(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:
Are rivets a viable option for an average FIRST robot frame?
What kind of rivets are best for this? Aluminum is the cheapest option, but stainless steel rivets have higher strength by orders of magnitude.
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?
Is there anything in particular to look for in the way of damage after the robot has taken a few hits?
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.
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]
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.
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!
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.)
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.
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.
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.
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.
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.
I would have to agree with Dylan on this one…we were really happy with the way our framae held up during all the matches. Our robot even got flipped over for the first time in finals at nationals and it still was in tact.
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.
If you can make it work you get a High 5.