Riveting up a frame
 

(I searched "rivet" and didn't find anything, so here goes.)

So I know that there are those of the riveting school of thought, at least when it comes to your frame. I'm looking at the option of riveting up the kit frame next year (assuming it's the same and blah blah blah), as it seems to be an easy way to both drop some weight (albeit less than welding, but with the advantage of easier repair) and cut out the issue of locknuts backing out.

This leads to a few questions in my mind:

1) Are rivets a viable option for an average FIRST robot frame?
2) What kind of rivets are best for this? Aluminum is the cheapest option, but stainless steel rivets have higher strength by orders of magnitude.
3) If you've riveted the kit frame, is it best to just put rivets everywhere the bolts should go, or can you do well with less?
4) Is there anything in particular to look for in the way of damage after the robot has taken a few hits?

Re: Riveting up a frame
 

That actually is a good idea in the beginning, however, from personal experience rivets break easily especially under strain, also if you use rivets you have to use washers to allow the rivet to grab and hold the metal together. Once again they are very weak and in a match if someone hits you your frame might break apart.

Re: Riveting up a frame
 

Don't do it, unless you find some really large rivets.

Re: Riveting up a frame
 

Rivets are weak in shock load, but great for static loads.

A loose bolt is much weaker under cylical loads than a properly tightened one (ask the Mech Engineering guys why). A rivet (of the type you are considering) cannot be 'tightened' - the tightest you can get it is not very tight. (Rivets for big steel, like the GW Bridge, are installed hot, so they shrink and 'tighten'). So, loose rivets and cylical loads equals premature failure.

Also, the rivet starts to get loose quickly, and it's ability to be strong* drops significantly. That means instead of tightening up nuts and bolts, you get out the hammer and tighten up the rivets.

*Strength doesn't actually change, but a loose member has a little bit of distance available to allow it to build up some momentum before it hits the end of the rivet...and that isn't good.

Don

[Edit: The above refers primarily to standard peen-over rivets, not Pop Rivets mentioned by Deepwater]

Re: Riveting up a frame
 

Given the kit frame's quarter-inch holes, I'm looking at McMaster 97525A553 (stainless steel) or 97447A652 (aluminum), or the other rivets of similar size. Bigger than what I'm accustomed to, but I don't know what qualifies as really large these days.

Re: Riveting up a frame
 

See this post in this thread. Contrary to chakorules opinion we had excelent success riveting the KitBot chassis last year.

We riveted the KitBot chassis last year and had ZERO problems, ZERO lost rivets, and ZERO failures. We went all the way to the finals at our one and only regional (Colorado) and only lost by a few points in the last match. We found a riveted KitBot to be very strong and effective. We will probably do it again this year unless something drastically changes.

Absolutely! They are cheap and effective. They can easily be drilled out if needed and do not weaken the frame like welding. They save a significant amount of weight over nuts and bolts and there is no chance of the nuts loosening and falling out. They are simple to install after you do one or two and get the hang of it and are actually much faster than nuts and bolts because you don't have to hold a wrench in a hard to reach location.

We used .25 diameter aluminum rivets with an aluminum mandrel. Specifically MSC item #04045431 - $7.06 per hundred. You will need a couple of boxes. You will also need a rivet tool that can handle 1/4" revits. The small ones you get at the local home store won't cut it. We used MSC item #74327552 - $93.91. The tool is a little expensive but works and was the least cost tool I could find that would handle 1/4" rivets. Buy it once and it will last for many seasons.

We basically replaced the 1/4" nuts and bolts in the KitBot with 1/4" rivets. We put them in the same holes plus or minus a few where we attached our roller pillow blocks and upper ball holder frame. We also riveted diamond plate to the KitBot frame. You could probably do with less rivets but they really don't weigh much each so it isn't a big loss to put a few extra in. If you properly rivet the KitBot frame together replacing each of the 1/4" bolts with a rivet you will have a very tight, strong, and durable frame and save more weight than you think. When you get your kit this year open up the KitBot box and put those two little bags of nuts and bolts on a scale and see how much they weigh. IIRC it was almost 2 lbs. If you put a nut and bolt in each hole as instructed you won't have many left over.

We never had a problem with damaged rivets. We were a big target and got into a lot of pushing and smashing matches. Our 0.020" diamond plate got smashed a bit in places but our rivets and the KitBot frame are still just as good as the day we put it together during the first week after kickoff last January.

Any other questions just let me know. I have to give two thumbs up to a properly riveted KitBot!

Re: Riveting up a frame
 

In one of the prototypes, I believe team 1114 used quarter inch steel rivets and it worked great for them. See this thread.

Re: Riveting up a frame
 

I know that 1126 rivets their aluminum frame together instead of welding it. Right Dylan?

Re: Riveting up a frame
 

We riveted our upper frame last year (1/8" aluminum riveted w/ 1/8" aluminum rivets) and it worked pretty well, but as someone already mentioned, rivets don't take heavy shock well.
Also, repairs can be a bit tricky. We found that in most cases it's easier and faster to add more rivets than to replace the old ones, which is fine if you're using small rivets, but on the kit frame, you'd need some big ones. (We didn't rivet our drive base.)

Re: Riveting up a frame
 

Team 104 has used 1/4" steel rivets with back up washers since 2001 except the stack attack when we tried a 8020 frame. We have never had a riveted joint fail. For 2006 we bolted the kit chaise together and when the design became fixed backed up the bolts with rivets. We built up the kit frame with 1" 6061-t6 angle. The frame worked just fine.

Re: Riveting up a frame
 

Team 1501 uses a frame completely made from sheet aluminum and pop rivets. You will not find a stronger frame.

http://www.huntingtonrobotics.org/

Re: Riveting up a frame
 

Im pretty sure welded steel is a bit stronger...



As for rivets, I would use them in the less vital area's, but not for heavy frame rails. They dont react to shock very well, and could also reak havok on the field with wheels and drivetrains if some were to come loose.

Just my 2 cents. :) If you can make it work you get a High 5.

Re: Riveting up a frame
 

I am from a team where we usually only rivet our robot no welding. We have never had rivets break if you use the aircraft quality. these can take up to 26,000 lbs of shear force, only cost a couple dollars for a 1/4 lbs of them, and come in varying sizes. We find it is also safer than welding because we the students do almost all of the work. These are not pop-rivets though if that was what you were referring to.

Re: Riveting up a frame
 

Why cant students weld?

Re: Riveting up a frame
 

Most students we can trust to do work like that but there is those few who don't know when joking around should not be done. Also riveting is a lot easier to learn how to do rather than welding.

Re: Riveting up a frame
 

We used rivets in 2005 and 2006 and those were our best robots, by far. We used 1/8" aluminum rivets with aluminum mandrels in most places, but 1/8" aluminum rivets with steel mandrels in places where we could not use a lot of rivets, but needed strength. Our entire drive base, main structure and end of arm in 2005 were riveted sheet metal. Our entire drive base, tower, and shooter frame in 2006 were riveted sheet metal.

Anyone who says the rivets are not strong enough have either not used it, or implemented the rivets improperly. Strength to weight ratio is out of this world and I will race anyone changing out a component riveted together vs. bolted together. Our riveted components can be repaired and replaced much faster with rivets than with nuts and bolts.

Using 1/4" rivets in the kit frame should prove very effective. Also remember, you want to have a mechanical fuse when it comes to collisions. We usually do not have the weight to design our components against severe crashes/mishaps, but the rivets will break in key areas in order to save components.

Re: Riveting up a frame
 

Personally, I find it alot easier to lay a bead then riveting, but to each his own.

and who cares if it works. :)

Re: Riveting up a frame
 

yeah thats correct we used rivets this year more then any previous year and we were quite happy with how it held up.

Re: Riveting up a frame
 

Re: Riveting up a frame
 

we did use rivets but it was mostly in the upper frame around the shooter and such...i dont think that we would ever use them on the driveframe...but i think that they did hold up quite well. but again you must be careful where they are place and the amount of stress.

Re: Riveting up a frame
 

177 Uses POP rivets in similar ways to what Paul said above for 217. We also use solid aircraft rivets installed with a pnuematic hammer and bucking bar in application where higher shear strength is needed or if we need the rivet to be flat headed. We have made arms capable of lifting a robot of the ground this way using aircraft construction methods. Needless to say we believe the strength is there.

A word of advice if you plan on using big diameter rivets is to get a pneumatic tool for installation. Particularly if you use a lot of them.

Just a general comment, we find a mixture of joining using welding, rivets, rivnuts, and nut/bolt fastening depending on the application gives us the best solution for the problem. Don't rule out any of these methods unless you are not properly equipped to do them.

Re: Riveting up a frame
 

Interesting discussion - good question Billfred. I'm surprised to hear the amount of success using rivets and the kitbot, especially using backing washers. Normal design practice for rivets - at least in my work experience - is to avoid tensile loading and just use them for shear loading (obviously they have some amount of tensile capability, but they aren't designed for it) Installation involves match drilling close fit holes - I would think that the kitbot standard clearance holes are nowhere near adequate to get a good interference fit after bucking or popping. Has anyone run any calcs or tested tensile load capacity?

S.P.A.M. (I can't say 'we' anymore) has used rivets very successfully on some structural components, but not the chassis. Definitely the lightweight solution if you can make it work.

Re: Riveting up a frame
 

What do you call a 747?





A million rivets flying in formation!


Back in the days when Northrop Grumman was just plain Northrop, we built the fuselage for 747s. We also installed 3/4 of those million rivets. (Actually I think it was 995,000 but at that point who's counting?)

In modern aircraft structure rivets are often used for joints that are never intended to come apart. Just walk down the F-18 line with me sometime and listen to all the rivet guns, and just why do you suppose hearing protection is required in all the assembly areas?

Used properly, rivets are a very practical fastening method, but they have to be done right to work. That means matching the rivet diameter and length to the hole, countersinking to the correct depth for flush rivets, and using the proper mandrels and riveting tools. But if it is good enough for a modern fighter aircraft if ought to be good enough for a FIRST robot.

Re: Riveting up a frame
 

We use 1/8" rivets EVERYWHERE.

See how to link here:
http://www.huntingtonrobotics.org/in...d=1&Itemid =2

Or Video here:
http://www.huntingtonrobotics.org/in...=1&key=1&hit=1

The whole frame is "ribbed" and "skinned". Just like an airplane is made. No need for welded steel. It does get "dented", but it never has "failed" on us yet. Even the wheels are riveted with bulkheads and quite strong.

Re: Riveting up a frame
 

What is this pick on chakorules day? LOL ;-). I didn't get a chance to respond to myself in that post. I meant, kitbot and rivets don't mix well because we don't normally use the kitbot frame, we make our own frame. I didn't mean it as it "reads" like we used rivets on the kitbot frame. We have never tried that to my knowledge. We always use the bolts and normally we use the kitbot to build a proto-type frame to the programming team, that's where I come in. I don't think I've ever even used the pop-rivet gun yet in three years on the team, woooo.....I am gunna get it for saying that....

Re: Riveting up a frame
 

I went on a tour of some production lines and was amazed at how many rivets were being used.

Re: Riveting up a frame
 

Nah, I didn't mean it that way. I guess my sense of humor didn't come through on that one. I guess I was trying to point out that I tried to start this very discussion about riveting KitBot frames back then but nobody seemed to take the bait at the time.

Re: Riveting up a frame
 

We have aluminum pop riveted some assemblies with excellent results.
A good design practice is to use a splice plate or gusset plate at connections between two structural members & install multiple rivets in each member.
For instance at a right angle connection between two tubes, put a triangular gusset top & bottom with 4 rivets thru the gusset plates into each tube.
This also spreads the load over a larger area of the frame tubes, reducing the likelyhood of exceeding material yield at a single concentrated point if using one rivet.
A 3/16 rivet is the same size as a #10 screw. Holes are easy to drill and they are plenty strong for anything on a FIRST robot if using multiple rivets at a joint.

1/8 rivet are great for adding small plates for limit switches etc. or reinforcing structures after it's all bolted together.