Powering Arduino and Dynamixel Motors

ROBOTIS Hardware Support
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#1

Use the following template to help create your post:

  1. What model of servo are you using?
    XM430-W350-T

  2. Describe your control environment. This includes the controller or interface, and any power source.
    Arduino, 12V 5A power Supply, Dynamixel Shield

  3. Specify the operating mode for applicable models, and any firmware settings you are using.

  4. Include pictures if possible.
    image

  5. Include a full description of the issue.

I recently bought a WidowX Dual Pan/tilt system from Trossen Robotics that I was looking to control using an Arduino Board. I was able to control the motors with some basic code but noticed that it still functioned normally even with the awkward set up shown in picture. The Arduino is powered from the distribution board sending 12V 5A amps to the 3 XM430-W350 Motors. My question is, is it safe to continue to run the system like this? Will it damage my equipment? Also will I be able to run additional motors off of this set-up? I want to power a 12V DC brushed motor off of this set-up? I would prefer to continue being able to run my set-up like this because it reduces the number of wires in.

#2

This method of power delivery is perfectly fine. You should be able to power your additional motor as well, as long as it does not have an excessively high current draw.

#3

Hi,

  1. Yes, as far as I know DYNAMIXEL Shield powers DYNAMIXEL directly throuth the 3 pin or 4pins (TTL / RS485) on the shield. As @Jonathon said that you should be careful of the connector safety (AWS 21, Maximum 3A) in wiring.

  2. Hmm. What does U2D2 do in your application? If your application is working with Arduino + DYNAMIXEL Shield, U2D2 may be uneccessary unless you are using it for DYNAMIXEL Wizard 2.0.

  3. If you want to use 12V DC brushed motor, Duty ratio regulation is an approach and is of course supported by Arduino pins thorugh the DYNAMIXEL Shield GPIO pins (See Arduino Pinout). But make sure that you might be required to power the DC motor separately with DYNAMIXEL and some additional circuit might be as well.

#4

The U2D2 doesn’t do anything in my application. I just initially used it to check if my motors were functioning correctly @Jonathon How do I ensure my motor doesn’t draw excessive current? It has 20 ohms resistance with no load. I previously spoke to reps from Trossen and they told me that same set-up I have has run up to 20 dynamixel motors in the past. Can I run the power straight off the screw clamp connector on the expansion board that came with the pan/tilt product from Trossen Robotics or will I need to rig it through one of JST connectors?

#5

I might have to add some opto-isolators in between the motor and the power hub board. The power-hub/ power expansion board is the little one with the JST connectors next to the JST connectors in my picture.

#6

The idle draw of the 3 XM430s is 40mA, so there is a good amount of current available when the actuators are at a low load. The expected maximum draw of the XM430s is 6.9A at stall torque, which is enough to push the power supply on it’s own. If your motor isn’t a large industrial actuator or anything too heavy duty like that it should be more than fine as long as you don’t plan to be pushing your actuators hard frequently. If you want to be sure, you can always test the configuration and monitor your actuators for any brownouts or power loss.

It would be best to connect the additional servo to a separate JST connector, in order to avoid passing too much current through one JST port. Plus, it makes it easier to maintain if every discreet component is easily disconnected without needing to touch others.

I would also recommend leaving the U2D2 in the case, if you don’t need the extra space. Just in case you need to do any more testing.

#7

For my purposes, I want to run the three dynamixel motors and the actuators one at a time so I’m assuming with that set-up current won’t be a problem if I use it like that and don’t stall my motors but run it into a wall or anything. What way would I specifically use to check to make sure that it isn’t an issue? If electrical questions aren’t appropriate here then I could ask elsewhere.

In all honesty, the motor I am trying to run is a linear actuator rated for 35Lbs and it will only be used to move the pan/tilt system and a camera (horizontally not even against gravity) which weighs about 4 lbs all together so most likely I am being paranoid with the current questions but its better to be safe than sorry when risking over a grand in equipment.

#8

With your description of your use, I am certain that your current power supply will be sufficient.

The simplest way to check for yourself is just to add the idle current loads of all connected devices together, and then do the same for the stall current loads. That will give you a very good idea of the expected minimum and maximum current draws of your system. While consistently exceeding the current rating should be avoided, occasional peaks at or slightly above the rating should be acceptable; most power supplies underestimate their maximum current rating slightly for safety and reliability reasons.

For DYNAMIXELs the current ratings can be found on the ROBOTIS eManual page for the actuator in question, and for most actuators there is also an NT graph that can show you a more precise estimation of current draw based on load or RPM.

In the case of DYNAMXELS, they also have built in current and voltage protection circuitry. If you are being reasonably safe and careful in the design and use of your system, they should automatically shut themselves off in response to unsafe voltages or currents before any significant damage occurs.