if you are designing your robot in cad. it is a simple command of using Mass Proprieties. in autocad’s case the command is massprop. the mass properties will tell you the volume of 3d objects all you have to do is take that volume and multiply it by how much that material weighs. like a cubic inch of aluminum weighs 0.0975 pounds roughly. this sitehttp://www.allmeasures.com/Formulae/ has spreadsheets and tables that let you just let you plug in your numbers and you have your weight.
Thanks for the tip. Although I think anyone who models their robot in AutoCAD is at a great disadvantage. Inventor is the way to go. And you can set the material properties for each part and find out the weight of an entire assembly instantly!
Thanks for sharing tytus but I also agree it is much easier to use inventor. Althoug if the only thing abelable is AutoCAD then yes this would come handy and save some time.
You could just build the robot and if it’s too heavy in the end, take a chain saw to the parts that are heaviest…lol. But I guess that doesn’t really support the careful engineering aspect of FIRST now does it?
Please note that many prefabricated models of FIRST-specific parts made available over the internet are not accurately modeled and require some modification such that they accurately reflect their true weight. The battery model available at www.firstcadlibrary.com, for example, weighs 5 lbs. as per Inventor.
To correct these errors, the easiest thing to do is learn the component’s weight and manually manipulate the density of the model so as to make it match its real counterpart.
Further, please understand that both wiring and fasteners can quickly become a significant portion of your robot where its weight is concerned – sometime as much as 15%. Modeling these things is both difficult and resource intensive, so many people leave them out.
I used inventor to estimate the weight for last year’s bot. I estimated that there might be about 10-20% error becuase of wires, fastiners that I didn’t feel like modeling all of, welds, and just plain error. Inventor estimated about 105 lbs with battery, and I think it came out to 110 lbs with battery. So not to bad, as long as you expect some deviation. It can help you with planning, but you still need to weigh it.
As far as the battery goes, if you model it and the weight is off, weigh the real thing and use a calculator (or paper) and the volume info on Inventor and change the density appropratly (density=mass/volume), but you might need to convert units.
Here is what I think… Inventor is a good tool to use but Autocad is the only software that has been used in the industry (there are some companies who uses inventor). Yes… it is easy for us to draw in inventor but Autocad is a really powerful tool.
Few examples teams using Autocad to design a robot:
I personally use inventor and have drawn bunch of robots. But, I haven’t been able to find a Robot cad drawing like this in inventor (like swampthing’s and Pink’s).
Autocad does have it’s own way to weigh the robot. You just have to know what you are doing.
Tytus: I personally would like to challenge you to find a robot drawn in inventor that looks like this.
I think most automotive, aerospace, and other large engineering companies use one of the big three: Unigraphics (GM/Delphi), Dassault Systems/IBM Catia (Boeing/Ford?/many foreign car companies), or Pro/Engineer. I think Autodesk products (Inventor, at least) are more geared toward small/medium business. I like Inventor, but I don’t think it’s used widely in big companies.
OK. Autocad is great, and its been in use forever. But, as soon as you try to use it to draw something 3d, your digging a hole with a stick. It’s old, archaic stuff. It’s not even in the same class as Inventor.
Yes, you can use it to go 3d, but why? Inventor or Solidworks were made from the ground up to do parametrics. Autocad was made to make flat things, like floor plans and such, which is why it’s still used by architects. The last time I checked, you still had to make holes using Boolean subtraction (make the plate, make a cylinder, subtract the cylinder from the plate and you have a hole. Need to move the hole? Fill the first hole back in with a new cylinder, then subtract another from the new location. Inventor is as easy as drag and drop).
If you have to make a 2d design, Autocad is fast and will beat Inventor every time for speed (although inventor certainly can do it, it just needs a better spline tool). As soon as you try to make something more complex then a flat piece of sheet metal, drop autocad like a ton of bricks and boot up Inventor. There is no way you could pay me to draw up a drive train in autocad. I’m sure some people do it, but there’s no reason to anymore. I would be amazed if the teams shown used autocad to do anything more then lay out the design.
On a side note, Inventor is geared for small to mid sized business. Something like Catia costs tens of thousands of dollars to implement (not just the software, but the computing power needed). So programs like Catia and Pro-E are used almost exclusively by large companies that need that kind of power. For the rest of us with more like four thousand to spend, there is Inventor and Solidworks (the two major players, there are probably others). Inventor is made by the same people who make Autocad, so you would think that with the massive built in user base Inventor would just own the market. But, Solidworks has taken a big lead and is mopping the floor with Inventor. Both are pretty good programs, but preference is for solidworks.
I have been taking a Drafting class for almost a year and a half now, and I have had the opportunity to work with both Inventor and Auto-CAD. To tell you the thruth as far as mechanical designs is concern Inventor is a lot better. Anything you can do in Auto-CAD you can do in Inventor a lot faster and with a lot more helpful tools.
As far as weight is concerned you can always find the weight of things that you downloaded from on-line like motors and batteries and then change its properties in Inventor.
Honestly if I was asked to draw swampthing’s robot i would choose Inventor without hesitation.
For the longest time, no one in my team knew Inventor, even though we had out own copies. People just did autocad. Many people could do 2d autocad, few could do 3D autocad. Those that could, were so good at it, they created very good models of previous year’s robots. It took a lot of time, but they did. At the beginning of last years build season, I knew some about Inventor and had been playing around in it. I modeled some of what the designs were in Inventor while the 3D autocad guys took off with their consiptualization. I tried to convence them that Inventor was better than autoCad for what they were doing, but they thought they could go faster. That was until they wanted to change the plan some. It took forever, while I, already having done as much as they had, made the change in a few clicks. That changed their minds some. But they wern’t convenced untill they saw that I had most of what they had designed in Inventor and knew the approx weight, center of gravity, the height that it could reach, how small it would collapse, technical drawings with dimentions and lables, and all the other details that they couldn’t get easily in autocad. THEN they just came to me for every thing they needed. But they still wern’t interested in learning how to do it themselves.
Conclution, AutoCAD can do great things and is fairly easy to use. Inventor is different, but can handle a great many things that you just can’t do in a good length of time in AutoCAD. It isn’t because AutoCAD is bad or outdated, just that Parametric Modeling makes such things easier, but makes a bigger program and cost more becuase of the extra baggage that Parametric Modeling carries with it. If you don’t need Parametric modeling, don’t use Inventor.
It’s like comparing a drawing application with Paint. Paint can do drawings, but are a pain in the butt to change. Drawing applications make changing things easier along with some other things, sometimes, but can’t do it all. Paint is easier to do, but drawing applications have the power. Which is better? Depends on your application.
I didn’t mean to post something that would be offensive for all the inventor/solidworks. Me, myself is a inventor designer. I like inventor… the reason why I use it. All of my designs that has been posted here was created in inventor.Yes you can get the mass of the robot using inventor properly.
Point of this thread was Tytus pointing out HOW to get the robot weight using Autocad. It had nothing to do with how you weigh your robot using inventor or solidworks. The thread wasn’t created to bash the inventor or solidworks user. It was a tip for the rookies who are using Autocad.
Let’s keep the thread on topic…
and thanks Tytus for giving the Autocad users the tip.
My tip for rookies or anyone using AutoCAD is: don’t. It is inferior to Inventor in several respects. The reason is still used in the industry is because the industry does not keep up with modern times. The most complicated piece of electronic hardware found in many businesses is the thing they use to run credit cards, and they just got that only about a year or two ago. Computers are still a very new thing for a lot of older folks out there. A lot of the people who ventured into computers when AutoCAD was the latest greatest thing simply don’t know there is anything better or are too stubborn to try anything else. AutoCAD is an archaic piece of software with a catchy name and it stuck. People don’t realize that we have moved on. Inventor is much more suited to doing just about anything that’s not 2d, but the industry hasn’t discovered that yet. Also, I find it a nightmare to do anything in AutoCAD, but I think a competent 8 year old could manage Inventor just fine.
For carbon epoxy composites (the most commonly available form of carbon fiber) you can use a density of 0.056 lbs/cuin. That is for a high performance, aircraft grade composite with about 33% epoxy content. If you’re slapping wet resin on carbon cloth it will be a little lower strength and density.
I hate to have to disagree. AutoCAD is a great program, and has its uses. I would, however, reccomend inventor to FIRST students simply because all teams have free access to it.
For many things, AutoCAD is actually the prefered method. Inventor is a great modeling program, but AutoCAD is primarily a 2D application and a great one at that. You cannot even really compare the two. I’ll stop there. It has been covered already here.
As a frequent user of both AutoCad 2005 and Inventor 9, I can say the following:
Inventor is for anything that has to do with motion and is 3d. You can do active springs in Inventor. In version 9, you can FINALLY stop parts from intersecting too. It’s just very realistic. As for the 2d drawing part, its ok. It could be better, but for robotics its fine. If you get to know all the keyboard shortcuts and all, you can CAD really fast. But basically its best for assemblies and 3d stuff.
AutoCad is ment for 2d sketching. It is like drafting, but a whole lot faster (duh, no more pencil and graph paper). It is more powerful than Inventor, as in you can do more stuff faster, but who cares? This is robotics, not the real world (laughs). If you learn how to use AutoCad well, it is much better than Inventor at what it was made for.
In the end I prefer Inventor. I started on Inventor so I am much more comfortable using it. Also I am always dealing more with assemblies than with individual parts. Also I like how Inventor can export to a lot of different formats, especially .dxf, which you can just send right to a CNC watercutter and poof you have a robot.
However, for all you people that want to go to college for mechanical engineering, I would learn AutoCad as well. Because nobody uses Inventor. Though I personally think they should.
