Learn Hardcore German: Wir haben heute das Fahrrad vom Mechaniker repariert bekommen. - Today we had the bicycle repaired by the mechanic.

So "Wir haben heute das Fahrrad vom Mechaniker repariert bekommen." focuses on us as people who received the service of the bike being repaired, not on the act of repairing itself.

Why do we say "repariert bekommen" and not just "repariert"?

If you said:

Wir haben heute das Fahrrad repariert.

this would mean: We repaired the bike today ourselves.
We are the ones who did the repairing.

By adding "bekommen":

Wir haben heute das Fahrrad repariert bekommen.

you say: We had the bike repaired / We got the bike repaired.
This makes it clear that someone else did the repairing, and we are the beneficiaries/recipients of that action.

Who is actually doing the repairing in this sentence?

The repairing is done by the Mechaniker:

vom Mechaniker = by the mechanic

The subject wir are not the ones repairing; we are the ones whose bike was repaired, i.e. who got the service.

So the roles are:

Wir – subject; the people who got the service
das Fahrrad – the thing that was repaired
vom Mechaniker – the agent (the person actually doing the work)

Why is the helper verb haben used and not sein?

The auxiliary belongs to bekommen, not to reparieren.

The main finite verb in the sentence is bekommen.
The perfect tense of bekommen is haben + bekommen:
- Ich habe etwas bekommen.
- Wir haben das Fahrrad repariert bekommen.

So you use haben, because bekommen always forms its perfect with haben, never with sein.

Why are there two participles in a row: "repariert bekommen"?

It only looks like two equal participles; grammatically they play different roles:

repariert: Participle of the main action verb (reparieren)
bekommen: Participle of the auxiliary-like verb that makes the bekommen-passive

The perfect tense is built on bekommen, and repariert stands before it as a kind of “verbal complement”:

infinitive pattern: etwas repariert bekommen
perfect: Wir haben etwas repariert bekommen.

You could compare it loosely to English:

“We have had the bike repaired.”
(where had and repaired appear together)

What tense is "Wir haben ... repariert bekommen", and how would the simple past look?

The sentence is in the Perfekt (present perfect):

Wir haben heute das Fahrrad vom Mechaniker repariert bekommen.

A simple past (Präteritum) version would be:

Wir bekamen heute das Fahrrad vom Mechaniker repariert.

This is correct but sounds a bit formal or written in modern standard German. In everyday spoken German, the Perfekt version is much more common.

What does "vom Mechaniker" mean exactly, and why vom, not von dem?

vom is simply the contraction of von dem:

von (from/by) + dem (dative masculine/neuter singular article) → vom

So:

vom Mechaniker = von dem Mechaniker = “by the mechanic”

Grammatically:

von takes the dative case
dem Mechaniker is dative masculine singular

In the context of passive-like constructions, von + dative marks the agent (the doer) of the action.

Could we also say "durch den Mechaniker" instead of "vom Mechaniker"?

You can say:

Wir haben heute das Fahrrad durch den Mechaniker repariert bekommen.

but in this kind of sentence "vom Mechaniker" is more natural.

Rough rule of thumb:

von + dative = typical for agents in passive / bekommen-passive:
- Das Fahrrad wurde vom Mechaniker repariert.
durch + accusative = stresses the means or instrumentality, often used when the agent is more like a mechanical or impersonal cause:
- Die Stadt wurde durch ein Erdbeben zerstört.

With a concrete person as the agent in a passive-like structure, von is the default choice.

Where can "heute" go in the sentence? Is the word order fixed?

The given order is:

Wir haben heute das Fahrrad vom Mechaniker repariert bekommen.

This is very natural:
subject – finite verb – time – object – (other info) – participles

Other acceptable variants:

Wir haben das Fahrrad heute vom Mechaniker repariert bekommen.
Wir haben das Fahrrad vom Mechaniker heute repariert bekommen. (less usual, but possible)

You can also front heute:

Heute haben wir das Fahrrad vom Mechaniker repariert bekommen.

What you cannot do in a main clause is break the verb brace incorrectly, e.g.:

✗ Wir haben heute das Fahrrad vom Mechaniker bekommen repariert. (wrong)

How would this look in a subordinate clause with dass?

In a dass-clause, all verb forms go to the end, and the order is:

other elements
repariert (the lexical participle)
bekommen (participle of the auxiliary-like verb)
haben (finite auxiliary)

Example:

..., dass wir heute das Fahrrad vom Mechaniker repariert bekommen haben.

Wrong versions to avoid:

✗ ..., dass wir heute haben das Fahrrad vom Mechaniker repariert bekommen.
✗ ..., dass wir heute das Fahrrad vom Mechaniker haben repariert bekommen.

What is the difference between "repariert bekommen" and "reparieren lassen"?

Both can express that someone else did the repair, but there is a nuance:

bekommen-passive – result / experience focus
- Wir haben heute das Fahrrad vom Mechaniker repariert bekommen.
  → We got the bike repaired; we ended up with it repaired.
  Focus: our state/result as recipients of the service.
lassen – commissioning / causing focus
- Wir haben heute das Fahrrad vom Mechaniker reparieren lassen.
  → We had the bike repaired / we arranged for it to be repaired.
  Focus: our decision / initiative to have it done.

In many everyday contexts, both are possible and very close in meaning. If you stress that you organized it, lassen often fits slightly better; if you stress the result that you have it repaired now, bekommen works very well.

How would you negate this sentence, and what changes in meaning?

Default neutral negation of the whole event:

Wir haben heute das Fahrrad vom Mechaniker nicht repariert bekommen.
→ We did not get the bike repaired by the mechanic today.

If you want to say that the mechanic wasn’t the one who repaired it (someone else did), you’d negate the agent phrase:

Wir haben heute das Fahrrad nicht vom Mechaniker repariert bekommen.
→ We got the bike repaired today, but not by the mechanic.

So the position of nicht tells you what is being negated:

nicht repariert bekommen → the repairing never happened (for us)
nicht vom Mechaniker → the repairing happened, but with a different agent

What is a good natural English translation of the whole sentence?

A very natural translation is:

“We had the bike repaired by the mechanic today.”
or slightly less explicit about the agent:
“We got the bike repaired today (by the mechanic).”

These capture both the meaning and the focus on “we” as recipients that the German bekommen-passive expresses.