Asked June 2 2014

Community Question

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.
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June 2 2014
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?
June 3 2014
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.
DJ Sures
June 3 2014
June 3 2014 has some nice breakout boards that can be used to go from RS485 to UART serial.
June 4 2014
@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 EZ-Builder 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.
June 22 2014
Thank DJ