Standard vs. Custom Frame

Technical Technical Discussion
1

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

2

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.

3

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

4

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.

5

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

6

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.

7

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.

8

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. :wink:

9

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.

10

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 :wink: If you want to do something different, don’t try and transform the kit-frame into something it isn’t.

11

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?

12

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.

13

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.

14

I’m writing this from the perspective of a (tor)mentor of two different teams over the ages, both Kitbot users and one-event teams. If your situation is different, your conclusions may well be different.

The teams I’ve worked with only have one shot at the game–there’s no second regional, Championship, or off-season event. Now, you can argue (and I’ll agree with you fully) that the season was a success if the kids were inspired and/or learned something, but it still doesn’t feel good to go to lunch on Saturday not seeing your team number in the bracket. It didn’t feel good as a student, it still doesn’t feel good today.

Since we only have this one chance, I’m hesitant to bring onto the field a crucial part of the robot that hasn’t been tested or proven–if it doesn’t work, there’s little chance of fixing it. Other factors tend to limit our own off-season prototyping, so I’m forced to rely on the experiences and thoughts of other folks who have done so. To me, the kit frame has been proven in competition as much as any robot part to date–hundreds, if not thousands, of robots have used it over the past two seasons, and I have yet to see one become so damaged on the field that it couldn’t finish a match.

There’s also the factor that the frame is, for all intents and purposes, a freebie. Like many one-event teams, the budget is pretty small. I could use this amount of money on parts for a ball pickup mechanism or towards a pair of AndyMark shifters, or I could use it on frame materials. To me, that’s a no-brainer–I’ll use the kit frame.

Now, there may well be a situation where I wouldn’t use the kit frame. I know for a fact that it’s rather hard (but not impossible) to do a kiwi drive with the kit frame, plus a few more items. Standard four-wheel omni drive would be rather cumbersome with it, and there are other configurations (6WD with the center wheel driven off the gearbox comes to mind) where the frame is more impractical. But until there’s a game where the benefits of rolling our own frame outweigh the costs (both real and opportunity), you’ll probably see me advocating the kit frame.

15

We will be doing both this year.

Our veteran team will, as always, have a custom al. tube frame. We have been trying out a 3/4" square (1/8 wall) frame this fall and believe it will work for competition. We have used 1" square for the past 5 years and have never had a problem. We have a couple robot awards over that time also.

Our rookie team will be using the kit frame & welding the joints after we are happy with the design. This should help them with the flexability in design they need and still get some experience welding. Kiss. The rookies think that if they keep it simple they should be weeks ahead of the vets. More time for programming, more time for practice & problem solving.

As far as the number of competitions the robots will go to, the Vets will go to FLR & Championship & the rookies get FLR & may go to Championship if they qualify through winning the regional. Both will attend the ruckus in the fall but we get lots of tim to modify & fix before then. We probably will build a new machine just for that competition.

16

I anticipate using the kit frame next year with our young team, but we’ll see. We are engineering resource limited (although we have a “Tytus” which makes up for it) so we’ll use every available asset we can.

Here’s another process that I have applied to components in general - treat the kit chassis as the prototype chassis, and test out your prototype mechanisms on it. As resources become available to design & fabricate the actual “production” components (including the chassis), replace the prototype component with the production component. If any production component doesn’t get completed, you have the prototype to compete with.

17

In 2005 (that time I was mentoring team 134) team 134 decided to use the kitbot frame, rather than replicating our 2004 chassis (which was sweet).

What did we gain?

  • A fully drivable base within the first week, to evaluate and for testing.
  • A solid base for the rest of our super structure.
  • Cheap Cheap Cheap.

Now albeit the results for the year were not spectacular, the robot base and frame did what it needed to, with no problems. And after the 05’ season, we compared the results from 04’ to 05’ and we had came to the conclusion that neither one was any superior than the other.

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.

As far as I know, a robot chassis is not judged on “sex appeal”, and I’m sure the kitbot frame is comparable in weight to your frame. Please elaborate on why its not possible or practical to do “things” with a kitbot frame? You seem to always know everything, and I’d like to be enlightend.

18

I’ve got no ideaw what Dave thinks the kitbot’s shortcomings are, but here are mine-

No easy/good way to directly output to the center wheel in a 6wd format

No way to tension chains by sliding the wheels

No easy way to use live axles

No easy/good way to run your wheels outboard of the frame.

That list isn’t meant to be a complaint. The kitbot is great for a number of teams, and anything that keeps teams from showing up to a regional with a robot that doesn’t drive is great in my book. It’s just not very optimal when you move on to more advanced designs.

19

i would go custom, in the end it ends up being easer because you can diesgn it to fit the robot and not the other way around. and who needs CAD, i do everything to a 1cm for complex to 10cm for big simple components on graph paper, and the best part…you still have the design at 3:00 am ship day when the power goes out. another helpfull thing is full-scale cardboard mockup, you can never go wrong with cardboard and duct tape.

20

I’ll concede all the points except live axles–I remember 1293 switching Ockham (which was originally kit frame and dead axles) to a live-axle setup in a leisurely-paced Saturday during the off-season. They used the bearings and blocks (and wheels, for that matter) from 2004.