Previous in Forum: Calculate The Weight Of The Mini Quadcopter   Next in Forum: Motion in Perpetuity, Not Violating Thermodynamics
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
17 comments
Rate Comments: Nested
achpek
Member

Join Date: Nov 2015
Location: Richmond, VA
Posts: 7

Help Needed With Bearings for U-joint

05/02/2017 3:45 PM

Hi all!

I'm designing a u-joint for a robotic arm type of thing. Its my smallest joint and it can fit in a 1" or 2" box.

Assume, the max deflection between adjacent joints is 30 degrees. There is practically no RPM, so friction isn't a factor. Constant room temperature. Load is moderate, say 5 kg per bearing, but absolutely no idea about momenta.

My connecting rods (qty 2) that keep yoke, bearings (qty 4) and both sides (qty 2) of u-joint together are 5-6 mm in diameter, roughly 1/4". So the bearing ID is 5-6 mm or 1/4" and OD is about 10 mm.

Here is the catch: I need to achieve superior precision in positioning and repeatability, I want practically no lash at all.

What type of bearing (bushing?) would be best? Angular contact ball bearing?

Do I have to get high-precision bearings such as ABEC-7 or ABEC-9?

Can I use lower grade bearing and just pre-load it?

Is less Bearing Internal Clearance better?

Am I missing something in my picture?
Register to Reply
Pathfinder Tags: bearing precision u-joint
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
ronc
Power-User

Join Date: Dec 2016
Location: Baytown Tx. USA where you get your gasoline,chemicals,plastics and floods
Posts: 278
Good Answers: 6
#1

Re: Help needed with bearings for u-joint

05/02/2017 4:00 PM

McMaster Carr.

__________________
 formally known as texasron (proud to be an Aggy)
Register to Reply
Jpfalt
Guru

Join Date: May 2016
Posts: 1746
Good Answers: 87
#2

Re: Help Needed With Bearings for U-joint

05/02/2017 4:22 PM

Use opposing angle contact ball bearings and preload them.

Have you considered that with the angle offset, given a constant rotation rate on the driving shaft, the driven shaft will accelerate and decelerate during the rotation with the acceleration curve being sinusoidal.

If you want constant input rate and constant output rate, you will need to use a constant velocity joint or a flexible coupling, rather than a u joint.
Register to Reply Score 1 for Good Answer
No more "Almost" Good Answers.
achpek
Member

Join Date: Nov 2015
Location: Richmond, VA
Posts: 7
#4
In reply to #2

Re: Help Needed With Bearings for U-joint

05/02/2017 4:54 PM

The is no driving or driven shaft. It is basically like an arm, nothing is rotating.
Register to Reply
Andrew Westman
Guru

Join Date: Dec 2016
Posts: 2914
Good Answers: 115
#5
In reply to #4

Re: Help Needed With Bearings for U-joint

05/02/2017 5:06 PM

But it is rotating, yes? When it rotates through an angle, is its rate important, say, for motion-planning the end-effector's position vs time? If it is, the sinusoidal relationship between input and output rate will at least need to be accounted for in software and the servo rate profile adjusted accordingly.
Register to Reply
2
Jpfalt
Guru

Join Date: May 2016
Posts: 1746
Good Answers: 87
#6
In reply to #4

Re: Help Needed With Bearings for U-joint

05/02/2017 5:08 PM

So it is a clevis, rather than a u joint.

Use opposing angle contact ball bearings and preload them.
Register to Reply Good Answer (Score 2)
No more Good Answers. Go to first "Almost" Good Answer
Andrew Westman
Guru

Join Date: Dec 2016
Posts: 2914
Good Answers: 115
#7
In reply to #6

Re: Help Needed With Bearings for U-joint

05/02/2017 5:14 PM

A clevis makes much more sense for robot arm elbow joint and rotate the end-effector with a wrist.
Register to Reply
achpek
Member

Join Date: Nov 2015
Location: Richmond, VA
Posts: 7
#8
In reply to #6

Re: Help Needed With Bearings for U-joint

05/02/2017 5:19 PM

Yes, it is basically clevis system, or a non-rotating u-joint, if you will
Register to Reply
James Stewart
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 14331
Good Answers: 162
#3

Re: Help Needed With Bearings for U-joint

05/02/2017 4:24 PM

I am a chemist, so what do I know, but I will say that a cheaper bearing preloaded might just work at least in the interim, until you (or someone else) comes along and sees the need for an upgrade. If the item fails to function according to your specs, then you didn't lose much by going with a lesser evil at first. Never go beyond the necessary evil.

__________________
 If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Andrew Westman
Guru

Join Date: Dec 2016
Posts: 2914
Good Answers: 115
#10
In reply to #3

Re: Help Needed With Bearings for U-joint

05/02/2017 5:25 PM

Register to Reply Off Topic (Score 5)
James Stewart
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 14331
Good Answers: 162
#14
In reply to #10

Re: Help Needed With Bearings for U-joint

05/03/2017 8:44 AM

Is that really a necessary evil? What is that?

__________________
 If it ain't broke, don't fix it. Just build a better one.
Register to Reply Off Topic (Score 5)
Jpfalt
Guru

Join Date: May 2016
Posts: 1746
Good Answers: 87
#15
In reply to #14

Re: Help Needed With Bearings for U-joint

05/03/2017 10:40 AM

It's one of them P3/H1 P1H2 P2H5 hingey thingeys. Top quality slime that bends in the middle. Kinda like Nancy Pelosi taking a bow.
Register to Reply Off Topic (Score 5)
James Stewart
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 14331
Good Answers: 162
#16
In reply to #15

Re: Help Needed With Bearings for U-joint

05/03/2017 10:48 AM

Looks like something Ms. Pelosi would blow out her nose while whining about R. agenda.

It could be found on her matching dress as a brooch.

__________________
 If it ain't broke, don't fix it. Just build a better one.
Register to Reply Off Topic (Score 5)
Andrew Westman
Guru

Join Date: Dec 2016
Posts: 2914
Good Answers: 115
#17
In reply to #15

Re: Help Needed With Bearings for U-joint

05/03/2017 10:49 AM

That's Nancy's son, Clevis.

Register to Reply Off Topic (Score 5)
SolarEagle
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33392
Good Answers: 1817
#9

Re: Help Needed With Bearings for U-joint

05/02/2017 5:23 PM

Depends....

http://www.societyofrobots.com/robot_arm_tutorial.shtml

__________________
 All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Andrew Westman
Guru

Join Date: Dec 2016
Posts: 2914
Good Answers: 115
#11
In reply to #9

Re: Help Needed With Bearings for U-joint

05/02/2017 5:30 PM

Depends on what? All the joints in that tutorial are separate clevis- and wrist-joints, some in combination with linear actuators. The OP's question concerns a clevis joint and for that kind of joint Jpfalt's reply nailed it.
Register to Reply
achpek
Member

Join Date: Nov 2015
Location: Richmond, VA
Posts: 7
#12
In reply to #9

Re: Help Needed With Bearings for U-joint

05/02/2017 5:34 PM

Yeah, I've seen it. Not going to work for my application. I'm talking about micrometer resolution here. Someone else is working on the actuators, but my concern is the joints with absolutely no lash. I need to know more about the bearings' types tho
Register to Reply
Andrew Westman
Guru

Join Date: Dec 2016
Posts: 2914
Good Answers: 115
#13
In reply to #12

Re: Help Needed With Bearings for U-joint

05/02/2017 5:42 PM

Overview: https://en.wikipedia.org/wiki/Ball_bearing. Pre-loading is key to minimising lash.
Register to Reply
Register to Reply
Have a Different Question?
17 comments

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

achpek (3); Andrew Westman (6); James Stewart (3); Jpfalt (3); ronc (1); SolarEagle (1)

Previous in Forum: Calculate The Weight Of The Mini Quadcopter   Next in Forum: Motion in Perpetuity, Not Violating Thermodynamics

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Mechanical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (62 right now)
Show Members
Advertisement