You can buy linear actuators off the shelf, but none that allow for accurate displacement measurement AND high load rating for this price. The finished model shown can push or pull up to 300 lbs and it moves at about 0.5 in/min. I used it on a special project but you can use it for whatever you want!
This assembly is a component of the Testrbot open source universal test machine: http://www.instructables.com/id/TestrBot-The-300-Universal-Test-Machine/
I've also provided 'Base Type 2' files if you want to make a higher speed configuration. (In this config you wouldn't need the gears, as seen in photo 3.)
For complete Excel bill of materials see 'Actuator' section of TestrBot BOM here:
I picked a stroke of 5.375”, but the actuator can have any stroke you want. I have provided the equations below for determining the actuator component lengths for a given stroke, in case someone wants to use this design for something else.
Stroke = You pick!
Small PVC pipe length = stroke + 3.125”
Large PVC pipe length = stroke + 1.625”
Anti-Rotation Rod length = stroke + 2.625”
Threaded Rod length = stroke + 4”