Standard vs. Custom Frame

[brennerator]

We are trying to decide whether we should use the standard stock frame that comes with the kit of parts or build our own custom frame. Since we don't really have any adults helping us with CAD-ing, our concern is that we would make technical mistakes while designing the frame (this happened to us last year). Can anybody weigh in on the advantages and disadvantages of using a custom built frame instead of the stock frame? Also, could anybody give us a link with drawings of frames that teams built last year?

Thanks,

Daniel, Team 1560

[sanddrag]

For me it's not even a question. We have been doing 1/8" wall thickness welded aluminum box tubing frames for the past three years. Why? Because it is stronger, lighter, and more elegant, and will not fall apart over time like a bolted together frame. We do things with custom frames that are not possible or practical with the kit frame.

[Kyle Love]

Main advantage, less weight, more adaptability and more customizing.

[Pavan Dave]

Custom Frame hands down. It is much lighter and it is much more easier to change. Also if you need to add support to it later it is more simple because all you have to do is add some trusses and make a few other changes and you are "made in the shade."

Pavan

[Arefin Bari]

To answer your question Daniel, it really depends on what the team wants and what they are looking for as well as how much resources does that specific team has.

Now let's look at a veteran team who has members who have been through this design process a few times, engineers to correct their mistakes, resources to make what they want. Ofcourse they will want to go with a custom frame where they have the flexibility to work with what they want. After given the game, they will design chassis such ways to satisfy their needs.

Let's look at a rookie team, or a 1st or 2nd year team. They have dedicated members, engineers who are there to help. But they haven't been exposed to FIRST or they haven't been to as many competitions as a veteran team has. What I am trying to get to here is experience. Due to less resources, teams may want to go with the kit of part chassis.

In both ways, there are pros and cons. You ask how? If you use a custom frame, it will take time to design it, machine it, put it all together (like Cody pointed out in his post). On the other hand, if you decide to use the kit of part chassis, it will only take you the first week of build season to put it all together. That's just one example.

There have been many teams that have been successful with the kit of part chassis. For example, Team 121 and Team 1625. The reason I used those two teams as an example is because one of them is a veteral team and the other is a 2nd year team.

My team (team 1345) is a 4th year team. In the first two years, they have used extrusion and aluminum tubing to make their frame. Last year, they used the kit of part chassis. This coming year, we will be using a custom frame, we will see how it turns out.

Bottom line is, if you have the resources to make a custom frame, then why not? But if you don't have the resources, don't take the risk.

[Donut]

I think a custom frame would be preferable if it is possible; but if you don't have the resources to pull it off effectively, and want to save yourself some time, the kit frame is definitely a good option. So many pre-drilled holes give you lots of nice places to bolt stuff onto (not that you need pre-drilled holes, as I assume your team owns a drill, but they're nice), and the frame is extremely adaptable, being able to fit most designs you can think of (cut a few frame pieces and you can make almost anything fit).

The only thing to worry about with the kit frame is strength and possibly weight; not strength from taking a hit and coming apart, but more from a mechanism or large amount of weight causing the C channels to start to collapse. We had to wedge a piece of extruded aluminum into the frame to keep it from folding in underneath our motor mount for our conveyor belt. Weight I suppose could be an issue, though we haven't had it be a problem yet.

[Gabe]

Originally Posted by Donut

The only thing to worry about with the kit frame is strength and possibly weight; not strength from taking a hit and coming apart, but more from a mechanism or large amount of weight causing the C channels to start to collapse... Weight I suppose could be an issue, though we haven't had it be a problem yet.

You can always cut a piece of wood board to fit perfectly into the c-channel pocket. This would prevent it from collapsing as well as being light in weight and cheap. (Plus wood is all-around easier to work with.)

My vote is with the kit chassis, because it's light weight, strong, free (-6K), and easy to find replacement parts at a regional simply by asking other friendly teams. Just remember to replace the nuts that come with the kit for real nylon insert locknuts or else you will end up missing some screws here and there.

[EricH]

We use custom and always have. (There wasn't a Kitbot frame back in 1997 or so.) However, just because another team uses a custom frame doesn't mean you should. Some things to consider:

• What attachments will you be adding and how? Will you need special modifications (such as a raised end to help slurp up balls last year)?
• What do you have readily available? If you want to do an easy custom frame, are parts easy to come by? Can you get the frame welded? (very important for many teams)
• What drivetrain are you looking at? A basic 4 wheel, 6-wheel, or mecanum drive could be used with a kit frame, but for swerve or holonomic (non-mecanum), it would be much harder, and I'm not sure about tank treads.

The other thing is that nothing is stopping you from using a combination frame. What I mean is that you could use the kit frame as a base, then secure the rest to the top. You could even weld the kit frame together, thereby avoiding having "robot droppings" as nuts and bolts work loose.

For 330's base the last two years, we have used 1"x2"?(not totally sure)x1/8" box tubing, arranged something like this:

--------------------------
I I I
--------------------------
I I
I I
--------------------------
I I I
--------------------------

edit:the I's should be in the middle of the center, spread out, and at the ends and middle of the outside--Firefox spell check doesn't like all the spaces though./edit
We also have something across the ends of the center.

[=Martin=Taylor=]

Aside from the wheels, I have a lot of respect for the kit-frame. It is strong, relatively light, and easy to build.

The downside is quite simple. Everyone uses it.

If you want to get an advantage over other kitbots you are going to have to modify it.

This is what my team did last year and it was a huge mistake. We tried to use 25 chain, smaller wheels, custom transmissions, and a modified front-end for collecting balls. Mounting these parts on a frame that was not designed for them proved to be a disaster. In order to climb the ramp we had to implement a diabolical series of chain tensioners, as a result our chains repeatedly came off. The modifications also weakened the structure and it slowly bent over time.

As the name implies, the kit-bot is a kit and I would recommend following the instructions If you want to do something different, don't try and transform the kit-frame into something it isn't.

[Tom Bottiglieri]

Here are some things you may find useful if you decide to pursue building your own frame.

http://www.chiefdelphi.com/media/papers/1705 - Nice paper on different types of drive train setups
http://www.chiefdelphi.com/media/papers/1682 - Copioli and Patton. Cant go wrong.
http://www.chiefdelphi.com/media/papers/1522 - CAD Help
http://www.chiefdelphi.com/media/papers/1443 - Drive train basics

Keep in mind building a reliable and effective chassis is more than just welding some aluminum tubing together and slapping some motors on. Your chassis is a system that relies on each and every part put into it, and the physics behind them. The kit frame is a well engineered solution, but there are some inherent set backs you will see by using it. Its up to you as a team to decide what is important to you and whats not. Your first custom designed chassis may not be the best thing out there, but you'll learn something by going through the paces.

As the 2007 season is fast approaching, I would not recommend going belly up into a new drive train design. Either stick with the kit frame for another year, or find a team in your area (or online) who will be willing to mentor you through this stage of moving from an inexperienced rookie team to an intermediate team who can come up with their own innovations.

PS - Theres a lot of white papers for different gearboxes and code ideas, but not a lot for fr ames? Whats up with that?

[clean399]

We usually go custom frame except for two years age on the triple play game we added webs in on the kit frame made it much stronger but only experienced welders should weld aluminum because it is hard we learned that the hard way. Every since then we build custom and rivet much lighter and stronger than welds.

[Gdeaver]

We have used the Kit frame with good results. WE start with the kit frame and build it up with 1" 6061 aluminum angle assembled with Steel pop rivets with back up washers. Our robot played defense this year and took some serious hits. Frame has some dings but is fine. The key is the box we build off the frame has allot of reinforcement. We try to make ever piece off metal added to the frame also structural. The electronics board can be an excellent structural element.The KOP frame and drive train was meant to ensure low resource teams do not fail and can be competitive. Look at the resources your team has and make the Kop or custom choice. Our team has about 600$ to build the robot and basic hand tools. Of course we are going to use the KOP stuff. We are very resource constrained. The only resources in abundance are enthusiasm and brain power.

[Cody Carey]

On the other hand, Using the kitbot frame could save you two weeks of design/build time. You can do alot to a manipulator/shooter in two weeks. The weight difference to our teams extruded frame was negligable, and the strength of the kitbot is anything that you would need for FIRST competition. We have used the kitbot frame for two years now and have been strong competitors for both of those. There is something to be said about having a driveable base a week after kickoff.
The one thing I would suggest improving though, is the et of wheels that comes with the kit. While they'll get you where you're going, they are by no means the grippiest wheels out there. There are numerous things you can do to increase their traction, but there are also quite a few alternatives.
Colson Wheels are one of them, but there are a number out there.
If you are worrying about CADing a frame, then look to Extruded Aluminum.
Welded frames are fine and dandy if you have an experienced welder at your disposal, but if you don't exactly know how, they can result in a lot of wasted material and a mediocre end result.

[Viper37]

Originally Posted by Cody C

The weight difference to our teams extruded frame was negligable, and the strength of the kitbot is anything that you would need for FIRST competition.

You must not get very far then.

2 years running we have used the kitbot frame. 2 years running the front and rear are badly smashed in.


Time to get our brand new TIG/CNC Aluminum frame from HP's machine shop!

[Donut]

Originally Posted by Viper37

You must not get very far then.

2 years running we have used the kitbot frame. 2 years running the front and rear are badly smashed in.


Time to get our brand new TIG/CNC Aluminum frame from HP's machine shop!

2 years we've used the kit frame, and 2 years we've made the semi-finals at the Arizona Regional (one we won Industrial Design award as well).

Is it just the different strategies teams pursue that cause such a wide range of results with the kit frame? Some teams are reporting complete failures with them where they come apart frequently and make for a poor robot, while others report perfect durability and being extremely competitive. Is it the attachements, the driving strategy, or what?

If teams are looking for a good adjustable chain tensioner for the kit bot frame I'll try to get ours up, I looked but we don't have any good pictures of them off hand. It uses an idler sprocket that can be adjusted with a wrench.

There is a certain satisfaction in doing a custom frame I believe; I know our team would certainly like to try it. But when you absolutely don't have the possibility of doing it, the kit frame is certainly not a "well we're going to be mediocre at best" choice, and if done right there are probably times you'd still want to try it over the custom frame. If nothing else everyone has a nice practice/demo bot chassis to use.