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So there was this one anime/cartoon when I was a kid that I watched but I can't remember its name.
But I remember that there were a boy, a girl, and a guy robot if you could say. The mission was to drive around with the tank and collect some kind of gems/diamonds (they are all different colour) and when they collect all 7 (I think it was that much) they will save the planet from blowing up.
Hamos The Green Chariot (Nogsaegjeoncha Hamos (original title) )
Originally aired: Dec 12, 1997 to Jun 12, 1998
The Planet Terra, once called a morning star in galactic system, was so beautiful. However, Terra is now under crisis that it may disappear with big explosion in universe due to the pollution and warfare. Dr. Chaco is the only one who knows the key of saving the planet Terra. The only way to save Terra is to make rainbow system work with seven mysterious crystals. To find 7 crystals, Dr. Chaco holds a race to achieve his plot to build his own universal dynasty with the power of the crystals. Riding Hamos, Rick joins the race not knowing Dr. Chaco's plot. Rick comes to know the secret of the crystals on the way of the race, tries to revive the planet Terra. This causes a war between Dr. Chaco and Rick to get the 7 crystals and rainbow system.
You can watch the whole series here. (Warning, Serbian dub)
Opening here:
Pretty sure you are talking about Power Stone.
It's an anime from the 90s/2000s, there are seven diamond-shaped colored stones, there is a boy, a girl and the MC transforms into something that resembles a robot. Not sure about the planet blowing up though.
Opening:
