You sometimes do need to use the future tense in dependent clauses.
We need to review the sites you will visit in Venice.
*We need to review the sites you visit in Venice.
But you don't do it if the future is already implied by another verb in the sentence.
Write to me and tell me all about the sites you visit in Venice.
*Write to me and tell me all about the sites you will visit in Venice.
(Actually, the last sentence sounds fine if you will be writing before you visit Venice.)
What I think is going on is that you use the future in the dependent clause only if the action in the dependent clause takes place considerably farther in the future than the action in the main clause. That is, you judge whether the tense in the dependent clause should be the present or the future by looking at the time of action relative to the action in the main clause. Consider:
We will teach you everything you will ever need for your job.
*We will teach you everything you ever need for your job.
Here, you need to put the dependent clause in the future because it takes place in the indefinite future after being taught.
In your sentence,
We might be able to figure this out from the schedules you send us,
the dependent clause clearly has to happen before the action in the main clause. Thus, you cannot put this dependent clause in the future.
For some additional examples, consider the following sentences:
Go to Union Station, figure out which train will leave for New York at 4pm, and watch it to see whether Dr. X boards it.
The verb in first dependent clause (will leave) takes the future, because the train leaves after you find it. The verb in second dependent clause (boards) takes the present and cannot take the future, because he will be boarding it while you're watching it. You could instead say "which train leaves for New York at 4pm", but only because it's a habitual action—a train leaves for New York every day at 4pm. To see this, consider the sentence:
Go to the garage, ask the attendant which car Dr. X will drive to New York, and leave this note on it.
Here, if you said "which car Dr. X drives to New York", you would be implying that he always drives the same car to New York.
You sometimes even have to use the past tense for dependent clauses that are set in the future, if they are in the past relative to the action in the main clause:
Next Tuesday, go to the Grand Hotel, figure out which room Dr. X slept in on Monday night, and ransack its wastebaskets.
Dr. X sleeps before the action in the main clause, so you have to use the past tense.
The first conditional is a special case of this rule
If his train comes on time, we will miss Dr. X at the station.
In a conditional sentence, the dependent clause almost always takes place at the same time or before the action in the main clause, so you cannot use the future in the dependent clause.