PDA

View Full Version : EX-106 position control over 360 degrees



pzucchel
05-27-2011, 07:46 AM
Hi To All,

anybody that knows how we can control the EX-106 over 360 degrees, bypassing the limitation to 280 degrees? since it has the same encoder of the RX28M, it should be possible...but how? is the firmware of the servos available for implementing some modifications?

The same applies to multi-turn control: it is evident that the position is correctly recorded up to 10 turns, e.g. up to 65535, but it is impossible to set it to such an angular position....

Thanks in advance!!! :o

lnxfergy
05-27-2011, 12:33 PM
Seeing as 0 and 4095 (the full 12-bit resolution) maps to the 280 degrees, it's clearly not the same as an RX-28M, so I don't think there is going to be any hack to get position in the backside 80 degree deadzone. That said, you could switch to continuous rotation, power through the deadzone and then switch back to position control once through the deadzone...

-Fergs

darkback2
05-27-2011, 01:48 PM
I wonder if you couldn't use gears to accomplish something similar. so a 28 toothed gear mated to a 36 toothed gear...something like that, that would give you the 360 degrees you need.

DB

Xevel
05-27-2011, 04:04 PM
I wonder where you got this information pzucchel... as far as I know, the MX-28 is the first Dynamixel to have a magnetic encoder, and they are looking into upgrading all their line of product with this kind of encoder at some point in the future.

DresnerRobotics
05-27-2011, 04:33 PM
I wonder where you got this information pzucchel... as far as I know, the MX-28 is the first Dynamixel to have a magnetic encoder, and they are looking into upgrading all their line of product with this kind of encoder at some point in the future.

The EX-106+ has a magnetic encoder, but it's not tied directly to the output shaft (it's on the motor). The MX-28 is the first to have it directly tied to the output shaft, hence the 360 degree range of motion.

Xevel
05-27-2011, 05:02 PM
oh, I see. Thanks for this precision :) and sorry for the confusion.

pzucchel
05-28-2011, 10:13 AM
I wonder if you couldn't use gears to accomplish something similar. so a 28 toothed gear mated to a 36 toothed gear...something like that, that would give you the 360 degrees you need.

DB

Hi,

it's a possibility and a good idea - but it wouldn't work for multi-turn: it can make a full revolution of the second gear by position control of the servo, but then the dead band would appear in the next turn....:sad:

pzucchel
05-28-2011, 10:14 AM
The EX-106+ has a magnetic encoder, but it's not tied directly to the output shaft (it's on the motor). The MX-28 is the first to have it directly tied to the output shaft, hence the 360 degree range of motion.



Hi,

your consideration makes sense....but if the encoder would be coupled on the motor, it would revolve 200 times per turn! I think it is somehow on the output axis, but with the dynamic range of the magnetic encoder covered by the ADC of the ATMEL processor limited to a lower voltage range (or the output o the magnetic encoder mapped to a higher voltage range that would be equivalent)....

Any of you that opened an EX-106? can you buy today a RX28M for evaluation?

Thanks a lot, and happy robots to everyone! :tongue:

Bullit
05-28-2011, 10:37 AM
Any of you that opened an EX-106? can you buy today a RX28M for evaluation?


Yes, I have opened many Ex-106's, there is a potentiometer on the output shaft and a low resolution encoder on the motor.

No, you cannot yet purchase the MX-28, as they are now called. Hopefully ROBOTIS will release them soon.

You can view some internal photos of the MX-28 here:
http://robosavvy.com/forum/viewtopic.php?t=7027&highlight=

As mentioned earlier the MX-28 has a magnetic encoder magnetically coupled to a diametrically magnetized NIB magnet on the output shaft.
http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encoders/AS5045

Hope this helps

hizook
06-19-2011, 09:58 PM
It looks like the MX-28 just became official. I was lucky enough to be a beta tester, and I wrote up some of my impressions -- including photos of the servo's internals, complete with the new contactless magnetic encoder:

Review of the Robotis Dynamixel MX-28 Servo
(http://www.hizook.com/blog/2011/06/16/new-robotis-dynamixel-servos-mx-28-sport-360-degree-rotation-and-4x-angular-resoluti)

I suppose y'all already know the major benefits: 4x resolution, 360-deg rotation, magnetic encoder. But I just got word... the MSRP is $219 USD. Too cool.

Also... My previous article about the RX-series Robotis Servos (http://www.hizook.com/blog/2010/03/14/robotis-dynamixel-servos-overview-applications-tear-down-and-open-source-software) had teardown photos showing the contact, potentiometer encoders on the older variants.

tician
06-20-2011, 01:05 PM
With the lab having permanent access to 20 RX-28M (http://youtu.be/tJpvahsOkRM?t=16s) and temporary access to 2 MX-20 during beta... :D:D:D. Also, metal frames are awesome.

OT: Really wish I had the attention span and programming abilities to experiment more with the DARwIn-OP. Mostly the focusing thing, but also partly a case of having too many possibilities (solved by choosing none) and partly parents/siblings nagging me to find a real/paying job :( (guilt is a powerful demotivator).