When the Mars-2 and -3 probes landed on Mars in late 1971, the Soviets announced that one of the mission objectives was "the development of technologies for future Mars rovers". This announcement took a new meaning in the early Nineties, when the Russians revealed that each lander carried a tiny rover having a mass of 4.2 kg, designed to collect data on the soil characteristics.
The rover was built by the Institute for Mobile Vehicles Engineering "VNII Transmash" and was called PrOP-M (Pribori Ochenki Prokhodimosti-Mars, Martian cross-country capability evaluation instrument) or "Marsokhodik" (tiny Mars rover). It was a small squarish 25 cm long, 22 cm wide and 4 cm tall rover using a couple of skids of an "articulated quadrilateral" configuration to walk at a speed of 1 m/h to a maximum distance of 15 meters from the lander. Marsokhodik was deployed on the ground by a six joint torsion spring actuated boom and was connected to the lander by a communication and power cable. On the front of the rover was a two pieces bumper used as a contact sensor. The rudimentary artificial intelligence of the rover could thus identify the position of an obstacle, after which the robot was to move back some step and to try to walk around the obstacle. To make a turn the two skids moved in opposite directions (I have seen a movie of a PrOP-M making a turn and I can tell you it to be most impressive!). Every 1.5 meters walked PrOP-M stopped to take measurements of the mechanical characteristics of the soil using its two instruments: a penetrometer and a radiation densitometer. More data could be collected by the analysis of the traces left during the walk, which was to be imaged by the lander's camera.
The Soviets planned to use the data collected by the robots to design the wheel systems of the future Mars rover. This approach was the same as used on the Moon, where Luna-13 collected data on mechanical characteristics of the soil using the "Gruntomer" penetrator and the "Plotnomer" densitometer, and these data were then used to design the large Lunokhod rover. Unfortunately, both Mars landers failed. Two additional PROP-M rovers were then flown on Mars-6 and -7 landers in 1973 but these too failed, Mars-7 missing the planet altogether.

I would like to thank James Garry for the huge amount of informations on Soviet rovers he provided me

Bibliography
Bogatchev, A., et al.: Walking and Wheel-Walking Robots
Kemurdjian, A. L., et al.: Soviet development of planet rovers in period of 1964-1990  In: Missions, Technologies et Conception des Vehicules Mobiles Planetaires; Toulouse, Cépaduès
Kemurdjian, A. L.:  From the Moon Rover to the Mars Rover; Planetary Report, Vol. X No. 4, July/August 1990, pp. 4-11
Kovtunenko, V., et al.: Prospects for using mobile vehicles in missions to Mars and other planets  In: Missions, Technologies et Conception des Vehicules Mobiles Planetaires; Toulouse, Cépaduès
Perminov, V. G.: The Difficult Road to Mars; Washington, NASA, pp. 7-8
Specimens of Space Technology, Earth Based Demonstrators of Planetary Rovers, Running Mock-Ups 1963-1990; Saint Petersburg, Joint-Stock Company Russian Mobile Vehicles Engineering Institute

Related Links
Science and Technology Rover Company Ltd.
Mars-3 Image of Mars Surface
A discussion on the Mars-3 Image
The Virtual Space Museum includes a virtual reality model of PrOP-M

For questions, suggestions and comments you can email me

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