I'm looking here for suggestions.

I have a HS-805BB with Torque (Kg-cm/Oz-in): 24.7/343 @ 6.0 V to rotate a robot body up and down from one side. It seems to me that this servo is always running at its maximum torque which is not good for its life span and battery consumption, so I thought of two solutions:

  1. Install a second servo on the other side and have both servos working parallel.
  2. Build a gear box to increase the Torque limits.

What are you suggestions as to which option is most preferable?


1 Answer 1


Installing a second servo for moving the same axis might be problematic from a controls point of view. Since (I assume) your servos are position controlled (and not torque controlled) delays in commanding them and mechanical tolerances of the assembly may lead to stations where the two servos act against each other at the beginning or at the end of motions (maybe even during). E.g. fits servo receives a command to pull, starts pulling, the other one receives the same signal a few ms later, until then the first one is acting against the second one.

If you have rpm reserves, installing a gearbox would be a good solution.

You can also install some kind of balancing (e.g. preload with a spring) or counterweight mechanism is your application allows this (e.g. elevator have counterweights, robots have springs sometime in the lower joint acting against gravity).

  • $\begingroup$ Using springs as mechanical energy suppliers was an idea I had previously but fitting it on my actual design was a bit of challenge to me with my lack of experience in robotic design. My concern with the gearbox option is that it will limit the max rotation the robot will have. $\endgroup$
    – Iron Fist
    Commented Mar 26, 2018 at 8:12
  • 1
    $\begingroup$ When considering springs, don't forget about torsional springs. They can be mounted right on the axis of rotation, and finding the space for them can often be a lot easier than for linear springs. $\endgroup$
    – SteveO
    Commented Mar 26, 2018 at 13:37

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