How do you know when to CAD vs draw up on paper quickly

[CamFam1]

How do you decide which design items must be CAD'ed before proceeding with building and which things can be drawn up on paper with quick dimensions?

It seems there are different views on whether everything must be CAD'ed before proceeding or using a low tech solution of "paper, pencil, and ruler" to get a design that's good enough to build off of.

When time is running short do any of you let go of the desire to CAD and use paper and pencil?

In managing the project, how do you know which things need to be dependent on CAD-ing most and which things can be good enough on paper and pencil?

[EricH]

It depends on time available and accuracy needed. It also depends on whether nearby items need CAD.

If I'm low on time, and I don't have a CAD, I'll grab paper and pencil/pen and do a freehand or ruler-assisted drawing. This is also good for a quick concept model. I do pretty well at freehand perspective drawings, though.

I'll often turn the items drawn up into CAD models, too.

A good perspective drawing course and some practice can really help you make crisp, clear drawings. I've been known to make two quick sketches in half an hour to an hour that wound up in a PDR slideshow after conversion to electronic form. One of them had to show internal structure as well as outside skin.

The time (and maybe money) investment in learning to draw with pencil and paper is well worth it. You might not produce full-on shop drawings, but you'll be pretty close.

[artdutra04]

I usually only draw things on paper when sketching initial ideas (I'll fill up dozens of D size sheets during the first two weeks of the build season doing this), or if making a quick drawing to give to the machinists if there's no printer around.

Otherwise on Team 228, everything mechanically is modeled in SolidWorks. Part numbers are assigned* and official drawings created for every manufactured component on the robot. From there, exploded assembly drawings are also created for some of the critical sub-assemblies, while others are just assembled using laptops with the CAD model open as reference.

Doing this, we were able to machine almost 70% of all components for both of our robots before anything was even bolted together. Ironically, the battery holders were the first completed sub assembly of our 2009 robots (they fit perfectly into the robot chassis' once they arrived back from the machine shop earlier this week). ;-)

Why do we go this far and model everything now? Because for years we did minimal CAD modeling and relied almost entirely on hand-drawn drawings. Without out a doubt, they worked well. But at the same time, it's a lot harder to tell if there is interference between two components in an assembly when it's drawn on paper instead of SolidWorks. And that came back and bit us. A lot. And because of it, there was a lot of "redoing" parts over again (which frustrated our machinist).

This year, by doing everything in SolidWorks ahead of time, we haven't had to redo anything. On the plus side, we now have an entire binder full of SolidWorks drawings for every part on the robot; so if anything breaks and we need another, we're covered.

* I really did give part numbers to everything. Need another Delrin spacer for the rear mounting of the pneumatic cylinder on the right side of the ball intake mechanism? That's 09-BI-026. Need another transmission housing with corresponding bearing spacer? They're 09-STR-006 and 09-STR-007 respectively.

[AdamHeard]

I'm of the belief that every team that can should CAD 100% of the robot, then build from properly dimensioned drawings. The properly dimensioned is the hard part for most.

If this is done, assembly should be painless. Our base went together this year in about 30 minutes, tops. The only interference or fit issue was our battery tray hitting a driveshaft.... and you guessed it, it's location had been changed on the spot from the CAD.

Compared to years past with non-CAD designed bases I've worked with, or even CAD designed ones without proper fits and dimensions, it was awesome.

[mplanchard]

Orginial brainstorming with sketching on a white board or on paper works well.

But I agree with the other designers, if you create your parts and assemblies in CAD, then you will be so much better off in fit. You can check interference in SolidWorks between components and simulate how components are assembled.

I see you are from MN. There is a southern SolidWorks Minnesota Users Group http://www.swugn.org/pages/calendar/calendar.html that meets in February. There may be some engineers there that can give you suggestions. SolidWorks users are very helpful to each other - no matter what their age. It may be too late for this year but you have to think about the future. Marie

Here's a good way to think about it: Would you trust yourself riding in a car you didn't do CAD for, and only sketched it roughly out?

There's a fun exercise you can do to test this out. Have one of your team members go grab a random part from an old robot, mainly one that was Milled simply. Have him/her sketch it out "quickly" on a piece of paper, with all the dimensions THEY think you'd need to make it. Give that drawing to a team member who has not seen what part it's drawn from, and have them try to make it. Unless your student has taken some drafting courses, or is quite gifted in conveying all the details of the part on a sheet of paper, I'm pretty sure there will be errors.

If you sketch it out as you go, you'll always be building under the pressure of the clock. If you CAD it entirely, all you have to do is put the model together. Motion can be tested, speeds can be calculated, and interference can be looked for before hand. You'll end up with a more honed and precise machine, which should elevate your level of competitiveness.

[CamFam1]

Thanks for all your guidance everyone. Please consider another dimension to the question.

If you are running short on time, when would you come to a point where you would say do it in paper and pencil and forego putting pressure on CAD so you can have a robot rather than possibly risking not having a robot?

I see how it's ideal to CAD. When do you let it go and try using paper and pencil? Have you had any experiences like this? How did it go?

[Akash Rastogi]

Originally Posted by CamFam1

Thanks for all your guidance everyone. Please consider another dimension to the question.

If you are running short on time, when would you come to a point where you would say do it in paper and pencil and forego putting pressure on CAD so you can have a robot rather than possibly risking not having a robot?

I see how it's ideal to CAD. When do you let it go and try using paper and pencil? Have you had any experiences like this? How did it go?

If you think about it, having full CAD of all the components can save the time you are losing by perhaps figuring out dimensions on paper. The fabrication process goes a lot faster, which is what Adam basically said.

We learn how to create properly dimensioned tool assisted drawings too though.

Graph paper is the shizzz.

[CamFam1]

Maybe I'm asking a different question than I should be asking.

How about this question. In which week do you like to have your CAD work completed by? What should you do if it is taking longer than you had expected?

[artdutra04]

It was only two days ago in which I finished up the CAD of the elevator and shooter on 228's robot. However, the chassis and ball intake were completed over two weeks ago. The date in which the CAD has to be done is entirely dependent on how fast you can fabricate parts and how many revisions you want to go through before you shoot the designers and build it.

Because I was slow on the last bit of the CAD, now I get to spend all my free time running parts on the CNC mill.

[Molten]

AutoCAD, the speed of hand and the accuracy of computer. This makes it where I start. When I don't have it, I'll resort to hand/Inventor. But my start is always AutoCAD.

[s_forbes]

Originally Posted by CraigHickman

There's a fun exercise you can do to test this out. Have one of your team members go grab a random part from an old robot, mainly one that was Milled simply. Have him/her sketch it out "quickly" on a piece of paper, with all the dimensions THEY think you'd need to make it. Give that drawing to a team member who has not seen what part it's drawn from, and have them try to make it. Unless your student has taken some drafting courses, or is quite gifted in conveying all the details of the part on a sheet of paper, I'm pretty sure there will be errors.

What we do instead is try to make all of the students understand the importance of being able to draw things correctly with proper dimensions. "Did you draw a picture of it?" has kind of become a catch phrase on our team.

As far as our robot design goes, we don't use CAD software as often as we could. If something can be drawn to scale on paper, then we just do that. There are always a few things that are easier to do in CAD though, like our helix this year. It's nice to know that it will actually fit on the robot before we put it there.

[R.C.]

In terms of how to model up designs. The best way to visualize them 3d is too use a simple modeling program such as 3ds Max (Sorry not tooo simple) or Google Sketch Up (I am learning it). We used it for our bot and we got 4-5 concepts drawn up in about a day which made the Cadding easy. And I use paper to start because it makes it easier to CAD.

[Paul Copioli]

Team 217 does exactly what Arthur explains happens on 228. We do everything in CAD and simultaneuosly do prototypes for critical items. If the prototypes find a particular geometry that work, then we will immediately CAD it in SolidWorks to get the manufacturing dimensions. See the attached pdf for an example of one of our assembly drawings.

[Paul11]

Our entire robot was CADed before we cut metal. Hand drawings are good for early design or if a team member must convey an idea or a part placement to the designated CADer.