The Frame thread
 

So, every year, my team makes the same exact frame, just modified for the years game. It weighs too much, and doesn't do a particularly good job of anything. Since I will have a leadership position on the team next year, I've made it one of my major goals to change this. One of my friends came up with this quote:

"The frame should be build to hold the robot; the robot should not be built to put in the frame"

This leaves me with a dilemma: We need the frame done early (that has been one of our biggest shortcomings in years past, not getting the frame welded until the end of week 2). On the other hand, I agree with my friend, which means we can't begin designing the frame until the design is done at the end of week 1.

According to Inventor, the frame weighs a whooping 35 lbs, not counting the supershifters, or the treads. Add those in, and your at 50 or so.

The problem is, we have used the same frame/style of frame for so many years now, our team has pretty much forgotten how to do anything different. So, I thought to myself, this is FIRST, teams like to share information, right? And people like to show off their designs, right? People like to critique designs, right?

I would be very grateful if other teams could show me pictures, or CAD of how they do their frames/drive trains. In return, I will show you and tell you a bit about ours!

We build a lower frame out of 1x1 aluminium T-slot. Very strong, very durable. Very heavy. We sandwich treads between two pieces of those T-slots. The treads are made from fan belts turned inside out and driven with a sproket from the supershifters (last year we used toughboxes). We build an upper frame out of 1/16 aluminum to support various mechanisms. The whole assembly is welded together, and we use T-slot sliders to put many things into the system.


Thanks in advance for other teams' help!

Re: The Frame thread
 

When I look at a FIRST challenge with whatever team I am involved with, I like to have my options open, which is why I am a big fan of a super simple drive type that can be built off of. The T-slots and the extra attachment points seem to make the design you built very modular though, which I like.

Let me get to the point, T-slot is heavy. Switching to a gusseted or welded tube frame will get you to a happy place. If you have sheetmetal options, you can go with that. I also became a fan of the kit frame working with 2702, we built a very solid, and reasonably light drive with it alone (much lighter than what you have quoted). I am sure you can find plenty of pics of the structural tubing design, whether it is a WCD Derivative or something else, they all seem to work pretty well.

I shall provide my take on the tubing frame as well, I have posted this before, but I challenged myself to make a warp resistant (keep welds away from the drive components) gusseted frame that was relatively light. Heavy 254 influence below. This has never been built, but it sums up a lot of peoples ideas.



Probably the big thing I tried to improve with this frame was robot torsional stiffness. By that I mean the frames ability to keep the two drive component rails parallel. The stringers between the drive component rails really help if you don't put a top box on the frame like you have on your design. That is the advantage you have at the expense of weight, nice torsional stiffness.

Look into Team 221 LLC's bearing block tensioning system as well as 254's. They are both good ways of going about things if you choose to go live axel.

Re: The Frame thread
 

Week 2 is reasonable in terms of timeline for welding. Seriously, that's not an issue.

50 lbs of frame might be a bit much, even including drivetrain.

330's traditional frame is welded 1/8" wall aluminum tubing, typically something like a 1"x1.5" or 1"x2" (though we have been known to use 1"x1" with drivetrain stuff mounted on blocks). Sorry, I don't know how much it weighs offhand, but at a guess around 10-20# depending on the year. Quite a lot of teams do something similar; others use the KOP frame for its adaptability and strength.

You could also try modding the West Coast Drive for tank treads. THAT would be interesting--and not all that difficult, I don't think.

Re: The Frame thread
 

The one thing that pops out to me is all the 80-20 in there. Dropping that 80-20 to 1/8" wall aluminum alone would almost definitely shave quite a bit off your weight. We've always used 1" C with corner brackets for our chassis.

Re: The Frame thread
 

Here are three diffrent chassis i've made over the year ... 1st one is our new chassis that we will most likely make. 2nd is the type of chassis that we use to use, and probably wont again for a while. and the last one is the same type that 1114 used this year (minus demesions and some fixing up on it).

Re: The Frame thread
 

Having a moving robot for the first time in week 3 is very good. We haven't had one moving in the last two years until sometime at the beggining of week 4. Your current timeline seems fine to me. Except: Your frame may a bit too complex if it takes a week to cut and weld parts. Spending a few days to achieve a simpler solution can save you days in the future.

For this next part, don't think I am saying any of this is wrong, but they are questions you need to answer:
1. Why shift?
2. Why treads?
3. Why T-slot?
4. Why multiple heights of tubing structure?
5. Live vs Dead axle

These are all questions you have to answer for your team. There is no universal best option. The best way to design and build a drivetrain is the way that works for your team.

Re: The Frame thread
 

8020 is incredibly heavy. Even 1/8" thick 1x1 aluminum tubing. For over 5 years, our team has used 1/16" thick, and we've only broken one segment (unguarded, whole section was pushed inward about 3 inches).

If you use 1/16" you can use these Brunner Connectors. They are light and excellent. Just attach a small aluminum gusset with sheetmetal screws to the tubes and you're done.

Re: The Frame thread
 

I'm curious what exact belts and pulleys you're using. Looks like it would be for a large supercharger.

Re: The Frame thread
 

Also, if you want, I can send the cad files for a very simple drivetrain and chassis that we put together.

Here is a photo:

Re: The Frame thread
 

The simplest, most reliable, easiest to fix and cheapest to build drivetrain we ever built was also our best performer.

It took seven years to get to this point... we used composites, the kitbot (which was pretty good actually), TIG welded aluminum tubing (which was better)...

And my favorite was this one, seen here airborne and with its twin.

Jason

Re: The Frame thread
 

I've always wanted to do this. It goes really well with our Frog Green project, but we just haven't had the time or resources to build something like this during the offseason.

Re: The Frame thread
 

http://www.simbotics.org/media/videos/presentations

If nothing else, you can build a super easy drivetrain like the one above, that is also "better than 90-95% of teams". Certainly better than the tank drive and very simple.

Re: The Frame thread
 

why is one of the transmissions rotated 90 degrees, would it be in the way of something or is it just something you haven't noticed yet ?

Re: The Frame thread
 

Kit Chassis and transmissions.

We usually play around with wheel configuration and drive ratios, but our record with the kit chassis speaks for itself.

2 Quality Awards
5 Finalist Awards
4 Championships
1 Trip to Einstein

Re: The Frame thread
 

If it is the same type of tranny as the AM supershifters then by rotating one 90 degrees puts the output shafts at the same level.