Where We've Seen Scissor Lifts

This Apply section will help students understand how converting motion with linkages is used in the real world by analyzing scissor lifts. The questions on this page can be explored as a group by facilitating a class discussion or individually having students write their ideas in their engineering notebooks. This can be used as a summative assessment such as a homework assignment or in-class formative assessment. Click this link (Google / .docx / .pdf) for the engineering notebook rubric and this link (Google / .docx / .pdf) for the collaboration rubric. The Motivate Discussion section provides questions to get students thinking about in what situations scissor lifts or linkages in general can be useful.

Scissor lifts are seen in the majority of major cities as well as construction sites and are helpful in making work environments more stable, safe and secure. Prompt your students to discuss how scissor lifts can be useful.

Q: What is the benefit of using a scissor lift compared to a ladder?
A: A scissor lift can usually extend further and remain more stable even when there are external factors such as wind or slight shaking. A ladder also requires a structure for it to lean on, while a scissor lift can raise vertically in the air without depending on another structure to be close by. This can be helpful when fixing power lines or other situations where the area of interest might be isolated. A ladder also usually only has the capacity to support one person at a time, while a scissor lift usually has a platform on the top that can support multiple people at once.

Q: Linkages can be used to create mechanisms such as the Grabber or scissor lifts, which can extend vertically (straight up) or horizontally (outwards). Are there other types of linkages that could enable mechanisms or robots to move?
A: Yes. A possible answer can be the four-bar linkage, which would allow a robot to raise and lower an arm or other device in an up and down elevator fashion.

Q: What could happen to the Grabber if more links were added to allow it to extend longer?
A: The Grabber could extend longer but also require more force to extend it as additional sections were added. It would also potentially become less and less stable the more links (Beams) that are added without reinforcing the rest of the design. If more Beams are being added, more 1x1 Connector Pins may need to be added as well to help reinforce the structure. Another option may be to use a stronger material such as steel.

Q: Scissor linkages are not only used for lifting. They are also commonly used for extending over a space or retracting to their compact forms on the side of a space. Where might you have seen a scissor linkage being used to extend over a space?
A: The best example is a scissor gate that is used for remaining compact while also being able to extend over a space. Some of the most common places to see scissor gates are at the tops of stairs in home with animals or young children, on storefronts as added security, in airports, or in old elevators.

To expand this activity, try the following:

• Have students work in groups to find pictures online of scissor lifts in use and then create a collage of these simple machines. Students can label each example with the profession in which it is used.

• Another option for this activity would be to build a scissor lift out of a different material such as cardboard. Cut out rectangular pieces of thin cardboard and connect them in the same design as the Grabber using push-pins or thumbtacks as the connecting pieces like the 1x1 Connector Pins. Experiment with different sizes of rectangular cardboard pieces. Instruct students to reflect on different designs by comparing and contrasting materials in their engineering notebook.