Our team has been using mainly ABS cut from our laser cutter to prototype different parts for our robot, but we have been noticing that many teams have been wood that has been CNC’d for their prototypes, and in some cases, even their final robots.
So, a few questions:
Is there some kind of advantage to using wood as opposed to a different material?
Is the strength of wood a concern when it’s being used?
What other materials do teams use other than plastic and wood?
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Wood is cheap, easy to work with, and strong enough for most prototyping. We use our laser and plywood for most mid fidelity prototypes, although cardboard and old spare parts also make their way into prototypes. We did use metal for one that needed the strength but I would not recommend trying to use metal for prototyping
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Love wood, both for prototyping and the final robot when applicable. Baltic birch is great. It’s cheap, strong, and much easier to machine. No complaints here.
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We use wood cut on our laser cutter for most prototyping because its cheap and fast. The CNC cuts much slower than the laser and if its fast, we are more likely to iterate several times and land on a better design.
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More people (students and mentors) are likely to be familiar with working with wood in a relatively quick and efficient way than other materials.
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- Wood is cheap (less so when you’re in a pandemic, though I think it’s back to “normal” now)
- Wood can be taken apart and put together very quickly (screws are faster than bolts for structure)
- Wood is faster to modify than most other materials we use - fast to cut on saws, fast to cut on our router/laser
- Wood can be cut into complex shapes (round sides, etc) faster than metal (bandsaw, CNC machines)
- The shape/length of wood can be easily modified in-place (jigsaw, handheld circular saw if needed) (note that we don’t allow students to use portabands, or dremels for safety/liability)
Depends a lot on the situation. What kind of load will it see? We usually see wood fail when we’re trying to test out arms and other cantilever beam situations, so one way we mitigate that is by using bearings, hubs, or bushings with the wood. Bushings can be pushed in easily, hubs can be screwed in, and flanged bearings can either be put into a hole (use small screws to hold it in) or held in using versabrackets or old gearbox plates.
Also consider more properties than just strength - wood may sometimes be too rigid for your application!
- Cardboard for general structural geometry and visualization…though we advance past this pretty quickly. You can up your cardboard prototyping fidelity by using bolts as axles instead of tacks, paperclips, or tiny little pieces of cardboard,
- Coroplast (corrugated plastic) is a step up from cardboard and helpful when a little more rigidity is needed
- MDF (medium density fiberboard) is a good alternative to wood if you’re having issues with plywood splitting off plys or being super warped (MDF can warp, just usually not as bad off the shelf as wood). It will hold up against splitting much better, though if you drill too close to the edge it’s possible to rip things out.
- 80/20 or any other kind of extruded/configurable rail is convenient for fast adjustments, such as testing compression/wheel spacing for intakes and wheeled shooters.
- We also use a lot of old robot parts and small COTS parts for prototyping once we are done with pure geometry and are getting more to testing movement patterns and applying loads. Bearings, bushings, pillow blocks, shaft collars, etc.
These are slides we have used during training as a really basic overview of the common materials we use. These aren’t prototyping-specific, but there is no definite list of materials that prototyping is limited to - we teach our students to think about what qualities you need in your prototype, what you’re testing, and also to please not cut a brand new piece of versaframe for a prototyping, grab something out of the scrap bin
(note, these slides were made before 3d printing REALLY took off on our team)
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We loved prototyping in wood this year, with a large format laser. CAD, print, assemble.
We loved it so much that we accidentally went to SFR with everything but our intake made out of wood. Our students experienced it as “we didn’t finish the robot” which is also true facts. Our drivetrain was done, our drivetrain took us to Finals as a third robot.
We lost one motor mount repeatedly due to the 1/4" Baltic birch flange it was on not being nearly enough to support it, and almost lost a second shaft for similar reasons. But the rest of the robot was fine, that’s one motor out of four.
And we went pretty much straight to plastic (routed) from there.
I’d love to invest in (laserable) plastic sheets so we could laser final parts too. I think your program could save $ by starting in wood before you go to plastic, but you won’t necessarily want to use the wood parts on comp bots.
ABS would be much more competition ready than the usual laser plastic: acrylic. Acrylic is really easy to shatter.
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We use 1/8" Baltic Birch plywood for prototyping because it’s cheap and quicker to do. Lasering wood typically takes less setup and time to do than milling. We’ve used plywood parts at competition before (this year for example) when it’s a part that doesn’t see any load and is easy to replace if needed. It’s also light weight. We needed to adjust our intake this year with some added parts for ball control, but didn’t have much time between competitions, nor weight left. We just laser cut extras and replaced them as needed since they could be swapped in about 2 minutes flat. In the past we’ve used it for simple brackets, that do not take load or impact.
Your primary prototyping materials should be:
- accessible (either cheap or something you have a lot of stock of, or both)
- quick to fabricate with (can be laser cut, or assembled with gussets, slider blocks, etc)
- sturdy enough (needs to hold its own shape without hand-holding)
From there, any other requirements of your prototypes depends on what you’re specifically trying to do. Make prototypes stronger, more rigid, able to spin freely, etc. if the mechanism would benefit from those details being improved. Something like a shooter, for example, needs to support ball bearings, real motors, and needs to behave in a rigid manner similar to the final robot. Something like an intake needs the geometry to be correct but probably doesn’t care as much about legal motor use or competition-quality bearings. So because of these varying constraints, there’s no general “this will always work for prototypes” answer - but your “baseline” for prototypes should accomplish the above things.
If you have access to a desktop laser cutter, that is an invaluable prototyping tool. Wood or delrin or even acrylic can be used to make precise shapes really quickly, and you don’t really have to care about if they are strong enough for the “real robot” in terms of impact. Systems like VersaFrame, team-designed proto-pipe systems, 8020, etc. are also useful for quickly adjustable mechanisms, especially in absence of a fast-cutting machine like a laser cutter.
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So what laser cutters are teams using for their prototyping? We are in the market for a laser cutter.
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We use Masonite and signboard mainly to prototype, both pretty cheap and just have them around cus of older projects. Masonite is also great cus it’s a quick laser cutter cut and signboard most of the time gives enough structural support for testing. It also cuts out on CNC quick.
We use 1/2 Baltic birch (12mm) for prototyping using my X-Carve. Some makes it on our comp bot every year. We also use polycarb and delrin, more expensive but still easy to cut.
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Wood is cheap, light, relatively durable for prototyping, and can be cut on a laser cutter pretty fast. A majority of the things we prototype are cut out of either 1/8" or 1/4" Baltic birch on our laser.
Allen Gregory has posted about this fairly extensively, I believe 3847 uses a Thunder Laser Nova 35.
@AllenGregoryIV Tell me about your Thunder Laser Nova 35.
Nice chart, but I’m a bit surprised by how you’ve characterized HDPE in your slides as “expensive” and “heavy”. Compared to Lexan, it’s 66% of the density, and generally cheaper.
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UHMWPE has -great- impact properties; even better than polycarb… Impact modified HDPE is also quite good.
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Don’t forget that Delrin can be laser cut. It is too expensive for prototyping. We use 1/4" underlayment wood for our prototyping with the laser. Stuff is cheap. Less than $20 for a 4x8 sheet last I checked. We use 2 or 3 layers glued together if 1/4" is not enough. We have a 60 watt laser. The only pain is that the boards have to be perfectly flat to laser cut and just storing them leaning against the wall for a few weeks will warp them too much to use. Have to be stored flat.
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We typically use plywood, either the 5mm or 1/5" depending on what is in stock at the Home Depot I’m going to be near. It is about $23 for a 4x8 sheet.
Definitely strong enough for prototyping. We used it for our shooter and intake and did a couple interations until we got it dialed and then cut the competition pieces out of polycarb.
Both are done with our X-Carve.
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