×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Unique rack an pinion system with fixed and movable rack

Unique rack an pinion system with fixed and movable rack

Unique rack an pinion system with fixed and movable rack

(OP)
Hi

There is a special rack and pinion system that uses pinion travel along a fixed rack to drive a second rack coupled to it for double the distance and hence double the speed.In other words the movable rack will travel double the distance that is traveled by the pinion.Now as per my calculations it doesn't seem this mechanism causes any increase or decrease in torque applied but I would like a second opinion on this. I attached a drawing of system for clarification.

I'm thankful for sharing your thoughts.

Regards

RE: Unique rack an pinion system with fixed and movable rack

For a rack and pinion moving a load vertically, if you have a load attached to either the second rack or the pinion stage itself (in a case without the second rack) that load would be moved twice as far with the load attached to the second rack for a given number of turns of the pinion gear. The potential energy of the case with the second rack is twice as much as that for a single rack and pinion so it required twice as much energy to get there.

Neglecting weight of the rack and pinion components and any additional frictional losses.

From an FBD perspective, the difference is the weight of the load acting on the axis of the pinion or acting at the gear radius so when you sum the moments about the pinion axis it will double the torque required.

RE: Unique rack an pinion system with fixed and movable rack

(OP)
Thanks for your response.

my actual interest here is in torque required to move second rack. I did a FBD and fund the torque required to be the same since pinion radius is the same between both racks. meaning force of load on moving rack will be the same as force moving the pinion.

allow me to show you and please correct me if I'm missing something. excuse my bad drawing skills.

RE: Unique rack an pinion system with fixed and movable rack

There are two loads on the pinion, both acting counter clockwise, so a 2X 200 N-m = 400 N-m of torque and it will take 400N vertical force to support the pinion pivot.

If the pivot of the pinion was fixed, there would be only the 200 N-m torque on it from one rack and 200 N vertical force to support it.

RE: Unique rack an pinion system with fixed and movable rack

(OP)
in the example I'm giving in my FBD there is one load acting downward on Movable rack. how does this translate into two loads? the movable rack induces torque which when divided by distance between pinion pivot and fixed rack will produce downward motion in pivot; since distance between pivot and both racks is equal the force induced in pivot should be same as force acting on Moving rack.

atleast that is how I see it; is their a flaw in my analysis?

RE: Unique rack an pinion system with fixed and movable rack

Each rack is applying a load to the pinion and they must be added. Two loads with a lever arm equal to the pinion radius.

Another way to look at this is that the moving rack is applying a load to the pinion, which then pivots on the stationary rack. In this case you can look at it as one applied load but the lever arm is the pinion diameter rather than the radius.

RE: Unique rack an pinion system with fixed and movable rack

(OP)
How can the fixed rack apply load to the pinion when its stationary?

the way I see it torque induced in the pinion transforms into downward force due to interaction with fixed rack. in other words fixed rack only helps pinion convert torque into force but it doesn't apply any force on its own.

RE: Unique rack an pinion system with fixed and movable rack

Stationary is a relative term. If you wish to consider the fixed rack as your frame of reference, then you analyze it the second way I mentioned above. If you take the pinion as your frame of reference, you use the first method. You could also use an energy method to to analyze what is happening. Work is force times distance and energy must be conserved. You cannot switch frame of reference in the middle of an analysis.

We cannot explain it any clearer than this. Now it is up to you to understand.

As for "How can the fixed rack apply load to the pinion when its stationary?" Try to remove the fixed rack and see what happens. What do you think it is doing?

RE: Unique rack an pinion system with fixed and movable rack

Look at the pinion and its interactions with the racks on either side. The center of the pinion's shaft (where the force is applied) and the two contact points on either side are literally a class 3 lever.

This applies if the assembly is static, and disregarding additional forces due to accelerations of the components, at any 'snapshot' during movement.

RE: Unique rack an pinion system with fixed and movable rack

(OP)
Thanks alot jgKRI for the good explanation and drawing. I can see my mistake very clearly right now.

My major mistake is I applied the moment created by force on moving rack around the pinion center; while the actual moment was created about interaction point between pinion and fixed rack.


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


Resources

White Paper - Strategies to Secure Connected Cars with Firewalls
White-hat hackers have demonstrated gaining remote access to dashboard functions and transmissions of connected vehicles. That makes a firewall a vital component of a multilayered approach to vehicle security as well as overall vehicle safety and reliability. Learn strategies to secure with firewalls. Download Now
White Paper - Model Based Engineering for Wire Harness Manufacturing
As complexity rises, current harness manufacturing methods are struggling to keep pace due to manual data exchanges and the inability to capture tribal knowledge. A model-based wire harness manufacturing engineering flow automates data exchange and captures tribal knowledge through design rules to help harness manufacturers improve harness quality and boost efficiency. Download Now
White Paper - What is Generative Design and Why Do You Need It?
Engineers are being asked to produce more sophisticated designs under a perfect storm of complexity, cost, and change management pressures. Generative design empowers automotive design teams to navigate this storm by employing automation, data re-use and synchronization, and framing design in the context of a full vehicle platform. Download Now
eBook - Simulation-Driven Design with SOLIDWORKS
Simulation-driven design can reduce the time and cost of product development. In this engineering.com eBook, we’ll explore how SOLIDWORKS users can access simulation-driven design through the SOLIDWORKS Simulation suite of analysis tools. 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