Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Back-driven Gearbox and motor

Back-driven Gearbox and motor

Back-driven Gearbox and motor

What kind of gearbox is best for being back-driven (driven in both directions - not sure if 'back-driven' is the exact term)? The driving torque would be quite small, to the point where the motor's rotor inertia needs to be taken into account. I wouldn't want a reduction ratio any greater than 20:1. I was informed that a cycloidal drive may be the way to go but I was hoping for a second opinion.


RE: Back-driven Gearbox and motor


Worm gears over 30:1 generally are not back-driveable. The problem is not the gear ratio. It is the worm's lead angle. As far as I know, most other drives are back-driveable, including harmonic drives. Talk to your gear/gearbox vendor, and/or read your machine design textbook.

The inertia of whatever is being driven is multiplied by the square of the gear ratio. For your 20:1 speed increaser, this means your driven inertia is multiplied by 400. That is a heck of a lot! An output shaft that does not budge will turn when you apply enough torque, perhaps with a wrench.

I worked with a system that had a 500:1 MicroMo gearmotor. I was unable to grab and rotate the output shaft. I was able to turn the scanner housing the shaft was attached to. I felt comfortable applying 100 lb.in of torque to the thing. I worked out the torque needed to accelerate the very tiny motor armature to its maximum allowable torque. This proved to be 40 lb.in. I asked, and I was told that gearmotors were breaking.

Do you have a mechanical engineer on site? This can be complicated.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close