See title for question.
I’ve struggled with bumper mounts due to wanting them to be very secure and easily removable. What have teams done in the past to accomadate these needs? Not looking for reversibl bumpers as a solution to the second part.
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While a lot of teams use either quick release pins or over-center latches, we have always used rivnuts in the frame and 10/32 bolts to attach the bumper brackets to the frame.
Following what we saw on HOT’s 2012 robot, we built our 2016 frame perimeter using 2x1 1/16th wall aluminum tube. Our one-piece bumper fits tightly (< 1/16th clearance) to the frame and is attached using aluminum angle. Vertical 1/4-20 bolts run through the angle and frame in four places, secured using nylon lock nuts. Takes a couple of minutes to remove the bolts and lift the bumper off.
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1983 secured their one piece bumpers with toggle clamps and seemed to work well.
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3928 has used Stainless Steel Snap latches (found on McMaster here) since 2013. At around $6.00 a piece, they aren’t cheap, but make for very quick bumper attachment and removal. They are attached to the bumper by an L bracket. The latch slides over a spacer on a 10-32 bolt that is on the frame. This makes them fairly adjustable. Taking bumpers off or on takes less than 10 seconds for two people.
http://s32.postimg.org/f6naau1zp/Screen_Shot_2016_05_10_at_1_14_05_PM.png
We had a 1x1x1/16 aluminum tube that went around our frame perimeter. The bumpers had 8 aluminum U extrusion pieces 2 inches long that were mounted inside pockets on our bumpers. This allowed us to get a tight fit between the U channel and the 1x1 tube. 1/4 inch holes in the 1x1 and the U brackets allowed for a quick release pin on each bracket http://www.mcmaster.com/#98470a135/=12cpcnp. To put the bumpers on or take them off was about 30 seconds.
My explanation might not be the greatest but once we get our crate back from fedex I can post some pictures.
How about a quick and dirty MS Paint diagram in the mean time?
For 2016, 2667 had a really nice connection-- basically two halves with bolts that were all facing the same direction (in from the left or right side), so that putting them on or taking them off was just a matter of four wing nuts per side. They held up extremely well for competition, and were so simple that even with extremely low resources (money, time, and experience). I’ll see if I can find some pictures.
Here is a cross section of one of the mounting points. The bumper is on the left and the U Channel is recessed into a pocket on the wood of the bumper. This allows a tight fit between the outside of the frame and wood part of the bumper, the top of the 1x1 and the U, and the outside part of the 1x1 and the outside part of the U. The pin goes all the way through both sides of the U and the 1x1 with a .25" hole.
To take the bumpers off, slide the pins out and pull up vertically on the bumpers. To put them on push the bumpers down until the brackets sit flush on the 1x1 and push the pins in.
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1678 has used the snap latches shown in bstew’s post but we last used them in 2014 and had to replace them because they couldn’t hold up to the huge impacts that year.
I very strongly suggest the rivnut + bolt + drill driver or the rivstud/PEM stud + nut + drill with nut driver methods. It is super fast and easy to swap bumpers that way. Over-center cam type latches are also great but can be harder to implement properly.
Team 330 used a similar mounting system this year. The only difference is that the “bottom” of the U channel is screwed into the wood, and the quick release pins are vertical.
The entire mounting system is rotated counter-clockwise in comparison to bcampbell’s diagram.
It worked extremely well, and the wood screws only needed to tightened once or twice throughout the season. (primarily due to how our robot has to be lifted off of the tower after a scale)
Rivet nuts and screws are a quick easy way to do this.
GUS uses a tapped standoff on the chassis side with a hole through it for a cotter pin. An L bracket with a clearance hole for the standoff is mounted to the bumper. Just skip the bumpers on and then slide the cotter pin in. Very quick, very easy, no tools required.
As did 1197.
A word of caution on wood screws: you can never have too many in your bumpers, and keep 'em tight. Experience talking (thankfully not mine…this time).
If you gotta make a mistake, go with “more secure”.
Add me in the Rivnut/PEM nut catagory.
Jay you know our bumpers weren’t the quickest to get on/off this year but that was pretty much entirely the design of certain aspects that kept the access down to almost nothing. In the future it would have worked a lot better if we kept the space above open for tools like a ratchet or drill and could have considered wing nuts if we had more space. Keeping all the bumpers mounted on the top side of the robot would have helped too and with a one piece bumper it could have helped reduce the number of mounting points.
For reference we used Rivnuts with a 1/4-20 bolt coming up through the bottom and used non-locking nuts to hold the bumpers on. Often just hand tight due to access but a few received a ratchet.
After doing something similar in 2014 I think it is a good balance of low effort and strong connection between the frame bumpers and frame.
These automotive panel nuts work the same as rivet nuts, bit they’re cheaper, and easier to install as long as you have an edge close to your frame rail. They fit the Andymark kit chassis perfectly! We used them to hold our bumpers (and our manipulator) to the frame this year: http://m.lowes.com/pl/Standard-sae-u-nuts-U-nuts-Nuts-Fasteners-Hardware
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CIS 4607 had a two piece bumper that were reversible. These mounted to the 1X2 welded aluminum frame with 1’ angle mounted to the bumpers and four 1/4 - 20 bolts.
This year we were a very physical robot that focused on defense. We both delivered and took a beating every single match and the bumpers held up very nice.
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From a robot inspector who has seen thousands of attachments, a mount that is attached to the bumpers that fits into/over/on the frame and has hardware/pins/latches that are installed from the top of the robot are the best. Screws/bolts that need to be driven in from the interior of the robot frame are OK but you will eventually drop that hardware in the robot and it will take special tools to install or remove the bumper system. This year had some defense but not as much as I expected. Bumpers are meant to take the full punishment another robot can inflict. Make them secure and easy to remove.
There have been many different excellent attachment methods mentioned in this thread. The most important thing to do is to pick one and design it in along with the rest of the robot rather than leave it as an afterthought. Otherwise that xxx-latch that worked so well for another team won’t work so well when there is no room to install it, it can only be installed in a hard to reach place or there is nothing strong enough to attach it to.
Some (many?) of you may have had wood screws strip out. If so, remove the screw and drip some thin (not gel) cyanoacrylate (super) glue into the hole and wait for it to set. It soaks into the wood and makes the wood swell a little so the screws have something to grab. The CA will make soft wood as hard as maple or oak so the screws won’t strip out again.
Forgot about that trick–it’s great for a quick hardening of wood when you’re building a model airplane. (Actually, add a little when the screw is in there–that’ll really make it hard to get the screw out.) Just don’t stick your fingers together, it hurts.
Our team had a reversible bumper that wrapped around the robot, and it was secured with aluminum bumper mounts and rivnuts, which made it very easy to remove.