Questions about Elevator Specifics

[Jon Stratis]

Let's imagine a 2 (moving) stage elevator.

Continuous means you have a single cable that runs through every stage. Whel you pull on it, you'll (usually) have just the smallest stage moving (the one your mechanism is attached to, holding the game piece). Pull up 4 ft, and that stage moves up 4 ft until it hits the top. At this point, that stage is motionless, relative to the next stage. That next stage then starts moving, and if you pull another 4 ft, you get 4 more ft of movement. So in the end, 8 ft of pull gets you 8 ft of movement.

Thus, continuous results in the same size spindle for both up and down.

Cascade is a little different. The wire from the motor hooks on the outer stage, while the inner stage has a wire that goes over the outer stage to attach to a fixed point. So, when you pull on the wire, you start moving the outer stage, which also moves the inner stage. As a result, pulling 4 ft of wire pulls the outer stage up 4 ft, and the inner stage up 4 ft relative to the outer stage - 8 ft total. As a result, to power it down your spindle needs to be twice as big to give you twice the distance for the same rotation.

Now, for speed. In continuous, we saw that 1 ft pulled = 1ft moved. In cascade, 1 ft pulled = 2 ft moved. So, cascade moves twice as fast as continuous, assuming equal gear ratios, drum sizes, motors, and required force for lifting.

Now for force... This is where it gets tricky (and where I wish I wasn't on my ipad so I could draw a free body diagram for you). The inner most stage has a weight of w1. The outer stage has a weight of w2.

In continuous, your pulling up w1+w2. Pretty simple.

In cascade, you directly pull up w2. However, since the inner stage is affixed over the outer stage and attached to a fixed point, you end up doubling the weight. Think of it like this: the inner stage pulls down w1 AND the fixed point pulls down w1, otherwise he inner stage wouldn't stay up. Thus the outer stage has to pull up 2 x w2. So overall your pulling up w1+2 x w2. Essentially, you're doubling the weight of your game piece to lift it!

To put all of this in perspective, my team built two elevators in separate years. For Overdrive, we had a continuous elevator. It was slow, but had no problem picking up a trackball. For LogoMotion we had a cascade. It was very fast, and had no problem picking up an innertube, although I doubt it could have picked up the trackball. They were both powered by a fisher price motor through the FP gearbox.