Hey Hal,
I was thinking of the the one-man straight lift Genie. As long as the "level switch" is not disabled and the legs are in position they are very hard to tip over. They make many different Models, featuring different Heights and Loads.
I do understand you're not being comfortable with the small scissor lifts. They also have "level switches", that will not allow the lift to be raised on an unlevel surface. Most(excluding very old units) have a device on each side of the lift that lowers to the floor for added stability when the lift is raised. It's a pseudo outrigger type device.
You are correct that the small scissor lifts can be tipped over on it's side from a relatively small force applied to the side as it is raised. Each Unit is supplied with the specs regarding Load Weight, Platform Height at extension, Platform extension (if equipped) Load at Height, etc... I believe the Manuals list the minimum Force needed to tip them over.
These scissor type lifts are also made in different sizes, with again, different Loads, Physical Sizes, Different Heights attainable.
Only once is thirty years did I have a scare with any type of lift. Another Tech and Myself, were behind a Huge,(40'x 100') Flown, Video Wall. We were about 35' off the floor, changing an
intermittent cable and the Rigger saw another lift move from behind the wall. (He didn't know there was two back there) He "bumped" all of the hang Motors down, and did another quick "bump" in as the wall swayed a bit and caught the guard railing of the lift. As the Video Wall came in about 6"-1' it finally broke free from the railing and the lift bucked back, away from the wall with a great force, almost throwing us out of the lift.
Needless to say, the Tech and I had to do a drawer check!
Lesson: stay at least two feet from anything that moves.
Cheers,
Hammer