My take on the Awesome RoboticsHobbyist Hexapod


#1

Just wanted to share a little about the hexapod I have been building based on the designed kindly shared by RoboticsHobbyist on Thingiverse - if you want to see the original designs they are here: https://www.thingiverse.com/thing:3103547

So a little bit of history. Way back when, in the distant past (in hobby robotics terms) I was asked if I would beta test a new robotics education/construction kit from a company called Robotis. This was the original Bioloid Comprehensive kit and came with 19 AX-12 dynamixel servos. It didn’t take long for me to fall in love with the dynamixel servos and subsequently, nearly all of my homemade walking robots have been based on them. Run forward to mid 2017 and I wanted to get a new hexapod up and running. My first robot back in the early 1990 had been a hexapod and subsequently I have always had a soft spot for them.

The initial build was based upon a circular, commercially available hexapod chassis, with 18 AX-12 servos and a laser cut deck for the electronics. The electronics where based on the Arbotix M controller (Arduino compatible with 3 wire serial TTL interface for the servos) and an Arduino Mega with touch screen for the sensors and main control. The Arbotix was interfaced to the Arduino Mega via I2C and just managed the walking gaits and locomation using NUKE and Pypose. It walk well and was a lot of fun, but wasn’t quite what I had in mind visually.

So late last year I was browsing around Thingiverse and stumbled upon the designs for a hexapod that RoboticsHobbyist had uploaded. That was the look I wanted, inspired by the PhantomX Hexapod from Trossen but with designs that could be customised. The new build started.

My initial design change was to look to laser cut the chassis rather than 3d print it. The first prototype chassis plates where cut in 3mm plywood and I decided that the chassis needed some additional length to accomodate my additional electronics. I used Inkscape to tweak the SVG files I had created from RoboticsHobbyists 3d designs and added about 46mm to the length of the chassis. The resulting chassis was laser cut in 3mm acrylic, red for the bottom and black for the top.


#2

The legs where built using RoboticsHobbyist’s leg design, but commercial Bioloid brackets I had from the original beta testing, but I did 3d print his wonderful feet for all of the legs. The some electronics as were in the original hexapod where transferred to the new chassis, including an I2C sonar distance sensor (not shown in the photos). Everything was I2C interfaced and a custom gait management application has been added to the arbotix to allow it to receive commands from the Arduino Mega (which has been changed for an Arduino Mega ADK to allow an android phone to be added at a later date as the robots main ‘brain’). The result was a robot that looked like this:

Now we were into the software… I’ll keep this brief but feel free to ask questions if you want more information.

Using Valadium Labs’ Pypose and NUKE (nearly universal kinematics engine) http://vanadiumlabs.github.io/pypose/, I have created a set of basic walking gaits that run on the Arbotix. These are a little rough but work and can be tweaked later. The Arduino Mega monitors the sensors (currently just the sonar) and manages the user interface on the touch screen. To date we can walk forwards, backwards, turn left and right and crab. I have also ordered a remote controller for the Arbotix so the hexapod will have 2 modes - autonomous (managed by the Arduino) and remotely controlled (managed by the Arbotix Controller over Xbee).

So that is where we are. We have a working hexapod thanks to Robotics Hobbyists’ great designs and I am working on the software. Two things are holding me up currently:

  1. The UK distributor of the Arbotix Controller is out of stock and I am waiting on delivery, since early December.
  2. NUKE and PyPose are pretty old projects. At least 5 years old in fact. I have had to tweak the code to get it to work correctly on Windows 10 and still need to do some more work to optimise the walking gaits.

But we will progress as soon as the Arbotix Commander arrives :grin:

More photos and details of my build can be found in the ‘Makes’ section of the orginal RoboticsHobbyist’s designs here

Carl


#3

This is awesome. Looking forward to seeing this in action.


#4

Absolutely fantastically awesome!!! You guys are something else!!! I am so going to need to up my game!!!


#5

So, finally, my Arbotix Commander has arrived.

About 10 minutes of assembly required to get to this. I had already configured the Xbee boards as a pair so, in theory, I should be able to add the other Xbee to the robot and walk it about…


#6

It’s a pretty cool controller, I have the same one for my Hexabot, and absolutely love how easy it is to use.

I was thinking of giving it a try on the Bioloid/Humanoid I am working on.


#7

So SpidyBot lives. Here are his first steps:

I am running Kurt Eckhardt’s Phantom Phoenix firmware so the autonomous features are disabled. You may also notice that I appear to have a dead coxa servo on the right hand front leg. I need to investigate this tonight.


#8

Looks really good. See if you can find these in your local hardware store. This is what I used for the feet to keep the robot from slipping on the floor, it also quiets the steps down a bit. I forget the size I used.

I had a similar issue with one of my servos when I built mine, it was a bad/loose cable. Maybe yours is that simple of an issue. The other thing I seen cause this with the Dynamixels is that I ID’ed it wrong so the software didn’t know how to address it.


#9

Absolutely awesome!!!

Sounds like River Dance!!!


#10

I found the issue with the right front coxa servo. It has and ID of 1, the Phantom Phoenix firmware has some code to try and find a servo that has lost its ID. Apparently, if an AX-12 looses its ID it resets to an ID of 1, so they had moved the front right coxa to ID 19, there was a config option to revert it back to one. Set that and all is fine on the servo IDs.

Will look for some rubber feet today.


#11

Cool, I am glad you found the issue. This is probably the most common issue with these servo actuators.


#12

I’ve added some rubber feet and am amazed at the performance change. With a couple of tweaks to the PhantomX Phoenix firmware, SpidyBot is running soooo fast now. (I know it is missing two legs to be a spidybot but hey, the name kind of stuck :stuck_out_tongue_winking_eye:)

Will try and get a video early next week, as am working this weekend.


#13

Glad this worked out for you. This is what made me design them to accept the rubber vacuum caps. My first revision didn’t have any type of rubber on the feet. The bot was slipping and sliding, I redesigned the feet with the thought of the rubber feet and was impressed too.