Hey everyone, this question is mainly for teams with low budgets, such as not having CADing capabilities or machine shops, but I was wondering during the build season how most teams do their prototyping. I have seen the 80-20 aluminum work very well for prototypes, but that would probably be a final component of our design on our robot since I think it can get a bit pricy.
Also, here are some more specific questions I have:
How does your team divide up the work and how long does it take to get a final design?
What could our team do to learn more about gearing/motor couplings like for the small andymark motors if we want to attach a high torque gearbox to it, such as a spool for an elevator? (Resources would be great for this one)
We break the mechanical subteam into three groups, one for drivetrain and two for scoring mechanisms. Four students per group seems about optimum, with two experienced students paired with two newcomers. We try to have a mechanical mentor assigned to to help each group. For instance, last year we had a driveteam group, a shooter group (which included aiming), and a ball handling group. On the first weekend, we brainstorm many ways to accomplish the game tasks, and then narrow the wide number of choices down to 2 or 3 we want to prototype. The results from prototyping are used to narrow the choices to the final concept. We strive to have prototyping completed and our Plan of Record (POR) nailed down by the end of week two. Whenever possible, we use “paper prototyping”. For instance, an hour with graph paper, a circle template and a ruler were enough to show us the differences between the how a narrow and wide robot might look when traversing the bump, and the risk of each tipping over while doing so.
This basically comes down to having industry experience, or putting in the time to do research. Study the Andymark, Banebots, WCProducts, and Team221 websites thoroughly. Do google searches and searches through the CD archives. Download models of previous robot designs from frc-designs.com, and study how other teams have solved design problems in the past. Go to the websites of top tier teams and study the documents, photos, and robot videos they publish. When you go to competitions, take the time to crawl around and really study how other robots are built. Take pictures and notes to remind yourself of all the good ideas you find. It’s this willingness to “do the work” that makes a great engineer.
This question actually is very important, because you can get hurt if things go badly. First, the thing you are spinning needs to have a bit of shaft exposed you can clamp the drill chuck onto. When you chuck onto it, be sure you don’t chuck into a keyway. Finally, if the drill you are using has a clutch brake that stops the chuck when you let off the trigger, be very very careful. See my post here: http://www.chiefdelphi.com/forums/showthread.php?t=100032&highlight=drill+safety
We usually just take whatever we have in the shop and make a model out of old, not-very-usable stuff like aluminium pieces with lots of holes in them, broken wood, or even cardboard then the circumstances allow (i.e. when this kind of model is enough to draw conclutions out of). We then examine the models and try to see what we can learn from them.
The way I have approached prototyping is to create a analog that best demonstrates a concept with the least amount of effort and materials. When I designed our team’s ball pickup (as a student), I used some KB channels, 1/4-20 bolts, big sheets of plywood, old polycord, c-clamps, and other junk parts around the shop. Our team’s prototype of the shooter went a little better, but not much. It was actual metal, but it was just scrap metal that happened to be about the right length (or was too long and got handed to the band saw). It did have an actual motor, but because we wanted to see which motors would have the power to do what we wanted and we didn’t have the math to figure it out on paper. We have generally stayed away from the 80/20 stuff because of the price, and because it generally can’t do anything we otherwise can’t with scrap U-channel, plywood, or whiteboard drawings.
Once you learn CAD, statics/dynamics, and/or how to mathematically model systems, that is NOT a substitute for an actual prototype. CAD (and all of the things I listed before that) merely helps you formalize what the prototype should actually test, and this gets more into test articles rather than prototypes. Ideally, for each prototype/test article you build, you should learn something valuable from each. Otherwise, you should just go and stick that prototype/test article on your robot, since you can’t learn anything new (and therefore can’t improve on it).
Prototyping really is the most creative part of what we do. You have a concept of what you want it to do, and you basically get to look around the shop and find parts you can stick together quickly in order to get it done. For example, last year our shooter prototype went very quickly - some shafts from a previous robot, old kitbot wheels taped in place (after all, securing them to the shaft for a live axle setup “properly” would have been too time consuming!), and two 2x4’s with holes drilled in them. Then we just clamped the drills onto the shafts and ran it! All said, maybe an hour start to finish, which included discussion time and investigation in back spin before we were ready to show the rest of the team.
Autodesk Inventor and Solidworks are both active FIRST sponsors and give their software away to students and mentors for free, so money should not be a concern for CAD. It is one of the cheapest and quickest ways to test out a lot of ideas.
We prototype a lot – but we try to limit prototyping to mechanisms that will directly interact with game objects or the field in some meaningful way. In other words, we don’t prototype an arm joint or a four-bar linkage, but will prototype a shooter or roller claw or ball magnet.
For the rest, we are confident with our design skills and work out part construction and geometry in CAD and then go straight to production from that.
We normally prototype with things in the KOP. Last year when prototyping the shooter, the only tools that we used were a vertical band saw and a hand drill. We have also used some TETRIX and VEX parts to prototype because they are easy to put together and have a variety of different pats and pieces. Remember, prototypes do not need to be exact, they are just rough estimates on what you guys are going to make. Also, try to make your prototypes as “open source” as possible. What I mean by this is make it so you can easily adjust some factors to find what is the optimal configuration.
If it is your first year, I would recommend you to buy some VEX or TETRIX parts. It is worth it and will be a big help for the success of your robot.
There are very few things you cannot prototype with 2x4s, plywood, PVC Pipe, 3/8 threaded rod & nuts, drills, and polycord. You can drive basically anything by chucking it into a cordless drill, just be sure to have enough batteries!
We intend to have the prototype (the future practice bot) completed by week 2 but I think the earliest we have the practice bot completed by week three and four. We intend to have the competition bot finished by week four but usually have it done by week five or early week six.
We prototype using materials at hand: foam, wood, 80/20, scrap aluminum, even paper and cardboard. We like to think we use CAD to prototype but that is still a dream.
Our design process runs in specific steps, usually we are done with all prototypes at the end of week one, and we start building the practice bot. The steps include figuring out what strategy will win the game, what capabilities are needed for that strategy, what methods can be used to implement those capabilities, and what mechanisms we can use to get those methods. Much of our prototyping revolves around proof of concept.
Regarding the drills: we just chuck the shaft into the drill and turn it on. Great variable speed drive system, super flexible. A little dangerous perhaps, but we try to be careful.
I was a design engineer doing 3D CAD work for 5 years. The most useful thing I ever did was print up a scaled drawing of a part, and tape it together to use as an example when explaining it to others. Call it poor man’s rapid prototyping, it’s really the way to go for mocking up parts.
No matter how awesome your skills are are doing 3D models, you still only display them on a 2D surface. Adding that 3rd dimension is very helpful to get group understanding. Not everyone has the inate ability to see things in 3D without them actually BEING in 3D.