topic Re: Curved rack in Fusion Design, Validate & Document Forum

Curved rack

pjreijiri — Fri, 10 Feb 2017 14:54:13 GMT

Hello everyone,

I need some advice. I am trying to design a rack for guiding a machine that travels parallel to the ground. The track have linear sections and curved sections. I started my design with a rack and pinion. Is there any rack that is similar to the one in picture?

Or should I have the teeth on rack perpendicular to the floor?

Thank you

Re: Curved rack

etfrench — Fri, 10 Feb 2017 19:16:26 GMT

No, it isn't possible to have a set of gears like that. As you suspected, the teeth have to be on the vertical faces.

Re: Curved rack

pjreijiri — Fri, 10 Feb 2017 20:57:30 GMT

Would the pitch be different or it stays the same?

Re: Curved rack

etfrench — Fri, 10 Feb 2017 21:11:06 GMT

The pitch (or module) of the curved and straight sections must be identical. If you put the teeth on the outside of the curved sections, you can use the built-in spur gear script to create those teeth. See this video for more details: https://www.youtube.com/watch?v=khG4Zk5XZrw

Re: Curved rack

pjreijiri — Sat, 11 Feb 2017 06:19:01 GMT

One me question. The chair lifts, the ones that are used for elderly people and people who cant go up the stairs. How do they operate? What is their concept? Is it rack and pinion or wheels? Since it has movement in the horizontal and vertical planes

Re: Curved rack

etfrench — Sat, 11 Feb 2017 06:42:30 GMT

They can be either rack and pinion or cable driven.

Re: Curved rack

pjreijiri — Sat, 11 Feb 2017 06:55:44 GMT

If it is rack and pinion how do they get up the stairs (vertical inclination) and have horizontal movement as well with a rack since it can't have curves in both direction?

Re: Curved rack

etfrench — Sat, 11 Feb 2017 07:12:50 GMT

It depends on your point of view. If you used the rail you show in the first post for a stair lift, it would need to be rotated 90 degrees.

Re: Curved rack

pjreijiri — Mon, 13 Feb 2017 11:20:34 GMT

This is how the rack would look like. Any thoughts? is it feasible?

Re: Curved rack

pjreijiri — Mon, 13 Feb 2017 14:36:55 GMT

If you check this video, you can see the rack curved. I want to see how to design a rack like that.

You can see it at 4:15 and later on in the video as well

https://www.youtube.com/watch?v=B5qik-AAO1w

I am not making any advertisements in any way.

Re: Curved rack

TheCADWhisperer — Mon, 13 Feb 2017 14:45:18 GMT

On mating gears you want the pitch to match.

Since this rack is curved a liberal amount of clearance (backlash, slop, whatever technical term) must be allowed because you will not achieve perfect pitch along entire length.

Because the application is low speed, the extra clearance should not be an issue as long as the teeth do not skip because of the clearance.

I would run the mechanism in analysis software to verify.

Re: Curved rack

pjreijiri — Mon, 13 Feb 2017 14:58:26 GMT

would proper joints and contact sets in Fusion 360 do the trick in trying to do the simulation?

also is it good practice to have the straight sections with backlash equal to an amount A and on the curved sections have a backlash bigger than A and then it goes back to A?

EDIT: another approach that I am thinking of is instead of changing the rack pitch I just increase the distance between the rack and gear, for the curved sections and then decrease it to the previous distance.