Standard vs. Custom Frame

I was refering to not being able to just bore the frame out for a bearing. You could mount your own pillowblocks for sure.

For several years, we’ve used a “custom” frame made from 1" x 1" x 1/8" square aluminum tube. We just cut, drill and bolt it together with quality bolts and nylock nuts or nuts and lockwashers. Nothing special, but it has never failed us. We’ve learned to do this because we have a low budget and nearly zero access to machining and welding facilities. Besides, it is really inexpensive and durable.

http://joemenassa.com/Images/ROBOTICS2006/day18/pages/IMG_3865.html

That is 121’s chassis, I believe it was live axel, it was definitely 6 wheel drive, and they tensioned the chain with out using sliding wheels. This drive system proved to work out very well for them with regional wins both years that they used the kit frame. 121 certainly used it for more than just showing up with a driving robot. I would say that their designs were certainly effective. The kit bot doesn’t seem to limit what you can do.

We have used the kitbot frame with different wheels for the past 2 years.

Besides, it is really inexpensive and durable.
That is mainly why we have used it.
In 2006 we won our regional, and had a good bot (i think). However were not able to collect balls as well as some teams with a different frame.
The kit bot doesn’t seem to limit what you can do.
It can limit your robot’s ability and quality, but it doesn’t require any designing, is easy to build and is is strong.
Although a custom frame is more versatile it can be hard to design and more complicated to build.

I never said you couldn’t make a good robot using the kit frame. Just that it’s my personal opinion that I wouldn’t if I had the resources to do otherwise.

Looks like there are sprockets attached to the wheels to me. Dead axle drive.

Hmm… seems like they tensioned the chain by pushing in the slack in the middle of the chain run. It looks tight in this picture, but remember this is a picture from the build season. In my experience FIRST robots get about a link and half of chain stretch over an event. Having an adjustable, simple tensioner may (or may not) prove to be worthwhile.

I am almost positive it is live axle, I know I talked to Rob from 121 about it, if you look at pictures of the robot from the year before you can see the drive system better, the design is almost Identical, other than the addition of more clearance this year.

They used bushings.

If you want to use bearings (which most people do), you can’t do it without mounting pillowblocks on the top of the frame.

Touche

This thread has started to drift a little, but I will pull it back towards the original focus.

The kitbot frame is one of the best things FIRST has done to help rookie teams. Teams that don’t have access to machine shops or lack the engineering support to design their own frames can use the kitbot frame easily. It is robust, comes with a fairly good drive train already, and is already designed and fabricated. There may be a weight/customizability/quality trade off, but if you have the choice between having your not-so-hot self-made frame breaking and you being dead for the rest of the competition and using a less-than-perfect kitbot frame, I think the decision is easy.

i was just dyeing to say this…NYLOCK IS GOD!!!

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!

Personally, even if it would be a resource stretch, I would rather my team go with a custom frame. Here’s my reasoning.

Engineering experience: For a real world experience, you aren’t going to be given a base chassis, drive system. You need to be able to design one. Adapting an old one is good, but it doesn’t come up very often.

Plus, designing and building your own fram gives you a very real sense of the design phase. If you mis-measure, you pay the price by having a component not fit. By having heavier consequences for design failures, you learn to take more time on the design.

[/soapbox]

edit: also, as far as strength… custom is far superior. Just by hitting another bot at full speed from 5 deet away, we bent in their straight frame, and sent a gearbox flying. It made us feel very bad, and so we helped them fix it.

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.

In my 25 years of engineering design experience (in 3 totally different fields), I’ve had HUNDREDS of times where I was required to design components to adapt to an existing platform. In fact, it’s more likely that you will be required to modify an existing system or component, or add something to an existing system or component, and the desire is to change as little as possible on the existing system. Clean sheet designs are few and far between in the engineering world when compared to modifications.

What this means is that you need to evaluate the performance of the existing frame for its task. If you think it’s going to bend locally, beef it up! Custom isn’t stronger because it’s custom, but because you put the stiffening in the right places. There’s not much wasted weight in the kitbot chassis, so put an extra gusset or brace here and there - you probably need attachment points anyway. The great thing about the perforated angle and sheet is that you can assemble it, test it, modify it, all in the same night.

Umm, okay.

We have to be careful about making all encompassing statements on these forums. It’s one thing to say “My team chooses to use a custom a chassis, because we have enough resources to build something better than the kit chassis”. It’s another thing to say “custom is far superior”. Yes there are custom frames that are better than the kit frame. By no means it the kit frame the ultimate solution. But, to imply that all custom frames are better than the kit frame is ludicrous and insulting. I’ve seen many teams design custom frames in lieu of the kit frame, and fail miserably because of it.

The decision on whether to use the kit frame or not depends on a variety of factors. If your team feels that you’re losing part of the FIRST experience by going kit, that’s a personal decision. When it comes to a sheer engineering decision, here’s the guideline I offer to teams.

Step back and honestly evaluate your team’s resources. Do this in terms of finances, experience, manpower & talent. This will help you answer the following questions.

  1. Consider the custom frame you’re considering building. Does it provide a large advantage over the kit frame? Consider strength, rigidity, ease of mechanism integration, and ease of repair.

  2. With this frame, can you have your drivetrain completed in 2 weeks?

  3. Will building this frame still leave you with enough resources to work on and complete the rest of the robot at a high quality? (Will you still be able to build as good of a mechanism as you want?)

If the answer to these three questions is Yes, then it sounds like you’re ready to go custom. Otherwise, stick with the kit frame. The easiest way to make your robot perform better at competition is to have a well practiced driver. That means having the drivetrain done early. This is why I feel more teams should use the kit frame. The kit frame allows you to get your drivers practicing before week 2 even finishes! This is such a huge advantage. Time is such a valuable resource, it can’t be wasted. Plus, by using the kit frame, you can allocate resources to your mechanism.

I’m frankly tired of a lot of the “kit bot snobbery” I hear from people in this program. I definitely agree that it’s not for everyone. There are some teams who can whip out a wicked, strong welded aluminum tube frame in a couple of days. If you don’t use it, this doesn’t mean you need to come out and say that it’s a horrible product, and that teams who use it are making a dumb decision. The kitbot is a great tool for all teams. For those low resource teams who need a kick start, and for those savvy teams who don’t want to re-invent the wheel and would rather spend their time practicing and building an awesome mechanism.

Based upon the original statement that resources are very limited, and assuming that you’ll want spend those resources designing mechanisms to play the game, I would strongly suggest the kit frame. Having used the kit frame this past year, it works very well and stood up to 3 events for us without issue.

I’d suggest spending your limited resources on the drive train design (that will run in the kit frame) and the remainder of your robot.

Good luck with whatever you choose to use!!

Karthik,
Thank you for your post. It’s what I tried to point out earlier but, you said it better. The kit base alone is not enough to survive a physical game the 2006 comp turned into. The kit frame is a beginning. How it’s added to and reinforced can be the difference between success and failure. In 2006 bumpers were introduced. Not all teams took advantage of them. If the bumpers are allowed again for 2007, I would encourage both kit and custom teams consider their use. The strength of the plywood bumper frame should not be ignored. In fact with the proper type of plywood the 2006 bumpers can be considered a structural element. Better yet a major structural element that is not part of the weight budget or size limitation. If the bumpers are back, this opens the possibility of incorporating the bumpers into the frame design and eliminating some material and weight with out sacrificing strength. I would try to avoid home center plywood. Grade B/BB 3/4" 15 ply Baltic Birch would be a good choice.

Ok here’s a perspective from a team that built many good and troublesome custom frames and have used the kitframe for the last two years. Before the kitframe was introduced for most teams the most complex and important aspect to their robot was the drive system. This was because on field success mainly stemmed from the strength of their drive systems (look at the 2002 and 2003 games). However the 2004 game brought a different direction in the games (in my opinion), going from a relitivly basic and one-dimensional game in 2003 to a very complex and multi-dimensional game in 2004. I believe that FIRST saw that innovative robots came from their success at manipulating the game objects and not how they drove around the field. This is not say that teams who built more complex drive systems (swerve for example) were not innovative, but a drive system is something you are going to need every year and inevitably many teams will be using the same design for their drive system.

FIRST introduced the kitframe in 2005 to try and stem innovation in how teams manipulated the game objects and increase the success of the rookie teams. As Karthik noted it also provided any team with a valuable resource, more time to build the important part of your robot the manipulation of the game piece. This is why my team, team 610, has used the kit frame for the past 2 seasons. The first year we used it we were able to build our first 6-wheel drive system in only 2 weeks. Last year we decided to use the same design, with the addition of an andymark 2-speed, and were able to finish it in just over a week. Giving us more time to work on the most important part of the robot, the manipulation of the game piece. This is why I am surprised more ‘veteran’ teams have not used it.

We have also used a tensioning system with the kit frame where we can slide the wheels to tighten the chain (which some people said cannot be done…). Basically every wheel is supported by 2 pillow blocks, pieces of 1.5" angle, with slots milled where they are bolted to the kitframe. Its the same system we have used for the last two seasons and has worked well for us, allowing us to slide the wheels back in fourth to our desire.

Team 228 is by no means a rookie team, as this upcoming FRC season will be our ninth. But for the 2007 game, we’ve begun to seriously consider using the Kitbot frame as the basis for our robot chassis. While evaluating its possible pros and cons, we’ve begun to seriously consider manufacturing custom CNC’d 1/8" sheet metal flanges, brackets, and more to fit/weld onto the Kitbot chassis to uberly-strengthen it. Rather than re-invent the wheel by designing an entirely custom-machined frame, a “CNC-modded” Kitbot chassis could be up and running faster and cheaper, while still having the same or a very similar end-result.

Plus, a chassis done in the first or second week of the build season has plenty of time to go off to be powder-coated, and still come back quick enough without interrupting the design and manufacturing of other robot components. :smiley: