One way to achieve linear motion using the VEX IQ parts is by using the rack gears in conjunction with the linear slider. Linear motion just means that the motion will be in a straight line.

Below is a common example of where students go wrong when constructing the linear sliders.

In the good example, the axle is supported on both sides of the gear, whereas in the bad example the axle is cantilevered, or only supported on one side. In VEX, it is generally a good idea to not cantilever wheels, gears, etc. The following examples are just a taste of what is possible to create using the linear sliders.

In the above example, one motor rotates two 12-tooth gears which make contact with the rack gears, causing the linear sliders to rise up the lift. This type of lift would be especially useful if you wanted to lift your payload linearly upwards (remember, linear=straight line!) rather than in a circular upward motion, like the arm lifts discussed in lesson 1.

In this second example, the horizontal linear motion of the rack and pinion is converted into upwards motion via the interconnected single bars, which make up the scissor lift. Scissor lifts are useful in that they can start out really short, then expand to many times their height. One downfall however is that they are often flimsy if constructed poorly, and it is quite hard to build a solid scissor lift.

## Design Challenges

1. Construct a “pusher” which uses the linear sliders to push the hexballs off of the middle wall in the VEX IQ Starstruck game
2. Build a mechanism which will tilt the VEX IQ Starstruck ramp in either direction using the linear sliders