My team has a metal factrory that helped us in this season. We want to improve the way we are using our resources. We are going to make drivetrains like this from sheet metal. The problem we had this season was the chains; it was hard to connect and disconnect the chains because it was tight. it is almost a closed system so we had to put the gearbox not inside the drivetrain as you can see in the photo attached.

So my question is: What the other teams that build sheetmetal drivetrains do in the case of chains?


If I am reading this correctly…you mean that there was too much tension in the chains??

This is when chain tensioners come in. Make the chain the next smallest size and add a chain tensioner.

You can use this:

Or for a more DIY approach: Cut a 1 1/2" long, 1/2" PVC down the middle of the circle. Make notches for zip ties with a file. The attach it to the chain.

No, I meant that there is not enough work space in order to connect and disconnect the chains

Funny you should ask this–we ran into this quandary on our 2010 robot that I had to dig for photos on.

Our fix that year was to pull the side of the drive system off, fix it, and put it back on. That would involve drilling out ten rivets, which isn’t TOO bad…but we put them on tight enough that across five events and two robots we never really had to do it.

As one of our mentors say: “we have a real estate problem”.
We don’t have problem during events, but we want to put the gearbox inside and when we tried to do so it was almost impossible dealing with chains.

One thing that can help is visible in that photo: those white plastic cylinders allowed us to route chain around things (such as the space the bumps that year would occupy). That year’s gearbox setup was basically the guts of an AndyMark Shifter (plus another input gear as an idler to fit the third motor), so a Toughbox or CIMple Box would be even easier to implement.

The key, as ever, is good planning and starting with snug chains. I would try it out as a prototype before putting it into production on an FRC robot.

I hope some teams that have enclosed drivetrains can comment on some of their ways to address this.

The short version is that it’s a design issue. You need to consider the chains and create access to them for installation and service. It could be as simple as a removable plate.

If you recruited a sheet metal sponsor and would like to pursue drive trains like the one you linked to; simply make the outer chassis rail removable. Then you can take the entire outer rail off to access the wheels and chain.

If you are going this route, calculate your chain paths ahead of time and design for an exact number of chain links. Then when it comes time to assemble the drive train, you can simply make all the loops of chain ahead of time and pop them in place as you mount the wheels, sprockets, and any spacers or shaft collars.

For tensioners, you can use floating idlers in the chain runs, or add a lot of standoff mounting options in the drive train. Press a Delrin sleeve over the standoffs and then move the standoffs around as necessary to act as a chain tensioner.

We’ve always used enclosed drivetrains from our first bot back in '07.

Our method has always been to make the axle out of a shoulder bolt with a single nut. Pop the nut off and remove the axle and the wheel can drop out the bottom. Work on the chain to your heart’s content, then replace the wheel. Of course, doing this requires exactly what Art mentioned - you have to know your centerpoints ahead of time, or use tentioners on the chains.

At nationals this year we were across from Wildstang. During pit setup day, they pulled their ENTIRE right drivetrain off with just a couple fasteners and serviced it. I pointed it out to our kids so they could get a couple ideas.

We encountered this too, I think this is where the first couple weeks of design really help. When designing you really have to think about how to get to every part of the robot in case of repair. We simply made all the pieces next to the drive system easily removed. We welded where we knew we would not need touch ups and screwed in where problems would usually occur.

Additionally, the mounting holes for the rollers were slotted, so that they could move in and out to help tension the chain.

The axles for both the wheels and rollers were tapped at both ends; to drop them from the bottom of the drivetrain we would simply unscrew the bolts holding them in.

This year was our first year doing our whole robot in sheetmetal and we will be doing it (hopefully) Forever. Great decision to do sheet.

So what makes putting the chain on a lot easier it to make BIG lightening holes on the sides. then you can get your hands in there. IF you are going to cover the tops and bottom of the drive trains, the put the chains on first and make sure they are easy to come off in case you have to replace the chains at competition.

Sheet-metal, and really all types of robots, need to have a lot of thought about assembling, disassembling, and replacing parts. Your designers need to learn what kinds of things should be done to make all those things easier and quicker to do. (PS: RIVETS ARE AMAZING WITH SHEETMETAL!).

Another thing, when putting the chains on what I do is lay your chain out over the sprockets, with the end of your chain on the sprocket, measure which link needs to be removed, then cut the chain. Then when you are putting it on to put the master-link in, put both the ends of the chain on the sprocket so they are at the distance they should be at. then you can easily put the master-link in. (sorry if that was a terrible explanation)

Hope this helps :slight_smile:

What is the thickness of the sheetmetal you were using? it looks great and very light

Slightly off topic: Regarding installing master links, has anyone used a pair of “pliers” (somewhat modified with hooked tips) that hook into links at the ends so the chain can be pulled tight enough to insert the master link?

akoscielski3: That explanation was fine, but on small sprockets it can be difficult, and often side access is tight near the sprockets. We used that technique for our #25 chain that’s out in the open.

I would imagine a large zip-tie would also work if the tension is low enough (with safety glasses in case of high-energy zip-tie failure events::safety:: ).

I’d like to note that should you go with this then be ready to explain to an inspector what you’re doing. I dunno if it was just the inspector, but boy did he give us some trouble in St. Louis for using zip ties…

There is a tool like you describe. We use one like the “B” style on that page.

We also use the Dark Soul Chain Tool for 25 chain, and found an equivalent for 35 chain. We seam the chain outside of the robot, then put the axles and sprockets in with the chain in place.

We have both tools and are using them. the problem is to lock the connecting link - very small parts that need plier and hands but not enough space for the hands… I realized that our problem was the gap between the 2 sheetmetal, we had 5 centimeters gap but in other drivetrains that were posted here I saw a lot more.

So THAT’S what that tool is used for! I saw something like that in our cart for years, but never had a clue what it was.

Our solution to working with chains in tight places was a set of small fingers (mine) and adjustable chain tensioners. I don’t know why the design worked the way it did, so I’ll try and dig up some pictures, but all you had to do was loosen or tighten a bolt at the end of the drive train (we used extruded aluminum, and the ends were left open) and it would move the axle/sprockets to pull the chain tight. The chain was initially seamed outside of the chassis and then put in at the same time as the sprockets and axles, but if it needed to be removed at competition for whatever reason, loosening the chains helped to make the masterlink more accessible - if the axles were close enough together, we could pull the linked section up through the top of the chassis and take off/put on the link with plenty of space.

I don’t know how this would work for 4WD (shown in your picture) as opposed to 6WD (what we used), but I’m sure that something similar could be designed to suit your needs.

One way I always worked around using a tool like this was to assemble the masterlink on a sprocket. You would pull the chain tight, and slowly rotate the wheel/sprocket to a point where the links could easily stay on the sprocket without much effort. Then assemble the masterlink with the chain ends on the sprocket, and poof.

Of course this assumes you have access to the wheel/sprocket, which we usually allowed for.