Pololu's Wixel + Arbotix Commander V2

[Gertlex]

For a project I just started, the Wixel MCU from Pololu seems to be sufficient for what I need (namely: 1 UART for Dynamixel servos, and a wireless serial connection).

I figured I'd use my Arbotix Commander for the controller. Since the Wixel's use some custom hardware wireless communication method, I need two of them (and I bought two of them for $20 total on Black Friday); one on the bot, and one to forwards the commands from the Arbotix.

I used some of the spare connections on the Seeeduino that is part of the Arbotix Commander V2, wired these to some female headers on a chunk of perf board, and stuck stuff together with double sided foam tape.

I first verified that the Wixel forwards the Arbotix Commander signals with the USB-to-Serial App that Pololu provides. And I've now succeeded with using the Wireless Serial App on both Wixels so that Arbotix Commander signals are sent to a PuTTY terminal on my computer. Not to be a shill, but that was easier to set up than any MCU + Xbee configuration I've seen.

And pictures: (Click to embiggen)

[Gertlex]

A modified app for the Wixel now compiles with the Commander code included. This is useful for the Wixel that is listening to the one plugged into the Commander.

Non-clean code can be found in my fork of the wixel-sdk repository. All I've done is copy the code I used for Numa + Commander, and comment out stuff I'm not using, and re-arrange .h/.c files a bit. The relevant app is in apps/wireless_serial_twitch. https://github.com/erelson/wixel-sdk

Had to skip the UART's buffer flushing after each complete Commander packet since there doesn't appear to be a comparable function in the Wixel libraries. (If I'm feeling like it, I might ask on the Pololu forums at some point...)

[Gertlex]

I realized that with the Wixel on my Arbotix commander, if instead of forwarding the bytes generated by the commander, I instead forwarded the bytes received by the commander's xbee (i.e. from the robot), then I can hook a paired Wixel to my computer and get e.g. temperature information from the servos.

To preserve the ability to use the Arbotix Commander to drive my Twitch robot (which uses the Wixel for control), I added some header pins and two jumpers (plus a cheat sheet). Switching between usecases just requires some pliers or small fingers.

[jwatte]

Award: Best thread necro :-)

[Gertlex]

I should also document the 3d-print encapsulated switch wired to one of the push buttons, giving me the ability to set a mode. E.g. TwitchMX's turret mode + laser was toggled in this manner

[Gertlex]

At Maker Faire 2019, I had Numa 2 sending temperature information back over the Xbee. I had my added-on Wixel in turn relaying that to my computer. The goal here was to be able to monitor temperatures while moving the robot, but setting up a computer just to display that is tedious... and given that it's ultimately more useful during testing than during matches, reducing the friction of this realtime monitoring of temperatures better ensures I'll actually use this capability as I refine Numa 2.

So, I threw on a 64x48 pixel OLED display that I got years ago from sparkfun. It's controlled via SPI with the Wixel. Thanks to Oestoidea's implementation, it was pretty straight-forward to get the display working for a simple "rotate through rows of an array and display (only) numbers" usecase. (After spending several days banging my head against a wall before noticing issues with integer overflow and unsigned integer math...)



Now I can finally finish up my write-up of Numa 2...

And though no one should use it, the wixel side code lives here.

[jwatte]

I tried doing exactly this (with a slightly different OLED) with an Arbotix Commander and a PhantomX quad, but the Xbee turn-around time latency made the Phantom way too jerky in its control. (I've never managed to use an Xbee in duplex mode without at least 200 ms dead time each time it decides to send data the other way.)
Are you using the Wixel one way, and the Xbee the other? That seems to avoid this kind of problem!

[Gertlex]

It's bidirectional via xbee. My data rate from the robot is to send one row of data (12 bytes) every 4s or so. I'm actually doing a single read of a single servo's temperature once per second, and sending data when I've updated all four values. Definitely an overabundance of caution against interferring with other things.

Certainly the arduino could be driving the display, but my life is made easier by only maintaining build environs for micropython and SDCC (wixel), and not including Arduino