Cont. Rot. Servo to use in place of a DC motor or should I just get another motor?

[lsu_tiger]

Hi,

I currently have several robotic vehicles that are using Pittman brushed DC motors as their propulsion (one for each side - tank style). The motor is a Pittman GM8712-31 and I’ve included the specs below. Speed is not as critical as torque and very low current. Currently the motors are running at 12volts and draw less than 1.5A at full load. I was looking at HS-805BB and GWS S677/2BB, but I can’t tell if either is continuous rotation and I saw in another thread that the duty cycle for the HS-805BB is recommended at 20-25%. Since these are propulsion motors, my duty cycle is 100% for long periods of time (multiple days).

Am I just crazy to be looking at servos at all? I am also open to another DC gear motor so if anyone has a recommendation on those, that would be great too. The one I found on RobotShop.com so far is the PGHM-02.

Any help is greatly appreciated.

[cbenson]

Neither the 805BB nor the 677 are continuous rotation, though you can modify either (voiding the warranty) to rotate continuously. If the robot is small, people often select continuous servos for their ease of installation, price and easy to install accessories (such as a wheel). However, these robots are usually restricted to robots you can easily hold in your hand. As the robot becomes larger, most people opt for DC gear motors. Take a look at the Drive Motor Sizing Tool for ideas.