PhatomX with XL430-W250 servos

[jwatte]

The OpenCM9.04 has a USB port, so you could just use a short USB cable to talk to it using serial port.
However, the serial USB implementation of that board has always been a bit finicky for me -- send too much at once, and the firmware locks up.
To use the serial port on the Pi 3, you may have to do some hacking of the boot config file on the Pi, because by default the "good" serial port is used for the Bluetooth and the "limited" serial port has issues (slow, not buffered, I forget what else.) In fact, I don't even remember if the serial pins are enabled at all on the Pi 3 by default. (They may be, just configured for the "bad" port.)

[KurtEck]

@jwatte - I have not played as much with host talking quickly with large amounts of data through the OpenCM board.

I have tried to fix some of the latency issues of the OpenCM board talking back to the PC...

For a long time, the hard coded 3ms timeout was always used on the OpenCM board to force the USB to send back to host, which I saw, so worked with Robotis to add Serial.flush() support, and to add calling it to DynamixelSDK... But the flush() is still not as optimal as it could be, it just zeroed out the ms timeout counter so the next ms timer would do it then.


As you mentioned, the Serial port on RPI3's expansion connector is a bit flaky and I normally swapped them... There are several links on the net about this including: https://spellfoundry.com/2016/05/29/...ncluding-pi-3/

I also forgot to mention, that in some of the Phoenix/PhantomX code bases I have a version of the Input code that does not talk through XBess. There was a simple handshake between the two.

[xenoc]

Thanks guys for the help. I got it working ok using a simple cross connect of Rx and Tx over the serial ports
RPI3 Tx on GPIO14 (Pin 8) to OpenCM9.04 Rx on A5
RPI3 Rx on GPIO15 (Pin 10) to OpenCM9.04 Tx on A4
The initial problem I had was due to not having a common ground (thanks for reminding me Kurt).
Initially I used the ttyS0 Serial port to prove it worked ok. After that I swapped the serial ports to use the high performance ttyAMA0
I commented out the XBee configuration code as well.
I'm using wifi to connect to the RPI3 from my PC over VNC so don't need a high performance bluetooth interface.
I'm now able to simulate the Commander buttons and joystick using Python code so the next step will be to connect the Lidar and the Pixy2 to the RPI3.

[minim]

How did it go with the XL430-W250 testing? I'm having a hard time finding people that have used it on the PhantomX. I want to build me a hexa (endgoal) but I'll prolly start with a simple arm and a teensy 3.6 to learn how it all works first. Will be re-using the servos and controller so picking the right one the first time is prefered

[KurtEck]

I need to get back to it.

I was sort of out of it for awhile, recovering from surgery... And have been busy with helping with the Teensy 4 beta stuff, which should hopefully be released soon.

[minim]

No rush. Recovery is way more important I just figured since these are supposed to be the upgrade of the AX-12 that it's what I should look at. To bad there is very little reviews and info around tho. If you know about any that I haven't found then I'd appreciate a link or tip on where to read about it.

Sounds like that's something I should wait for to then :-) Always something better around the corner when it comes to tech but the teensy 3.6 has been out for a long time.

Edit;

btw can I ask you if you use the RS485 expansion board on that OpenCM controller? On the XL430-W250-T (-T for ttl) they write the following text in the documentation "Controller : OpenCM9.04 485 Expansion Board, OpenCR1.0". I still don't get why they list that 485 expansion board when the OpenCM9.04 has ttl support on the board itself. Is it just to use it as a hub? Am I missing something?

[KurtEck]

I am getting ready to start playing again with this. But while doing so, I am probably going to redo a lot of what I was doing with it in the first pass of the conversion.

In the first pass, I converted the code to use the Robotis DynamixelSDK to talk to the servos with either on OpenCM or OpenCR board. Which is OK, but this library was well as Dynamixel Workbench sort of grew out of their Linux and or Windows interfaces and they did lots of memory allocations and frees... And lots of similar things that maybe were not appropriate on smaller memory devices.

So a little while ago Robotis released yet another library/hardware Dynamixel Shield, which they made work with controllers like Arduino Uno... Since then, they have an underlying library which now the DynamiixelShield library is now derived from: Dynamixel2Arduino.
So I am probably going to see about converting to use that underlying library. I picked up one of the Dynamixel Shields which is more or less just the OpenCM485 board adapted to Arduino Shield...

I have been communicating with the developer at Robotis who is working on this library and I think we can set it up to make it easier to be used for other processors, which of course I will adapt to Teensy boards, especially including the new T4

The library is already setup where you can configure it to say: Dynamixel2Arduino dxl(Serial1, 2); Which says to user Serial1 and pin 2 is the direction register... So if you have boards like I have which use the direction chip, then they should sort of just work.

There are a few other issues to deal with, like the library is setup that for different processors, there are max number of servos and max number of bytes you can set/query in sync reads or writes... And for example OpenCM it is 16 servos... Which is probably not enough for hexapod with at least 18....

Sorry I have not answered your questions:

OpenCM485 board makes it easier to connect up the newer servos, then the OpenCM9.04c boards. As the OpenCM9.04c board have the XL-320 servo connectors, and sort of the capability for power for those servos... The 485 board is setup with both TTL(AX type) and 485 type connectors, and Robotis sells AX->XL430 like servo cables. The 485 board also has some power support, like wider traces... to better run these servos...

But we also hacked up the design of the AX hub, and created an adapter hub: https://www.trossenrobotics.com/3-pi...power-hub.aspx that allows you to use an XL320 servo connector to connect up to hub which then has XL430 like connectors that allow you then plug in your newer servos with external power to the HUB. But this does not give you any of the power conditioning that the Robotis stuff does (not that I have worried much about that ...)...