Next steps with a PhantomX AX Hexapod Mark II & BBB

[CreedyNZ]

Hi,

I've had my Phantom hexapod for about a month and have had a lot of fun so far just tinkering with the machine. Currently running the Phoenix code and loving the smooth gait.

At the same time I've been playing with a BeagleBone black and currently have it running some Python code that reads an IR distance sensor, an ultrasonic distance sensor, a compass, and camera then feeds info back to my PC via WiFi.

I've been thinking about bringing the two projects together. I can easily mount the BBB on the Hexapod and have been pondering how to communicate commands to the m-Arbotix movement controller. One thought is to have the BBB supply commands via a serial connection using I2C, effectively using the BBB as a "smart controller".

Anyone done something similar? Is there a better way and/or is this a hairbrained idea that will only lead to frustration.

Ideally where I'd like to end up is a Hexapod that can be directed using the controller still, but which can be switched to 'semi-automatic mode' and navigate itself around obstacles.

Andrew

[KurtEck]

It is very much doable. I have had the Phoenix code base running on Raspberry Pi, Beaglebone Black, and Odroid U2/U3 boards.
I have used the Arbotix Commander on all of these. There are threads about this up on this forum as well as Lynxmotion (now Robotshop) forums. I am a little rusty on some of this as I have been taking a rather long diversion with using Teensy 3.1s.

All of my stuff is up on github: https://github.com/KurtE/Raspberry_Pi
Note: it is called Raspberry Pi as that is what I was working on when I created the project, but works with all of the above. Also my Readme as part of the project has lots of my notes on how to set up these different boards.

As for hooking up Arbotix commander: There are at least two different ways.
1) Plug xbee in to BBBk using USB adapter like: https://www.sparkfun.com/products/11812
2) Configuring to use one of the UARTS on the BBBk and using simple adapter:
3) Oops can't count, could try one of the capes like: http://elinux.org/BeagleBone_XBee_proto_cape

Note: I have done 1) and 2) above, have not tried 3...

How to control the AX servos. Again you might be able to control the servos using one of the built-in usarts, but I have not tried it. What I have used is a usb2ax (http://www.seeedstudio.com/depot/USB...ml?cPath=91_92)
I think earlier I also experimented using the usb2dynamixel (http://www.trossenrobotics.com/robot...dynamixel.aspx), but it has been awhile... Also with the USB2AX, I added my own extensions to the firmware of it, such that it could offload the interpolation processing from the main processor.

So again yes this can be done and makes a lot of sense.

[KevinO]

I agree with Kurt. You can do a lot once you step over to a BBBk or Raspi. Here is one of my past projects using the PhantomX and a Raspi.

[CreedyNZ]

Thanks Kevin and Kurt for your helpful and encouraging posts.

A few more links and options for me to research and experiment with.
This stuff is very addictive and much more exciting than my last project www.weather.blognz.org

Today's effort was to mount the BBBk on the hexapod, along with a 5v switching regulator (plenty of headroom for future usb or other devices that might be required) to begin experimenting. Both are mounted on a clear section of Plexiglass so I haven't needed to drill any holes in the hexapod body.




I'll post an update once I've progressed a little further.

Andrew

[CreedyNZ]

Well, after being distracted by work and building a multicopter for far too long, I got back into upgrading the Hexapod.

I decided to have a go at writing a Python script to run on the BBBk that would in effect act as a relay for the remote commander and provide its own automated commands when the remote commander is not switched on. The BBBk is then communicating with the Arbotix-M via a serial connection. i.e.

Remote Commander ----XBEE Serial-----BBBk-----Serial-----ArbotixM-----AX12

So far all seems to be working OK with the Arbotix still running the Servos (using Phoenix code) while the BBBk runs everything else.

Before I get too far though, I can't help wondering if I've overcomplicated things and maybe would be better just running everything off the BBBk with a USB2AX and the BBBk ported Phoenix code?

Interested in hearing from those who have travelled down either or both paths to help decide which way to proceed?

Andrew

[jwatte]

The ArbotixM can allow you to do things like automatic interpolation with speed/target position values, which might be nice.
You can also use it for additional GPIO/sensors, especially if timing is more crucial than what the Linux kernel can give you (and you don't want to lock up the BBB with interrupts disabled.)
Yes you CAN use a straight BBB (or RPi, or NUC) without another microcontroller -- I ran Onyx that way for a long time -- and that works fine, too, as long as you don't need whatever the second controller can give you.

[Xevel]

It would be interesting to see if the BBBk PRUs could do the IK/FK/interpolation computations + communication, with the main CPU dealing only with higher level commands...

[CreedyNZ]

Thanks for the pointers - I think the extra GPIO connections and the timing advantages are enough for me to stick with the Arbotix-M and the BBBk. My next step will be to add the capability for the serial connection between the BBBk and the ArbotixM to send status messages back to the BBBk. At this stage my serial connection is one way only i.e. sending commands from the BBBk to the Arbotix.


One issue that's arisen today is that the Arbotix will occasionally free and needs to be reset, so will need try and track down the cause of that one.

[KurtEck]

FYI - I have had good luck with the USB2AX with linux boards. My version of the firmware moved the interpolation stuff to it instead of having the main processor do this.

However I am also looking to use a Teensy (either 3.1 or LC) to take over this work. The LC runs at 48mhz and the 3.1 I normally run at 120mhz. It also gives you lots of IO pins and the like. I have my own carrier boards for it, but thinking of making a newer smaller one, not sure of how small yet. Also thinking of trying to make a sketch for it to see how well I can emulate the USB2dynamixel or the like, using raw hid USB... Or I may also just stick with Arbotix Pro...

[CreedyNZ]

Wow KurtEck, I'm impressed by your use of just about every controller board known to man!

I've had another look at your code repository, what a treasure trove.

Might experiment down the path of BBBk (or maybe the new RPi2 that arrived at home yesterday) with the USB2AX (currently on its way from Seeed).

Is your code in the Raspberry_Pi/Phantom_Phoenix/ repository what you've referred to above as having had good success? Looking at the notes, I'm assuming the USB2AX firmware needs to be changed? Is this to the firmware in the usb2ax repository?

Really appreciate the code you've made available.