Sheet Metal vs KitBot

[DinerKid]

Originally Posted by thefro526

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

[Jared Russell]

Originally Posted by DinerKid

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

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.

[Madison]

Originally Posted by thefro526

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.

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

[lemiant]

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

[DinerKid]

Originally Posted by Jared341

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.

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

[Jim Wilks]

Originally Posted by lemiant

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

Lighter weight.

[Karthik]

Originally Posted by MentorOfSteel

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

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.

[Chris is me]

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.

[Hawiian Cadder]

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.

[AdamHeard]

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.

[Andrew Schreiber]

Originally Posted by AdamHeard

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.

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.

[Ether]

Originally Posted by Chris is me

The kitbot isn't particularly rigid. 1114's suggestion to add a plywood base is a fantastic way to fix this.

You'll find some great ideas here, too.

[Sb28000]

Originally Posted by DinerKid

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

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

[rutzman]

Originally Posted by Sb28000

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

Ackerman drive is car steering.

[Aren_Hill]

Originally Posted by Sb28000

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

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