For the last two years we have used the standard KOP drivetrain and as we build our machine shop, we are looking at customizing our drive train, as well as the rest of our robot. But the thing that I didn’t understand is what the advantages of a west coast drive are. So, what are the advantages of a west coast drivetrain?
One advantage is that it’s not an East Coast drive.
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The main advantage is that the wheels are much more easily replaced. Another advantage specifically over KOP is that you can customize it much more and design it to be useful for your specific use case.
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The first question is, why are you looking to customize?
More importantly, what are you looking to customize?
The KOP chassis is perfectly fine for a huge portion of the teams out there. If you’re switching away from it, there’s usually some sort of motivation. If this motivation is mainly learning and expanding your abilities, then why do you need an advantage to be attached to it? If it’s not, your motive should be something like “we want more flexibility with x thing,” “we want easier maintenance,” or “we want a better way of interfacing between the chassis and mechanisms.” This step has to come before asking what the advantages are. There can be advantages, disadvantages, and advantages that are disadvantages in certain situations and vice versa. All of it comes down to what you’re looking to get out of the system.
Once you’ve got some idea of why you’re doing it, you ask whether designing a WCD addresses those specific goals you outlined. Look at what, say, your current maintenance issues are, and think through what they’d look like on a custom WCD. Does it fix the problem? A lot of the time the answers to these questions are a super unsatisfying, “well, sorta.”
I know this seems like a non-answer, but this idea is pretty important. Any time you change an existing pattern, standard, etc, you should have a specific justification, and a specific result you’re hoping to get from it—whether that be greater efficiency, faster assembly, better maintenance, etc. Identify an issue, look at concepts that avoid or mitigate that issue (and how specifically they do so), then do it, and see if it actually worked.
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You should look up wcd on CD using the search function, you’ll likely find a few other the many several hundred reply threads that already exist on the topic. These threads contain information about everything the advantages to the system to how to build a really good one and the little details you have to know. Sorry I’m unable to link these threads at this time, maybe someone with more time on their hands could do so.
Assembly is quick, complexity is low, maintenance is easy.
resource management is perhaps one of the most important thing to the success of mid level teams. A simple reliable drive train that can be designed and manufactured quickly is a huge benefit. Many teams crank out one or two WCDs in the first 2 weeks of build season. Some teams get this done even earlier. Giving a drive train to the programmers early can in itself be a huge benefit. The COTS drive trains are good options that should be used by more teams but if you want to make a custom drive train west coast drives can be the most simple option. WCD are versatile and easily adapted to different drive obstacles such as those in 2016. If you need to prototype with the drive train because of game objects WCD has advantages here again. Essentially by switching out a few plates you can test different drops and spacing. Many teams have found good ways of easily mounting sensors to WCD as well. They also can be easy to maintain at competition.
Does your team have the capabilities to reliably machine the 2 drive rails in house? If not the COTS drive trains are the way to go.
Since the introduction of VersaBlocks, machining the drive rails for a West Coast Drive can be easily accomplished with a drill press and a hole saw or step drill. You could probably even get by with a cordless drill. Just about every team has the resources to machine it.
Definitely a hole saw if you’re trying cordless. That at least won’t bite as suddenly, maybe… Big caveat: It’ll be a LOT easier in a drill press or by using a drill with an extra handle near the chuck–those big holes can really mess you up if you don’t have that extra counter-torque the handle provides. My wrist just went sore thinking about that experience.
We use step drills in drill presses. Actually got an accuracy boost this year when we center-drilled on the mill first.
We switched to West Coast Drive this year. We found the following advantages for this game in particular.
Easy to locate gearboxes at front, middle or back of robot. We chose back to improve center of gravity.
Easy to access and swap wheels. This was great, since we had two hubs fail at a regional. We detected the failure early due to visibility/access and swapped out the hubs easily.
Option for amount of center drop. Nice to have this year to make an omni versus Colson wheel trade-off.
Easy chain access with tension adjustment. This gave us confidence in using 25 chain, which was a step down from #35 for us.
Overall visibility. When we disassembled last years robot, we found significant rubbing that went undetected and unresolved.
I’ll add that using a WCD can easily let you do things like flipped gearboxes and chain-in-tube, which can give you a thinner profile and more space in the center of the robot. That can be very useful for certain games/mechanisms that need open space in the center.
Backing up a bit to answer this. If you’re asking this question cold, you may not know what a WCD is. Here is my understanding, gleaned from posts, and thus likely to be corrected by those who have actually built WCD.
In 2012 and 2013 (likely earlier, but I didn’t see it), the KoP chassis had a c-channel structure, with all the channel oriented such that the “missing” face was vertical. The gearbox was above the six dead-axle wheels, and drove the center and front (or center and rear) wheels via chain, with the remaining two wheels being driven by a secondary chain from the center wheels. The greatest vulnerability of this drive train was apparently throwing or breaking chains in such a way that all or at least most drive force was lost on at least one side, and a secondary issue was the difficulty of changing wheels, esp. for teams who used soft tires which they EXPECTED to change as a maintenance item.
West Coast drives (developed over several years by several teams on the West Coast) were designed to mitigate/solve these weaknesses. While there are likely other subtleties, the WCD is defined in my understanding by two key points:
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The gearbox was relocated so that its output axle drove the (usually) center wheel directly, and chains or belts then drove the other wheels. By doing this, teams had at least one wheel on each side which would not be affected by breaking chain. In 2014, the KoP chassis adopted this feature, and has kept it through at least 2018.
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The wheels were cantilevered. This change necessitated a second anchor point for each axle inboard of the wheels, which was solved by building the gearbox on a chassis frame of rectangular tubing rather than channel. This innovation allowed each wheel to be replaced by removing a single lug nut/bolt per wheel (most typically tapped into the axle). Bumper rules put a wrinkle in this, but changing cantilevered wheels is still usually much simpler than removing the outer frame, particularly if the team has the foresight to put some access holes.
Other items noted, such as the “flipped” gearbox, are not really specific to WCD so much as that they aren’t easy to do with the current KoP chassis, because it is milled specifically for the motors to mount to TB-mini enclosures themselves mounted on the inside sheet.
GeeTwo has it right, except that the timetable is a bit longer.
The KOP chassis has been 6WD drop center dead axle since 2005, in various forms. Not terribly dissimilar from the current version in function, more in shapes of individual members, who made it, and how stuff mounted.
The WCD was developed by two teams on the West Coast (254 and 60) in the 2002-2004 timeframe and actually slightly influenced the KOP chassis (most robots before that time were 4WD).
The loosely defining characteristics of a WCD are, in no particular order:
-6WD drop center (though 8WD drop 2 center and 4WD can be built and be counted)
-Direct drive to one set of wheels, usually but not always center, with chain (or belt) to the other wheels
-Cantilevered wheels on live axles
-Chain/belt tensioning system involving sliding bearing blocks
-Since 2009 at least, bumper backing points between the wheels or a rail above the wheels for same purpose.
-Multi-speed gearbox–it’s pretty rare for someone to label a single-speed as a WCD, though it’s not implausible or impossible
Obviously there are some differences between individual teams’ implementations, but generally if someone’s claiming they have a WCD all six elements will be present.
To go from KOP to WCD would require a somewhat major shift in a team’s thinking–the easiest starting place is to go from KOP to KOPoS, which involves using a shifting gearbox instead of a single-speed one on the KOP platform. After that, though, it’s all custom. Drill holes, place tensioners, use cantilevered wheels… The Versa system makes this easier, I will say [cue geezer mode–er, wait, don’t].
To me the main advantages are the ability to pick the exact position of the wheels, be able to tension the belts or re-tension the chains when they get loose and that the WCD has COTS designed 2-speed (shifting) transmissions with a lot of gear ratios, so you can fine tune your output speed vs pushing power or acceleration.
There are also COTS devices to simplify building other frame styles.
For example if you want to build a mecanum frame, COTS products simplify the method of powering each wheel.
See Versachassis Examples.
If you want to switch between 2 different kinds of wheels like mecanum and traction wheels, there is a COTS product for that kind of frame as well.
These specialty frames have advantages and disadvantages over the standard tank drive. You can read up on these in CD or try them out during the off season to learn which is quicker to build, easier to drive and on which games its likely to be an advantage.
Dave
One overlooked aspect in my opinion is the spacing. By moving the wheels to the outside, you save about 3 inches on each side of the robot, allowing internal mechanisms to be much larger or have more freedom of movement. You also widen the base of your robot and a huge part in 2018 and 2019 is how far your front and back wheels can be apart. When driving up onto the platform, you don’t want to get centered. Team 254 was able to avoid this quite easily just by moving their wheels to the very front and back edge of their frame.
Live axles instead of dead axles, and every time my team has done it it ends up being lighter than the KoP chassis.
Luckily we knew this would come up and have provided a guide on how to walk through one of these drive systems start to finish. I recommend live axle cantilevered WCD. You save space, maintenance is a cinch, you save weight, the ratios available are comprehensive and cover any type of robot, I could go on. Most importantly, it is obtainable for any team with CAD and a drill press.