These robots were made from a few Cylinders and some Slabs.
1 Cylinders
Drag with the cylinder tool to create a cylinder, then use the height and width sliders to shape it.
Use the rotate tool to turn it 90 degrees into place.
Use "Duplicate" (Ctrl+D) to make some copies and scale them too.
(The same process was used for the spheres)
2 Slab
Draw a rough outline with the Slab tool. This will give you a smooth sided shape.
Use the Curve Ruler tool to drag out straight sections onto the original curve.
Draw another curve inside the first to cut a hole in the slab.
Use the "Redraw as Ellipse Arc" on the hole's curve to neaten it up.
Change the Slab's depth with the depth slider.
3 Screenshot
I used the "View/Panels/Camera" panel to change the camera distance to enhance the perspective in the scene.
Then "View/Screenshot Popup" and I saved a Layered Screenshot as TGA to get an alpha channel cutout of my drones as well as an ambient occlusion render.
Backdrop and colour added in GIMP.