Polycarbonate vs. Aluminum
 

My team is currently in a debate over whether we should use polycarbonate or aluminum for an intake which extends past the bumpers of our robot. The concern that some members of the team have is that 1/4" polycarbonate would crack or shatter if impacted by other robots. Teams that have had experience with using polycarbonate (or other plastics) structures that extend past the bumper and would be susceptible to impacts, how has it gone? Did your drivers need to exert caution when driving or could the plastic hold up to sudden impacts?

Re: Polycarbonate vs. Aluminum
 

See the original intake from the 111 2012 robot or the 1678 2014 robot for examples of polycarbonate intakes.

The idea here is that you want a material that is tough, not strong. While strength is a measure of the amount of stress a material can take before failure, toughness is a measure of how much energy the material can absorb before failure, and is a mixture of the strength and ductility of the material. You want the polycarbonate intake to deflect when it is hit instead of breaking, but this naturally means that your intake won't be stiff. On the other hand, you can have a very stiff aluminum intake that will always be in the same spot relative to your robot frame, but you will then have to build it to be strong/tough enough to withstand impact.

Re: Polycarbonate vs. Aluminum
 

Polycarb, 100%.

Our intake arms for our 2014 robot were 1/4 poly carb and in more than 1 match ended up getting caught on another bot and dragged them around the field by our intake. Those arms lasted for at least 150 matches, they finally died after being exposed to UV and then the heat of our crate during our last offseason event. Polycarb does not shatter like acrylic. Aluminum will just die this year.

11/10 Highly recommended.



Ask me your questions.

Re: Polycarbonate vs. Aluminum
 

In contrast to RoboChair...



Our 2014 robot used 1/4in aluminum plate for its intake and we had zero issues with it all season. We too got our intake caught up in other robots that year and never broke it. The air cylinders used to deploy them were about the smallest air cylinders we could use, so they collapsed neatly when hit. And we got hit a lot when opening up to catch a ball.

It doesn't matter what material you pick, it matters how you execute your design.

Re: Polycarbonate vs. Aluminum
 

I recommend polycarbonate. Any mechanism extending out of our bumpers (within volume constraints of course) are polycarbonate. Polycarbonate rarely cracks or breaks on impact in standard conditions. The only time we have ever cracked polycarbonate was in 2015 with our polycarbonate tote intake. The only reason we thought it shattered on impact was because loctite was used on the screws that attached our motors to the polycarb plate. We think that the loctite reacted with the polycarbonate during its assembly and made it brittle instead of flexible, and that's just our hypothesis. The only areas where there was evidence of shattering was in our motor mount holes. After avoiding loctite on the rebuilt intake, it never experienced any cracking after several more regional and championship matches.

Our lesson was to be careful of what possible reactive chemicals come in contact with polycarbonate. And DON'T use acrylic. That's guaranteed to shatter.

Re: Polycarbonate vs. Aluminum
 

Polycarbonate is tough stuff, and will likely survive robot-to-robot interaction. It usually bends out of the way and springs back to shape. It's more likely to get bent or tear if you overload it, rather than cracking into pieces like other hard plastics.

Don't let loctite get near it though!

We are designing an intake that goes out past the bumper this year, but are planning on using aluminum with pneumatics that take the impact load, similar to 95's robot above. Both methods are feasible.

Re: Polycarbonate vs. Aluminum
 

Ok, hypothesis confirmed haha.

Re: Polycarbonate vs. Aluminum
 

Team 16, 2008. In the blue.

https://youtu.be/NYNEAL_dK6I

Re: Polycarbonate vs. Aluminum
 

As a professional Plastics Engineer - you will likely what to use Poly-carbonate. You can get to any strength by changing the thickness of the material. Polycarb will flex, bend and take an impact without permanent deformation, while aluminum will deform and require you to reform. At similar strain so PC should work out best. hard to confirm WO a design to review.

Senior Mentor team 6443
Mr. Krafty

Re: Polycarbonate vs. Aluminum
 

I would definitely recommend polycarb for the reasons people posted above.

Another point is that it is extremely easy to cut and drill. We use our small CNC router for polycarb but a hand drill and a jig saw could be used to make even the most advanced looking polycarb mechanisms.

Re: Polycarbonate vs. Aluminum
 

Another point is that polycarb stands up well to cold bending without too much worry on cracking at the bends after lots of abuse, so all sorts of shapes can be made with it.

Re: Polycarbonate vs. Aluminum
 

How did those VP mounts hold up?

Re: Polycarbonate vs. Aluminum
 

I find this statement a little out there given the context of the conversation. Perhaps you care to clarify?

I found a couple sources that confirm these numbers: http://www.usplastic.com/knowledgeba...contentkey=446

Wherein the minimum bend radius for .125in pc is 12.5in, 100x material thickness! I have only heard of teams having success with hot-bending PC, but I would be very interested to see good cold-forming results.

Re: Polycarbonate vs. Aluminum
 

To play devils advocate: I can replace every instance of PC in your post with aluminum and everything would still be true. I say this owning my own CNC router that I routinely cut aluminum with and having cut plenty of aluminum with a jig saw.

Re: Polycarbonate vs. Aluminum
 

You can also cut polycarbonate with a xacto knife. The point is not just that it's possible to cut the material. The point is the ease of doing it.