I've copied your question and inserted my comments. You'll see them below.
For the study stage, we can post two pictures on the board with a sentence next to it:
1) Picture of a farmer milking his cows: ‘The farmer milks his cows at 5 am every morning.’
2) Picture of cows with full pails of milk next to her: ‘The cows are milked at 5 am every morning.
I can see how this would work but the choice of subject is unusual. Low level students rarely discuss pails, milking, etc.
Now we highlight the differences between the two sentences:
‘The farmer milks his cow at 5am every morning.’
S V Ob
‘The cow is milked (by the farmer) at 5am every morning.’
S V Ob
I don’t think your grammatical structures are correct.
Next we write the form on the board: auxiliary verb ‘be’ + past participle.
Could you elicit this from the students rather than just giving it to them?
Here we can add, to indicate that the object is not important:
‘The cow is milked by the farmer at 5 am every morning’ = ‘The cow is milked at 5 am every morning.’
This is good
We can also give them the past simple form of the passive voice: rather than giving it, can you elicit it from students?
‘Yesterday the farmer milked his cow at 5 am.’ (Active voice.)
‘Yesterday the cow was milked at 5 am. (Passive voice.)
Form: was/were + past participle.
To check the students’ understanding, activities in the study stage for low level students can be giving a list of active and passive sentences and having the students identify them correctly.
Ex.: ‘The chicken ate the corn: active or passive?
‘The chicken was eaten by the farmer and his family’: active or passive? Etc.
This is a good activity