Custom West-Coast Design Feedback
 

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

Re: Custom West-Coast Design Feedback
 

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.

Re: Custom West-Coast Design Feedback
 

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?

Thanks,
daliberator

Re: Custom West-Coast Design Feedback
 

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.

Why do you need weight?

Re: Custom West-Coast Design Feedback
 

Re: Custom West-Coast Design Feedback
 

Why's that?

Re: Custom West-Coast Design Feedback
 

Ok, I think you're right. Aluminum is probably be the better material choice.

Re: Custom West-Coast Design Feedback
 

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.

Re: Custom West-Coast Design Feedback
 

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.

Re: Custom West-Coast Design Feedback
 

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.

Side note, what cad software do you use?

Re: Custom West-Coast Design Feedback
 

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).

Re: Custom West-Coast Design Feedback
 

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?

Re: Custom West-Coast Design Feedback
 

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.

Not so black and white.... much more grey... ;)

Re: Custom West-Coast Design Feedback
 

Oh, ok. I wasn't quite sure what you meant.

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.

Re: Custom West-Coast Design Feedback
 

You have to put slots and mounting holes on the versa chassis yourself. Otherwise they're not there. And regardless, you still design it all in CAD.

Re: Custom West-Coast Design Feedback
 

This is entirely your opinion, and not fact.

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.

Re: Custom West-Coast Design Feedback
 

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?

Re: Custom West-Coast Design Feedback
 

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.

Re: Custom West-Coast Design Feedback
 

Good point. I just thought that the OP's cad was an example of their machining resources.

Re: Custom West-Coast Design Feedback
 

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.

Re: Custom West-Coast Design Feedback
 

COTS parts can be very expensive for teams to just dish out the money on off the shelf solutions. I know many teams who operate under having unlimited access to aluminum stock (tubing, sheets, blocks, etc) or other materials and limited budgets that push them to instead focus on making their custom parts and save the money on the upper assemblies.

Another downside of relying on COTS as we saw this past year is when the supplier has issues delivering or keeping up with demand. Obviously some of what happened was out of VexPro's control but its a risk teams face.

If a team wants to devote more of their time to machining over buying similar parts more power to them. Some of us might not agree if its the most time efficient manner to build a robot but that is their choice as a team since we all accomplish the game differently and seek to gain different lessons from participating in the program.

If the OP and team want to make a fully custom WCD in the off-season to try new design and build techniques go for it if that's how they feel they want to spend their off-season. I happen to remember your team did something similar last year Andrew.

Re: Custom West-Coast Design Feedback
 

I apologize for the double post.

That's a very unique design you have their but unique designs are good! Exploring something new is a fun experience.

Before you settle on one style of drivebase, would you care to explain how your team decided that building a WCD style base was the right ones for you? What type of advantages do you see in building one? What are your design criteria(s) such as lightest, simplest, ease to build, ease to swap out parts, space efficient, etc.

Our team listed out what we wanted to see in a drivebase separate from a certain type of base and in the end we came up with a very decent solution that was extremely easy for us to build based on our immediate resources, was highly reliable considering it hasn't broken since we assembled it and put it through 6 competitions, and highly competitive as it gave is a good high speed our driver could control coupled with nice traction wheels and low gear for pushing through defenders.

Re: Custom West-Coast Design Feedback
 

Thanks for the reply!
We're not quite done deciding, but we really liked how the west coast robots performed at the events we were at. We have fairly good machining resources, so it seemed like a logical step up from our KoP drive this year.

As for my design, after what I have seen in this thread, I have gone supports crazy. I grossly overestimated the amount of structural elements I need, as well as the fact that steel may be way overboard. I'm working on a new design that will feature aluminum. Are there any other changes you could reccomend?

Thanks,
daliberator

Re: Custom West-Coast Design Feedback
 

Yes, WCD style bases many times lend to perform better but this is typically from the components they are using such as wheels, motors, no. of motors, gearboxes, wheel type/tread, wheel layout 6wd vs. 8wd, driver skill, etc among many other little details. WCD does give you some advantages in how you package these items to be lighter, take up less space, and provide a more efficient setup.

I personally have never built a WCD base only designed a few in Inventor. Some of the reasons teams jump to do a WCD is because its easy to change out a wheel and if you use bearings blocks you have integrated chain spacing which were two features that stuck out to our team a lot after last year. In the end we opted over building a WCD to try new products/techniques while improving performance. For instance we used solid rubber Colson wheels for our drive wheels and found a C-C chain spacing calculator from team 1640 to calculate the space between each wheel to eliminate chain tensioners (we used #35 chain). These two decisions allowed us to never touch the base and accomplished our two main reasons for looking at a WCD which is why we haven't made one. Our base was really easy to make and it built off of what we were comfortable with.

Its just always good to discuss why you intend to build something compared to doing something that a majority of high performing teams do just because they do it. Yes their WCDs are very, very good drivebases but their drivers are what really make them shine and that goes for every team. WCDs aren't very popular up here in New England but we do have our share of extremely good base drivers that can compete with the best. Most notably, team 195 the Cyberknights driver destroys the playing field to be honest. He is very in tune with the match play and more importantly how his robot best moves on the field. He does all this with just a modified kitbot. They swapped the front wheels for omnis and upgraded the gearboxes to 3 CIM single speeds and he uses them to the full potential which is something a lot of teams overlook. I use 195 as one of the many examples we have up here but a little goes a long way.

If its performance you are looking for make some small mechanical tweaks but really give your driver that time to practice especially in the offseason. That is what makes good drivebases. ;)

Re: Custom West-Coast Design Feedback
 

There's a world of difference between designing a part and drawing it in CAD and putting it in an assembly. You're just making models, not designing a part.

Perhaps this is pedantic but I would also say you are not "designing" a drivetrain when you take COTS parts, decide how long four pieces of tubing should be, and then put them together in a preconfigured pattern. It's like saying building a Lego model from the instruction book is design. About the only design work being done is the choice of gearbox, wheels, and gear ratio. That's not to say COTS is bad or whatever, but using the VersaChassis isn't exactly the same as designing a custom drive at all.

--

What is right for your team depends on your resources. Basically, do you have more money or more design resources? Most teams have not enough of either, but money is way easier to get more of than design and build resources. I agree with others who say that focusing design effort on the manipulator and sticking to COTS drives is a general good idea. However, it depends on the team. In the off season, you have a lot more freedom to experiment with new ideas (and usually, less money to spend), so working on custom drives is a very good idea, even if you stay COTS for another build season or two.

There's no universal right answer, there is no single optimal solution. Nothing one size fits all. Asserting facts as such is probably a bad idea.

Re: Custom West-Coast Design Feedback
 

There are distinctions between component design and system design. It certainly still is system design.

As I posted before a fair amount of good design in industry is actually configuration.

It's a valuable skill to have, few industries fabricate everything.

We certainly can all agree that each team is unique, and there is no universal correct answer here.

Re: Custom West-Coast Design Feedback
 

I'm definitely getting to the point where I'm just splitting hairs here, but I interpreted Andrew's post as "buying a COTS part is the exact same amount of design as making your own", which it isn't since one stops doing component design. That's not to say component design is better or necessary, it's just not the same set of skills being used and practiced.

The parts that I would refer to as the system design (excluding the choice to use VersaChassis itself) would be the choice in gear ratio, gearboxes, and motors (perhaps power transmission as well). Certainly few real world situations involve engineers doing detailed design of every component - lots of off the shelf parts or reused designs are implemented in lieu of all this extra work.

My point is essentially that it's the off season, and the OP is building an off-season drive. The constraints likely are in favor of more time and less money rather than the other way around. This I don't think the notion of doing something custom should be inherently knocked in favor of a COTS chassis. They could just buy and build it in the build season if it makes sense to run then.

Re: Custom West-Coast Design Feedback
 

+1. A lot of people overlook the fact that the driver is at least 50% of how well you do at competition. A lot of the top teams spend years training their drivers before they even get to drive at competition. Make sure to chunk in time in your schedule to practice with your drive base.

Re: Custom West-Coast Design Feedback
 

Totally true. Driver practice is the bomb.

Re: Custom West-Coast Design Feedback
 

IMHO steel is a acceptable material for making a robot drive train. I like it because it will keep the weight down low to improve your COG. Steel is appx 3 times heavier than alum but designed correctly can be much stronger/ less costly in the same size package.

Steel is much cheaper in terms of cost/lbs vs alum. CRS and stainless sheet is readily available from material suppliers. Steel can be easily spotwelded and mig welded. Welding steel is much easier than welding alum. Laser cutting light guage steel is significantly faster than cutting the same thickness aluminum.

Here's some stats you can use for you analysis
Cost/lbs of Cold roll sheet sheet is appx. .55/lbs
Cost of Alum 5052 is appx 2.00/lbs
density of steel is .29 lbs/sqft alum .098 for alum.

Take a look at using .036 or .048 CRS for your sheet stock and using .065" thin wall 2x1 , 1x1 tube.

Here's a website of a company that can laser cut tubes. Think of designing tab and notches to click together your frame and use the sheet metal as gussets and brackets


http://www.tubeservice.com/index.html

Re: Custom West-Coast Design Feedback
 

I would use 6061, not 5052 for a cost analysis unless it is a sheet metal chassis. 6061 is cheaper and stronger, but harder to bend.

Re: Custom West-Coast Design Feedback
 

Thanks for replying!
This is main reason I wanted to go with steel in the first place; we don't have a massive budget and I wanted to incorporate some welding into the project.

Thanks,
daliberator

Re: Custom West-Coast Design Feedback
 

Having 1/8" of drop is pretty standard, +/- how much sponginess your tread will have. 3/16" should be ok for most drivetrains, although I don't know what tread you are using.

Re: Custom West-Coast Design Feedback
 

A rule of thumb I've always followed is 1/8" for flat wheels (ie colsons, kit wheels, etc), and 5/32" or 3/16" for blue nitrile. The properties of the blue nitrile tread allow for even the slightest amount of contact to affect turning, and because they grip the carpet so well the increased drop is sometimes needed to ensure there is no contact.

Re: Custom West-Coast Design Feedback
 

We ran 1/8 drop with blue nitrile in both 2013 (6 wheel WCD long base) and 2012 (10 wheel center 6 dropped wide base) and ran it with a 1/16 drop this year (wide base 6 wheel WCD) all wheels being between an inch and an inch and a quarter. We haven't experienced any turning problems, but one of the things we are hoping to look into this summer is playing around with the drop amount.

Re: Custom West-Coast Design Feedback
 

I'm surprised you could get to 1/16 drop without experiencing drag. The diffierence between 5/32 drop and 1/8 becomes more apparent in 1.5" - 2" wide wheels, but it should still be a factor in 1" wheels. Could you provide more information (pictures or CAD models, maybe?) on your 2013 and 2014 drives?

Re: Custom West-Coast Design Feedback
 

The new chassis size restrictions of the last 2 years have changed the dynamics of drop center drives a lot. The old rules of thumb kind of go out the window. As chassis tend to be squarer rather than longer, the need for drop is substantially less than in previous years. With the right wheels you can probably get away with 6WD no drop in a square configuration and still turn fine. Maybe you still need a bit of drop for wide roughtop, though.

We ran 1/8" drop this year on Colsons and that was probably too much. I'd rather have gone 1/16".

Re: Custom West-Coast Design Feedback
 

Did you cut tread into your colsons?

Re: Custom West-Coast Design Feedback
 

We left them untreaded for one event and cut treads in them for our second event. Turned great both times but was a bit rockier than I wanted. Perhaps that's just the tradeoff one has to make.

Back in 2011, 1/8" was just right for a long base with Colsons.

Re: Custom West-Coast Design Feedback
 

For clarification - was it rocky both times because of the drop, or was it rocky after you cut the treads? Also, did the treads affect the smoothness of the wheel's ride (did driving feel more bumpy)?

Re: Custom West-Coast Design Feedback
 

I dont have easy access to all the CAD right now but here's some more information on the two drives.

2013:
6 wheel WCD with two speed 4 CIM custom shifters geared for 9/19 fps before frictional losses. The wheels were 6inch custom 3d printed and if memory serves they were 1 inch wide. The robot frame was 30"x24", dont rember wheel spacing exactly but it was ~11 inches give or take. Here's a CAD render of it.

2014:
6 wheel WCD with two 3 CIM Ballshifters geared to 6/16 fps before losses. The wheels were the 4 inch AM performance wheels and the frame was 23.5"x32" with about 8" between wheels. We almost went with no drop on this but decided to go with a very slight drop to be safe. Wheel also almost made it a four wheel WCD but decided against it. Here's a render of the robot.

Re: Custom West-Coast Design Feedback
 

Very interesting. And very beautiful robots as well - thank you got sharing. As Chris said above, with the new frame perimeter, it appears less drop can be run with these wheels than before.

Re: Custom West-Coast Design Feedback
 

Just a thought along the side-- I interpreted the post as "we include everything in the CAD, whether we're building it or buying it"-- not "since we downloaded the model, it's the same as designing it" (which I think anyone would agree is a ridiculous statement). In that regard, I'm certainly in favor of having as complete of a CAD model as you can-- when I've designed drive trains and assemblies for robotics in the past, I've found that it's nearly always worth taking the extra 10-15 minutes to make sure all the bolts and rivets fit where they're supposed to (because you know what they say about assumptions...). Just my requisite money paid to mail a letter to the editor.

Re: Custom West-Coast Design Feedback
 

Out of random curiosity, what do they say about assumptions?

Re: Custom West-Coast Design Feedback
 

They make an a*s out of you and me (assume)


By rocky, I think he means actual rock back and forth due to the drop center. Along the axis of the drop center

Re: Custom West-Coast Design Feedback
 

Yes, that is what I'm asking.

Re: Custom West-Coast Design Feedback
 

Yeah, that's what I was referring to. "Rockiness" literally meaning tendency to rock.

Re: Custom West-Coast Design Feedback
 

2363 over the past year used a 1/4" holed lexan (the holes were put there in the manufacturing). It was easier for the team to use that for wiring and with weight. In 2013, we used garalite, but found it too fragile and would shatter easily.

Re: Custom West-Coast Design Feedback
 

It was the 1/8" perforated polycarbonate from AndyMark.

Re: Custom West-Coast Design Feedback
 

My mistake, I thought we used thicker lexan.