West Coast Concerns

Trying not to be repetitive here by creating another WCD thread.

My team has been working on building a new West Coast Drive prototype in preparation for the upcoming season to replace our previous chassis design. The design and assembly has been going well, but a concern was raised over the chain runs. Like many other teams, we are (planning on) running the chains on the gearbox side of the 1x2 frame tubes instead of the wheel side. Concerns have been raised by multiple people about this being difficult to assemble, service, and replace if necessary. Although I don’t believe this is true, is it more difficult to maintain than having chains on the wheels once you get electronics, mechanisms, bumpers, and anything else mounted onto the drive train?

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Point of reference: 3 of our past 4 robots were west coast drive, with chain running on the inside.
Two of those robots made it to champs. There were other issues, but not related to drivetrain chain. The takeaway: there’s one or more permutations where it works just fine.

In my experience, drivetrain chain is one of the last things to break on your robot. It’s quite well protected, can easily be oversized, and is easily visually inspected between matches.

When answering the question of “which design is best”, it’s really hard to make any across-the-board statements. This is because, no matter what argument I construct, you can always create some special & weird robot permutation that is the exception.

The best answer I can give to you, going into the kickoff in just two weeks: Be prepared to do either. After you see the game and get some idea of what you’re up against, make the decision: Do you constrain your mechanism and electronics board design to be slightly smaller, and allow for easy access to inside chain? Or do you say “nope, not worth it” and put the chain on the outside?

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I’m totally with @gerthworm on this one. Additionally, by combining a chain puller/ holder:


with your Dark Soul or similar chain splicer [or master links :disappointed:], in the rare case you’ll need to, you can change chains out without disassembling the rest of your robot, provided you leave the clearance for this operation.

We use that exact chain puller now, and the dark soul break. They work very well.

Since every decision needs to be strategic to a game we haven’t seen yet, I would not say no to any ideas yet. However, under most circumstances for a WCD, the optimal choice is between inside the frame and inside the tubes. They each have advantages and disadvantages over each other, risks and rewards. Both have been proven on any number of diverse teams and designs and strategies over many years now. I can think of no additional rewards that a chain outside the frame brings, and I can think of a couple of additional risks. It would be a neutral move on ease of maintenance but brings the risk of carpet debris, for instance.

For another point of view on this …

The teams I have mentored over the past 20 years have always put the chain on the outside of the tube rail, but inside the wheels. Even though chain doesn’t usually break, sometimes things happen like getting a wheel stuck, or something jammed and the chain is the thing you WANT to break.

To me, there is not that much to be gained by putting the chain on the inside for the drive base (don’t get me started about chain in tube) and it only takes one time in 100 for the chain to break and you wished it was on the outside.

Again, plenty of people run chain on the inside of the robot frame and inside of the tubes themselves, but my teams are just not those teams.

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No design concept is perfect. Your results will depend at least as much on the quality of the execution of the design concept as the quality of the design concept itself. Your team’s concerns about manufacturability and serviceability relate to the quality of the execution of the design concept. Learning how to design mechanisms that work well AND are easily manufactured and serviced requires a lot of careful study and experimentation. Every year, we see teams “copying” designs from the best teams and getting poor results because of poor execution of the design.

Chains, as mentioned, are no problem. Master Links are your friend. Do be careful to design center-to-center distances accurately.

Belt, on the other hand, can be troublesome to replace. Just over-specify them so they don’t…

In any case: Consider the worst-case of what you might have to repair, and alter the design to make it as easy as reasonable.

Hard pass on this. Chain tools like these have been revolutionary in terms of avoiding chain issues.

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Agreed. We’re never using a master link again.

Counter point: we’ve had 0 issues with master links themselves on #25 chain and the rapid disassembly the provide for has saved us a match or two over the years.

Both options have room for error (I’ve been puzzled by more than one mangled chain tool) but master links are far from guaranteed failure in the same way that a chain tool can’t ensure success. It comes down to which method your team is willing to learn to use correctly.

I literally can’t count the number of times people have blamed masterlinks for a poorly designed and maintained chain run on here and at comps that also would have failed with “welded” chain.

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Our team has historically done WCD and run our chain on the inside. And to echo @troy_dietz sentiment, we have had 0 issues with master links on our drive train. If designed properly as suggested by @DonRotolo and you do the center-to-center calculations, chain maintenance becomes fairly minimal. This is the chain calculator we use: http://www.botlanta.org/converters/dale-calc/sprocket.html It does a great job, and we have found adding an additional 0.018" keeps things nice and tensioned even when using the WCP cam.

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