If you’re making a robot, you might not even need or want vertex groups. Especially if your meshes are tubelike or rods and you don’t want them to deform i.e. like human flesh. If that is true, then select the Armature, and change to Pose mode (CTR-Tab), then select EndMesh, and then SH-Select EndBone, press CTR-P and choose Make Parent to Bone, and do the same for the other two bones.
If you want to use the vertex groups, select all of the meshes, then SH-select the Armature and press CTR-P and choose Make Parent to Armature / Dont’ Create Groups. (You’ll have to LMB 3 times on the Dont’ Create Groups prompt … once for each bone/Mesh pair.
Now deselct everything (“A”), and for each mesh object :
select the mesh object
on the Buttons Editing (F9) / Modifiers panel, you’ll see a “Armature Parent Deform” entry, with a button labelled Make Real. Press that button and an Armature Modifier will be created. On the Armature modifier, click the Envelopes button to turn it off, leaving only the Vert Groups button turned on
You might also experiment with joining all the meshes into one object (select them all, press CTR-J) and parenting that joined mesh to the armature. It might give you a slightly different effect than your “separate” mesh setup.
Also instead of using the CTR-P / parent mechanism, you could select each mesh, add an Armature modifier manually using Add Modifer, then filling in the armature name in the Ob: field of the armature modifier. The main difference with this methdo vs the CTR-P method, is that if you select and move only the Armature while it’s i n OBJECT mode the mesh(es) will NOT “follow” automatically unless they are also selected (since they are not parented to the armature). If you only manipulate the armature while it’s in Pose mode, this is not a problem.
The difference between CTR-P/parent vs “manual Armature modifer add” is not clearly documented anywhere (that I’ve found yet), so I would use the CTR-P / “automatic parenting”.
The CTR-P mechanism also has the ability to “create groups from closest bones”, that would have saved you the job of creating them manually. It doesn’t work perfectly all the time though, so “tweaking” the vertex group assignments is usually neccesary, either with Weight Painting (select mesh CTR-TAB), or editng the mesh / Vertex Groups panel.
For more on this, look at the Bsod docs on the Wiki (links in my signtaure), particularly the Intro to Character Animation, and the Introduction to Rigging articles.