Does anyone know anything about scissor lifts? I'm making a small lifting table (not for people, and not very high, so safety's not a huge concern for me). I came across this equation for calculating the force needed by a linear actuator to power it: http://www.engineersedge.com/mechanics_machines/scissor-lift.htm I can do the equation well enough, but the ideas behind it have me confused. For example, by dividing the weight by the tangent of the angle the arms move to, the force needed is vastly higher for a device that only extends the arms a small amount (hope that makes sense). In other words, if you make the lifting arms extend almost to vertical, you need much less force. This would make sense to me if you're talking about total work, since the load would move over a greater horizontal distance. But it's force. Moreover, a larger angle (and therefore lesser tangent value) must move through that smaller angle, with its greater force requirements, en route to its final position. So how could that greater angle possibly require a lesser force? I know that's confusing; I'm just trying to wrap my head around this so I understand it rather than just plug numbers into the equation. By the way, here's the specific design I'm looking at. The table will support up to 200 pounds (a tremendously rounded off figure). It would consist of lifting arms that are 21 inches long with a raised angle of 45 degrees. There would be two tiers of the scissor lift, raising the table 30 inches. This would require a force of roughly 400 pounds for the linear actuator, according to the equation. Any advice/thoughts would be greatly appreciated!
A couple quick notes. The 400-lb supply of force and resulting 200-lb payload were determined largely by the selection of linear actuators I've found online. The travel distance of the actuator's arm to raise the 21-inch lift arm to 45 degrees would be roughly 6 inches.