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