Materials for FRC

[,4lex S.]

Information about materials is actually one of the things I find is pretty easy to locate on the internet, on places like matweb.

It might be more useful to make a presentation on how to use the material properties available, and what they mean. I have wanted to write something such as this for a while, but have been waiting to know more about this topic (IE, I want to finish my second materials course in Uni and get some MODS behind me). If you are interested in collaborating on something, just PM me.

Another thing that might be useful would be some graphs of common FRC materials for Specific Strength vs. Cost, and other stuff like that that might aid in design decisions.

[lbarger]

Originally Posted by ,4lex S.

Information about materials is actually one of the things I find is pretty easy to locate on the internet, on places like matweb.

It might be more useful to make a presentation on how to use the material properties available, and what they mean.

Alex, your points are well taken. However, I am hoping to take the information one step further than simply listing specific properties, especially with more common materials.

For example, I saw several robots this past season that used acrylic for shielding the electronics. Acrylic is brittle and can shatter on impact. Polycarbonate is much better suited for this role. Also, while both materials are clear plastic, it is relatively easy to identify the two without potentially destructive testing. The edges of cleanly cut acrylic sheets are usually bright because it is very clear optically. On the other had, the edge of a polycarbonate sheet is typically a dark purple. Furthermore, with polycarbonate, while it is great for impact loads, it does not fair well under constant loading: tighten screws too much and in a few days you will see star burst like fractures.

[JamesCH95]

Sounds like a fantastic idea. I'm sure plenty of people, myself included, would help contribute if you desired.

I would focus on aluminum and steel alloys. Things like strength-to-weight and stiffness-to-weight, weldability, machineability, and cost would be good parameters to discuss.

We used plywood and aluminum (bar and angle stock) this year, along with some steel (Tube stuck? Square stock? Little help here?) and the C-channel in the KOP.

We had a robot with a aluminum C-channel chassis, and a half-inch piece of plywood to hold electronics/pneumatics. Our kicker and kicker mounting were made of steel, and we had a plywood-and-aluminum angle stock sticker-ed 'tent' as a roof for the electronics, which, I must say, looked pretty cool.

I found that steel is very hard to cut but very strong and won't bend with any of the impacts we took (even with me driving) Unless you have a circular saw, I'd recommend that you go with aluminum in the pit, because a hacksaw takes considerably longer with steel than aluminum. You have to go slow on a drill, with the speed up high, way high. (careful, the holes get hot then)

Plywood is a piece of cake to cut, but don't use a metal blade for it. Drills go through fine, too, but sometimes get stuck. I wouldn't recommend it for structural material, because it will break reasonably easily and splinter.

For aluminum, a hacksaw with a metal blade works fine, and drills go through on a high speed setting reasonably well. Definitely don't use aluminum bar stock for major structural stuff, because it bends easily (our ball magnet bent it almost three inches back) Angle stock works much better, and looks cleaner.

For all of these, remember to deburr holes and file edges, and PLEASE PLEASE PLEASE don't cut them anywhere near electronics!!! We lost a couple of JAGUARs this way! Also, when using screws in wood, make sure not to sink the heads in too far, as this will cause the backside to splinter some times, and make the screws easier to rip out. Don't tighten screws in aluminum too much either, because aluminum bends easily and this could cause the structure to warp.

Hope this helps


Thaine

[Chris is me]

It would be cool to see an inclusion of pultruded fiberglass and wood. Both can be used in a lot of places but few know the advantages and drawbacks of either. If you'd like some input on the former drop me a PM.

Originally Posted by lbarger

For example, I saw several robots this past season that used acrylic for shielding the electronics. Acrylic is brittle and can shatter on impact. Polycarbonate is much better suited for this role. Also, while both materials are clear plastic, it is relatively easy to identify the two without potentially destructive testing. The edges of cleanly cut acrylic sheets are usually bright because it is very clear optically. On the other had, the edge of a polycarbonate sheet is typically a dark purple. Furthermore, with polycarbonate, while it is great for impact loads, it does not fair well under constant loading: tighten screws too much and in a few days you will see star burst like fractures.

The only thing I would list acrylic for would be to state that one should never, ever use it on a robot.

[lbarger]

Originally Posted by ThaineP

We used plywood and aluminum (bar and angle stock) this year, along with some steel (Tube stuck? Square stock? Little help here?)

Thaine,

Thanks for the description, it is helpful to know how others build their robots.

As far as your question on terminology, "square stock" usually refers to solid square extrusions. (A more generic term would be "bar stock" which includes rectangular cross sections.) Though many people use the term "tube stock" it does not explicitly define the geometry as there are round, square and rectangular tubes (along with more complex shapes). For hollow, square extrusions I prefer to use the term "square tubing" or "square tube". Hope this helps.

[AdamHeard]

Originally Posted by lbarger

Alex, your points are well taken. However, I am hoping to take the information one step further than simply listing specific properties, especially with more common materials.

For example, I saw several robots this past season that used acrylic for shielding the electronics. Acrylic is brittle and can shatter on impact. Polycarbonate is much better suited for this role. Also, while both materials are clear plastic, it is relatively easy to identify the two without potentially destructive testing. The edges of cleanly cut acrylic sheets are usually bright because it is very clear optically. On the other had, the edge of a polycarbonate sheet is typically a dark purple. Furthermore, with polycarbonate, while it is great for impact loads, it does not fair well under constant loading: tighten screws too much and in a few days you will see star burst like fractures.

We've had good success mounting polycarb with lots of rivets (to spread the load) or mounting it with velcro.

[Dick Linn]

There is some good sheet metal reference information here:

http://www.precisionsheetmetal.com/home/materials.htm

[TerryS]

Sorry to resurrect an old thread, but this sounds like a great resource if was ever completed. I searched, but couldn't find any follow up posts regarding a released paper or presentation. Was anything published or was it overwhelming and tabled?

[Akash Rastogi]

Originally Posted by ,4lex S.

Information about materials is actually one of the things I find is pretty easy to locate on the internet, on places like matweb.

I've been using that for about two years now and definitely recommend it. I find myself using it very often for work too.

.

[PriyankP]

http://frcsupplierscanada.wikispaces.com/

A page Mr Lim started! (I believe its still under construction) It would be most useful to a Canadian team.

[Dick Linn]

Lee,

That's an ambitious project and a good one. Perhaps it could be broken down into topics/chapters by material and you could solicit input here on one topic at a time. A good outline of the desired content would help -

available forms & cost
strength/weight
stiffness
workability
alloys and variants
forming/machining/welding/gluing
sources
links to application notes & technical data
tips & techniques
application examples

[R.C.]

I'm highly interesting in starting a powerpoint for this. If anyone would like to or a group of people, we could always start a google presentation for this?

If anyone is interested, send me an email.

-RC

[Siri]

Hello all,
I've volunteered to help R.C. (and whoever else would like to join) organize this project. Currently, we're trying to determine a layout/organizational structure. Thus far, people have mentioned the following:

Materials
Metals: including steel and aluminum alloys
- C Channel (U Channel)
- Bar/Rod Stock
- Tube Stock (including circular & rectangular)
--I'd like to add Angle and 80/20 T-Slots to this list
Polymers, Plastics: including acrylic and polycarbonate
--This could delve into things like belting: polycord, latex, etc if anyone was interested. (I don't have the background to do this in full)
Wood: including plywood
Fibers
Composites

Topics
Basic Properties (values, meanings, uses)
- Mechanical
- Electrical
- Thermal
- Identification Techniques
Correlations [by material and stock shape/dimensions]
- Strength vs. Cost (and cost in general)
- Strength vs. Weight
- Stiffness vs. Weight
Uses
- Forming
- Machinability
- Weldability and/or Adhesives
- Fasteners & Tools
- Tips & Tricks, including Safety
Sources/Suppliers (?)

This should be a really good project! Does anyone have any comments, suggestions, etc on the layout (i.e. the table of contents)? Would you like to add anything to the list or volunteer for a section? R.C. is making a Google Doc, the link will probably be up shortly.

[lbarger]

Originally Posted by Siri

Hello all,
I've volunteered to help R.C. (and whoever else would like to join) organize this project. Currently, we're trying to determine a layout/organizational structure. Thus far, people have mentioned the following:

That is the whole reason I started this thread!

The knowledge of the CD community is much more vast than the knowledge of any single individual. However, having no experience with open documents and being a registered Professional Engineer, I am curious to learn how one can ensure the accuracy of information provided by 'the public'. If the information is not accurate, it could be worse than useless. It could be harmful.

I strongly encourage a white paper format versus a presentation. Done correctly, there would be just too much information to throw at people in one sitting. Besides, most people would only need information on a select few materials. Its just that there are so many material available, each with good and bad qualities. One or more presentations could be condensed from the white paper once it has a good selection of material.

The outline I have is divided into chapters based on material types. Within each chapter, the paper would discuss the different variants available in more detail. Based on input I've seen thus far and my own ponderings, the guide is looking something like...

Chapter I: Aluminum
Chapter II: Steel
Chapter III: Plastics
Chapter IV: Composites
Chapter V: Wood and Fibers (non-composites)
Chapter VI: Lubricants
Chapter VII: Rubber/Elastomers?
Chapter VIII: Misc (If it doesn't fit anywhere else...)

Within each material class, we should highlight the most commonly used variants and variants with unusually good characteristics. (A Variant would be a specific aluminum or steel alloy, specific plastic or wood, etc.)
1) General Description and Identification Techniques
2) Mechanical Properties
3) Electrical Properties
4) Thermal Properties
5) Available forms (i.e. u channel, bar, rod, tube, powder, corrugated. t-slots, cable), sources and cost
6) Rating on forming, machining, welding, gluing, etc.
7) Links to application notes & additional technical data
8) Uses/Tips and tricks for use within FRC (1 hour repairs?, safety, fasteners and tools)
9) Application Examples
10) When to avoid use? (probably under safety)

I hesitate on including correlations (Strength vs. Cost, Strength vs. Weight and Stiffness vs. Weight) as these involve both material properties and geometric forms. This could/should be a complete white paper in itself.