How to build good bumpers

[GeeTwo]

Originally Posted by marshall

These things:

http://www.mcmaster.com/#standard-qu...e-pins/=zg9mm4

They are SOOO worth the investment. I really hope any new bumper rules allow us to continue using them.

How do you use these to attach bumpers? Do you orient them vertically (which is basically like what I suggested but with a pin rather than a bolt), horizontally parallel to the bumper, or horizontally through/into the wood of the bumper? Do you use the receptacles, retaining caps, or just holes in your chassis to catch the sear balls?

Originally Posted by MrRoboSteve

I'd rip 5" x 96" lengths of plywood in our shop, as it's much easier on the big table saw than at a competition.

Unfortunately, those would constitute manufactured parts, at least the past few years. It would be lovely to be able to bring a nice supply of these and (similarly manufactured) 15.5" wide strips of red and blue cloth to provide for teams whose bumpers are not up to spec (or nonexistent). Cutting a 1x6" down to 5" in a pit sounds a lot more feasible than cutting a 5" strip from a sheet of plywood.

[EricH]

Originally Posted by GeeTwo

Unfortunately, those would constitute manufactured parts, at least the past few years.

I'd be interested to know how you'd fit a 96" bumper on your robot while still following all the bumper mounting and support rules. (Other than in 2015, that is.)

I would rather suspect it'd be counted as "trim for transport", which does not automatically render it a manufactured part.

[GeeTwo]

Originally Posted by EricH

I'd be interested to know how you'd fit a 96" bumper on your robot while still following all the bumper mounting and support rules. (Other than in 2015, that is.)

I would rather suspect it'd be counted as "trim for transport", which does not automatically render it a manufactured part.

Perhaps in an "excess of caution", 3946 has considered any cuts that we'd made other than directly across a piece of stock, whether wood, aluminum, wire, or tubing (and that, if it was to a specific length) in a part prior to the competition event to to constitute a manufactured part. Where is this "trim for transport" rule? I've searched the 2015 rules, and this phrase does not appear. All occurrences of "transport" refer to "TRANSPORT CONFIGURATION" or transportation of the robot to the venue. The only occurrence of "trim" concerns the input leads of motors, servos, and solenoids. I don't plan to search for "for".

The way we understand the rule, we'd have to pre-cut to (perhaps) 5 7/8" before competition, then cut down to 5" and to length during competition in order for a bumper segment not to count as a "manufactured part". Doable, but less than ideal.

[EricH]

Originally Posted by GeeTwo

Perhaps in an "excess of caution", 3946 has considered any cuts that we'd made other than directly across a piece of stock, whether wood, aluminum, wire, or tubing (and that, if it was to a specific length) in a part prior to the competition event to to constitute a manufactured part. Where is this "trim for transport" rule? I've searched the 2015 rules, and this phrase does not appear. All occurrences of "transport" refer to "TRANSPORT CONFIGURATION" or transportation of the robot to the venue. The only occurrence of "trim" concerns the input leads of motors, servos, and solenoids. I don't plan to search for "for".

The way we understand the rule, we'd have to pre-cut to (perhaps) 5 7/8" before competition, then cut down to 5" and to length during competition in order for a bumper segment not to count as a "manufactured part". Doable, but less than ideal.

It's an interpretation of a rule--but it's obsolete*. (My bad on that one.)

On the other hand... it needs some revisiting (Frank et. all, if you're reading this...). I believe that your cutting to 5 7/8" would also cause that plywood to be counted as a Fabricated Item, and that would naturally cause some problems. This would also apply to stock aluminum, PVC, and pretty much anything else that is in a different dimension than it came from the supplier. (So... anybody want to see how unsafe transporting large plywood scraps into the venue is? No? Anybody want to enforce that rule? Yeah. Right.)


*There used to be a third category of material in addition to COTS and Fabricated. "Raw" material referred to material as it came from the supplier, with just enough cuts to get it into a more transportable form--e.g. cutting an aluminum tube to two 10' pieces instead of one 20' one--which many places will do anyway--or ripping plywood in half.

[marshall]

Originally Posted by GeeTwo

How do you use these to attach bumpers? Do you orient them vertically (which is basically like what I suggested but with a pin rather than a bolt), horizontally parallel to the bumper, or horizontally through/into the wood of the bumper? Do you use the receptacles, retaining caps, or just holes in your chassis to catch the sear balls?

We've used them in the past by attaching via angle on the backs of the bumpers and then slotting that into spacers on the chassis. If I can find time tomorrow then I'll try to take a picture and upload it.

[AllenGregoryIV]

Originally Posted by GeeTwo

Perhaps in an "excess of caution", 3946 has considered any cuts that we'd made other than directly across a piece of stock, whether wood, aluminum, wire, or tubing (and that, if it was to a specific length) in a part prior to the competition event to to constitute a manufactured part. Where is this "trim for transport" rule? I've searched the 2015 rules, and this phrase does not appear. All occurrences of "transport" refer to "TRANSPORT CONFIGURATION" or transportation of the robot to the venue. The only occurrence of "trim" concerns the input leads of motors, servos, and solenoids. I don't plan to search for "for".

The way we understand the rule, we'd have to pre-cut to (perhaps) 5 7/8" before competition, then cut down to 5" and to length during competition in order for a bumper segment not to count as a "manufactured part". Doable, but less than ideal.

I would definitly say that's "excess of caution". Also to clear things up you are allowed to reuse bumpers and build them any time you want or at least you could in 2014.

4.4.1 R13
ROBOT elements created before Kickoff are not permitted. ROBOT elements, including software, that are designed before Kickoff are not permitted.
Exceptions include the following:
A. BUMPERS,
B. OPERATOR CONSOLE,
C. battery assemblies per R5-A, and
D. software and designs with source files publicly available prior to Kickoff.

[Jon Stratis]

Originally Posted by AllenGregoryIV

I would definitly say that's "excess of caution". Also to clear things up you are allowed to reuse bumpers and build them any time you want or at least you could in 2014.

Piggybacking on this (assuming it stays the same for this upcoming season!), it's important to note that the rules in 2014 made it pretty clear that bumpers were not part of the robot, but rather were required to be attached to every robot. This means that pre-cutting parts to make bumpers for other teams at an event would NOT count towards your withholding (assuming we have withholding again), as those parts are not intended for repair or upgrade of a robot.

2015 R17:

At an Event, Teams may have access to a static set of FABRICATED ITEMS, not bagged per R14, known as the WITHHOLDING ALLOWANCE, that shall not exceed 30 lbs. to be used to repair and/or upgrade their ROBOT.[...]

So please, being as much precut bumper wood, cloth, and noodles as you want!

[MrRoboSteve]

Originally Posted by GeeTwo

Unfortunately, those would constitute manufactured parts, at least the past few years. It would be lovely to be able to bring a nice supply of these and (similarly manufactured) 15.5" wide strips of red and blue cloth to provide for teams whose bumpers are not up to spec (or nonexistent). Cutting a 1x6" down to 5" in a pit sounds a lot more feasible than cutting a 5" strip from a sheet of plywood.

Yeah, since it's not part of the robot it escapes the fabricated part rules.

You would not need to walk far into the pit at a competition to find items that are normally sold "by the foot" (e.g., extrusion, wire) being treated as COTS items for purpose of the withholding calculation. Updating rules to reflect this commonly accepted practice would be an improvement, IMO.

[Drew250]

Hey My team found a great site for 1/4" diameter, 2.50" grip length quick release pins! One-handed release should make for a quick bumper removal. (http://www.vlier.com/product_index/s...alllock-b.html)

[rich2202]

One other tip on making a bumper:

If the minimum height is 4" off the ground, then make your bumper 5" to allow for sagging of the noodles.

[GeeTwo]

Originally Posted by rich2202

One other tip on making a bumper:

If the minimum height is 4" off the ground, then make your bumper 5" to allow for sagging of the noodles.

How do you get an inch of noodle sag? We have never had as much as 1/4" of noodle sag, even before doing clamps and just pulling the fabric tight by hand.

IIRC, the more recent games (excepting 2015) have required bumpers to fit in the "bumper zone" between 2" and 10" above the floor. The bumpers are nominally 5" tall, giving 3" of design leeway. In 2014, when we were picking a big ball up over the bumpers, we went low. In 2013, when we did not have a frisbee pickup, we went a bit higher to reduce the chance of our bumpers and drive getting caught on a frisbee. IIRC, in 2012 (before I was directly involved on the team) we put the bumpers near the middle of the bumper zone as we intended to play defense. Unless you need to have 4+" of ground clearance, I don't know why you'd go to the top of the limits.

[rich2202]

Originally Posted by GeeTwo

How do you get an inch of noodle sag? We have never had as much as 1/4" of noodle sag, even before doing clamps and just pulling the fabric tight by hand.

I've seen a lot of sagging bumpers. If your wood ends exactly at 4'" (assuming the limit is 4"), I can guarantee you that some part of the noodle/covering will materially sag below 4". Especially after it has encountered another robot (or the wall) a few times.

As I recall, the noodles themselves are not stapled, or otherwise attached to the wood, so all that is holding up the noodles is the cloth. That cloth will loosen up.

[MrBasse]

Originally Posted by rich2202

I've seen a lot of sagging bumpers. If your wood ends exactly at 4'" (assuming the limit is 4"), I can guarantee you that some part of the noodle/covering will materially sag below 4". Especially after it has encountered another robot (or the wall) a few times.

As I recall, the noodles themselves are not stapled, or otherwise attached to the wood, so all that is holding up the noodles is the cloth. That cloth will loosen up.

I wouldn't guarantee that. Ours never have since we started focusing actual energy on our bumper design.

And properly attached cloth won't loosen up very much. If it did we would all have pants that fall off and baggy seat fabric in our cars and on our couches. Make them extra tight at first and any slop that develops will bring the bumpers to the place where you want them to be by competition time.

[Basel A]

Originally Posted by rich2202

I've seen a lot of sagging bumpers. If your wood ends exactly at 4'" (assuming the limit is 4"), I can guarantee you that some part of the noodle/covering will materially sag below 4". Especially after it has encountered another robot (or the wall) a few times.

As I recall, the noodles themselves are not stapled, or otherwise attached to the wood, so all that is holding up the noodles is the cloth. That cloth will loosen up.

A game update was applied in 2014 to allow the noodles to be attached. I would hope that the updated rule is applied in future games that have bumpers.

Originally Posted by Team UPDATE - 2014-02-11

To assist in applying the fabric covering, fasteners may be used to attach the pool noodles to the wood backing, so long as the cross section in Figure 4-8 is not significantly altered (e.g. tape compressing the pool noodles).

As such, my team had duct tape holding the noodles in place against the plywood. This eliminated concerns about noodle sag.

[pmangels17]

With regards to the backing material, I do have some expertise I'd like to share. I spent four summers (plus two high school years) working at a lumberyard, and I build a lot of stuff with wood at home too. Firstly, almost any plywood is going to be way more robust than any dimensional lumber or planking, because there are no grains. If at all possible, buy plywood, you will not regret it. Secondly, though the difference between S2S (sanded on two sides) and sheathing isn't huge, and both will work for your purposes, S2S ply is so much nicer to work with, it doesn't chip the way CDX or sheathing might, and overall it can be heavier and stronger if you get the god stuff.

Also, if you go to your local lumberyard and ask if they'd like to sponsor the team and donate the material:
1. There's a good chance that they will be willing to help you out, because...
2. They probably have scrap cuts leftover from homeowners who came in but didn't want a 4x8 sheet
3. Nobody wants to buy these cutoffs, so they tend to stack up
4. It's probably good stuff, because people (read: contractors) who buy CDX are doing sheeting work and buy in bulk or cut it on site, and homeowners who buy good furniture-grade wood in sizes that fit in their sedans, and leave the cutoffs behind