Expansion Questions

I gone through a lot of vex forums, and searched online, but I still have some more questions about how to create a good expansion.

  1. I have two different widths of string: one is 3.2 mm and the other is 4.625 mm. The minimum is 3.125 mm and the maximum width is 6.35 mm, so which string should I use? Are thinner strings better since they are less heavy, and should I be that close to the limit?

  2. Another question is how long the string should be. I’m assuming that the robot would be in one of the corners when expansion deploys, so should the string to be 12 ft long for each expansion, or should it be longer to reach more squares or shorter to avoid expanding outside? (pythagorean theorem? → 12^2 + 12^2 = c^2 → c = 16.97 ft long???)

  3. How would 3 catapults should be released if we are using a motor? I was thinking that the 3 catapults would be all together facing out in 3 directions, with the back end of each coming out of one point. The back ends would have a standoff poking out, and then a red motor would have some sort of hoop that can be spun down onto the standoffs. I’m not sure if the force from the expansions would cause the hoop to be stuck when trying to lift off of standoffs, or the force from the expansion might prevent the hoop from locking them in place. Any ideas for a release mechanism with a motor for 3 expansions? (see below for sketches- sorry for blurriness)

  4. Last question is how the payloads are stored. I don’t think I have any of those huge nuts that 606X uses in their expansion, so what payload would I use and how would I mount it so that it won’t accidentally fall off or misfire?


3 expansions facing outward with back ends coming out of one point

Using angled gussets as the hoop(kind of like in 606X expansion video)

Using just a piece of metal extending outward from gear with standoffs connecting at the end as a hoop, and when motor spins, hoop spins off of standoffs. The little loop in the bottom drawing are rubber bands to counter the force of expansions lifting upward, but the torque motor can still spin and release expansion.

  1. I would recommend using the 3.2mm string since its overall lighter and takes up less space when you pack up the string, although the difference isn’t a huge deal.

  2. Most teams either use 4-6 strings for expansion. Usually, you have two of the string facing towards the edges of the field at the low goals. Those strings are shorter compared to the other 2-4 strings that face towards the opposite corner. Avoid making your string too long to prevent it from expanding out of the field.

  3. I’m not entirely sure what you mean by “catapults”, but I’m assuming you’re referring to the weights that are winded up using rubber bands on the ends of the string. My team uses pneumatics to launch our expansion, so I’m not very familiar with using a motor for releasing expansion, but yea I would think your idea with spinning the metal to release the standoffs would work, just make sure the entire mechanism is connected to all your expansion setups since it is a waste to use more than one motor for your expansion.

  4. My team uses HS shaft colours and thread a zip-tie through the hole and create a loop that wraps around the standoff that releases the string. The weight doesn’t have to be insanely heavy as long as there is enough tension on the rubber bands. Just make sure that the tension isn’t too much or otherwise the weight can recoil backwards when the string reaches its maximum length.