[TBA Blog] Crash Course FRC – Materials


#1

Crash Course FRC – Materials
By Tim Flynn

When building a robot, there are tangible objects that go into the robot, not just the sweat, tears, and colas of build seasons past. Of course, we’re talking building supplies and where to get them. Let’s take a look at the goods and services that teams have benefited from for years, and that your team might just learn something from.

Most folks in robotics know of metals and plastics, but there are specific materials within those categories that folks may not be aware of how to best use, let’s dive into it.

Check out the the rest of the article here: http://blog.thebluealliance.com/2018/12/27/crash-course-frc-materials-suppliers/


#2

Just for clarity, “AGMA 11” is a grade for gears, not steel gears specifically.


#3

It’s a good article but there is also some detail missing about loctite and polycarbonate or some other plastics (I believe ABS as well). IIRC, it’s the acetone in the thread-locker that causes the cracking in those plastics and it’s not limited to just red Loctite, it can happen with many varieties.


#4

Thanks for the clarification JB and Marshall, I’ll update the article to reflect that. Not exactly a master of mechanical so your insights are appreciated :slight_smile:


#5

Also, I think the picture for ABS vs PLA is actually showing acetone bath post-processing. Neither ABS not PLA are naturally that smooth and shiny without an acetone treatment, which isn’t a good idea for FRC parts because it weakens the material. You can see the same image being used to describe the treatment here.

Overall though, very good article for FRC newcomers to get an idea of the common materials choices and why to use each.


#6

Your article says PLA is susceptible to Tetrahydrofuran, not acetone. Can confirm from experience that acetone doesn’t seem to do much to PLA.


#7

…yes

I meant to say acetone for ABS and THF for PLA. Either way, the picture doesn’t show the different between ABS and PLA rather before and after post-processing.


#8

Some comments:

This is a really, really basic guide. More details would make it a lot more useful to people who don’t really know much about material selection. Right now it’s pretty dumbed down.

6063 is not “difficult” to machine. It may be slightly gummier than 6061, but it by no means is difficult.

If you’re going to differentiate between 6061 and 6063 you should probably mention that 6063 is roughly 25% weaker by yield strength.

The recommendation to pocket, but do the math is sort of at odds with the target audience. If someone reading this doesn’t know the difference between aluminum/steel alloys/tempers, they surely don’t know how to do FEA to ensure their pocketing will be safe.

I’m not aware of anyone who does extensive sheetmetal construction utilizing widespread steel sheet parts on their robot. Maybe one or two in a very high load situation, but I would be shocked if anyone has built even an entire subsystem structure out of sheet steel.

AGMA 11 refers to the tolerances on gear teeth, it has nothing to do with the quality or type of material.

It would be more helpful to explain why you brought up 12L14 and the differences between it and 1117 steel (for what it’s worth I would say both of these have extremely low relevance to FRC and 7075 Al would be a better choice than them in most scenarios).

You don’t explain why a team would even choose to use steel. Teams don’t fabricate versaplanetary gears so it’s not really relevant that they are steel. Things like high load shafts, ratchets+pawls, high impact/toughness/wear parts, etc, would be a much better example.

You briefly mention baltic birch, but not why it’s good for FRC use. There’s a big difference between crappy sheathing plywood that is ubiquitous at home depot and high quality baltic birch. This is worth pointing out.


#9

Gotcha! Wasn’t sure I understood then.


#10

It would be more helpful to point out aluminum that can be bent like 3003 vs 6061 than what is best machined.

Also a team like 1024 who has had a lot of success with steel tubing.


#11

Also 5052. And to clarify: it’s not that 6061 can’t be bent - it’s that any metal whose strength is dependent on tempering will lose that extra strength whenever it is significantly bent or welded.


#12

More importantly from a functional standpoint the bend radius for equivalent bends is going to be much larger in 6000 aluminum than 5000 aluminum.