This small yet powerful motor is great solution for small robot operating at 6 Vdc with a reduction ratio of 250:1 and 50 rpm
 

Specifications and Features:

• Rated voltage: 6VDC
• Tested voltage range: 3V to 9V
• Speed at free run, 6V: 50rpm
• Current at free run, 6V: 40mA
• Stall Current, 6V: 360mA
• Stall torque, 6V: 0.3kg-cm (Approximately = ~0.029Nm)
• Weight: 10g
• Gear ratio: 250:1
• Shaft: D-shaped with 3mm diameter, 9mm in length
• Motor dimension: 10 x 12 x 34mm
• Sample applications: small mobile robot, sumo robot, small balancing robot, miniature parking gate