Kumbhakarna was a mechanical Robot?

The first Robot used in the wars was Kumbhakarna described by Valmiki in Ramayana, the world's oldest epic poem. In Ramayana, Kumbhakarna is referred as Ravana’s younger brother.
But he was not a living being at all, but a Yantra (machine/robot) similar to a tank but in human form. Ravana used Kumbhakarna sparingly, meaning, only during very difficult battle-situations, and it instantly turned the tide in Ravana’s favour.
May be due to its high maintenance, it was made to sleep for a period of about six months and awakened only when need arises or when it has to be re-fuelled.

Sage Valmiki writes the thoughts of Brahma when he saw Kumbhakarna :

    ध्रुवम् लोकविनाशाय पौलस्त्येनासि निर्मितः |
    तस्मात्त्वमद्यप्रभृति मृतकल्पः शयिष्यसे || ६-६१-२४
    (dhruvam loka vinaashaaya paulastyena asi nirmitaH |
    tasmaat tvam adya prabhR^iti mR^ita kalpaH shayiSyase || )
Translation: It is sure that you were created by visravasa for the destroyal of people. On that account, you will be sleeping apparently dead from now onwards.

Here, he clearly uses the word निर्मित (nirmitaH), which means ‘built/created‘ by Visravasa, who was Ravana’s father.

When Kumbhakarna was approaching Vanara Army and crushing them under his toes, they started to runway in fear. Then Ravana’s brother Vibhishana reveal the truth of Kumbhakarna to Rama and his army.

    उच्यन्ताम् वानराः सर्वे यन्त्रमेतत्समुच्छ्रितम् |
    इति विज्ञाय हरयो भविष्यन्तीह निर्भयाः || ६-६१-३३
    (uchyantaam vaanaraaH sarvE yantram etatsamuchchhritam |
    iti vijNaaya harayO bhaviSyantiiha nirbhayaaH ||)

Translation: Let all the monkeys be told that it is a kind of machine, advancing forward. By knowing this, they can become fearless by now.

    प्रक्षिप्ताः कुम्भकर्णेन वक्त्रे पातालसंनिभे |
    नासापुटाभ्यां निर्जग्मुः कर्णाभ्याम् चैव वानराः || ६-६७-३६
    (prakSiptaaH kumbhakarNena vaktre paataala samnibhe |
    naasaapuTaabhyaam nirjagmuH karNaabhyaam chaiva vaanaraaH ||)

Translation: Hurled by Kumbhakarna in his mouth which was looking like a hole in the earth, the monkeys again came out from his nostrils and ears.

How can person enter into a gigantic person’s mouth and come out of nostrils and ears, unless the giant is a machine with no internal anatomy ?

But in same Ramayana, it was clearly stated that Kumbhakarna was married with Vajramala and had kumbh, nikumbh as sons. These sons were killed by Hanuman. So, Kumbhakarna must be an alive brother of Ravana, who had developed a robot and was using it himself in great wars. Therefore the
Robot was named as Kumbhakarna. Kumbhakarna operated this Giant robot from its inside similar to AMP suit in Avatar movie.

AMP Suite of Avatar

Valmiki describes that Kumbhakarna used to kill even his own soldiers if they came in front of it. If our soldiers come in front of our tank they will be crushed, same thing happened there. Brother of Ravana could not see clearly who came close in front of his machine.

Rama

Rama used Vayuvyastra (a wind forced missile) to cut-off Kumbhakarna’s arm and then he hit arrows inside the mouth of the Robot and killed the brother of Ravana who was sitting inside. When Kumbhakarna was shot down by arrows of Rama, he died and the robot which had nobody to control it, fell into the sea.
Upon knowing the death of Kumbhakarna, Ravana and his sons wept.

In later (mis)translations Kumbhakarna has been (mistakenly) thought to have been a gigantic demon, while the Vanaras have been turned into monkeys. Infact Vanaras are humans with tail. Vaala(tail) + Nara(human).

Yoga Vasistha and Samarangana Sutradhara also has described war machines or Robots in ancient India.
 
Source:  Indian Culture and Science by Dr. P.V. Vartak