I know the rules could change for the 2010 game but I’d be interested in what systems teams have used to facilitate rapid attachment and removal of bumpers.
We’ve always put threaded inserts inside the bumper and then bolted them onto brackets on the frame. This seems simple enough but given the cramped quarters inside the robot and subtle alignment issues it can be a tedious 30 minute job to take the bumpers on and off for weighing.
There has to be a better way? Care to share pictures or descriptions?
We had a nice setup in 2008 using fanged elevator bolts (from McMaster Carr) in the bumpers, and coupling nuts to hold them on. And we even made the bumpers well enough that we can use either side bumper on either side, and either end bumper on either end. Too bad we couldn’t make it work so well on the 2009 robot. And too bad I didn’t get good pictures of it.
Our team’s 2009 robot used sheet metal plates on the corners with appropriate holes for the bumpers to attach. The bumpers had 1/4 20 thread sticking out of their backs, which went through the holes. Inside the plated, we used nuts in conjunction with these knobs to facilitate easy removal by hand.
Here is what FRC1995 used last year. There were two of these mechanisms at the top of each bumper. There was also another piece of aluminum-angle mounted on the bottom of the bumper. This lower piece has holes at either end, which would slip over fixed-mounted bolts on the lower side of the drive frame.
The upper mechanisms were activated by hand. By pushing down (1st picture) the white block with bolts would lower, leaving room for the bumper’s aluminum angle to be inserted so it is just below the upper lip of the drive frame. By releasing the mechanism, the spring will push the assembly up, inserting the two locking bolts through the bumper aluminum angle and through holes in the drive frame. This locks the bumper in place. You can see the mechanism closed in the 2nd picture. Sorry, I don’t have a good closeup of the lower aluminum angle.
These mechanisms worked fairly well for us in the 2009 season. Unfortunately we were behind schedule, so the mechanisms, while planned from mid-season, were built last minute. Better fabrication would help these perform better.
We took some 3/8" 7075 aluminum rod and drilled and tapped one end. Then we put a chamfer on the other end and drilled a transverse through hole. These became our “bumper pins” these were screwed to a 1/8" metal plate, abut 1/2" wide and 2" long with three holes, one for the pin, and two to screw it to the wood in the bumper. We 4 of these sticking out of the bumpers on either side of the robot. They would go through 7/16" holes in the frame, and then hitch pin clips were placed through the transverse holes to secure it. Then we used a tee nut in each end bumper piece (the small front and back bumpers) with a 3/8-16 knob bolt to secure it. The end bumper pieces were attatched internally to the sides, with aluminum angle.
This is what we did - purchased steel U channel that fit over our frame (perfectly). Then we drilled holes vertically with the bumpers on and dropped 3/16" quick pins in (bolts work fine - no need to thread or put a nut on, friction will keep them in just fine). This got us our “backing member”, and got us within a 1/2 pound of max bumper weight which is where we wanted to be.
Team 228 turned aluminum pins which were inserted into holes in the frame and held to the frame with hairpin cotter pins from McMaster. The bumpers were held onto the pins with larger hairpin cotter pins as can be seen in this photo:
The bumper brackets were 0.125" aluminum angle bored to the OD of the pins on one flange and bored for deckmate screws into the bumper plywood. This system only required the pulling of 14 cotter pins to remove the bumpers and reinstall. We averaged under 5 minutes to remove/install all the bumpers.
We were fairly happy with this first generation design and had no failures in any component. We will probably change the design slightly so that instead of holding the pins to the frame with cotter pins, the base of the pins will be bored and tapped and bolted to the frame. This will remove the play that can be seen in the photo. We will also design a new bumper bracket to hopefully be produced in CNC sheet metal, like our frame, improving tolerances. These brackets will also hopefully incorporate wrapping the corners of the plywood with aluminum angle.
We usually build our chassis with Bosch-Rexroth aluminum extrusion (20mm profile in recent years), so we outfit our bumpers to take advantage of the T slots in the extrusion.
The bumpers have bolts put into them (head side out). We usually mill out the sides of the channel at the top of vertical members (in the corners of the chassis) so that there’s a place to insert and remove the bolt heads. All you have to do to add or remove a bumper is to put the bolt heads through the hole and slide them down into place.
Our bumpers had two fanged head bolts that came out of them and went through matching holes in the frame. Wingnuts held the bumpers onto the frame. We could mount/dismount the bumpers in a few minutes.
If you are using the kit frame, AndyMark sells a bracket that fits over the frame rails: http://store.andymark.biz/am-0317.html. Last year we had one of our sponsors bend up some channel for us that fit over the frame, and I found out about these later… although getting them donated by a sponsor is cheaper
We secured them with 1/4" hitch pins through the vertical holes. Carrying the robot by the bumpers was no problem. I was able to remove a bumper in less than 30 seconds when smoke started coming out of the robot while doing some testing.
If the GDC goes back to requiring “bolted fasteners” (or whatever the wording was in 2008), then a 1/4" bolt can replace the hitch pin, but that takes a little longer. As a robot inspector, I really (really, really) hope that they do not go back to the 2008 requirement. Being able to remove and install the bumpers quickly has a significant impact on both how smoothly your inspection goes, and also on the ability to perform maintenance and repairs on your robot.
Ok, let me say that again: whatever method your team uses to attach the bumpers to the robot, you should be able to remove and install them quickly. In fact, the rules last year recommended that you should be able to complete the process in less than 10 minutes. I have seen teams that it takes an hour, and they are still not what I would call “solidly attached”.
There are several excellent ideas presented so far in this thread, and I hope to see even more. The biggest thing that I see in the good ideas vs the bad ideas that I see every year, is that the good ideas take bumper attachment into account during the design process, and the bad ones treat it as an afterthought.
For the rookies here and those working with bumpers for the first time in the coming weeks…
The GDC wrote very specific rules for bumpers in both 2008 and 2009.
The rules are not open for interpretation by inspectors and the GDC believes the rules to be clear enough for compliance and understanding by all teams.
The bumper rules are intended to minimize robot damage by insuring that any robot to robot or robot to field interaction take place only through the soft parts of the bumper.
I would suggest that teams take some time this week and review the 2009 Q&A on bumpers and the bumper rules in the robot section of the 2009 manual. It will help you in the coming weeks to understand whatever changes may be introduced by the 2010 manual.
What our team has done, is to use 3/4" x 3/4" ( 1/8" wall ) square aluminum tubing, for the structure of the chassis, then use 1/16" aluminum U-channel
( which is 3/4" wide and 1/2" deep ) to fit onto the tubing. 2 small pieces, about 2" long are placed on the bumper board, inside, so that it is locked into place vertically, and then 2 pieces are placed to lock into the vertical structural components, to keep the bumper from moving forward and backward. We then simply drill 4 clearance holes for the nylon bolts, washers, and wingnuts ( # 10-32 ) that will hold them in place. Our bumper weight, last season was around 10 pounds, easily within specs.
Was chatting with RC last night and we also came up with cotter pins + clevis pins as a cheap alternative to another solution. You can just buy steel clevis pins from mcmastercarr since the weight goes with the bumpers and for the most part bumpers seem to be underweight.
Downside is they are about 20 bucks a piece though theoretically you need just 1 per bumper right in the middle of the span if your bumpers are secure enough they shouldn’t be able to bend up at the edges if they get yanked.
This is very similar to what we did for 2009, and it worked fairly well for us. The bracket may have been the AM one, but I didn’t make the bumpers, so I’m not sure. However, we had some issues with getting a few of the pins in - issues with lining up the brackets with the frame exactly, and a few of the pins had to be pushed in at EXACTLY the right angle…while using a hammer. If the pins had gone in a bit more smoothly, we would have had a much easier time. I have the feeling that we’ll also be modifying our system this year (game pending), but the pins are much easier than what we’ve used in the past, so we might just stick with them.
I have a feeling our team will use Pins this year if we can, getting bolts out of a cramped robot to release the bumpers is not a fun experience, the first year was awful, last year was mildly better.
