Would like to try this out myself but would appreciate some opinions first to see if it’s even worth trying out.
I was thinking 1/4" Lexan with an aluminum angle support (probably two- top and bottom). The angle should add a good amount of stiffness.
Anyone see any issues with that? I’ve never seen Lexan break ever (and that’s the point of using it right?) before so I imagine durability will not be an issue.
Curious to find out if the extra room for foam would balance out the thinner backing.
Are Polycarbonate/Lexan Bumpers A Good Idea?
Definitely don’t even bother prototyping
Great idea! Haven’t tried it but seems to have potential
We’ve tried it and it sucks
We’ve tried it and it’s amazing
0voters
Edit: Will probably stick with Baltic Birch backing. Although it’s become a bit of a pet project of mine so will probably make a second set made out of polycarb and extra thick foam composite layers. Specifically laterally placed high density EVA with a thinner, softer layer underneath.
Will try doing some very basic tests to see how an extra thin backing + extra thick foam fares to regular thickness wood backing and thinner foam.
I imagine pretty much any option utilizing better foam will provide better impact performance than plywood+pool noodles though .
Just have a large surplus of Lexan and would be nice to have lightweight and (hopefully) indestructible bumpers with room for extra foam padding. Would love to be able to drive our robot like we stole it with no risk of breaking the bumper.
I wonder if it they would be durable enough to last multiple seasons actually? Might depend more on the foam quality I guess.
My first year was 2003. A few years before bumpers were a mandate. Back then it was allowed in the rules and was worded roughly " if you punched it with a fist and it didnt hurt - it’s ok."
we took some squishy foam at your local craft stores, wrapped it in a layer of beautifully painted 1/16 or small polycarb. Then wrapped the entire robot frame in another layer to keep them all intact. Was annoying, but so beautiful after the blue metallic paint and vinyl graphics.
I would not characterize polycarb as lightweight, nor is lightweight even desirable when mounted so low on the bot. So that may be a complelling reason to try.
However the limiting factor imo is fabric attachment. Staples into wood are too dang convenient for me to want switch. I would rather spend the design time elsewhere during the season.
(Ply)wood also serves as another layer of “padding” to protect against dents with the field.
In fairness to polycarb: if you have some odd bumper geometry (e.g. say a hypothetical comp bot has rounded corners) the fact you can heat bend polycarb easily to fit that contour is super nice.
The issue with using 1/4" polycarb is that its MUCH less stiff than 3/4" plywood. SO, impacts transfer the load directly to your frame without any significant spreading. Plywood is acting as a structural member in the bumpers.
Yeah the not being able to use a manual stapler is probably my biggest gripe with this idea tbh…
We have a pretty low CG and without bumpers on we’ve been able to drive it like a madman fully extended up without any tipping issues. Although have not tried slamming into another robot yet.
Might try to make two sets to switch out if need be. Second set being 3/4" Baltic Birch backed.
Yes was considering that too but with the new foam rules was thinking this might be less of an issue if going with the hard outer shell, soft squishy inside bumper design.
Was planning on doing >2" lateral floor tiles/3.5-6lbs/ft³ EVA and about 1" 2.2lbs/ft³ EVA on the inside as per the recommendations on the bumper foam material testing thread.
Outer shell would help to absorb a lot of the impact and evenly distribute load to the softer layer underneath.
Will have to try this out for myself though. Will have wood backups just in case.
It’s worth noting that stiffness is related to the cube of the thickness, so going from 1/4 to 1/2 effectively makes your backing 8x stiffer. That combined with the fact that staples get extra grip strength from that extra thickness would make 1/4 backing a no-go for me.
However, I’m still a huge fan of upgrades over the traditional way. This year, we built our bumpers with 1/2 inch HDPE backing, custom 1/8 aluminum brackets from Fabworks, and billet-machined EVA foam. While this is extremely overkill, we feel confident we won’t have to rebuild our bumpers this year - it’s a great update from plywood.
We got it from Foamorder - a local company, so we didn’t have to pay shipping. We buy it in 3-inch thickness (gluing up 3 layers of 1 inch, etc also works), cut some rough blanks, workhold with painter’s tape and spray glue, and then each “side” takes around 30 minutes of machine time with a special foam-cutting endmill.
That’s lucky that you never broke any bumpers! I’m pretty sure we built at least 6 or 7 last season.
What type of glue did you use to glue layers of your bumper foam together?
To the OP, given you’re asking now, I would build whatever you can build the quickest/easiest. Performance benefits of other materials seem marginal to me, especially this year where I’d anticipate fewer highspeed collisions than 2023 or 2024.
We use 3M spray glue, the same stuff we use to adhere it to the HDPE. Works great. Using slightly weaker stuff for the work holding is probably advisable to make removing it easier.
Yeah honestly it’s more of a pet project for me while the students work on everything else. Might try during the off season or perhaps between events.
We already have a set of wood bumpers which technically are competition ready but going to make a “proper” set. Likely Baltic Birch backed at this point.
Also curious about the glue! I’ve been recommended rubber cement and will give that a try.
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