Published: Friday, 14 February 2014 06:13
Written by Kyle G
For a long time I've been trying to come up with a reliable way to have one of our PhantomX Hexapods follow me around autonomously. The dream would be to have some kind of cheap/easy/effective way to track an individual. I'm still playing with some vision tracking ideas, or using a Wii-mote camera, but that's for another post.
While trying to come up with a cheap/easy/effective way to implement person-tracking, I started thinking about alternative control options. I realized that a joystick like in the ArbotiX Commandercould be mounted to the Chassis of the Hexapod and pulled from a string or a leash. By tying the analog input from the joystick to the inverse kinematics engine in the crawler, the movement of the joystick will directly control the movement of the joystick. Whichever way you pull the leash, that's the way the crawler will go.
Now it's not quite as easy as just slapping any old joystick onto the Hexapod. I've been using our RobotGeek Joystick since it's got nice mounting points and are pretty plentiful around here. The size was just right for being able to control the hexapod. For the longest time I was using some washers and the mounting points for the turret on the main chassis of the hexapod. This held up pretty well, but wasn't really ideal. Finally I asked our production manager Kevin to cut me a custom plate with the 2x3cm pattern so I could just fit the joystick mountin holes on correctly.(If you're a hexapod user interested in a plate, drop me a line, include your order number, and I'll get you one)
Early on we didn't have the tall-stick add on for the joystick, so I made the small mushroom style stick cover work. I would use a small zip tie around the thumbstick, leaving just enough slack to put a leash clasp through. This worked pretty well, but sometimes it would get stuck around the zip-tie. Also, there were definitely some angles that worked much better than others - very steep/shallow angles worked well, but ~45 didn't always get the crawler moving. However now with the tall-stick add on, things are much easier. I've drilled a small hole in the stick, allowing me to thread a twist tie in - this then connects to the clasp, and movement is much easier.
I've taken the leashed cralwer to a few events, and it's always a big hit. Kids and adults love it, and it's a great ice-breaker into explaining robotics to people. Almost every kid I meet asks 'is that a playstation controller?!' when the look at the joystick.
The PhantomX Quadruped can function in the same way. I find you have to be a little more gentle when you start the quad moving, but it's fairly stable once it gets rolling.
- When I went to RoboGames last year, I needed to switch back and forth between having the joystick mounted on the top of the quad to having a pan/tilt video turret mounted on it. I didn't want to reprogram the 'bot every time, so I used a jumper and the ArbotiX's internal pullups to give me an easy way to switch the behavior of the cralwer.
- I'd like to come up with some other ways to change the gaits and speed of the cralwer. Buttons would be an easy choice, and it might be possible to make it change speed based on objects around it. I'd really like to have some code that would slow down/speed up depending on the number of tugs on the joystick - tug twice and it goes faster, tug to many times and the crawler resists! This mighe lead to more complex behaviors ( the quad follows the leash when it wants to, but not always - it would be cute if multiple crawlers could 'recognize each other)
I'll have more photos and a video up by the weekend's end.
Code is available here. If you've found this post before setting up your cralwer for some reason, check out the cralwer Getting Started guide for getting setup with the ArbotiX-M Hardware, software, etc.
Thanks to my sister for all the great photos!