Custom West-Coast Design Feedback

[asid61]

Originally Posted by Andrew Lawrence

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?

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.

Originally Posted by asid61

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.

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.

[roystur44]

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

[asid61]

Originally Posted by roystur44

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

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.

[daliberator]

Originally Posted by roystur44

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

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

[AdamHeard]

Originally Posted by asid61

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.

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.

[asid61]

Originally Posted by AdamHeard

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.

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?

Originally Posted by asid61

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.

[asid61]

Originally Posted by Andrew Lawrence

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.

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

Originally Posted by asid61

Okay, I agree 100% with you. My own experience with bad CAD and apathy on my team has made me a stickler for CAD and custom parts. It just really annoys me when team members try to make things by hand that should really be machined. I feel like if my own team tried this, we would end up doing a lot by hand that should really be sent to a professional. Thus, I say 2x1 because versachassis looks "finished" and could end up badly if people start messing with it with hand drills.
Not sure if I'm getting my mindset across here.

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.

[BrendanB]

Originally Posted by Andrew Lawrence

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.

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.

[Chris is me]

Originally Posted by Andrew Lawrence

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.

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.

[AdamHeard]

Originally Posted by Chris is me

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.

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.

[Chris is me]

Originally Posted by AdamHeard

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.

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.

[cadandcookies]

Originally Posted by Chris is me

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.

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.