Sheet Metal vs KitBot
 

I just watched:

http://www.simbotics.org/media/video...itbot-steroids

They seem to be really advocating the KitBot in this video, yet 1114 themselves and most of the advanced teams build a sheet metal chassis. Which is better?

Re: Sheet Metal vs KitBot
 

Do you have a sheetmetal shop and designers with sheetmetal experience?

Yes? Build sheet metal.

No? Build Kitbot.

Re: Sheet Metal vs KitBot
 

It's not about which is better, it's about which is better for your team. For a lot of FIRST teams, they have the resources (financial, material and experience) to build custom drivetrains that can be very lightweight, yet maintaining robustness and effectiveness. However, most FIRST teams don't have these resources. As such the kitbot can be a great solution for them.

The "kitbot on steroids" as we've coined it, is a simple drivetrain that be put together in a couple of days using just the KOP and a few additional COTS parts. When constructed properly, it's extremely robust and reliable, and far more effective than the average FIRST drivetrain. (At least based on what we've seen over the years.) The time and resources saved by building this drivetrain allow teams to focus on practicing, programming and of course the designing and building of other manipulators. For years it's frustrated our team to see so many teams with so much potential who end up with underperforming custom drivetrains, that could have been easily avoided. That's why we made this video and have been promoting it heavily. Look for us to publish improved documentation to go with it this fall.

Re: Sheet Metal vs KitBot
 

One sentence and Karthik sums up about 75% of the "which is better" threads on CD. Talk about hitting the nail on the head!

Jason

Re: Sheet Metal vs KitBot
 

I just want to open your eyes to what can be done with the kit bot.
the chassis in the picture is my team's (3339) chassis which is built from the C channel. We drilled holes to the outer wheels shafts in the c channel.
This chassis worked very good without any problem!

Re: Sheet Metal vs KitBot
 

Very cool! I really like this re-arrangement of the kit frame. Thanks for sharing.

Re: Sheet Metal vs KitBot
 

you can do what ever you want with the kit bot, you just need to think out of the box

Re: Sheet Metal vs KitBot
 

Here is the Robowranger 2011 "custom sheetmetal" chassis:


It probably looks familiar.

Custom sheetmetal? Yes.
Reinventing the wheel? No.

2005 Kitbot FTW!

Re: Sheet Metal vs KitBot
 

It looks like you were set up to run 6wd as well. Was that a contingency plan if the nonadrive didn't pan out or you were too close on weight?

Re: Sheet Metal vs KitBot
 

I threw the tabs on for versatility reasons. We figured for the weight of 4 tabs we would now have the ability to switch to a 6WD if the game needed it.

We're very happy with our "Butterfly Drive" setup. We'd be happy to run this configuration again!

-John

Re: Sheet Metal vs KitBot
 

That's what I figured. It's a really clean frame layout and your nona/butterfly/whatever-crazy-drive-next-year certainly inspired a ton of teams this season.

Re: Sheet Metal vs KitBot
 

How about this?

http://www.andymark.com/product-p/am-0484.htm

Re: Sheet Metal vs KitBot
 

Our team, 3467, used this chassis this year and it worked really well! The only downside is this pre-assembled chassis comes with wedgetop, not roughtop tread which wore down us easily this year. If you talk to AM they should be able to give you roughtop plactions over wedgetop.

Just keep in mind when making the decision to go with supershifters over CIMple boxes the weight vs. having a lower gear. Also, if you use the supershifters be careful and fully aware of what you are doing during assembly. Somehow ours had an extra washer in one that would compress the tranny, overheat the cims, and cause them to shut down for a few seconds. At the beginning of the season/regional our driver was losing one side of the drive for a split second in a few matches over the weekend and we didn't thing much of it. In St. Louis the problem grew astronomically to happening every few seconds and lasting a while. We diagnosed everything electrical and mechanical and even had an AM rep look over the supershifter guts. When nothing worked we carefully examined the guts and realized there was an extra washer. Problem solved.

Lesson learned: even the smallest parts can cause a world of pain. Check, check, check, check, check.

Re: Sheet Metal vs KitBot
 

Thanks for pointing this out. As a FIRST newbie, I was extremely impressed by the quality and versatility of the kit chassis and drive train. It is a beautiful piece of engineering.

Team 3504 did something similar to "kit chassis on steroids" this year, but we had complications with chain tensioning system. In the video, it looks like the chain lengths just worked out without the need for extra tensioning, but that is not how it worked out for us. Is there a certain sprocket size you need to use? Is there some other trick we missed?

Thanks,
-George

Re: Sheet Metal vs KitBot
 

I'm not sure how 1114 routed the chains in the video, but we've dead spaced axles for the last 3 years (once using the kit frame) and haven't needed a tensioner. When using #35 Chain, if your axles and transmission are spaced using factors of 3/8" (3/8" is the pitch for #35 Chain) then you'll always end up using an even number of chain lengths.

I have found that especially with longer lengths of chain the stretch becomes a big issue. A chain run that seemed perfectly tensioned may be really loose after you drive the robot hard for a few minutes. We have tried pre-stretching our chains and it helps but we still threw on some tensioner this year.

~DK

Re: Sheet Metal vs KitBot
 

Two things that you can do to help alleviate (but never entirely eliminate) stretch:

1. Use #35 chain. Stretches much, much more slowly than #25.

2. Use high quality chain. You get what you pay for - we have found that different manufacturers' chain tends to stretch at very different rates.

Re: Sheet Metal vs KitBot
 

Keep in mind, of course, that this advice holds true only if everything is collinear.

Re: Sheet Metal vs KitBot
 

I will rephrase the question: When done properly, what advantage does a sheet metal chassis have?

Re: Sheet Metal vs KitBot
 

Thanks for the advice. We used #25 this year mainly because we figured we could make our lengths more precise because each link is smaller, we also used half links which we had back luck with and ended up scrapping. I will look into where we buy our chain from. Do you have any recommendations as far as good chain suppliers?

To add a bit to this topic we have always (in my years on the team) used the kit-bot chassis with some modifications (some minor some major). We have done 6 wheel rocker, mecanum and 8 wheel rocker and even Ackerman drive with the kit-bot chassis. We do not have access to a sheet metal shop but we have found that the kit-bot frame is a great foundation and with some more support it is incredibly sturdy.

~DK

Re: Sheet Metal vs KitBot
 

Lighter weight.

Re: Sheet Metal vs KitBot
 

As Dustin and Madison pointed out, if you use #35 chain and keep everything collinear, you can get the chain length to be exact and avoid using tensioners. This was done by properly spacing out out front and center wheels. For the other two chains between the gearbox and the wheels, the gearbox was mounted on slots and slid until it was in a position that worked. A half link may have been used to get things to be exact. Regardless, #35 chain is known to be pretty forgiving.

We built a kitbot on steroids (Simbot Ke$ha) and used it as a defense robot for our practice sessions. Ke$ha logged far more hours than any competition FRC robot would get in a season, and played constant, rough defense on 1114 (as well as 1503 and 2056). Despite this constant abuse it survived from October until now with minimal repairs and no tensioning issues.

Re: Sheet Metal vs KitBot
 

The sheet metal chassis can also be more rigid depending on the design. The kitbot isn't particularly rigid. 1114's suggestion to add a plywood base is a fantastic way to fix this.

Re: Sheet Metal vs KitBot
 

neither. in the past we have done sheet metal, 80/20, plate, welded tubes, and any mixture, after our frame this year (gussets, rivets, and tubes) i doubt we will ever go back to any other frame style. the tubes and gussets came together faster than anything we have built, it was much lighter than most of our frames, and it held up to competition like a beast. we use the kit frame for a practice robot, prototyping, and building our carts, but i don't think we would use it for the drive platform. one other thing is that in the process of designing a custom frame the team can learn more than using a pre-made kit frame.

Re: Sheet Metal vs KitBot
 

Another way to look at it is resource cost.

For most teams, they get much more functionality out of a beefed up kop drivetrin for lesser resource cost.

Many tops teams have perfected the process of drive trains and have also collected a good deal of resources, allowing them to spend time to get a drivetrain that is a little lighter, or performs a little better.

I feel we have one of the best 6wd designs in terms of efficiency, weight, and how difficult it is for us to make it. However, it's not *that* much better than a kop frame. It is certainly less efficient resource wise, but we have enough to handle it.

I believe that any team that hasn't fielded a robot that has every system of it at a top level, they should keep running a souped up kop drive so they can better spread out their resource and efforts.

Re: Sheet Metal vs KitBot
 

Adam, I've been meaning to ask you about your DT actually. I know that 973 and 1323 were very similar this year (how similar were they btw?) and I know that 1323 did not weld their frame. Did 973 weld their frame and have you found any major benefits to a welded frame over a bolted together frame?

Edit: apparently I'm an idiot, it just LOOKED bolted in the picture. Questions still stand but disregard my incorrect information.

Re: Sheet Metal vs KitBot
 

You'll find some great ideas here, too.

Re: Sheet Metal vs KitBot
 

I'm not familiar with the term "Ackerman drive", is it another name for crab drive or another drive system?

Re: Sheet Metal vs KitBot
 

Ackerman drive is car steering.

Re: Sheet Metal vs KitBot
 

Car style steering, front wheels point right and left (on those silly automobile things)

Re: Sheet Metal vs KitBot
 

Did you use independently steerable swerve modules for the Ackermann and compute the inside/outside Ackermann steering angles in software, or did you design a mechanical linkage capable of doing that?

Re: Sheet Metal vs KitBot
 

We used a mechanical linkage to do it. It was actually 4 wheel Ackerman (don't know if this setup has a different name). The front wheels would turn one way and the back wheels would turn the opposite way, while the inside and outside wheels also compensated for the variable radii of the turn.

We did this for Lunacy and it was really cool when it was working however we had some massive issues with some couplings we were using (the tolerance needed to be tighter than we thought) which prevented us from ever getting to really show it off in competition.

~DK

Re: Sheet Metal vs KitBot
 

Did your team ever post a paper or a presentation with some details?

Re: Sheet Metal vs KitBot
 

Here is a picture of it partially built. We didn't ever put together a presentation or anything like that. The helical couplings were what really made it happen for us.

~DK

Re: Sheet Metal vs KitBot
 

The drivetrain is an iteration of what weve run for a few years now. We collaborated with 1323, so they inherited our design.

You are correct that it is not welded. This made it faster and easier four us to build as welding has always been a bottleneck for us.

Re: Sheet Metal vs KitBot
 

Were there any major downsides to not welding it?

Re: Sheet Metal vs KitBot
 

It did make it a big uglier, as we put bolted some "endplugs" inside the frame rails, and then the crossmembers bolted to them. So we had some bolts and holes where we usually have nice clean frame.

Other than that, no. It worked out great. It was identical to this frame here, minus the intake and crossmember.

Re: Sheet Metal vs KitBot
 

Whoa. Those couplings are not meant to flex that far.

Re: Sheet Metal vs KitBot
 

Which is probably what led to this:

OTOH, FRC robots have such short lifespans it is kind of neat to see things used outside of their original purposes. (Obviously though, you've got to do some testing to demonstrate that it will actually perform)

"I don't care about what it was DESIGNED to do... I care what it CAN do." -Gene Kranz during Apollo 13

Re: Sheet Metal vs KitBot
 

We got them from Helical Products Company and this was one of the main things we discussed with them. The couplings we had were operating within their spec. we worked a lot with that company that year and I can assure you that it was not their fault. The shafts that we had put into the wheel side of the coupling were a few thousandths undersized, not enough for us to worry too much we figured we would have enough adjust-ability by tightening the end of the coupler. We were wrong. What ended up happening was the coupling would spin but the shaft was not held tight enough so the wheel shaft didn't spin along with it. It was in no way an issue of over angling the coupler or an issue with the quality of the coupler. Helical Products Company was a great recourse for us and in the end we made a fatal error.

~DK