Prototype material of choice?

What does your team prefer when you create prototypes of mechanisms?

erector set, vex, wood, bend up random metal, cnc perfect parts, don’t bother with proto?

As the team gets ready for the competition, I’m also looking ahead to building the program for next year, and this is one of my line items to check into.

Wood is always really easy to work with.

Wood and metal, whatever happens to be lying around the shop.

A lot of it depends on what you want to get out of the prototype. If you just want to demonstrate some mechanical concept or have a visual aid to help you think through the details, something as simple as cardboard and tape can be a valuable prototype. On the other hand, you want to test whether material A is able to grip cans effectively, or if some certain springs will be strong enough, you’ll want to make the prototype as close to a final mechanism as you can within your team’s budgetary and time limitations. Your goal with prototyping should be to get it to a point where you can either find out how your current design fails (and then figure out how to fix it, of course) or can feel confident in moving on to a more full prototype or final mechanism. If your team doesn’t use CAD when designing your robot, consider learning it over the summer too. A CAD model of a mechanism serves as a great sort of prototype in itself, allowing you to work through all the details and get a look at how it will move before you start spending any time or money making physical prototypes.

We have traditionally used 8020 (for more than a decade) but I’m starting to shy away from it myself. The skill level of those who are putting it together coupled with the poor dimensional nature of the stuff makes me want to move towards 2x1 and 1x1 aluminum tubing next year. Predrilled or fabricated, I don’t care.
I ran the mill this year, and for the first two weeks of prototyping I just sat idle and cadded away. Drilling hole patterns in 2x1 takes almost no time at all once the mill is set up. It’s much, much more precise and makes people actually design in CAD before building, not to mention it’s faster/easier (at least for us).

Last year was one of our worst, largely in part due to a massive 4 weeks of prototyping before deciding on a catapult. The prototypes were terrible indicators of whether or not an idea would work, as they did not resemble the final design and were sloppy in general. Forcing precision is my goal next year.

What I wish: Wood

What we use: metal

We are a small team and, in my mind, can’t afford (literally) to waste our metal.

My team uses wood because it is very easy to work with. For things that will be high load, we usually try to find some scrap metal from prior years. We also take advantage of the parts from older practice robots, since they usually have pretty nice mechanisms which are already put together (like this year, we took the intakes from last year’s prototype to test this years intake).

My team is fortunate enough to be based in the same room/machine shop as the district’s Engineering Technology class. Due to this, we usually have access to scrap aluminum that we can turn into prototypes, as well as a team stash of 80/20 extrusion that we can assemble rapidly. Also due to this, we rarely work with wood as a team (and never do when it comes to competition robots due to the comparatively available nature of machining resources and stock for aluminum parts). I like to think that it works out well in the end, but I’ll let the competitions this year be the final judge of that.

Whatever seems most likely to (dis)prove a concept the most quickly and within budget.
Last year (Aerial Assist), our prototype “Woody” (and also, by Hobson’s choice, the practice 'bot) had a 2"x4" lumber chassis and kicker and 2"x2" ball pickup arms; the pickup shaft bearings were an aluminum rod rotating in holes drilled through 2x2s (OK, we used a circular rasp to smooth it). The biggest issue came in the build of the competition robot. The group that worked the pickup arms worked from the floor, and the group that built the kicker worked from the top of the frame. Since the aluminum frame was only 1-1/4" tall (vice 3-1/2"), the pickup didn’t put the ball where it needed to be on “Buzz”, the aluminum competition model.
This year (Recycle Rush), the only wooden prototype was a lift frame that we set up just to find out how fast our motors went when under various loads. They agreed with the number-crunching that we needed to gear our chain down by a factor of about 2 (we finally geared down 32:15). Other than that, we went straight from the drawings or cardboard cutouts to aluminum this year; we never had a whole prototype robot, though we built two metal 'bots, Atlas and Peabody.

The first two years we used steel. Lots and lots of steel. I am the welding teacher in Becker and we have one TIG welder that is 20 years old and doesn’t handle aluminum well. Needless to say we always fought to keep our Robots underweight.

This year we transitioned to Aluminum and we still were cutting weight at the last moments! We used a lot of hardware this year…

We are finally looking into a new TIG welder - hopefully we can find a good one for under $1500!

Whatever makes sense for the prototype.

The key concept for a prototype is that it is “just enough.” Often when teams make all-metal prototypes, it gets people too invested in that particular idea. It’s very important in the prototyping phase to keep as open of a mind as possible.

1 Like

Couldn’t agree more with this.

We typically make mockups using Knex. We then prototype with a mix of wood and metal. Wood for structural material and metal for the actual mechanisms.

Also we create very simple CAD models of each mechanism we are considering as it gives us some idea of how we want the mechanism work and if its even possible. Once we have a final design we of course build a complete detailed CAD model before we start building the final product.