with Balloons and BOMs to assist our mechanical team during the assembly process.
All exploded view drawings are printed on 11x17 paper, and the BOM may or may not be on the same sheet or a different sheet depending on the size of the physical assembly.
This is absolutely my favorite picture from the 2020 season of a team member assembling our drivetrain gearboxes:
Maintaining a CAD Binder
In addition to assembly drawings, we also create drawings for Mill and Lathe parts. All of these drawings are added to a 3 ring binder to keep everything organized. Here are some tips we’ve picked up along the way:
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Every drawing gets a sleeve, when mechanical is referencing a drawing keep it in the sleeve; nobody likes dirty drawings
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Use dividers to separate different subassemblies
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Inevitably drawings may need to change, or parts might change. We ask the mechanical team to use a red pen to mark up any changes on the drawing itself, and then leave a comment for us for that part on our PBS
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Bring your CAD binder to comps to wow the Judges!
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In the next post I want to detail some of the CAD tips we use to work smarter not harder when it comes to designing an FRC robot.