For the new season, I am considering making some mechanisms out of non-shattering plastic that might not normally be (read: drivetrain), and am curious what the most rigid VRC legal plastic is. For example, I know that Delrin is less flexible than Lexan, but I am curious if there is a better option still.
You will, probably, need to bend it into L or C shape to have any rigidity without lots of extra screws. So important characteristic is how well it bends under heat and retains strength. Some sort of fancy origami you will need.
Sheet Lexan at a $$$ to use rate is your best bet when bending it to what you want.
Doing a 3D mill of material, I’d go with Nylon. Easy to cut, some flex but creating the shape and tapping the holes it’s your easiest strength option.
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Flexural Modulus of Vex Plastics, GPa, Various Sources
| Material | Wolfram Alpha (Mode Avg) | MakeItFrom | Specialchem (Min - Max) |
|---|---|---|---|
| Polycarbonate | 2.3 | 2.3 | 2.2 - 2.5 |
| Acetal-H (Delrin) | 2.8 | 2.9 | |
| Acetal-C | 2.6 | 2.6 | 2.8 - 3.7 |
| ABS | 1.8 | 2.1 | 1.6 - 2.4 |
| PEEK | 3.8 | 3.7 - 4 | |
| PET | 2.1 | 2.8 - 3.5 | |
| HDPE | 0.9 | 0.75 - 1.575 | |
| LDPE | 0.27 | 0.245 - 0.335 | |
| Nylon 6,6 | 2.8 | 2.8 | 0.8 - 3 |
| Nylon 6 | 3.1 | 0.8 - 2 | |
| PP-C | 1.3 | 1.0 - 1.4 | |
| PP-H | 1.5 | 1.2 - 1.6 | |
| FEP | 0.586 | 0.6 | 0.3 - 0.7 |
I would ignore the super high values from some of Wolfram Alpha’s results because they include filled plastics (with glass and carbon fiber) which are much stiffer.
From this it looks like your best options (for stiffness) are:
- PEEK (Only ~300$US for 1ft x 1ft sheet)
- Nylon 6 (Cannot buy in 1/16 sheets)
- Acetal Homopolymer (Delrin)
- Nylon 6,6
- Acetal Copolymer
- Polycarbonate
All things considered I would recommend Acetal Homopolymer (Delrin) because it is fairly stiff, laser cuts perfectly , low friction, strong, easy to machine, affordable, available. Last season I laser cut some Delrin and it was so smooth on the laser, even better than wood or anything. Just make sure to get the white color because the fumes from cutting the black color are way worse.
After that, Nylon 6,6. I haven’t tested it, but it seems good. It will probably laser cut very well. Strong, slightly cheaper. Good friction.
Then polycarbonate, but you aren’t supposed to laser cut it, its soft (not weak!), super cheap, poor friction, gummy on machining.
I asked in last year’s Q&A (sorry for stacking multiple questions in one) and whether or not legal base plastics with additives (teflon, glass fiber, carbon fiber) are legal. Not a very straightforward answer. Buutttt, if fiber reinforced plastics were allowed they would be the best for stiffness, but not for wear. Many fibers used are very hard and wear down mating surfaces. There are low friction modified plastics for wear.
(Also sorry for replying to old post I thought it said 2 day not 22 days)
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