- What model of servo are you using?
Several (e.g. 3+) XM430-W350 motors daisy-chained (connected serially)
- Describe your control environment. This includes the controller or interface, and any power source.
U2D2 (for PC-to-Dynamixel comm.), with separate VDD/GND connections from an 12V AC/DC adapter to power the motors under load
- Specify the operating mode for applicable models, and any firmware settings you are using.
Position control (all motors); latest firmware installed on all motors
- Include a full description of the issue.
I have several (3 or more) XM430-W350 motors daisy-chained together. Communication from a U2D2 and power from a separate 12V AC/DC adapter converge into a single connection to the first motor. The first motor passes comms and power on to the 2nd motor; 2nd motor on to the 3rd and so on. As as result, the first motor will receive (and need to pass on) enough current to power all motors beyond it along the daisy chain (including itself). What is this maximum ‘pass-through’ current that a single motor can safely handle? A XM430-W350 is spec’d to draw up to 2.3A at 12V. If there are 3 motors behind it, this first motor may need to pass along an additional 2.3A*3 motors to those subsequent motors (if all are operating under max load). I presume there’s some limit on this ‘pass-through’ current (under 12V, for example) that a single motor can safely sustain without damage. What is this limit for the XM430-W350?
It is good that you are checking on these issues before using your DXLs.
First a misconception needs to be corrected. Although the DXLs are daisy-chained serially, their individual power circuits are in-parallel, and their control circuits too.
The DXLs use 21 AWG wires for their cables which are rated at 1.2 A. Normal use does not go that high.
From my use experiences, when there are too many DXLs for a given power supply they just don’t turn as fast or could not fully hold their Goal Positions.
Only when there are internal shorts that the DXLs would burn up, usually at their PCB levels or at the DXL connector as the plastic would burn up before the wires. Plenty of smoke and nasty smells!
As @roboteer stated, DYNAMIXEL’s internal protection circuitry will protect the actuators from these kinds of overloads. Although, as you suspected this can sometimes cause DYNAMIXELs further down the chain not to receive adequate power during high strength movements. The recommended method to ensure adequate power throughout the entire chain is actually to add additional power inputs every 3 to 6 actuators, depending on your expected load.
The eManual page for the DYNAMIXEL communication bridge has some examples of power input solutions that can be applied to this situation.