The time machine is the primary means of time travel in the Doraemon series. Using it, one can travel through both time and space, usually by traveling in a "tunnel" of space-time.
One may decide the portal of access of one's time machine, homologous to a pier or parking place in common transport.
Doraemon's time machine
Doraemon's time machine is the most commonly seen time machine in the series. It consists of a nearly-square-shaped chassis, with various appliances mounting on it, such as controls, lightning, etc. According to official sources, the machine is magnetically powered.
Doraemon decided to place his time machine portal in the drawer of Nobita's desk, which is the exact place where Doraemon is introduced in the series.
In some feature-length stories, the machine has the ability of speech, helping the user to confirm the destination.
To conform with Doraemon's origins, his time machine is of a common model, and often prone to breakdowns or accidents, causing significant interruption to main characters' adventures.
In the 1973 anime, Doraemon's time machine had two seats and two levers. It was fully purple. The lightning wasn't present.
Dorami's time machine
To the contrary of her brother's machine, Dorami's time machine is of an advanced and luxurious model, priced at about 10 times of Doraemon's time machine. It is an orange (sometimes red) tulip-shaped machine with its leaf-like base works as solar panels.
The speed of Dorami's machine is double of Doraemon's, and also featuring much more safety measures. Dorami's time machine is more prominent in feature-length stories.
Dorami's time machine portal is in the mirror of her room.
Other time machines
There are also other kinds of time machines in the series. The most prominent batch are being used by the Time Patrol, thus comparable to police cars in the real world. There are also time machines used by time postmen for deliveries.
Many a times in movies, the time machine is used by the antagonists for the wrong purpose.
A king of the past used Time Machine mistakenly.
Time machine needs to be repaired sometimes.
When time bleeds occur, time machines could be displaces in time and fall in the vaccum of time.