Re: Welded Frame Horror Stories
 

#1 Rule: only have an experienced welder weld your robot frame.

Our robot is welded by a grad student who is on Northeastern's Mini-Baja team. He's been welding for years and is very proficient in welding aluminum because of aluminum tubing being used in their vehicles frame.

We were mentoring a rookie team and they had an inexperienced person weld their frame. It was disastrous and the frame broke apart before the build season was over. Our Mini-Baja guy cut all the old welds away and did it correctly. They never had another problem.

I would say if you don't know of anyone who is experienced on your team then you should call up local machine shops. Even if they won't do it for free the last thing you want to happen in competition is a broken weld.

Re: Welded Frame Horror Stories
 

We welded (or had it done, rather) our frame for the first time this year, and I was personally pleased, for it helped us cut down on weight (not too many steel bolts), but here's the thing- we built our robot for defense (remember our drivetrain? :D ), and we made the HUGE mistake of building our gearboxes into the frame as structural members (very bad idea, in my experience). In addition, we didn't use the ever-so-wonderful gussets to reinforce the corners, so after the first day we were doing some massive tweaking jobs just to get the frame square enough to keep our gearboxes from binding up.
As for fixing the welds that broke (all but five or six by the time season was over*), that was simple enough. When we first designed our frame, we had aluminum angle in all the corners and such, and it was welded with those on (we took them off after the weld job), and thankfully someone had the presence of mind to bring them along to the competitions, so when a weld broke, we told one of the newb's to find the right piece and fix it. No big deal, but sort of time consuming.
So I would make these suggestions:
-USE GUSSETS! they would have saved us literally hours of repairs
-make sure there aren't any "vital weakpoints" like our gearboxes
-have the materials and equipment to make quick repairs if you would have to, this saved us several times (all you really need are some flathead bolt, angle, and a drill and bits.)
I think a welded frame, when properly done, has a lot of advantages over a bolted one (like weight and bolts coming loose), so I'd go for it. I think we're going to stick with it, just making some adjustments
Good luck, y'all.

*this was not because of faulty welds, the guy that did them knew what he was doing and the welds were great, but we hadn't engineered our frame to take the kind of beating that it did. (remember our infamous defense? :yikes: )

Re: Welded Frame Horror Stories
 

Here's a welded frame done right. Here's a welded frame done light. The front 1x1x1/8" box tube in the second pic bowed in slightly after a lot of bashing but never caused any problems. Professionally TIGed, only one weld ever so slightly cracked ever.

Re: Welded Frame Horror Stories
 

one of the design criteria you should be using to evaluate different design approaches is servicability / repairability, or MTR (Mean Time to Repair)

simply put, if your frame is damaged, how easy will it be to repair? how long will it take on average?

dont paint yourself into a corner thinking there is no way your frame could be damaged. Bad things happen, crates get dropped off trucks and forklifts from 8 feet up, Robots fall off tables and carts, or down stairs. When something bad happens to good robots you will need to repair it, then the question is: will it take 8 people 4 hours, or 40 hours?

If the only approach to fixing a welded frame is to bring a complete spare frame, then thats what you must do. How long will it take you to transfer everything on your robot to the spare frame? Or it might be better to fasten the frame members together some other way. or maybe have welded subframes that bolt together?

Re: Welded Frame Horror Stories
 

Team 829 has done welded frames for three years. Here is this year’s frame. This frame was welded by our welding class. No breaks or bends and we were a very aggressive player this year. In the background you will see last years robot made from the KOP. We welded it too.

Re: Welded Frame Horror Stories
 

This is the one thing I'd like to try to avoid. We have the capability to build a second frame, and our design makes it extremely easy (comparably to most other drive setups) to swap an entire drive train, but I am still somewhat worried about a frame taking the kind of beating our team would give it. 393 might remember, and 177 definitely will- we aren't especially kind to our robot with defense. Basically, if we get a chance to shove, we will, regardless of the orientation of our robot, or the damage that might be inflicted upon it by pushing. (Basically, an 8-foot fall could be significantly kinder to the robot than a regional). As a result, stuff gets bent, out of whack, but it's nearly impossible to shear a properly bolted component- holes or bolts. If it gets too bad, you just drill a few new holes, grunt the pieces into place, and you're good to go- basically with a connection as strong as when you started.

If a weld breaks during one of our thrash/spin/flip maneuvers, it may be a far more dire situation than if we had used a bolted connection.

Questions:

1. I plan to use a large bolt in bushing that doesn't require mounting holes- the casing has threads to be clamped into a hole. the hole will be ~ .75" in diameter- can I cut that hole before welding?

2. I plan on using a plug (round tube) that welds into this hole in the frame so that I may clamp down on the sides of the channel without bending it in- can I weld two flush surfaces, sand off the weld, and still have a strong connection between the surfaces?

3. We will need a guard around the wheels to protect them, and I was considering a welded, 1/16" tube skirt, bolted onto the interior frame for ease of replacement. 1/16" frame people, will these skirts get beat up unbelievably badly? They can bend up some, but will they just end up as mangled robot appendages in need of amputation?

Thanks, I'm trying to compile all of your knowledge before we attempt to depart from our standard. I want to make sure this is really going to work, and is work the effort.

Re: Welded Frame Horror Stories
 

Just remember the spare part weight limit.... 20 pounds of custom-fabricated items may not be sufficient for a frame.

Re: Welded Frame Horror Stories
 

...but there is always sticking the spare in the crate, at which point you're only limited by how much you can fit in the crate. (Then again, knowing what they charge for crate overages, I'd almost rather deal with the broken weld. :rolleyes: )

Re: Welded Frame Horror Stories
 

Just remember.... welds difficult to repair and even when repaired not near as strong as the original....

I know welds work most the time and have their place but i guess i'm an old fashioned fastener type. :rolleyes:

-Q

Re: Welded Frame Horror Stories
 

That certainly works too, if you can disassemble the frame, or wedge it in somewhere. Or you can ship a second crate for spares*.

(Also, I'm now recalling that the rule was 25 pounds, not 20....)

*The 2006 rules say that you may enter one robot per team. But if the spare (meaning identical, for all intents and purposes) robot is a spare fabricated assembly, and is packed in "the crate" (presumably meaning "one of the crates", since teams are allowed to ship 2), are you really entering twice? I think not, since the robots cannot compete simultaneously. So you could do even better than just a spare frame, if you really wanted to annoy everyone.

Re: Welded Frame Horror Stories
 

Hmmm I think I hear phones ringing. Panic calls to the Rules committee to figure out how to close THAT loophole, which you could drive a truck through. Have you considered a career in Law Mr Lall?

Re: Welded Frame Horror Stories
 

So, you can't compete at the SAME event, but could you compete at a DIFFERENT event with the 2nd robot? I guess that would effectively be two seperate teams, with two separate robots, with two separate budgets, under just one school...

(Sorry, I'm not trying to hijack this thread... should we split it off into something different?)

BEN

Re: Welded Frame Horror Stories
 

this is an excellent example of a frame that could have been designed with 3 or 4 welded sub-frames, that are bolted together

then if one side got smashed in you only need to replace that subframe section, instead of needing to bend metal back into shape, or to weld on an alum frame (which conducts heat very well) at a regional.

Re: Welded Frame Horror Stories
 

is welding any better than bolting? we use extruded aluminum and we had a small problem with bending but if was easily fixable.

could someone tell me what is so much better or worse about the two

Re: Welded Frame Horror Stories
 

weight. You lose all the weight of the bolts by welding.

You also don't have to worry about bolts loosening themselves, and going around retightening everything