High torque Auto Chain Motors are virtually only a regular, internally commutated brushless DC Motors mounted with extra gear mechanism on top, to either increase the torque or to decrease the RPM (Revolutions per minute). These DC motors are peaceful effective and can be used in several hobbyist and commercial application.
Reducing the RPM whilst maintaining high torque would require adding up more technical gear mechanism hence the cost of these High torque DC motors mainly depends on the RPM, torque and quality of the motors.The electric motor shaft from the bottom motor though a transmission connects the tiny gear box fixed at its front portion, which in turn generates the necessary torque while keeping the RPM low, the whole gears and gear heads are doped with thick viscous grease lubricant.
These High torque Motors come on numerous RPM's such as, 5 RPM, 10 RPM, 100 RPM, 300 RPM, 1000 RPM and so forth. The expense of these geared motors is based on the RPM, usually lower RPM costs more than those of higher RPM.
Applications
High torque and low rpm DC motors are well suited for robotic and hobby applications, thought how big is the motor is a matter of concern because it is quiet huge in size due to additional equipment box but still it would save the trouble and 
cost of adding external gears to the assembly of robots where simply the standard DC motors wouldn't prosper. The High Torque, Low RPM DC motors includes inbuilt gearbox mechanism providing necessary torque for your robotic application. Hence these motors will be the many favorable choice for the hobbyist robotic tasks and tutorials posted right here.