Elevators & Cranes: The Engineering of Linear Slides

A construction crane extends telescopically. An elevator rises smoothly 100 floors using cables. In FTC, we frequently need to reach “High Junctions” (30+ inches). We use multi-stage linear slides (often called Viper Slides or Misumi Slides).

The Telescopic Challenge

Imagine stacking 4 drawer slides on top of each other. When the first one extends, it pushes the second, which pushes the third. But how do we power it? We can’t put a motor on the top segment (too heavy). The motor must stay at the bottom. We use String Rigging.

Continuous vs. Cascading

There are two main ways to wire an elevator:

1. Continuous (The Bucket)

One long string goes from the motor, up to the top pulley, down to the bottom of the next slide, etc.

• Behavior: The first slide goes up. Then it hits the stop. Then the second slide goes up.
• Pros: Low force on the motor.
• Cons: Slow.

2. Cascading (The Zipper)

Every slide is connected to the previous one with its own loop of string.

• Behavior: ALL slides expand simultaneously. The robot shoots up like an explosion.
• Pros: Insanely fast.
• Cons: High force. Requires precise string tensioning.

Bearings and Binding

The enemy of slides is Friction. If the slides tilt even slightly, they jam (Binding). We use Ball Bearings or V-Groove Bearings to ensure smooth motion. The best teams use 3D printed custom inserts to hold the string perfectly in place. Building a reliable slide is a rite of passage for a mechanical lead. It teaches you that “Straight” means perfectly straight.