Hey all,
How do teams like 254, 118, and 1114 make their one-piece bumpers? Are the pieces of supporting wood simply glued together at the joints, or are there extra pieces of metal holding them together?
My team builds each side, then connects them together with 90 degree angle metal brackets. This year, we made two u-shapes rather than a single piece, but the concept is the same.
We don’t even use brackets, we just screw right in to the end of the other piece of plywood. You have to make sure you use the right pilot though or you’ll split the wood. I’d also assume this technique works less well if you’re using hardwood. You get better results if you use right-angle clamps when you’re drilling the holes and putting the screws in.
There is a variety of methods used. Some teams will use angle aluminum at the joint, some will use hinges, some will get fancy and use joinery and glue. The hinges allow the bumper segments to be wrapped around the frame at the corners prior to securing the bumpers to the frame. Some will even make aluminum backing frames that will fit down over the robot frame, and lock in using clevis pins or some other one step attachment. Please remember the 1" hard parts rule as measured from the frame in your design.
See the pictures at R21F for two common ways to do this.
This year (and some previous years) we used 3-1/2" x 3/4" angle braces such as these.
http://www.acehardware.com/product/index.jsp?productId=53084686
We mount ours in the inside of the corner for better inspectability.
We were inspired to make uni-bumpers this year for the first time. Then our strategic design determined that we should cut the corners instead of 90 degrees. We used 1 inch steel straps bent at 23 degrees top and bottom for one joint and the other joint, 67 degrees, we counter drilled 1 1/2 inch screws into the end.
For the uninitiated, why those particular angles?
4901 makes unibumpers as well. We have metal angle support brackets on all corners of our frame. The bumpers just drop on over the top.
246 is another team that uses aluminum brackets. This year, because we have a hexagonal chassis, we just bent thick sheet metal (I think 1/8in) on a finger break to the right angle. They were pretty far off at first, but bent into shape when we put them on the robot and look a lot better when taken off now.
To expand on John’s post, we started doing this for Championship in 2014. Rectangular frame meant angle aluminum, boom done.
This year, since we had an octagonal frame, we took two pieces of 1/8" flat aluminum and put it in a sheetmetal break. (I want to say each piece was like 4"x12", but it really doesn’t matter.) We bent one piece for the front and back angles, and the other for the midship angle. Then they went on the bandsaw and were cut into shorter-in-height pieces with identical angles that made assembly pretty straightforward for a frame shape that obnoxious. 
I’m fairly certain those angles are just what it ended up being. However, the reason we did angled corners like that all is (a) the octogonal shape gives greater area inside the frame perimeter, (b) the shape of the corner (kind of) allows the robot to “lock in” against the tower and the driver station wall for batter shots, and (c) the cut off corner allows us to roll off of defenders more easily.
Randall,
They are pretty. Why can’t everyone take this much care in making bumpers? It would make things much easier.
4901 picked the angles we did because that’s what allowed the drivetrain to package neatly. We picked the octagonal frame to hold off defenders as well, but we also found it’s great for saving your butt if you get turned sideways in the outer works. Long-chassis robots sometimes have trouble getting clear of the dividers because they won’t fit well diagonally. (They usually got that way towards the top of the divider, which flexes more.)
We began with the idea that a tower defender has to be prepared for full contact battle, and that means protecting the robot’s innards.* So, our frame perimeter is miter-cut, welded 2x1 aluminum tube, 34"x25". Rhino tank tread modules bolt onto that frame by means of uprights (more 2x1), and a full 0.09" sheet metal belly pan. Our arm pivots at two joints (still more 2x1) welded to the frame a couple of inches behind the front.
The single piece bumper mounts to the top of the frame using 1 inch angle and 1/4 inch bolts vertically through the frame – this is very similar to the method we learned from HOT in 2012. Our plywood is also miter cut and joined with glue, then reinforced with aluminum angle on the outsider corners. We heat weld the stack of noodles and wrap them around the corners, securing with some gaff tape before covering with slick, reversible Robopromo sets. You can see the finished result at TBA.
The Average Joes did not invent any of these techniques – for a solid bumper system that performs well we thought it best to copy (and slightly tweak) proven methods developed by others.
*Why did medieval knights wear armor? Because they needed it!
We built one piece bumpers this year; we have a blue set and a red set. Wooden bumper elements were made on a CNC router and are joined with screws with aluminium plates at the corners for strength. The bumper is supported the whole way around by a 25x25x1.2mm Aluminium tube frame perimeter. The bumper is attached to this tube with small angle gussets using M5 bolts and wingnuts. We are using conventional Cordura bumper material for durability(even with this material they did get a few tears and punctures at the Australia Regional) and did a lot of searching for the firmest Solid core pool noodles. Because Australia is in the Southern Hemisphere, summer is December to February meaning that Pool noodles are widely available just when we need them.
http://www.chiefdelphi.com/forums/showthread.php?t=145796&highlight=4613