I saw one old industrial robot(Year 1988) end effector is having 2 DC motor for roll drive. After roll drive, yaw and pitch drives are connected and it has dc motors separately.

But roll drive has two DC motors. Why are they used like this? why not single with higher torque.

All the roll, pitch and yaw motors are same spec. Total 4 DC motors.

Two DC motor connected to single shaft using gears in roll.

  • $\begingroup$ Can you identify the model of the robot or provide a picture or sketch? I'm very curious as I've never seen one of this configuration.... $\endgroup$
    – Andy
    Oct 9, 2015 at 7:34

1 Answer 1


Reusing parts is a very important and common concept.

Using the same DC motor 4 times means you have to deal with only one motor type. If you choose a 2nd type of motor for the roll, you have to fiddle with the characteristics of two motors. Using a motor with more torque usually means that you need a different drive circuit. From here on the problems are proliferating.

  • What if the supplier of the bigger motor stops selling the motor?
  • What if the driver circuit of the bigger motor does not have the precision of the smaller ones?
  • What's the price to buy 1 + 2 motors vs. buying 4 of the same kind?

If you are a company building industrial robots you buy DC motors in bulk. You use few standard motors that your engineers are familiar with. The driver circuits are proven and tested.

If you face a higher torque requirement, you simply add another familiar motor. It's not economical to pay somebody finding a better suited motor, which has several possible drawbacks as pointed out above.

As a company your goal is to sell robots, not to overengineer them.

  • $\begingroup$ Hi, thanks for your answer. could you please elaborate any other technical reason behind this? $\endgroup$ Oct 9, 2015 at 12:24

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