New Dynamixel servos: XM-430

[Xevel]

Hey guys,

Robotis announced a few days ago at Robotworld 2015 their new Dynamixel servos : XM-430.
They are pretty different from the previous ones, from a mechanical perspective.

From the top of my head before I take some time to make a full review:

- the idler design can let one cable get out of the servo on the rotation axis, or can be replaced by a cap if not needed.
- case is mostly metal, with a few M2.5 threaded holes (4 on the sides and bottom, 2 front). No flanges, it's a parallelepiped.
- size is smaller than MX-64
- two choices of gear sets: one for speed, other for torque (about 50kg.cm iirc).
- 12V, RS485 but with new type of connector. Electrically compatible with previous MX-R series.
- they finally put a switching regulator to power the control electronics
- can talk either Dynamixel Protocol 1.0 or 2.0, it can be set in the control table.
- resolution seems to be the same as MX series (12 bits, 4096) but if needed it can be divided in firmware to use it as if 10bits, 1024.
- intended price is still unknown but hoped to be not too much above MX-28.
- release date unknown.

I'll get you a more comprehensive review of the thing later - I still have some demos to do at IEEE Humanoids with the robot I worked on for the MiniDRC event organized by Robotis - and for which we used 20 of these to make a Darwin-size rescue robot (I'll post about that too).

My experience so far is only with the Speed version. Pretty nice feeling, it makes me think of an MX-28 with more torque.
We've had a problem when the robot fell from about 15-20 cm high while all the joints were powered: the knees took a bad hit, and the shaft of both of them got a bit twisted (a few degrees) between the output gear and tip of the output shaft . I imagine (hope) they will fix that before release.

If you have specific questions, don't hesitate and I'll try to get you an answer.

[r3n33]

Very cool news. I'm looking forward to seeing more of the robot you built with these.

Did the assembly time feel much quicker with the XM-430s? If someone does something bad like strip or cross the threads I'm guessing repair parts will be available for that section of the case?

[tician]

My experience so far is only with the Speed version. Pretty nice feeling, it makes me think of an MX-28 with more torque.
We've had a problem when the robot fell from about 15-20 cm high while all the joints were powered: the knees took a bad hit, and the shaft of both of them got a bit twisted (a few degrees) between the output gear and tip of the output shaft . I imagine (hope) they will fix that before release.

When it comes to handling sudden shock loads, it pretty much break or bend. Do you want to replace the gearset immediately because the spline sheared off and there is only a screw holding it in place, or do you want to have the spline twist a bit and maybe be able to replace it at a later date? Stiff/brittle materials good for precision position control tend to not allow much elastic deformation prior to reaching the yield strength and starting plastic deformation then sudden fracture/rupture. Adding something like a spider-based shaft coupling (one toothed connector on each shaft with rubber cross interlocking the two connectors) or a drill clutch (servo saver) would help prevent breakage, but likely would not fit inside the case very easily. Having a three piece horn with a molded polyurethane or rubber ring connecting the spline to the mounting holes is another option I had contemplated for saving the knees and hips of a darwin-op during the many collisions and crashes they endured at the hands of the theatre students.

[jwatte]

Not bad! Although the smaller amount of mounting holes seems surprising.