Cape Town - Two primary school pupils from a school in Cosmo City on the West Rand have invented a robot that keeps caves clean in a bid to preserve them.The robot that they called ''Mrs Klink'' was invented by Meridian Curro Grade 6 pupils Rethabile Moeketsi and Tshimologo Mafokosho who were worried about the damage that litter does to a cave.''We wanted to make something nobody had thought of,'' said Mafokosho, who is 11, and hopes to compete in the International Robotics Olympiad."Then we thought of something to clean a cave. Because if it is not cleaned, acid is created which is bad for the animals and bacteria and organisms in a cave.''Mafokosho explained that the robot has a prong which not only picks up litter and carries it out at their command, but it can also get into small spaces that the human body will not fit into.It was not first time lucky though and, says Mafokosho, they had to experiment with many models before they got the design right.''Our parents participated a lot, and our teacher stayed late,'' said Mafokosho, referring to Amanda Calitz, the Intermediate Phase Head at Meridian Cosmo City, who was listening.Moeketsi, who turns 12 on Wednesday, said they had visited the famous Sterkfontein caves and were shocked to find that people had randomly dropped litter. They decided that the cave cleaner would be a good way to preserve the ancient spaces that are revealing some of the secrets of early man.Rubbish dumpOnce they had fine-tuned it, they were in for a treat - being allowed to test it in the famous Rising Star cave system in Sterkfontein, where over 1 500 Homo naledi fossils were found. Homo naledi is considered the oldest known human relative.Senior Exploration Technician at Wits, Steven Tucker, said the robot the pupils built picks up rubbish with a grip on the front to take out of the cave.''It is a very useful way to clean caves, especially in areas people can't go to and areas people can't fit into.''Tucker says many people use caves as a rubbish dump, and this adversely affects the animals, bats, hyenas and porcupines that dwell in there.''At the same time, the ground water is very high so rubbish can get into their ground water,'' said Tucker.He said the children had to modify the tyres because they were getting stuck in the sand, but once they ironed that out, their robot worked well.He said it could also be used to monitor the bat and animal life in the caves in the area.''At their age it is quite amazing that they have done it,'' said Tucker.The two intend competing at the International World Robotics Olympiad, which is held every year to find the most innovative designs in robotics.