Asked — Edited
Resolved Resolved by DJ Sures!

Ez-B V4 Dynamixel Servo Setup.

Don't have an EZ-B v4 yet, but am working on a project that is using dynamixel AX-12a servos.

I ran across some inconsistencies in the manuals.

The Dynamic Configuration Tool for Dynamixel servos says:

The EZ-B v4 supports the use of Dynamixel Servos connected to the D18 Port.Within the software, the servo ports for Dynamixel are labeled AX00 to AX50.

The EZ-B v4 data sheet shows:

  • D5 can control Dynamixel servos
  • D5 (TX) and D6 (RX) can be used as UART1

Think I ran across other spots in the manual that talks about dynamixel servos connected to D18.

A clarification would be appreciated.


Upgrade to ARC Pro

Take control of your robot's destiny by subscribing to Synthiam ARC Pro, and watch it evolve into a versatile and responsive machine.


Found that EZ-Script also talks about dynamixel on port D18:

AX12Led(id, on/off) Controls the LED status of an Dynamixel AX-12 servo by its ID on port D18. Check the port modes in the respective section near the end of this document. Example: AX12LED(1, on) Example: AX12LED(1, off)

But it also says:

Dynamixel Servos (Port D5)

Standard hobby servos use a pulse width modulation for setting the position. Optionally, more advanced users may use the higher priced Dynamixel servos for increased position resolution and strength. These servos are connected together in a chain of wiring (each servo connects to the previous servo). Connect the signal wire of the servo chain to the D5 Port of the EZ-B v4. This feature does not work on the EZ-B v3.

Which is correct?


@DJ, If the dynamixels are powered externally, is it possible to use other dynamixel servos, ie RX 28/64s? I'm not sure the differences in the servos as I have not done any research as of yet. But just checking with you first. Assuming that the communications are the same for all the servos.

Thanks in advance


Any Dynamixel servo can be used - they use the same communication protocol


Fantastic news! Thanks.


Dynamixel servos come with different interfaces for sure ones with TTL half duplex asynchronous serial will work as it matches the AX-12 series that are mentioned in the EZ-B v4 manual. Unless they have an additional feature on the D5 pin that hasn't been mentioned yet Dynamixel servos with the RS485 interface will not work. DJ Sures has the final say of course.


Robert, RS485 Dynamixel servos will work - that is what is natively supported.

Please disregard Robert's message as RS485 Dynamixel Servos do work. I don't want there to be any confusion:)


Thanks for the clarification DJ! I haven't seen any mention of RS 485 support on the EZ-B v4.


Traveling again, (texting from 30,000 feet ), when I return in a week the dynamixels should be waiting for me. I'll give them the run through.


DJ, the dynamixel RS-485 servos have 4 pins.

User-inserted image

They are gnd , vdd, d+, and d-. Would you connect EZ-B v4 pin D5 to the d+ pin and d- pin to gnd?


For the dynamixel TTL servos the connection is more straight forward.

User-inserted image

D5 connects to the data pin on the 3 pin connector.

#13 has some nice breakout boards that can be used to go from RS485 to UART serial.


@DJ Sures, Thanks for finding the page on hooking up Dynamixel Servos. I had been reading it a while before I posted the warning about the Dynamixel RS485 servos and I guess I didn't explain it well. I have worked with RS485 before and didn't think the connection grounding the D- and sending data into the D+ pin would work but I never tried it so I thought I would check. The problem is that the RS485 bus is a differential bus. And I couldn't see how the EZ-B v4 could support it directly but didn't know for sure. You are the expert there.

@Robot-Doc. The Spark fun breakout ( ) would be a great solution for just controlling the Dynamixel RS485 servos. If you want to both control and get data from the dynamixel servos you would need to control the direction pin on the breakout. It is setup so the Driver/Receiver Enable connected to normally connected to the RTS line. The EZ-B v4 documentation does not talk about RTS on the D5 uart used for the Dynamixel servos. So I don't see how a Dynamixel RS485 servo could be made to easily work on D5 uart if feedback is needed. I think the hope was that at some point the feedback data from the Dynamixel servos could be used by ARC and the EZ-SDK. With all the computing power they have put into the new EZ-B v4 it should be possible. I don't know as any of the feedback functions have been implemented yet or if they can be made to work. Thankfully for the project I have in mind I don't need feedback and Dynamixel has a TTL interface version of the servo I need. Just need an EZ-B v4 now and money of course. Dynamixel servos are not cheap. The 3D printed parts I am looking at are designed for the Dynamixel servos and it would be a lot of work to redesign for standard servos.

@DJ Sures, I still see some EZ-B v4 D18 references in the Manuals for Dynamixel servos and I found where you fixed at least one I think. It may be an issue with the on line manuals not being up to date with your edits.