Hello my team is trying to incorporate rough prototypes into our design process and is struggling to find sources on rough prototypes. In other words prototypes that are the first step from an idea but are not totally polished yet. I am mainly wondering how do other teams transfer from ideas to rough prototypes quickly and what materials do you use and how do you judge if a rough prototype has been successful? Open to any ideas…
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I can’t say that my team is always exceptional at this, and there are certainly others who have done it better. But here’s a presentation I gave on this topic (both for my team and for others at a Comcast FRC Bootcamp):
Some of it is tailored a bit towards my team specifically, and there are moments intended to be explained with hand-held objects, but I feel like a lot of the content could still be useful and translate.
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Plywood is definitely your friend when prototyping. Easily obtainable locally, less expensive than plastic or aluminum, easy to cut with a router or laser (for thinner sheets).
Prototyping blocks that work with aluminum tube are also a good option:
Setting motor speeds manually with a PWM signal from a servo tester and using a controller that accepts PWM input like a Spark MAX is quicker than writing code.
Of course, having a good stock of parts opens up the range of things you can try quickly. It helps to have a lot of wheels in different sizes and styles. Planetary gearboxes are pretty versatile. Having a good selection of gears, pulleys/belts, and sprockets/chain is helpful. Gears and pulleys can be quickly 3D printed. A supply of shaft collars is important to quickly retain shafts, especially if you are using lengths you have on hand and aren’t cutting them to exact size.
You judge if the prototype has been successful if it produces the desired result. Does it shoot as desired? Does it pick up as desired? Does it convey as desired? Does it do ________ as desired? The idea with prototypes is to iterate your design quickly, retaining features that seem to be working while making changes or additions for things that do not seem to be working.
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Here’s some slides that show some of the iterations of my teams intake, was meant to be presented so doesn’t really have text but might be helpful. 8033IntakeCaseStudy - Google Slides
Cardboard, tape, and hot glue will go a long way for playing with geometry of mechanisms. If you have a CNC router, get good at designing quick plywood mock ups. Vex or Rev tubing and gussets with cleecos are really great as well. You may be able to drive some prototypes with a drill, but have a setup to run the real motors with speed control and planetaries and record speed data. Keep a stock of intake and shooter wheels so you can prototype with as close to the final materials as possible.
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lots of caffeine
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Keep a bunch of random junk around, mock up an idea with whatever you can find, then, and this is the important part, take copious measurements and notes. If you can’t put the key dimensions into CAD, your prototype was a waste of time.
For something like an intake we might play with wheels on drills, and an old robot with bumpers to see how things interact. They we might mock up the intake as two pieces of plywood with bearings and axels between them sitting in front of the old robot. The wheels should be run off the likely final motors and gear ratios at this stage. This can be done with a jigsaw and a hole saw, or CNC. You may want to mount your mock-up to a drivebase and drive around picking up game pieces, so have a drivebase ready with code before kickoff.
Good prototypes require: knowledge/intuition on what needs to be accurate to a final version and what doesn’t, lots of different materials at hand without waiting for shipping, and copious note taking.
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This 
Early prototypes for intakes or game piece acquisition mechanisms can be stand-alone, but acquiring from a moving robot is a critical part of prototyping. Having a drive base ready to run and mount things to is incredibly useful.
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Taking this a step further, one thing I’ve thought of suggesting is keeping both an open front chassis and a typical closed chassis, with ability to at least simulate bumpers as well… for this purpose of mounting prototypes. I assume some teams may do this.
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Thanks Allen, your videos always help.
A lot of prototypes will require spinning something. We have a bunch of 3D printed bearing blocks similar to the “Hype Blocks” linked above. So bearing blocks, a stockpile of old bearings, pieces of hex shaft and aluminum extrusion frame are handy to have in advanced.
To drive these devices, we have a bunch of 1/2" hex drivers and drill motors. If I need something at higher speed or more power, we have a box of 25 chain loops and a bunch of hubbed sprockets. These can be be direct driven from our stockpile of CIM motors with 1/2" hex shaft adaptors. There are several ways to power the CIM with a manual variable voltage supply.
Frames can be built with aluminum extrusion, plywood, 2x4’s, etc. But I’ve found that being prepared for the spinning stuff make rough prototypes quicker.
Definitely keep last year’s kitbot drive base and bumper together. Super handy for intake prototyping.
David
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We had the ends of a couple of pieces of 1/2 inch hex shaft material turned down on a lathe so they would fit in the drill chucks. We found it more secure than using a socket driver in the drill when running at high speeds. It also allows the shaft to run without support bearings if the side loads are small. We keep them with the tools rather than with the other hex shaft material.
Best way for our Team to learn this - by doing it.
We hold a “proto-fest” in the fall to get new Team members comfortable with FAST prototyping.
We stress that it’s OK for this to be a mess/not work/look “janky”. If your first proto looks clean and pretty, you’re doing it wrong. Be brave enough to be bad at something new. Try something weird that might not work.
Once they get over the fear of being graded/judged and relax… the magic happens. Usually by round 3 (see below). At about round 4 or 5, they usually can’t progress any farther without CAD (cutting plywood on the laser for a more durable prototype and/or something we can bolt onto a drivetrain to try it out).
Proto-Fest: You will need:
- Your Team
- Workshop or other large space
- Prototype Goal
- Concept Prototype Supplies
- About 5 hours
- Snacks/Candy
NO CAD or COMPUTERS (except for the plagiarism/research phase)
Schedule of Events:
- Break into groups of 2-3 people
- 3 people max, veterans AND new members in each group
Will have multiple “rounds” - Each round is ~ 70 min
Announce the Proto Goal (what are they trying to prototype?)
- 5 min research (phones/computers allowed here ONLY)
- 40 min build… something
- 15 min “show your idea” to the group
- 10 min snack break
Repeat for next round (iterate your design)
Supply list: (pardon the terrible formatting)
Cardboard (Costco!!) Plywood Aluminum foil
Springs clips/clamps Drills
glue/tape Box cutters xacto/snap knives
paper fasteners Protopipe and PVC pipe Scrap anything
Foam board Any wheels Spare DRIVETRAIN
Rolling surface/dollys rubber bands 3D printers
polycarb/acrylic Old motors Glue gun
Hype blocks legos surgical tubing
Construction paper Red solo cups toothpicks
popsicle sticks cheap wire rope / twine
Medium zip ties pipe cleaner craft foam
paper fasteners dremel tool 1/2" dowel (wood)
rubber bands resistance bands fishing line
cardboard tubes slow motion video
assorted springs from the FANCY hardware store
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