Easy Reversible Bumpers with CAD

[alecmuller]

We use reversible bumpers that change colors without removing the bumpers from the robot - it takes about 10 seconds to flip the fabric up or down and secure it with velcro. It's designed to the 2014 game rules (because bumpers weren't required in 2015 and the 2016 rules aren't out yet), so be sure to check the new rules.

This PDF, CAD model and drawing has all the information needed to make them, and the CAD is designed to be very easy to edit in SolidWorks: change two assembly cuts (see PDF) to make it fit your robot width & length (and adjust or suppress a third cut if you need clearance for part of your robot).

It includes a STEP file for importing into other CAD packages, and it's simple enough that you could probably skip CAD and just tweak the dimensions on the PDF too. The PDF includes sources for the fabric, pool noodles, and hardware.

The weights for the materials in the SolidWorks file are accurate - about 14.4 lbs (without the cutout) as designed for a ~27" x 28" robot.

[Ari423]

We tried this in 2014, and we were pleasantly surprised with how easy they were. The only thing we had trouble with was the corners. They never laid right, no matter what we tried. How did you deal with the corners on yours?

[MrBasse]

Originally Posted by Ari423

We tried this in 2014, and we were pleasantly surprised with how easy they were. The only thing we had trouble with was the corners. They never laid right, no matter what we tried. How did you deal with the corners on yours?

If you cut the corners so they have a 45 degree angle cutout that will follow the "mitre" between each side. It's like wrapping a present. You can see it pretty clearly in a video I posted a while back here

We use bungee as we had issues with the velcro pulling off or weakening over time. Going through the season and having something be too strong at first and then too weak isn't something we wanted to deal with.

Edit: I almost forgot that we created what is probably a really bad white paper with pictures to explain the process we used. We started with inspiration from other teams and tweaked to get where we are now. The question about corners is covered on page four.
http://www.chiefdelphi.com/media/papers/2931

[GreyingJay]

This is brilliant. And, I might add, probably very similar to how magicians do those tricks where they magically and instantly switch the clothes they're wearing.

[GeeTwo]

Originally Posted by Ari423

We tried this in 2014, and we were pleasantly surprised with how easy they were. The only thing we had trouble with was the corners. They never laid right, no matter what we tried. How did you deal with the corners on yours?

I did a 3-d breakdown of what this profile should look like a few weeks ago. I've posted an image to CD-media, and will link when it's up. I based this on a single-colored bumper, but it should not be difficult to extend to reversible bumpers.

Here's a text description: From a center fold line, start your sewing line 2-1/2" past the end of the corner of the wood on the bumpers. Go perpendicular to the fold for 1-1/4", then follow a shape equal to 1-1/4" times a sine wave (from 90 to 180 degrees) for 90 degrees. Continue tracking at 45 degrees for another 1-1/4" away from the fold; this should end up even with the end of the wood. From the sewing curve just drawn, add a 1/4" seam allowance. Continue the cut along the 45 degree sew line for another 3/4" of wood thickness, then turn directly away from the fold for enough to put staples in the back side of the wood.

Edit: Here's the pattern of the cloth for the bumpers.

[alecmuller]

Originally Posted by MrBasse

If you cut the corners so they have a 45 degree angle cutout that will follow the "mitre" between each side. It's like wrapping a present. You can see it pretty clearly in a video I posted a while back here

We use bungee as we had issues with the velcro pulling off or weakening over time. Going through the season and having something be too strong at first and then too weak isn't something we wanted to deal with.

I like the bungee idea for robots with full-length bumpers on all 4 sides, and apparently it's not that expensive, either (50ft of 1/4" bungee cord for $17.59).

It would be harder to get it to work if you have any notches in your bumper (for example to load a 10" diameter round game piece through a hole in the frame).

[MrBasse]

Originally Posted by alecmuller

I like the bungee idea for robots with full-length bumpers on all 4 sides, and apparently it's not that expensive, either (50ft of 1/4" bungee cord for $17.59).

It would be harder to get it to work if you have any notches in your bumper (for example to load a 10" diameter round game piece through a hole in the frame).

We get ours from Home Depot for around $.30 a foot. And yeah, the full bumper vs gapped bumper is a constant struggle with us. We tend to hurt our performance some years in order to make sure our frame is strong and protected. One of these days we will have to have a gap in our bumpers and up the competitive level a bit.

[Dylan179]

Be careful with using bungee cord, we where shut down for one match in 2014 because when they where fliped down where "dragging" so we ended up putting velcro on it anyways.

[MrBasse]

The only time we have ever had hanging or sagging bumpers was when we used hook and loop. We use 1/4" heavy duty bungee and set it up so that it is very very tight.

[Robopromo]

These are great plans. Nice work. We created a pre-sewn reversible bumper material a few years ago that you can purchase for your team at robopromo.com. There is also a helpful video with step-by-step instructions on how to complete the entire construction for reversible bumpers. Here's the link for that:

https://www.youtube.com/watch?v=BUDMB-aiBpo