PR2 wrist, elbow, caster slip ring replacement

[Shingo Kitagawa]

Hello everyone,

I'm Shingo Kitagawa from JSK lab, Universitiy of Tokyo.

Our PR2 sometimes drops packets and drop connections to the r_gripper_motor MCB, and we are searching for the reason.

We thinks that slip rings got worse, so we want to replace them.

Does anyone know wrist slip ring product name?

If you have some information, I want you to share the information.

Or does anyone have the experience to replace the wrist slip rings?

Also, we want you to share information about other slip rings, too

We have the caster slip ring information, and already replaced with new ones, so I share the information.

Caster slip ring:

We had a lot of packet drops on our PR2 caster, which caused by caster's slip ring.

We bought LPC-0205-0402 from JINPAT and replaced them, and PR2 now works good.

It costs $51 per unit and we bought several units for the stock.

[Michael Görner]

Hi Shingo, greetings from Hamburg University,

we (luckily) did not experience problems with the arm slip rings
yet, but managed to solve some issues with the caster slip rings
during the last two years.
If the slip ring is the culprit of your connection problem, do you also
get "WATCHDOG safety lockouts" due to voltage drops? These are typical
for us when the caster slip rings start failing.

We successfully used a software-only workaround for the caster issues
multiple times now that might be interesting for others as well:
When the slip rings fail, that might be due to hardware defects, but is
apparently often a matter of dust particles accumulating on the ring.
As long as the connection still works rather reliably, we rotate the
slip ring at higher velocities to "clean" the contacts.
For the casters I prepared a small ROS package with controller
configurations and a short helper script:
https://github.com/TAMS-Group/pr2_caster_test/blob/master/scripts/turn_caster_test.sh

You could try something similar for the arm slip rings I guess.

Best,


Michael / v4hn

--
Michael 'v4hn' Görner, M.Sc. Cognitive Science, PhD Student
Universität Hamburg
Faculty of Mathematics, Informatics and Natural Sciences
Department of Informatics
Group Technical Aspects of Multimodal Systems

Vogt-Kölln-Straße 30
D-22527 Hamburg

Room: F-315
Phone: +49 40 42883-2432
Website: https://tams.informatik.uni-hamburg.de/people/goerner/

[Shingo Kitagawa]

Hi Michael,

Thank you so much for your reply.

we (luckily) did not experience problems with the arm slip rings
yet, but managed to solve some issues with the caster slip rings
during the last two years.
If the slip ring is the culprit of your connection problem, do you also
get "WATCHDOG safety lockouts" due to voltage drops? These are typical
for us when the caster slip rings start failing.

I didn't know that you already experienced the caster slip ring problem as our lab.

In our current wrist slip ring issue, we got "Safety Lockout: UNDERVOLYAGE" in diagnostics.

I attached the diagnostic output image.

We successfully used a software-only workaround for the caster issues
multiple times now that might be interesting for others as well:
When the slip rings fail, that might be due to hardware defects, but is
apparently often a matter of dust particles accumulating on the ring.
As long as the connection still works rather reliably, we rotate the
slip ring at higher velocities to "clean" the contacts.
For the casters I prepared a small ROS package with controller
configurations and a short helper script:
https://github.com/TAMS-Group/pr2_caster_test/blob/master/scripts/turn_caster_test.sh

Thank you for your information.

We also rotate our PR2 wrist multiple times by hand, and now it works better.

So maybe rotating the gripper at high velocity may clean up the slip ring, and the situation will be better.

I will try that.

We haven't shared the caster slip ring replacement information, so I attached the PDF.

If someone has a similar issue, you can probably try it.

I also attached the photo of broken caster slip ring when we replaced it.

--

北川 晋吾

Shingo Kitagawa

the University of Tokyo, JSK Lab

s-kit...@jsk.imi.i.u-tokyo.ac.jp

2021年8月29日(日) 3:39 Michael Görner <goe...@informatik.uni-hamburg.de>:

[Michael Görner]

Thank you as well, Yuki's slides are great and it's educational to see
one of the slip rings open. :)

Good luck with the wrist issues and if you find a replacement product
for the relevant slip rings there, please post here again! :)
There is way too few information exchange among the PR2 groups, but
when I wanted to discuss a common wiki for all such information with
IAS Bremen's Admins and Kei Okada 4 years ago there was not enough
interest to do so...
If you think it's worthwhile, feel free to create a wiki and invite
people to add their PR2-related issues/documentation.
For many of us it's probably a matter of copy&paste some files/texts
from internal resources...


Michael / v4hn

[Shingo Kitagawa]

Hi Michael,

Thank you as well, Yuki's slides are great and it's educational to see
one of the slip rings open. :)

It was actually a pretty interesting experience.

The plastic part of the slip ring got many cracks because of our rough usage, and it was totally broken inside.

So when we removed the slip ring, it was already open as in the photo.

Good luck with the wrist issues and if you find a replacement product
for the relevant slip rings there, please post here again! :)

Thank you.

I'm contacting the MOOG slip ring company, and I will post the further information. 

 

There is way too few information exchange among the PR2 groups, but
when I wanted to discuss a common wiki for all such information with
IAS Bremen's Admins and Kei Okada 4 years ago there was not enough
interest to do so...
If you think it's worthwhile, feel free to create a wiki and invite
people to add their PR2-related issues/documentation.
For many of us it's probably a matter of copy&paste some files/texts
from internal resources...

I think PR2 wiki is a good idea.

Some information is written in ROS wiki by willow garage, so ROS wiki is one choice.

I want to gather information about upgrading PR2 to melodic, noetic and ROS2 (probably?).

I also want to discuss the MCB replacement and battery system replacement, too.

--

北川 晋吾

Shingo Kitagawa

the University of Tokyo, JSK Lab

s-kit...@jsk.imi.i.u-tokyo.ac.jp

2021年8月30日(月) 16:53 Michael Görner <goe...@informatik.uni-hamburg.de>:

[Shingo Kitagawa]

Hi all,

We opened our PR2 forearm, and we found out the wrist slipring product name.

The wrist slip ring is MOOG AC6456-6.

You can see the slipring in the attached photo.

We haven't open our PR2 arm, but we gather the information about elbow slipring.

The elbow slip ring may be MOOG AC7092 (AC6305-9S with custom-made fringe).

We got the product design from MOOG, so if you want to see it, please let us know.

====

Summary:

Caster slip ring: JINPAT LPC-0205-0402

Wrist slip ring: MOOG AC6456-6

Elbow slip ring: MOOG AC7092 (probably)

====

--

北川 晋吾

Shingo Kitagawa

the University of Tokyo, JSK Lab

s-kit...@jsk.imi.i.u-tokyo.ac.jp

2021年8月31日(火) 14:24 Shingo Kitagawa <s-kit...@jsk.imi.i.u-tokyo.ac.jp>: