Archive for November 21st, 2009
|Source: Abbeyjean’s Toddlerbot
This started out as a balancing robot similar to the Gyro version of NXTWay and using Ramin’s RobotC program.
This worked first time which caught me by surprise – I mean where’s the fun in that? So I started playing around with the design. First I made it taller and taller but it still balanced ok so then I decided to see if I could make it stand up again if it fell down.
The result is ToddlerBot. I called it ToddlerBot because it is like a toddler tying to walk for the first time. It starts out face down on the floor, then it stands up and tries to move forward, but just like a toddler it falls dowm. After a few tears it struggles up again and toddles forward until it falls down again. And so on.
I used the HiTechnic Tilt sensor to detect when it had reached the upright position. I found I needed ‘arms’ at the rear as well when it stood up, otherwise momentum tended to make it fall over backward before it could start balancing.
A single touch sensor serves the double purpose of detecting when it has fallen on its face and also when the ‘arms’ are fully retracted.
It still has the sonar sensor to detect obstacles but this is pretty much redundant as it never stays upright long enough to reach any obstacles. The extra motor and all the other bits increase the mass of the robot considerably, with the result that the balancing motors have trouble reacting fast enough to counter the extra momentum created as the robot tries to balance. But then that was the idea anyway.
If it falls over backwards, you’ll have to get ‘mummy’ to help it get up again.
Front view balancing with arms up
Source: My Omnipotent Omniwheel
For the Lego World 2009 in the Netherlands I built an omniwheeled robot. It’s been done thousands of times before and the Internet is full of great (and not so great) examples. I wondered why I hadn’t jumped on that bandwagon so I got cracking.
This was the first prototype I made back in August. I was on a Lego expo together with Martijn and Daniel (and their respective better halves). I wanted to see if it were possible to build an omniwheeled robot using just the NXT 2.0 kit pieces. This is what I came up with.
It didn’t perform well at all, especially when it needed to do anything but spin around. It got me thinking, though, how could I build an omniwheeled robot that would perform well. Lucky for me, Martijn was more than happy to donate a couple of wheels to the cause. It was a little more than a couple, I guess he was expecting me to build a 6 wheeled robot or something. It came to about 200 wheels in all, 86 small ones and about 115 bigger ones.
I went through quite a number of wheel designs over the next couple of weeks. Some were ridiculous cart wheels shaped monstrosities that measured more than 20cms in diameter. Others simply defied explanation. The design I eventually settled on is shown below. It is loosely based on the omniwheel design that Steve Hassenplug made with some of my own modifications.
The wheel is actually made up of two wheels next to each other. They’re quite resilient. During Lego World I demoed the robot quite a bit and only 2 of the small wheels fell off during that whole time (5 days). Not bad.
Before I got my current design, the actual robot went through a number of prototypes over the course of about 2 months or so. I took pictures of some of them.
The first one is quite simple but it had quite a bit of flex in the axles attaching the wheels to the motors, so the outer wheels never actually touched the ground. The one in the middle had one half of the wheel on each side of a frame holding the motor. This one actually had suspended arms holding the frame housing the motors. It looked super cool but the whole thing flexed like crazy when you took a turn, it was terrible. The 3rd model was one I build during our camping trip. It was much improved, less flexing but I wasn’t happy with how little contact the outer wheels made with the ground. This caused a huge amount of bouncing around. I think in all there were about 10 prototypes. The final and current incarnation of the I present to you below.
The first picture was taken before Lego World, the other two were taken after. A couple of nice bumpers were added, a HiTechnic Touch MUX, a HiTechnic Compass and finally a HiTechnic IR Receiver to make the whole thing remote controlled. Here’s a little video I put together of it in action.
So there you have it. I’ll post some pictures of my remote controlled crane truck later this week.