Monday, September 24, 2018

Basics of power - Lesson 2

Today I'd like to get one of the other most fundamental aspects of projectile launching out of the way: power. How do we maximize the range at which we can throw projectiles? This will be a common goal for many builds, even if it's not perhaps a primary goal.

Today, our case study will be a famous pistol by a well-known veteran launcher builder Killerk, who now goes by Knex Lego Maniac on Instructables. Maybe we can go over more about him in a future "meet a builder" post, but back to his pistol. It was one of his first contributions and one of the most important to date. While old, its concepts are still relevant. Here are his instructions (note, you will be directed to I believe they should be easy enough for you to follow. His pistol expands on what we've already learned and adds a few new concepts that I'll go over below.


  • Striker lock - The tan peg connector at the back of the striker guide acts as a way to prevent the striker from being pulled out the back of the launcher on accident. It adds friction, but it can be well worth the trade-off to make it easier to recharge. 

Concepts - Maximizing range:

For striker-based launchers, these are the five main concepts for maximizing range.
  • Striker length - In general, the longer your striker has to travel, the more time it can build up speed and launch the projectile farther. So, in general, it's good to have a longer striker. Mostly commonly, you'll see a black/clear rod used. These colors use a less flexible material so the striker is less prone to bending when we stack on extra bands.
  • Striker guide length - This is always a trade off. In maximizing the distance the striker has to accelerate, you should have less dead space at the back of the launcher for guiding the striker. However, it's important to have enough to support the guide. The above pistol has a relatively long striker guide. Most modern builds will have about 2-3 connectors or a similar length to that.
  • Projectile lock - We learned in the last guide what these do, but they're also important for the range of a launcher. You don't want it to cause too much friction, and you want it to hold the projectile at the very end of the striker's range of travel to maximize the speed. On the above launcher, the ball socket connector acts as the projectile lock.
  • Friction - In general, we also want to avoid friction, anything that the striker or projectile comes into contact with. As such, you'll notice that many launchers don't have real barrels other than the chamber where the projectile is held. Barrels only serve to reduce the max range and don't really add any accuracy. So you'll notice that at the bottom of the instructions for the above launcher, he redesigned it to actually minimize the amount of connectors around the striker. 
  • Shock absorption - Finally, the striker is still made of relatively loosely connected plastic. It can only handle so much abuse before pieces fly off or perhaps even break. So, in order to stack on more rubber bands, you'll need to make sure the shock is adequately absorbed and distributed, and that the striker's construction is solid. However, this too is a balance because any extra pieces add weight and can reduce the length of draw for the striker, losing range. In general, make the striker as strong as it needs to be for the launcher and its intended use. 
So keep those in mind while building your own launcher. Speaking of which, have you tried designing your own yet? If you have, let me see them in the comments below by linking a URL to your pictures or video. If not, don't worry, we have more to learn and more opportunities for you to customize a launcher of your own. 

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