Is it possible to use JX PDI-6221MG for fingers

Kaarel Lumi

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Mar 18, 2018, 5:40:57 AM3/18/18

to InMoov

Hi

I have some JX PDI-6221MG servos which are 360 degree continuous rotation servos. Meaning they go infinitely in both directions.
These are also mentioned as alternative untested servos with good torque on this page: http://inmoov.fr/default-hardware-map/
And I can tell you they fit quite well in the wrist and servo holder for fingers.

The problem is that they have no 0 position or anything like that.

So there are probably a couple of options for using them: potentiometers and limit switches.

Has anyone tried to do something like this? Is it worth the effort or should I just give up and get different servos?

Thanks

gael langevin

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Mar 18, 2018, 6:26:00 AM3/18/18

to Kaarel Lumi, InMoov

Hello,

I wanted to test these servo since a while but never got the moment to purchase and try them out.

First, I am surprised to hear that they are continuous servo, because they seem to be sold as standard servo.

It would be interesting to open one of them to see, what's inside.

1-does the controller board has three pin holes for potentiometer connection. Green, yellow, red to potentiometer:

2-is there a place to set a potentiometer inside the casing. I found this picture on internet to illustrate inside the servo:

3-if all the above is a GO, hack it and try to make it adjustable.
Not sure how the servo micro board is going to act though...

But I sure would like to know the result.
:)

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

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Kaarel

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Mar 18, 2018, 9:40:39 AM3/18/18

to gael langevin, InMoov

Thanks Gael

I'll take one apart and share pictures.

Not sure if I have a suitable potentiometer on hand to try. Need to do some digging and may take some time.

Regards

Kaarel

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Kaarel Lumi

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Mar 18, 2018, 10:24:53 AM3/18/18

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Ok so first of all these come apart like magic.
They definitely have a place for the potentiometer and 3 connectors for it as well. Looks like plug and play almost.

Kaarel Lumi

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Mar 18, 2018, 12:24:10 PM3/18/18

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First attempt of connecting a 3.6k pot I found ... no effect at all.

But I didn't solder so maybe there's lacquer or something preventing a good connection.

Inconclusive.

gael langevin

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Mar 18, 2018, 9:42:59 PM3/18/18

to Kaarel Lumi, InMoov

Nice to see inside the beast.

Thanks for the feedback!

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

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gael langevin

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Mar 20, 2018, 2:22:04 PM3/20/18

to Ray Edgley, InMoov

Hello Ray,
That is better news regarding the degree rotation!

I was surprised to hear from Kareel, they were 360, because I had seen other builds of InMoov with them and nobody ever mentioned on the forum that matter.

Now, how do we know the seller is having 180 or 360 servos in his shop?

I always found very odd that it is never mentionned in the specs.

If you can recommend where you got yours, I would like to purchase a few for testing.

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

2018-03-19 6:27 GMT+01:00 Ray Edgley <ray.e...@gmail.com>:

These servos come in 2 flavors, 360 degree continuous rotation and 180 degree.
I have used a number of the 180 degree in my robot Fred.
I have been slowly replacing the MG996R servos I started with because frankly the MG996R's are crap.
The PDI-6221 MG have proven to be better in construction, they do not jerk on power up and have 20 Kg of torque compared to the 12.5 Kg of the MG996R

If you can get hold of the 180 degree version, I strongly recommend you use them,, I have yet to burn one out.

Regards,
Ray Edgley

On Monday, March 19, 2018 at 12:42:59 PM UTC+11, gael langevin wrote:

Nice to see inside the beast.
Thanks for the feedback!

Gael Langevin
Creator of InMoov
InMoov Robot
@inmoov

2018-03-18 17:24 GMT+01:00 Kaarel Lumi <terr...@gmail.com>:

First attempt of connecting a 3.6k pot I found ... no effect at all.
But I didn't solder so maybe there's lacquer or something preventing a good connection.
Inconclusive.

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Ray Edgley

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Mar 20, 2018, 3:34:51 PM3/20/18

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Hello Gael,

I picked mine up a while ago via Ebay.

Most of the stuff I get there is from China, but these may have been from an Australian Seller as the delivery time was less than a week.

On a completely different note, I have successfully tested a dual motor positioning controller for the knees and hip on Bart's leg designs.

The details are posted in the MyRobotLab site as a blog and the boys are looking into Borging in the controller so it can be used in MRL

It's based around an Arduino Nano and solves a lot of the overshoot problem we were having.

http://myrobotlab.org/content/new-i2c-controlled-dual-motor-positioning-controller

gael langevin

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Mar 20, 2018, 5:22:39 PM3/20/18

to Ray Edgley, InMoov

Ah ok thank you,

I thought you maybe had a hint for to define if a seller was shipping 180 or 360 servo.

Thanks for the link.

I have read it yesterday (I check on MRL what's up and new even if I don't have much time to chat on the shoutbox) and it's great to see some updates and improvements regarding the PID control for the legs!

Incredible work and documentation you have accomplished.

A lot of it is far beyond my understanding, but if in the end point we can have a nice small, worky controller, it will be awesome.

Currently I am still using the DIYservo from MRL coupled with IBT4. That's good enough for my research and development on the legs.

This is a bit off post...

Gael Langevin

Creator of InMoov

InMoov Robot

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gael langevin

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Mar 20, 2018, 5:23:51 PM3/20/18

to Ray Edgley, InMoov

Hello Ray,
what is the size in total of the dual controller?

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

Ray Edgley

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Mar 21, 2018, 1:54:17 AM3/21/18

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Hello Gael,

Here are some photos of my controller assembly..

The first is installed in a Bart's, knee assembly, Note the assembly is up side down, (I could say that because in in the southern hemisphere :-) but its more stable during the testing on the bench)

In this next one you can see the Arduino Nano that control's the motor drivers.
The motor drivers are dual channels.
These units are used as left and right hip drivers, there is also a single servo output

The Bart legs have 3 degrees of freedom, two are done by DC motors the rotation via a 20Kg JX PDI 6221MG.

The first controller i tested the controller with was a IBT-2, vert similar to the one you use but with control circuitry closer to my smaller 7A dual channel.

This system is controlled with I2C, once there is a service in MRL for it, it will be easier for everyone to use. It has the speed and accuracy we will need for walking.
I did see the video of you testing your knee, it look great, can't wait to see more of it working :-)

I do love the open source community, we learn so much from each other and you have given us a great platform to build on.

gael langevin

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Mar 21, 2018, 9:24:55 AM3/21/18

to Ray Edgley, InMoov

Hello Ray,

Thanks for these explanations and pictures.

We are highjacking this post about servo to talk about the legs... Anyway

Well the size for one dual set is good and small, I am surprised that these controllers don't require bigger aluminium coolers.

Looking closely at the ( reversed Australian) leg, I see you found some nice lead screw and holders. I was thinking of using something similar for the ankles. But something that doesn't require machining because most people don't have a cnc lathe machine. Is it accessories coupled from 3D printers and RC? And would you mind pointing me where you got them?

Gael Langevin

Creator of InMoov

InMoov Robot

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Ray Edgley

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Mar 21, 2018, 11:07:06 AM3/21/18

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Hello Gael,

I too don't have a CNC machine (yet) that can make those parts.

We are planning on using the same thing for the Y-Axis of the ankle, as such I currently have the following on order from ebay:

https://www.ebay.com.au/itm/T8-2mm-Pitch-8mm-Lead-Screw-Rod-Nut-Shaft-Coupling-Anti-backlash-Nut-3D-Printer/232576754917?ssPageName=STRK%3AMEBIDX%3AIT&var=531964418240&_trksid=p2057872.m2749.l2649

Because the output shaft of my 300 RPM geared motor is 6mm diameter and the above T8 thread 8mm in diameter I used the following coupling again from ebay:

https://www.ebay.com.au/itm/6mm-x-8mm-Bore-Stainless-Steel-Robot-Motor-Wheel-Coupling-Coupler-6mm-to-8m-E6H3/292352795707?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

At the time when I ordered the T8 threaded rod and nut, I did not know the length I would need, bu had an idea of the required travel, I opted for a length of coupling between the motor and the T8 rod.
I used the same method for the knee and the hip, for that generic 8mm all-thread rod was used and was coupled with:

https://www.ebay.com.au/itm/8-8mm-Aluminum-Flexible-Shaft-Coupling-Rigid-Coupler-Motor-Connector-D9R6/182982568575?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The geared motors i sourced from an online Chinese business called BangGood:

https://www.banggood.com/DC-12V-300RPM-Geared-Motor-High-Torque-37GB-550-Gear-Reducer-Motor-p-1068575.html?rmmds=mywishlist&cur_warehouse=CN

These are 12Vdc at 72Watts or 6A.

I found the listing for the Motor Driver unit again ebay:

https://www.ebay.com.au/itm/12V-24V-Dual-DC-motor-Driver-Module-Board-H-bridge-L298-Logic-7A-160W/262796610523?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Works well with the above motor and is the same units in the youtube videos.

As you can see none of the parts are what you would call expensive and as long as the 3dPrinted parts are designed to carry the nut or mount the motor, no machining is required..

I was looking at the photos you posted of your knee, are those metal parts at the bottom, a pair of universal joints?

is the the calf area of the leg?

It's looking good, I am curious about your progress.

I know most of the delay you have with the walking legs is a lack of time, (I have the same problem) this is after all a hobby and not a paid job. :-)

Regard's

Ray

gael langevin

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Mar 21, 2018, 1:03:08 PM3/21/18

to Ray Edgley, InMoov

Oh waoo,

thanks for the listing, this will save searching time!

Good prices too!

Yes for the ankles I'm planning on using universal joints, but the down point is the current backlash of the one I found on AliExpress.

The Universal joints allow the ankle to move in three direction, sort to speak. The idea is to set some linear potentiometers along the 10mm all-thread rod. to measure the foot position plus having three pressure sensors in each foot.

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

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Kaarel Lumi

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Mar 22, 2018, 3:33:48 AM3/22/18

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Great stuff guys.

Update about the PDI-6221MG.
I've decided to order some 180 degree versions of PDI-6221MG from ebay because I don't want to ruin perfectly good 360 continuous servos for this.

I've also messaged the ebay seller to double check that the servos are 180 because while the seller lists them as 180 the pictures on ebay are all of the 360 kind I think.

I've found a picture of a 180 version and what it should look like:
http://www.jx-servo.com/images/up_images/2016112816367.jpg
It actually says "PDI-6221MG-180" instead of simply "PDI-6221MG".

Ray, could you tell me whether all of your 180 degree PDI-6221MG-s have "180" written on them or is this not always the case?

I have also looked at some instructions on how to make a servo continuous but I don't think many people done the reverse.

Anyway finding suitable potentiometers is hard and also removing the soldered tiny resistors from the servo board to replace them with a potentiometer may be beyond by soldering skill. I would probably burn something. So I'm abandoning this idea until I have no other option.

Ray Edgley

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Mar 22, 2018, 4:51:39 AM3/22/18

to InMoov

Hello Kaarel,

I've just had a look at 2 installed servo from earlier batches and one from a recent batch still in its box ready for my leg project.

They all have the JX logo and the number 6221MG and under that digital, but none show the rotation.

I had assumed the 360 degree one were marked differently :-)

Obviously in this I am in error.

I have been starting to use these everywhere in my bot, and found the internal construction to be far better than the cheaper MG996R servos.

In general, if the servo has a metal housing, then you are already in front with the heat dissipation problems you can get in hard working servos.

For the larger servos i would consider the CYS-S2182. These are a 40Kg rated unit, I have two fitted to my robot Fred#2

Regards,

Ray Edgley

Kaarel Lumi

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Mar 22, 2018, 6:03:27 AM3/22/18

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Thanks! I guess I just have to be extra careful when buying them.

I can't find anything about CYS-S2182 on google though ... perhaps a typo in the name?

Ray Edgley

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Mar 22, 2018, 6:29:35 AM3/22/18

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Your right CYS-S8218

Dan F

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Mar 22, 2018, 10:46:37 AM3/22/18

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I bought a 4 pack from Banggood, they don't have 180 printed on them but they are the 180 degree models. Here's a link-
https://www.banggood.com/4X-JX-PDI-6221MG-20KG-Large-Torque-Digital-Coreless-Servo-For-RC-Model-p-1031156.html?cur_warehouse=CN

Marten de Groot

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Mar 22, 2018, 3:41:50 PM3/22/18

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Hi Guy's,

I'm thinking to order the 300 degrees version for turning the Wrist! (possibly also for other things)

https://hobbyking.com/en_us/jx-pdi-6225mg-300-coreless-metal-gear-high-torque-digital-servo-25-3kg-0-21sec-62g.html

Same servo: https://www.banggood.com/nl/JX-Servo-PDI-6225MG-300-Degree-PDI-6225MG-25kg-Metal-Gear-Digital-Servo-For-RC-Airplane-p-1138075.html?rmmds=search&cur_warehouse=CN

So it can turn a bit more then 90 degrees :)

gael langevin

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Mar 22, 2018, 8:07:54 PM3/22/18

to Marten de Groot, InMoov

Ahaha, Marten!

Yesterday, I ordered 8 servo 300 degrees for the new hand I am designing and some other project.

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

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gael langevin

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Mar 22, 2018, 8:14:38 PM3/22/18

to Marten de Groot, InMoov

@Marten,
https://www.banggood.com/fr/JX-Servo-PDI-6225MG-300-Degree-PDI-6225MG-25kg-Metal-Gear-Digital-Servo-For-RC-Airplane-p-1138075.html?rmmds=search&cur_warehouse=CN
@kaarel,

these servo are very good as far as I have tested:
https://fr.aliexpress.com/item/JX-Servo-PDI-HV2060MG-60KG-High-Torque-180-Digital-Servo

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

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gael langevin

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Mar 23, 2018, 10:49:26 AM3/23/18

to Marten de Groot, InMoov

By the way Marten,

On the new hand design, I have implemented the hall sensors and the little magnet that you gave me 3 years ago...

It works great!

I made a new finger type of finger tip that includes the magnet in the silicone for soft touch sensing.

If you want to see the code for MRL:
http://myrobotlab.org/content/sensor-and-sensitivity

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

2018-03-23 3:30 GMT+01:00 Marten de Groot <mart...@gmail.com>:

Hahaha... sounds "all" good and interesting !

It looks that these servo's are nice and strong enough to use with some InMoov things :)
I hope you get them soon, so we can see/hear some results.

I will order my 300 degrees servo's for the Wrist anyway.

Greetings ;)

Op vrijdag 23 maart 2018 01:07:54 UTC+1 schreef gael langevin:

Ahaha, Marten!
Yesterday, I ordered 8 servo 300 degrees for the new hand I am designing and some other project.

Gael Langevin
Creator of InMoov
InMoov Robot
@inmoov

2018-03-22 20:41 GMT+01:00 Marten de Groot <mart...@gmail.com>:

Hi Guy's,

I'm thinking to order the 300 degrees version for turning the Wrist! (possibly also for other things)
https://hobbyking.com/en_us/jx-pdi-6225mg-300-coreless-metal-gear-high-torque-digital-servo-25-3kg-0-21sec-62g.html
Same servo: https://www.banggood.com/nl/JX-Servo-PDI-6225MG-300-Degree-PDI-6225MG-25kg-Metal-Gear-Digital-Servo-For-RC-Airplane-p-1138075.html?rmmds=search&cur_warehouse=CN
So it can turn a bit more then 90 degrees :)

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Kaarel Lumi

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Mar 23, 2018, 2:53:29 PM3/23/18

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I wonder if higher range servos would work for the wrist ... wouldn't the wires and strings get all jumbled and too tight if the wrist moved too much?

Btw Gael I get this message on the main site: "Your membership account is awaiting approval by the site administrator." I'd like to post some pictures of my progress albeit modest as it is :)

gael langevin

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Mar 23, 2018, 5:03:05 PM3/23/18

to Kaarel Lumi, InMoov

Hello,

120 degrees for the wrist is pretty much the maximum rotation for the standard wrist, hand and forarm.

Marten has remodeled the servo wrist location, so maybe that's why he has more space for the tendons and less risk to tangle them.

I usually don't take care of members approval. Sebastien, our super webmaster does it or Wanguard does it automatically.

Just checking now the user list...

264 users on approval list...

Mmmh Sebastien had a lot of real work-work and couldn't take care of it.

I will see with him.

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

2018-03-23 19:53 GMT+01:00 Kaarel Lumi <terr...@gmail.com>:

I wonder if higher range servos would work for the wrist ... wouldn't the wires and strings get all jumbled and too tight if the wrist moved too much?

Btw Gael I get this message on the main site: "Your membership account is awaiting approval by the site administrator." I'd like to post some pictures of my progress albeit modest as it is :)

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Marten de Groot

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Mar 23, 2018, 10:30:15 PM3/23/18

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Kaarel Lumi:

I wonder if higher range servos would work for the wrist ... wouldn't the wires and strings get all jumbled and too tight if the wrist moved too much?

Well, the rotation wrist gears have a 2:1 reduction, so with a 300 degrees servo, the max angle is around 150 degrees.

And yes, with my remodeled rotation wrist, I get more freedom for the tendons.

I still need to find a way to edit the RotaWrist1V4.stl part, to get even more free space.

Here you will find more info about my remodeled rotation wrist: https://www.thingiverse.com/thing:1824042

Kaarel Lumi

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Apr 3, 2018, 6:10:08 AM4/3/18

to InMoov

Got some new servos today.

gael langevin

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Apr 3, 2018, 6:38:51 PM4/3/18

to Kaarel Lumi, InMoov

Hello Kaarel,

I received mine last week, I had ordered some JX Servo PDI-6225MG-300 Degree, and they are very good.

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

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