I entirely agree that it’s easier for my team than doing a kitbot would be, and has many other advantages for us. We’ve been making custom drives since 2004, so it makes no sense to abandon that now. It’s really the easiest part of robot design at this point. Also worth noting: we always have the metal and wheels in stock, so the $450 AndyMark voucher means a nearly free drive base. Bonus!
i think if where i lived had an actual machine shop my team would make our own chassis, instead we always have to deal with the KOP usually missing a piece or two
It’s not listed, but pretty much the only reason we use a Versa Chassis instead of the kitbot is because it’s easier to maintain. Cantilevered wheels come off in seconds.
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Main thing for us is dimensional flexibility, and design flexibility as well like doing chain in tube, and custom gearboxes to mesh with the chassis to free up space. BUT, I will say this, custom is almost ALWAYS cheaper, in my opinion. (Unless you’re getting the kit chassis in the kit and not buying it in season, which tends to be the case)
I had a really hard time getting 2x WCD to fit in under the budget of 2x kitbots, even after accounting for the voucher vs free kitbot. I’m sure you can do it with building up a few years of stock, but it’s definitely not the case initially.
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It can definitely be done but it depends on your manufacturing ability. We were able to get our WCD under the cost of the voucher. But that being said, we used a lot of custom parts which saved us a lot of money. For example, we made our own versa blocks rather than buying them from vex which saved a ton of money. You could even 3D print your wheels which would save you more money. It depends on your manufacturing resources.
I wouldn’t say that it’s hard to do a WCD even if your team has done a KOP frame for every year. Our team used the KOP frame every single year until this year and quite honestly, it was the easiest drivetrain we’ve put together. It’s insanely simple. If you really wanna save cost though, I’d highly recommend contacting companies in your area that may be willing to assist you build your robot. You’ll find there are quite a lot of companies that are willing to help
Go replace the worn out middle wheels on a KOP chassis and ask the question again.
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In recent years it’s been because its much easier to mount things to, it’s lighter, and it’s easier to pick gear ratios. However, after having had issues with our drivetrain every year we’ve gone custom, we’re likely telling design team to suck it up and use the kit chassis next season.
We have the machining ability to do it. Tube and gusset is our construction method for the full robot. The drive train frame is easy.
David
My experience in general and in particular with 3946 doesn’t really fit your poll. The first year (2012), we used a kit chassis but did #5 (cutout for intake). The next two years we did custom chassis because we didn’t stiffen the chassis around the cutout enough, and those who made the drive decisions blamed the kit (we did a 4 wheel skid steer and mecanum). 3946 used the KoP from 2015 to 2019, but we ran it as slide drive, 10 wheels (second layer of wheels on each side, and increased ground clearance), 4 wheels (cut off half) as well as two “stock” configurations. The KoP also allows mecanum (I have one here at the house). Also, I even saw a swerve drive at Arkansas this year which was built into a KoP chassis. Yup, swerve modules held together with KoP frame perimeter.
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Last year we cut out the frame and didn’t strengthen it enough and the drive suffered. This year we cut a gap again (against all my worries) and had no problems
Yeah, I feel like the Versablocks or traditional bearing blocks, as well as maybe the wheels are where it would become cheaper year over year with being able to reuse them. We’re looking at moving to WCD for other reasons than cost, but I figured I’d throw my experience out there as someone who did significant research on this question.
The coolest part about west coast drives is their simplicity and flexibility. Because they are so simple, if you have a team member who is well versed in variable based design/CAD, you can create a document where all of the parts are based on variables, meaning you can control the dimensions of the drivetrain with the simple changing of those couple of variables. (Making the drivetrain even more flexible). Then this document can be used in the future to very easily generate the drivetrain CAD in a couple of minutes. This can cut out a substantial amount of CAD time at the start of the season and lowers the barrier of entry even more for a team who is on the fence about KOP vs WCD.
I keep seeing ‘flexibility’ pop up for WCD. Recently, there was a post on drivetrains being able to ‘flex’ a bit to help with uneven grounds. The was also a post about having the freedom of doing whatever you want with it- customizable.
Which definition of ‘flexibility’ are we talking here?
Customizable.
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In my mind, two of the most important reasons haven’t been mentioned here. Those are the fun of it, and the coolness factor.
For instance we built a swerve drive this year, but that’s not why we went custom. We could have purchased the modules.
Our design is smaller, lighter, and cheaper than what you can buy, but not by enough to really warrant the effort. But it’s cool and fun to build a robot with a custom swerve drive.
Plus we had the design ready to go, and practice bot modules already built, so it wasn’t going to cost us too much build time.
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This should be everyone’s 1 reason. Changing that center wheel out is a huge pain. We try to make sure that center wheel is as bulletproof as possible because swapping it at an event is a nightmare.
Everything else about the kit drive is pretty fantastic though. Can’t complain about robustness or lack of power with it. I’d argue the vast majority of teams should be using it and focusing on their mechanisms, especially if it takes you a good deal longer to make your custom drive than it does to cut to size & assemble the kit drive.
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With the U4, it is considerably less of a nightmare. Once you have the bumpers off, you can at least access both head and nut of all the screws holding the outside sheet in place. (At least if you didn’t bolt superstructure to it in a way that hides them.)
For sure, but it’s still 10 bolts / nuts minimum to remove plus any other structures you’ve bolted to that outside sheet. Good luck doing it during a time out between elimination rounds. Come prepared with the right tools and it’s totally possible but it’s not easy.
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Yeah. For that reason, if we ever went back to the Kitbot, I’d recommend we go with an 8WD config like 7461’s design. It’s heavier and more expensive than 6wd, but much quicker to change all 8 wheels.
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