Motoman K6SB Retrofit

So the original drives for this arm, which I’m going to pick up from a kind enthusiast in Ohio, are SGDR-SDAxxxx; that model number isn’t listed on @dm17ry ‘s site as being mechatrolink compatible unfortunately, but I haven’t dug through (or found) the documentation to confirm. 

I have an SGDH and an SGDV drive coming from eBay, both apparently mechatrolink ii and thus Dimitri-compatible. If I can convince them to operate the servos in my arm, I can eBay a few more of them- they are reasonably affordable. The Dimitry setup sure looks least complicated!

The servos in the arm, btw, are, from base to wrist: 
- USAPEM-07YR21
- USAPEM-07YR13 (2x)
- USAREM-01YR41 (3x) (what’s the difference b/t USAPEM and USAREM?)

Anybody know anything about the proprietary absolute encoder interface?

 

andypugh wrote:

I _think_ that this can be solved in HAL, external to the kinematics. I have looked at it in the past and decided that it would work, but didn't have long enough with the robot to get there.

By which I mean use standard DH kins, then intercept the joint position commands before they go to the motors and mix them there before passing them on.

 

This does sound like it’d work, good idea. I was actually able to get that arm (my smaller one with the mechanical mixing) to work using the linuxcnc-provided puma kinematics module after fooling with the nontrivial kinematics DH settings for a while. This arm, I am happy to learn, doesn’t actually use any mechanical mixing- looks like I should be able to deduce the encoder and gear drive ratios, measure the joint center to center distances best I can, and be in business. 

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So the original drives for this arm, which I’m going to pick up from a kind enthusiast in Ohio, are SGDR-SDAxxxx; that model number isn’t listed on @dm17ry ‘s site as being mechatrolink compatible unfortunately, but I haven’t dug through (or found) the documentation to confirm.

no, they are not.
googling for SGDR and CN102 reveals some motoman manuals mentioning
CN102 as PWM amplifier control power
CN1 as PWM signal
so i guess SGDRs are "dumb" amplifiers with a current feedback only. encoders connect to a separate board, not to servopack.

USAREM are "Regular" series motors
USAPEM are "Pancake" style

no, i don't know what protocol encoders use

info.ammc.com/hubfs/Partner%20Documents/...20-%20150133-1CD.pdf

 

so i guess SGDRs are "dumb" amplifiers with a current feedback only. encoders connect to a separate board, not to servopack.

Hm, how does the amplifier unit know how to distribute the commanded current between the motor phases if the encoder isn’t connected to it - these servos don’t have halls or resolvers, right?

i don't have any experience with those older pwm interfaces, so it's just my speculation
i think amps usually get 3 pwm diff signals for u,v,w phases supplied by the control board. which is fed by the position data by the encoder. i believe encoders used on USA*EM motors provide A,B,Z,U,V,W diff lines - the later three should be commutation information.
i think i've seen park/clarke transform hal components in the linuxcnc docs. so it should be possible to generate u,v,w phase currents based on encoder data.
also, have a look at this thread: forum.linuxcnc.org/30-cnc-machines/20837...vo-drive-integration
it seems to me that your amps should be somewhat alike. and PCW - looks like he knows this stuff and probably Mesa has required interface hardware

andypugh wrote:

The park and clarke HAL components appear, to me, to be entirely un-useful.

However, the "bldc" component knows how to calculate phase duty cycles from commutation and encoder feedback.
It can be used to drive a Mesa 3-phase PWM module, or even a software PWM.
 

That’s what I had been thinking I’d use if I rolled my own from half bridges- the bldc Hal unit with encoder feedback. 

By “commutation”, do you guys mean halls/resolver on the servos, or is there another method I’m unaware of? Cursory glance suggests these servos have only the encoders for feedback, but I’m prepared to be wrong. 

phasefreq wrote:

Anybody by chance know the harmonic drive ratios on these arms? Or know which document would contain them? I’m told they are params in the ERC controller, but since I lack said controller that doesn’t help me much :-/

I missed these posts before until now, what information is currently outstanding on your project? The best place aside from motoman, who dumped all their manuals for free, is the one site posted earlier in the thread,
spaz.org/~jake/robot/
this page, and they have a pile of info on their hackerspace webpage,
if you still need the gearbox/servo info let me know, its just been a while since I went super deep into a
motoman so ill have to dig around for my documents/hard copies. your model is one model older than mine but a lot of things are still the same.