Random positioning machine
| Other names | 3D clinostat | 
|---|---|
| Uses | The RPM rotates biological samples around two independent axes to eliminate the effect of gravity. | 
| Related items | clinostat, free fall machine | 
A random positioning machine, or RPM, rotates biological samples along two independent axes to change their orientation in space in complex ways and so eliminate the effect of gravity. RPMs are often used as an alternative to sub-orbital flights or drop towers in research studying the effects of weightlessness or microgravity on biological systems.