This thread isn’t meant to an insult to any type of drive train or style of building, merely a genuine question. Over my time on chief delphi I have seen countless numbers of drivetrains where the gears are all on the inside of the tube their chassis is made from. What are the benefits to this? To me this would seem like a poor decision as it makes maintenance on your sub system difficult at best. Should you strip a gear or need to lube up your transmission, it is very tight with little to no openings. Speaking of tight space, getting the gears inside the tubing to begin with seems like a challenge. Surely its doable (heck teams do it) but it seems like it would take an incredible amount of time ensuring they’re seated correctly before it is assembled.
Again this is just me trying to understand the benefits to other designs to aid in the build in years to come. In no way do I feel that this style of building is bad, I may even find I prefer it once I’ve heard others opinions. Obviously all designs differ slightly, but this seems to be a common theme among a lot of them.
The main advantage is that it saves space. This year, some robots needed the extra space for the totes to fit inside their chassis. It also opens up more options structure wise. For example, this large cross member on 254’s robot wouldn’t be possible with a traditional WCD. Other benefits are chain protection and aesthetics. Of course it would be up to your team to decide if the extra space is worth the challenge.
While I haven’t done one of these drives, I believe that protection (both **of **and **from **the chain) is the biggest advantage. Aesthetics and volume savings also contribute. One other point I noticed in a post was that if the tolerances are calculated correctly, it becomes nearly impossible for the chain to come off the sprocket without something breaking due to the limited clearance.
I see. We ran the chain-in-tube design this year on our robot, and it was great. Since the chain can’t go anywhere (due to the constraints of the tubing) we didn’t have to do any maintenance on it at all, and it went through 3 regionals and Championships fine, still running great as we head into the offseason.
Like others said, it was actually integral to our design as we needed the space to fit our elevator system and totes into the robot. Another hidden benefit was the fact that noodles couldn’t get stuck in our chains as we saw with some other team because none of it was exposed.
Even installation wasn’t that time consuming; we actually finished our drivetrain this year faster than any other year, getting the practice robot drive chassis done within a week into the build season.
340 first did Chain in Tube in 2012 and it was a learning experience. The main advantage was the gain of internal space and the aesthetic of a clean looking robot.
The installation of the chain the first year was a pain but we’ve gotten much better at it over the years. The size of the pockets, the order of installation, and the right combination of tools really makes all the difference.
If you’re looking for an offseason project I would definitely recommend giving it a shot.
Seconded. We are working on a t-shirt cannon this off season and having the chain in the tube might be a good safety feature in addition to keeping dirt and other debris out of the chain. Do any teams use belt inside the tube?
It’s possible, but you’d have to use 2x2 tubing to get both of the belts to fit into the interior. From what I’ve read on Delphi, chain in tube is better than belt since chains (rarely) snap and don’t stretch over time, eliminating the need for a tensioning system.
While chains do not stretch over time like belts do, they do wear over time, which has a very similar effect. For the most part in my experience neither phenomenon is typically noticeable in a robot during a standard (1-2) event season, but both can be observed on a practice robot with sufficient hours of use. In a high-use demobot, both have a potential to give you issues if you use it long enough.
Both chain in tube and belt in tube have been done successfully in competition-- 1625’s Lobster Drive and of course 118’s chain in tube come to mind as examples of belt and chain respectively.
I could be wrong, but I am pretty certain chain definitely does stretch over time, more so than belts. Due to the fact roller chain has metal pins and bushings that all see general wear and tear, I think chain elongates the more use it sees.
319 hasn’t made a chain-in-tube drivetrain yet, but what I find attractive about the design is it’s simplicity and the volume savings. It may be a little less easy to work on, but due to the protected nature of the chain, the odds of you having to work on it are smaller. Mounting gearboxes becomes much easier as well.
Under the forces it’ll see in FRC, chain cannot stretch. It can wear, however.
I’m more concerned about the chance of snapping a drive belt, rather than the wear. It’s nearly impossible to snap chain in FRC if assembled correctly, from my (limited) experience it’s quite a bit easier with belts.
I see. I’d second Joey-- 15mm GT2 or HTD belt is in my experience on the same level as chain in terms of breaking. In my experience if you can get to 36t pulleys, 9mm HTD or GT2 is also pretty hard to break (as in, I’ve never had an issue with it).
It wouldn’t surprise me if the teams I’ve seen snap belts were using 9mm belts incorrectly, some teams in the PNW have a bit of a history making odd decisions.
Chain definitely stretches through wear, mostly the pins. Park Tools sells a chain stretch gauge for bike shops. The poor man’s way is to measure 24 links at 0.5 inches each totals 12 inches when new. Once the chain reaches 12.25", it’s time to buy a new chain. The stretched chain will wear out the aluminum chain rings and the rear cassette, and each costs more than a new chain. A new chain lasts 1000 - 2000 miles depending on cleanliness and lubrication.
Bike wheels are obviously much larger, so the chain life will be reduced accordingly. If we scaled 1500 miles down by 4 / 27, since 4 inches is a typical WCD wheel size, and 27 inches is a typical road bike diameter, you would get about 225 miles. That’s still around 11,000 round trips down and back on the 52’ field. The chain is quite unlikely to wear out based on revolutions alone. Work done to move each vehicle’s mass is at least within a factor of 2, and would benefit the robot.
Robots don’t get much road grime, and carpet fuzz isn’t very abrasive, but they usually don’t get much lubricant. The more lube you use, the more stuff sticks to the chain. By putting the chain in the tube, you can probably lubricate it a bit better without fear of contamination. I’m sure chains will typically last an entire season regardless. Putting the chain inside the frame tube probably helps protect it from game pieces and other robots as well.
According to Gates, a belt’s stretch is nearly un-measurable over the lifetime of the belt.
