im trying to convince the team’s captain to use WCD instead of the andymark am14u5 drivetrain that we already using but we haven’t figure out what’s the actual differences between both since they are both tank drive
Are you talking about WCD (West Coast Drive)?
WCD was pioneered by a few teams in the early 2000s (254 and 60 come to mind) and it was revolutionary at the time. The Am14u5 drivetrain is similar to WCD but doesn’t allow quite as easy access to the wheels.
Here is a thread about WCD: West Coast Drive, WCD - #2 by CIM
Here is the best picture I can find of old school WCD.
I’d be curious to know if any teams are using WCD in 2023. [Edit: After looking for like 2 seconds, it appears that some of the most famous tank drive robots this year, such as 971 and 316, use WCD] As far as I know, it became less popular after the advent of sheet metal manufacturing (as opposed to using welded tube stock), since it seems to be better to support the axles on both sides of the wheel when your frame is made of sheet metal. Also, the phase-in of bumpers from 2007-2010 introduced the concept of a frame perimeter, which means that WCDs now have to have robust elements sticking out further than the wheels.
We used WCD this year. We had two 1x1 rails around the outside that support our bumpers and the bottom one detaches with 4 bolts and slides up to the top one which makes access really easy. We also don’t have much sheet metal manufacturing, but I still like the wheel accessibility we get. We were able to get to and retension both sides of our drive train chains between matches at competition.
I don’t want to come off harsh, but there’s a greater topic in play here: You’re leaning on your team to adopt something you don’t understand the differences of yourself?
I say this because this is how you end up buying a Retro Encabulator. (Spoiler: It’s a guy in a nice suit with an impressive demo display spouting absolute nonsense jargon.)
I’m sure many will lay out the differences in this thread, but consider this a friendly nudge to make sure you understand if or how something new will actually solve a problem for you/your team/your company before you get on board with advocating for it. It’s a skill that will take you far in your career. 
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Thanks for including us in the same paragraph as 971
We made the switch from the kit chassis to a WCP variation in 2018 for two main reasons.
-It’s modular. You can make it any size you want, any wheels, and use any gearbox you want. You can build one in a day with clamping bearing blocks and a bit longer with traditional WCP bearing blocks.
-It’s easy to mount stuff to. While the new AM14Us are great, it’s still way easier to mount a superstructure to a 1" x 2".
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Not really. We using the am14u5 drivetrain this year and have some trouble with gravity, speed and mounting stuff on it ( its hard to find premade that using inches in Vietnam so we have to make everything from scratch) and a WCD drivetrain could solve those with its customizable but we still unsure if there is other benefit or the andymark drivetrain is still a good option (our budget is limited)
There are a few things we can unpack off of this.
(Disclosure: I used to work for AndyMark. It’s been a while. But we’re talking directly about their products so I’d rather be conservative.)
- Gravity (or I presume, center of gravity). We’ve run wide and long configurations of the AM14U recently (wide in 2022, long in 2020/21/23), and the wide configuration can get tippy if you go particularly tall. In particular, the dropped center wheel makes the wide configuration’s wheelbase super short. A comparable WCD could get the wheels a little closer to the edge, but we’re talking very short distances compared to how a stock wheel packages in the AM14U chassis.
- Speed. Assuming you mean drivetrain speed, you can tune it! Wheel size obviously influences it, but there are five gear ratios available for the Toughbox Mini. Check the bottom of page 3 of the assembly guide. And that’s not the only option–AndyMark sells alternatives like the EVO line of gearboxes (also on page 3) and their 3-motor upgrade kit. Others have their own products; we’ve used The Thrifty Bot’s version of that 3-motor kit the last two years with 6 NEO motors and had a robot that was a menace each time using little more than the guts of the Toughbox Mini. Case in point, Q44 at 2023 PCH Hartsville where we were easily the fastest tank-drive robot on the field (and perhaps a higher max velocity than 1102’s swerve though they were much more polished), or Q124 at 2022 Roebling where we were able to give 3310 fits. A tube-based WCD can certainly mount any gearbox you desire, but with the TB Mini’s ratios really haven’t found it to be the limiting factor.
- Mounting stuff. The 14U does nerf your options a touch, but it’s manageable. I think a lot of people get distracted by the flange on the top of the inner plate and miss the 2" hole spacing on the vertical face (I’ve highlighted the holes in green). Whether using a COTS gusset (perhaps while stocking up on gear ratio options so you can set your speed quickly) or simply designing a custom plate to use the holes, you can get a lot done.
I’m sure metric-using teams have their own thoughts on interfacing with a lot of COTS parts, whether the stock chassis or simply parts for millimeter-based tube. But hopefully this inspires some thoughts of what’s possible.
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The way I see the am-14U5 kitbot is that it’s a drive base that works. My team has experimented with custom drive bases in the past and every time, the drive train has been the most inconsistent/lacking part of our robot (at least from what I have heard, @Link2815 can confirm).
The kitbot, at least for us, provides a consistent and reliable drive base that we don’t have to think about. This frees up time, people, and brain power to think about/design and build more robust game piece manipulators and such things.
The age old question on our team is “why don’t we swerve?” And the answer is always “because it doesn’t make us better” what makes our team better is building more reliable manipulators and mechanisms. The kitbot allows us to focus on this. My team won’t stop using the kitbot until it becomes the bottleneck in our performance.
That doesn’t mean it’s better than a custom WCD, for example team 342 in the PCH district ran a custom WCD this year to great effect! (@HP020106 and @RedLeader342 congrats on finalist btw!!) The key difference in our robots is that they build better game piece manipulators than our team does, meaning they may not reach their robots full potential with the am-14U5.
The niche of the kitbot from my perspective is for teams that want to improve other build aspects of their robot, by not having to think to much about their drive base as much.
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I’ll say the biggest advantage to wcd over the kit chassis is customization
With the kit chassis you’re kind of limited on where and which motors/gearboxes you can use. You’re also kind of locked into a certain ground clearance.
These are all things you can change freely on a custom chassis.
But if you are in a situation like @Gandagorn said, you really need to spend more time focusing on mechanisms.
For us, we can pretty easily have a chassis designed in a day or two and cut on the cnc in another day or two. If you don’t have those capabilities, the kit chassis is really a fantastic way to go so you can spend more time on mechanisms. For example, I believe our alliance partners that were finalist captains at two events, were a kit chassis, but they had more complex and well functioning mechanisms than we did.
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The ability to customize a WCD chassis is a double-edged sword.
If a team has a rigorous design process such that they clearly identify what is needed to play the game in that season, iterate the design to optimize the design to serve their needs within that season and adapt it to subsequent seasons, they are likely to get a good result.
If a team just “throws the mud against the wall” without identifying clear goals and without a rigorous design process, like many teams I have seen in my area, they are unlikely to get a good result. Some of these teams have started from scratch each season, making it difficult to learn from past attempts.
Like any other mechanism, having a WCD chassis is not an advantage. Having a well thought out, well designed and optimized WCD chassis is an advantage.
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That’s a really good way to put it
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As someone around for the earliest days of 2815, can confirm there were years of drivetrain customizations both mild (2013) and wild (2010). You can argue whether the 2010 kit drivetrain was really optimal either (heck, if there was anything at all optimal about 2010), but I’d really love to go back and tell early 2013 me “put the shifter down”.
Yes and no? You’re more or less stuck with the gearbox in the center with a 14U-style chassis unless you really do funky cuts on your wheelbase, I’ll grant that. Ground clearance can also be fiddled with using the 8WD conversion kit. You could surely eke the wheel a little closer to the frame perimeter on a custom chassis, but I’d love for someone to whip out the CAD and figure out how much gain they’re really getting for the extra work.
Some gearboxes will be easier to integrate than others, but any Toughbox derivative has ratio options from 5.95:1 up to 12.75:1. AndyMark models that wheel speed range–on CIMs at 75% of free speed!–to be 8.4 to 18.0 feet per second on 6" wheels. Brushless would only kick it higher. I defy anyone still running tank drive to tell me there’s a need to be outside that range.
And you can do that with any remotely relevant motor–CIM, Mini CIM, Falcon, NEO, all of them work fine. Falcons will need different pinions or (on older builds) a swapped shaft, but people running Falcons chose that life.
I don’t begrudge anyone who chooses to go custom–you do gain packaging advantages with that, and some teams find quality-of-life benefits that suit their approach to robots. But I don’t know how many teams really contemplate the ways to get a 14U trimmed out with bolt-on or near-bolt-on options, either. So past employers aside, I do feel compelled to lay the cards on the table.
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I’d like to see the gearbox be able to be easily mounted on the end, instead of the center. Of course, this is lots of work for little gain. More customizability would be nice… but at a certain point it’s just extra weight.
Get a stopwatch and time your best mechanic as they complete the following task: Change out the middle wheel on one side of the drivetrain.
This is the biggest motivating factor that I know of to convince someone that “we should not use a KOP drivetrain”.
At least you’re doing it a LOT less often than swerve 
Fully agree that these are my two biggest challenges in using the 14U across most of the last decade. (14, 15, 16-if-Ri3D-counts, 17, 19, 20, 21, 22, 23). I’ve noticed the middle wheel gets much easier with the 8WD kit, in that every wheel becomes a dead axle.
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but they just came out with the hyper encabulator! it’s a must buy!
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But on a standard swerve you’re never changing the MIDDLE wheel
this is great.