During the last weeks I did some science with my homebuilt linear drive. Of course the spring scale used to simulate side load is also self made and my "kilogram" prototype is actually a very special 3.557kg version of the platinum-iridium alloy in Paris:

Getting geared motors seems to be a problem in some parts of this planet, thus the transmission is simple, but works fine:

Currently some long runs will show if the mechanics keeps it's accuracy over time...