View Full Version : [Question(s)] RAW Serial Communication

09-30-2011, 01:35 AM

I'm trying to connect to my PhantomX (AX-18F) using the usb cable. Windows7 installs the usb to serial drivers and I am presented with COM8.

I use a program called "Realterm" to connect to COM8 so that I can send it some HEX commands.

My Problem is The arbotiX does not seem to move the motors when I send it some HEX commands from the pdf "http://www.trossenrobotics.com/productdocs/Interbotix_Robot_Turret_Manual.pdf".

Can anyone help? I'm not sure what I am doing wrong or what I should check etc????


09-30-2011, 01:33 PM
Please post the HEX commands you are sending. Also note that the Hexapod firmware does not implement the extended instruction set.


10-03-2011, 12:17 AM

here are some HEX codes that I have tried, they are from the extended command set:

0xFF 0x00 0x00 0x00 0x00 0x00 0x08 0xF7 (move to one extreme)
0xFF 0x03 0xFF 0x03 0xFF 0x00 0x08 0x0D (move to other extreme)

I don't have a Hexapod, I bought a "KIT-BPT-PhantomX-RT-AX18F" (not sure what firmware is on it).

My goal is to be able to move the motors via the FTDI Cable.

Any hints/tips, I am very stuck+lost?


10-21-2011, 11:51 PM

It looks like you may have purchased your AX-18F about the same time I bought my AX-12 PhantomX. It may be that those Arbotix boards were inadvertently shipped with a PyPose sketch loaded instead of the CommEXT as documented.

When I send the following number string from RealTerm at 38400, 8-N-1 the pan servo moves, twitches a couple of times, and appears to center itself. Try this:

255 255 253 2 25 231

I got it from the Ultimate Arbotix thread in this forum - it is apparently a test command.

The darn thing had been silent since I built it so it startled me when it finally moved, but the cat sitting next to it went into low earth orbit! :eek:

I had hoped to bang this project out in an evening - back in September - and now it appears I'll have to figure out how to upload the CommEXT sketch as originally intended - but at least I have signs of life!

Hope this helps...

10-22-2011, 03:14 AM
Okay, here is what I have found. Despite what the Interbotix Robot Turret Manual suggests, MY arbotix board did NOT ship with "a default Comm_EXT firmware preloaded...". It appeared to be the PyPose sketch. After I waded through the various help guides and downloaded the Comm_EXT sketch (furnished in the Dynamixel_PanTilt.zip distro) to the Arbotix I began to get movement that roughly correlated to my serial commands.

Salient facts:
Serial communication is at 38400 baud, 8 bits, no parity, 1 stop bit - I used RealTerm from SourceForge
When the turret first powers up, it centers both servos
I'm reasonably certain I did not mix up the pan and tilt servos when I assembled the unit, but I found the Pan and Tilt fields swapped in the extended command packet when compared to the documentation.
Pan values less than 512 are CLOCKWISE from the centered position (nose right)
Tilt values less than 512 are COUNTER-CLOCKWISE from the centered position (nose down)
There was an unexpected (to me) amount of overshoot in position (~5%) when transiting at full speed from one position to another. And this was before I had any sort of load fixed to the turret with any sort of rotational inertia. Presumably, this can be fixed with modifications to the sketch.

Best of luck to others out there struggling with similar problems. It seems like the quality control could use some work. If I get the time, I'll better document the process I used to get to that elusive first successful serial command issued to the turret. Though I expect that will happen concurrent with reports of low-flying pigs and ice storms in Hell.

11-01-2011, 05:38 PM

I found that my arbotix board also did not have Comm_EXT on it.

Once I got it on i realised that both motors had the same ID. It took a while to work out how to change ids on the motors...