HerkuleX Servo's?

[tician]

If you are still looking for compatible pin headers, you might want to try the ones I linked in this thread. The dimensional drawings are nearly identical except the TE Connectivity drawings show all pins having kinks where the HerkuleX manual shows only the end pins having kinks.

[gaiajoypop]

(how well do they really do at going to a target position in a target time)

hi, everyone. it's my first post.^^"
i read a korean version herkulx manual.
refer to herkulex manual,
-herkulex can automatically make interpolated positions from start position(A pos) to target position(B pos).
-the interpolated positions are called as "desired trajectory".
-the desired trajectory is generated base on the given time and acceleration parameters.
interesting point is that the desired trajectory can be feedback, that is, i can readback the information of trajectory.
moreover, trajectory is very simmilar to the trapezoidal profile of industrial motor controller.

[JoeStrout]

Yep, that's all true. I also did a little test to see how well they work in practice. The result, in brief, is that they appear to work exactly as advertised.

You can read about my experiment, and see a brief video, in this blog post.

[gaiajoypop]

I found interesting videos about herkulex.
Herklex developer made ​​videos to explain overall function and interface.
but korean, not english.
just watch the video and enjoy ^^"

seminar #1 : general description, summary, few playing video
watch about 26:50 second of video, so interesting
http://www.youtube.com/watch?v=t49cOmnvRf0

seminar #2 : control method(protocol, example source code, etc)
http://www.youtube.com/watch?v=EGqxqqSZje8

[kert]

Anyone have any updates on Dongbu/HerculeX line ? I was looking at doing some discount shopping on smart servos and found these in stock now in US in a couple places.
I know the internals of Dynamixel MX line with magnetic encoders and Cortex-M cpus - seems like Dongbu has almost comparable lineup with DRS-602 and DRS-402 ( 02 seems to denote magnetic encoder feedback version, 01 is pot ) but whats for the brain ?

I'm mostly interested in feedback accuracy and capabilities, for an arm project.

[jwatte]

i was tempted to try some of the more capable Herculex servos. However, it seems that they do not use a full-rotation absolute sensor even for the higher end servos. Instead, they appear to use a 300 degree potentiometer for absolute position, and then a separate motor shaft encoder for higher relative precision, which is great for movement speed calculations, but not as good if you want high-precision absolute positioning.

[kert]

Hmm did you see a tear-down report anywhere ? Just going by the specs its hard to tell, but according to the distributor specs they say this :

To retain reliabilty under harsh environment, Swiss made Faulhaber premium Coreless motors have been applied for both DRS-0402 and DRS-0602. These high torque servos support 1Mbps data transfer rate, 12960 steps high resolution, magnetic encoder, and are fitted with metal inserted nut system for outstanding durability and easy assembly.

Im tempted to get their Arduino starter pack and two DRS-0402s to experiment with, but of course its not cheap. They do have some really interesting control and configuration features, the sort of stuff i keep reimplementing in my own DC motor control loops.

[jwatte]

I base it on this, admittedly not grammatically stellar, description:

Based on potentiometer applied DRS-0602 is featured with Magnetic Encoder to secure high precision, high resolution (12960 steps) and durability. The included magnetic encoder on the end of this faulhaber coreless motor boosts precision control characteristics and linearity.

Also, page 25 of the DRS-0602 manual shows a typical 320 degree working zone as "recommended" with a slightly larger (still not 360 degrees) as "allowable."

[kert]

Wait im not sure i understood what you are saying correctly - are you saying that they are not full rotation servos ? Some HerculeX ones certainly are as can be seen on this table rover video here http://botscene.net/2013/03/03/herkulex-table-rover/
It would be super weird if it had a pot limited to 320 degrees in there for some reason.

Ah, i checked that page and see what you are saying. No, i dont think this diagram has anything to do with the feedback sensors, its just in absolute positioning mode you have to have a "zero" reference somewhere and this range is mostly there mostly so firmare logic can cope with the concept of calibration etc. I have worked with similar industrial smart servos and they all have a similar notion.

The magnetic encoders they are using are probably the same absolute AMS sensors as everywhere else so a pot wouldnt be needed for any reason.

[tician]

As I read it, the servo has a 320 degree mechanical potentiometer on the servo output shaft that connects to the horn and a 64cpr magnetic quadrature encoder on the motor shaft (12962/202 = ~64). They achieve the multi-turn capability by requiring the horn be in the potentiometer's range at startup and then use the quadrature encoder to do relative motion from that point. I see nothing in that manual to suggest it has an absolute magnetic encoder.