Construction with gussets and bolts

[mrmummert]

We mainly use rivets with the Versa chassis...but in some areas we add
bolts as insurance incase of rivet failure if we have the weight and space
for them. We don't tap the Versa chassis for them. The only time we tap
any structural part for bolts is if we use 80/20 as part of the frame.
We've been able use both in the same robot. The past two years we've made
the basic frame from Versa chassis and added other structural parts using
80/20 by bolting them to the Versa chassis.

[Brandon_L]

Congrats on doing some off-season research! Selecting a set construction method for your team is immensely important and I see it often overlooked resulting in some 'slapped together' style robots that tend to fail often.

Having done both gussets+bolts and gussets+rivets each for a full season, rivets are pretty awesome. We used 1/4-20 bolts in 2013, and in 2014 replaced them with 1/4" rivets. Our hole patterns and everything were treated just as if we were using bolts, but instead we dropped rivets in the holes. And if worst comes to worst and you break a rivet for whatever reason (which has not happened yet) you can drop one of the million 1/4-20's you have laying around through the hole in a pinch*. Some would argue the weight loss is a plus as well. We've used 1/8 tubes with 1/8 plate for gussets but you could go for a thinner gusset plate and probably tube wall for sure.

2013
2014

Clarification #2: We have used a lot of rivets in the past, and do like them for certain applications; however, I'm specifically interested in trying out bolts on the critical parts of the frame- primarily drivetrain- where it can see a lot of stress due to collisions or hard driving. These would be parts that we shouldn't ever have to disassemble or replace between matches (fingers crossed) so I'm not really concerned about the speed of installing/removing them.

With the right kind of rivets, I guarantee you wont see them break. Here's what we've used successfully for a couple years now. They might even be overkill, but we opted to go for slightly stronger because of a bit of paranoia just to guarantee no issue. I have not used smaller rivets before, but I've also seen teams use smaller sizes (I believe 3/16"?) with a more aggressive pattern.

*Our kids also rigged up a system using the old KOP air compressor to allow us to rivet in our pit, which was pretty nice.

[asid61]

We use both rivets and socket head cap scews. Hex head bolts we never use. I prefer to use rivets wherever possible, generally 1/8" or 3/16" excepting the things like the gussets on the drivebase which use 1/4".
This year we used a lot more bolts because of a want to make assemblies removable, odd loading conditions that are bad for rivets, and ascetics in some places. In any situation where you're using bolts, do a weight calculation of locknuts versus 1/4" plate; surprisingly we often find that a 1/4" tapped plate is actually lighter than nuts, and that's without any sort of lightening.
Locktite is nice, but lockwashers can get the job done just fine. Our elevator back support was held on by bolts through 1x1 to 1/4" tapped plates and it never came loose due to lockwashers.
Buttonhead screws going into tapped plates also looks very good, due to the lack of a cylinder-like head and nut. I also like the increased holding area. However, for sizes 8-32 and smaller, I like to use socket head screws because the tiny size socket of button heads make it easy to strip out a screw if it's repeatedly removed and replaced.

[Ed Law]

Originally Posted by Joseph Smith

I've been investigating some new design and construction methods that my team hasn't explored in the past, and I really want to try assembling the frame and important structures with machined gussets and bolts. I have a few questions for teams who have used this construction method. In this scenario, I'd be using two gussets, top and bottom, to create a 90 degree joint between two lengths of rectangular aluminum tubing, all 1/8" wall thickness.
1. Is it better to put a long bolt all the way through and use a nut on the other side, or to tap the gusset and tubing and use shorter bolts?
2. If a bolt all the way through is used, are large washers needed to spread the load to prevent the tube from being crushed?
3. If the parts are tapped and a short bolt is used, would it be preferable to tap both the gusset and the tubing or to drill clearance on the gusset and only tap the tubing?
4. Is locktite a necessity with the tapping method?
5. What has been your overall experience with this method of construction? Pros/Cons?
Thanks!

I should clarify, with the pretapped method, we would be using machine screws or something of the sort.

Rivets are the way to go. There are different choices of rivets that will give you different strengths.
Bolts are heavy and time consuming to take out during quick repair in the pit. If it is a critical joint with a very high load, use bolts. I would get it all the way through and put a spacer in between if you have access. A washer will help reduce the chance of collapsing the section but if a student wants to use a drill to tighten a bolt and not paying attention, you can still collapse it. We always use lock nuts so no locktite is needed.
To save weight, I would use 1/16" high strength aluminum alloy for the two gussets.
We usually use rivets everywhere and more rivets in area with anticipated higher loads. If any rivets failed during matches, we just replace them. If it is in an area we do not want it to fail again, we would replace with bolt and nut. If you don't have access to use nut, then use self drilling screws for repair. They work really well.

[Bennett548]

If you are sure you won't be taking it apart, look into structural adhesives. The area between a gusset plate and tube is pretty big and thin, so an epoxy or CA glue can add a lot of strength. We love Black Max (Loctite 380) because it doesn't get brittle so it can survive impacts and shock loads. Be prepared, it is extremely messy.

I would suggest self-drilling, self tapping screws to hold everything together while the glue or epoxy cures, and to add a little strength.

[D.Allred]

Originally Posted by Joseph Smith

I've been investigating some new design and construction methods that my team hasn't explored in the past, and I really want to try assembling the frame and important structures with machined gussets and bolts. I have a few questions for teams who have used this construction method. In this scenario, I'd be using two gussets, top and bottom, to create a 90 degree joint between two lengths of rectangular aluminum tubing, all 1/8" wall thickness.
1. Is it better to put a long bolt all the way through and use a nut on the other side, or to tap the gusset and tubing and use shorter bolts?
2. If a bolt all the way through is used, are large washers needed to spread the load to prevent the tube from being crushed?
3. If the parts are tapped and a short bolt is used, would it be preferable to tap both the gusset and the tubing or to drill clearance on the gusset and only tap the tubing?
4. Is locktite a necessity with the tapping method?
5. What has been your overall experience with this method of construction? Pros/Cons?
Thanks!

I should clarify, with the pretapped method, we would be using machine screws or something of the sort.

Clarification #2: We have used a lot of rivets in the past, and do like them for certain applications; however, I'm specifically interested in trying out bolts on the critical parts of the frame- primarily drivetrain- where it can see a lot of stress due to collisions or hard driving. These would be parts that we shouldn't ever have to disassemble or replace between matches (fingers crossed) so I'm not really concerned about the speed of installing/removing them.

We've used this construction method for the past two years on our west coast drive base and on some superstructures. Here's specific answers to your questions.
1. Mostly tapped the 1/8" tubing and used short screws. Our build standard is based on M6 socket button head screws.
2. We use bolt through or rivet nuts for mounting the superstructure to the base. We typically spread the load with washers for heavy structures like our tower this year.
3. We used tight clearance holes on the gussets and only threaded the tubing.
4. Loctite is necessary.
5. Pros / Cons: This method is slightly heavier. Not much of an issue for the drive base, but superstructures with 1/8" tubing can add up even with pocketing. We used this method because we had the tooling not necessarily for reliability. But it does hold up to competition abuse.

One disclaimer - We are buying the tooling for 3/16" rivets next year. Just never got around to before.

Let me know if you have any other questions.

David