Hey CD!
This year in the off-season, my team is going to work on a custom drivetrain. It looks like it’s gonna be a west-coast, so I threw the attached design together.
Its main structural element is 16th inch steel sheet. For main supports, it has 16th inch steel tubing of varying heights, as well as a 8th inch steel chain-guard (For lack of a better word). The bearing blocks are 8th inch steel and the are at an interference fit with their respective bearings. I didn’t know exactly how much to drop the center bearings, so I just guessed at 3/16ths of an inch.
This is the first drivetrain I have attempted, so any and all feedback is welcome.
Thanks,
daliberator
I understand your want for structural stability, but from my experience going aluminum is fine (even 16th inch). My team ran a WCD with 1/16th thick aluminum 6061 2x1 extrusion, and a 1/16th sheet metal belly pan, and it we had no structural issues.
Thanks for the reply!
That was one of my hardest decisions for this build. I went for steel in the end mostly because this “bot” will not have any kind of superstructure, so I just wanted to weigh it down more. Do you think I went a little bit overboard with the supports then?
Steel is not worth it usually in FRC robots. I would only use it for weight, like on flywheels.
1/8" 6061 aluminum is super strong for a WCD. Lots of teams even use 1/16" 6061 for their robots.
Keep in mind steel takes much longer to machine than aluminum, so it’s easier on the machinist if you just stick with aluminum over steel. If you need the weight, add some plates, but I don’t think you’ll need it.
I’m going to assume it is the typical spiel of “look at/buy COTS options” before making your own. I don’t mean to be a cynic here, but you learn a lot more from making and failing with your own than buying one off the shelf. Granted, for the first couple of iterations of the design, the COTS option would likely perform better, but it’s not about the goal, it’s about the journey.
During the season, the Vexpro option would be my top choice, but since this is an offseason project, I would fully recommend working on your own.
Remember the VersaChassis isn’t a perfectly functioning west coast drive in a box shipped to your front door already assembled ready to drive out of the box, or a kit with parts you put together from an instruction booklet. It’s still a custom drivetrain. You design the dimensions. You choose where the holes are made and you drill them. You machine most everything and put it all together. The Versachassis components are in no way different from regular custom WCD components. The aluminum tubing is aluminum tubing. The bearing blocks are bearing blocks. The transmission is a transmission. The gussets are gussets. The difference is these parts are strategically designed to involve minimal required machinework to have a functional drive, and provide a lot more tolerance to mistakes. I think in an offseason drivetrain where your goal is to learn and test ideas, the added tolerance, the minimal required machining, and the seamless integration of allowable iteration is not only a great asset, but an achievable goal that those building their first west coast drives should strive for.
The drive enables low resource teams to build a competitive drivetrain, and high resource teams to spend less time on their drive system so they can focus on their scoring mechanismms. It allows teams doing their first west coast drive to iterate with a large tolerance window, and for the teams making their tenth west coast drive, it offers a simple, reliable system that is functionally equivalent to what is already used in west coast drives, readily available as a COTS resource.
Off the shelf is great, but I think it’s better to optimize for your application. For example, the vex ballshifters can be used as winched for hundreds of pounds of springs- not something you would see in a drivetrain usually. GRT maximized their ballshifter’s potential by using smaller shafts, bearings, etc. to make a smaller and lighter gearbox than what was on the market from any of the normal suppliers.
So looking at your cad file (please, export as .stp so I can see lines!) I am noticing a lack of detail. Being as this is your first chassis, why not put everything in? My first gearbox was horribly screwed up because I didn’t put all the components in the cad such as screws and nuts and led to a lot of problems down the road.
Download the cad files of all stock components (McMaster has cad for their screws and other products if your computer is decent) and keep a detailed parts list that is organized in some way. This includes wheels, screws, nuts, shafts(including e-clip or circlip slots), spacers, bearings, etc. Electronics are also a major plus even if the whole chassis will be open for them.
This produces a wicked looking cad and hopefully something that requires minimal effort to put together for testing. It takes less time in cad than in real life to change dimensions.
I totally agree with your reasons, but IMO it’s a better experience to design a chassis and use as many stock vex parts like bearings blocks than to just order all the parts and bolt it together. Designing 2x1 was a (cough) memorable (cough) experience for myself.
I guess it depends on what the OP feels is “too stock” and what is not. Personal experience says to design for modularity (have different gearbox mounting hole patterns) and use stock parts (like vex bearing blocks) without sacrificing learning (make your own WCD 2x1 with slots).
But you don’t just bolt it together. You design it all. That’s kinda the point of what I just wrote.
I believe there is a misunderstanding here - in what ways is buying stock aluminum 2x1 and machining your own slots and holes and adding gearboxes and gussets any different from the Versachassis?
Well, it depends on the specific instance of the team though.
Resources aren’t infinite. Time and talent are something all teams can’t get enough of.
As Andrew pointed out, you’re still designing some when you go that route. Configuration is the right word.
As an Engineer, I use configurable parts and assemblies all the time (misumi.com is AWESOME). Sure it’s less design than if I didn’t, but I learn just as much and dump less resources into it.
Team can take the time and talent they have left over by going with a less resource intensive drive, and focus on other systems.
For many teams I would argue there is a NET GAIN in learning by choosing to go with the configurable off the shelf option.
It should also be considered that for many teams it will likely be a higher performing and more reliable option, leaving them free to work on maintaining the rest of the robot, and winning more matches (or, with a bad schedule still losing, but having a much more competitive machine while doing so). For most students, this is far more inspirational. This inspiration often turns a kid that was a watcher into a do-er, and they might spend next summer designing a better custom option, as well as hunting down sponsors, etc… to make it happen.
Anyway,
buying the stock and cutting it yourself is different from just using versachassis, because you actually have to design in different chassis elements such as slots and mounting holes. This is good practice. The more custom work you can do in the offseason, the better for when COTS parts are not available or don’t exist. Anything new has to be done in the offseason or it has a much higher chance of not working/ failing.
Anybody can take the versachassis and use it during the season, but the offseason should be used for custom parts and designs. There’s little reason to just build a versachassis instead of actually inputting custom work somewhere into the equation; that can be accomplished during build.
Yes, it is less effort and more effective to use a versachassis, but doing a custom build makes good use of the time available.
My above post explains my reasoning, and the same logic holds true for offseasons. Teams might get much more out of dedicating their resources to arms, elevators, etc. than drives.
It’s certainly true that for some teams the reverse exists (or they have plenty of resources) and they can go custom and not negatively impact overall learning.
Each team has a unique circumstance, and it’s unfair to imply that teams are doing things right or wrong in this capacity.
In all fairness, many things said here are opinions. Very little that I say myself is “fact” and I (try) not assert myself that way. I should probably hack that into my signature so I remember.
I’m not saying anybody is doing things right or wrong, I’m sorry if I came off that way.
My apologies, I wasn’t considering making things other than drivetrains (I’m a drivetrain freak) so totally, arms and elevators are cool too. Especially given that we’ve had so many ball games, having a usable elevator design would be nice to have.
I’m not sure how resources factor into this specific instance; I am assuming the OP has resources to build a WCD?
Something I’ve learned over the past 4 years: Never assume anything that the OP didn’t tell you. One small piece of new information can change all possible applicable advice.
I totally get what you mean. I make sure that whenever we use COTS parts, everything is put in CAD and treated as if it were a custom part that we designed, sketched, extruded, mated, and assembled ourselves. The only difference between the CAD and the real part is that we buy the real part, we don’t make all of it (though like in the case with the versatubing, we do machine parts of it ourselves, but all machining is already included in the CAD model). This method allows our students to learn as much as possible as if we designed the part ourselves, but still have the ease of use, reliability, and time saving advantages that a COTS component normally has, like Adam previously mentioned.
