In a very exciting moment I connected a Lynxmotion PS2 wireless controller via a Lynxmotion PS2 receiver to to the arduino, installed Bill Porter's wonderful PS2X library, supplied power to the arduino and the outputs and downloaded the example program and - TA DA - I have remote control of my arduino, which means very very soon Bernie will be operated remotely. Many many thanks go to Bill for this lovely little library which makes this all so easy to do.
On a side note, having looked at the price of battery chargers and batteries it might be a while before he is moving around completely remotely...
I trialed the position of the servos with clamps, then used some right angle brackets from active-robots and some very useful plastic rivets to mount the servos onto the hips and shoulders.
He's not quite back together yet, but Bernie now has legs which is a big change and his balance has improved a lot already. The same pulley mechanism I designed on cardboard is done here with some brass hooks on the back of the legs.
I can't test this just yet though, because as you can see in the picture on the right all of the electronics are not currently inside Bernie. Since access is going to be tricky once the wing plate is attached I want to get as much tidied up as I can before his stomach gets any harder to access than it needs to be (the spare rib will still give me access when I need it, but it's going to be a bit of a squeeze to do anything in there).
Bernie woke up to a very bad morning. In order to add on legs there were a few modifications needed, so it was time to finally pull him apart completely.
While he was in pieces I took the opportunity to create a flat section on his back to support the wings he hopes to have eventually. This means he is going to have a metal plate inserted along his spine to carry the extra load, and also to make the body more rigid. Unfortunately once this is in place there will be a lot less access to the internal electronics, so I need to do as much as I can before I do that.
Servos are amazing things. Tell them to move and they get right to it and go to exactly where you told them to be within milliseconds. Dragons are much lazier, and might make it there eventually if you ask them nicely. Maybe. So the servos inside a dragon need to learn to relax a bit, take their time and meander their way to their destination slowly. I've been doing that in software to make the neck move nice and smooth, but once I add the legs and wings the load on the arduino is going to be too much and everything will slow down unreliably, making the movements very jerky and not in the least bit smooth. I found a design online for an RC landing gear which makes the servo act over a much slower timeframe, up to about 10 seconds long. This sounds more dragon like already.
I ordered 3 sample PIC12F629 chips from Microchip to play with and bought a big bag of capacitors, and I'm all set to build the landtastic circuit. Hopefully I can adapt this design to work with my dragon - I definitely do not want to have to spend the time building up a program in assembly from scratch it there are functional systems out there already!
It's been quite a long time since I've updated here, which sadly reflects just how long it has been since I've had some spare time to work on Bernie: between organizing the Melbourne Mini and studying for exams it's been a very busy couple of months! I finally have some holidays so I can get going on Bernie and flesh out some of the designs I've been working on.
Poor Bernie has been sitting there on the coffee table unable to move for a while now. He has developed a bit of a lean because his poor tummy is carrying all of his weight, He can't even wave when people come to visit him. Clearly this must be fixed, and as many a quadruped knows, limbs are handy things to have around.
I've been thinking about how to do this for a while now, because I want to use just one servo motor to control the whole limb. This will reduce the load on the arduino, simplify the programming and make the leg lighter, but makes the mechanism more complicated to design. I started by playing with some cardboard, and then went back to the drawing board to see how I could make this idea work. Like all of this project, there is a lot of documentation which will probably never see the light of day, but it sure does help fill a boring lecture and makes construction much easier and quicker.
Just like my very first bit of body construction I decided to make a cardboard prototype to see if my idea really worked. Initially I had different designs for the arms and legs because they are such different shapes, but I didn't like the extra complexity in the legs so I have decided to modify the design to work on a single concept. The joints work because the string does not change length - both ends are fixed to the leg, but there is a pulley point on the body so that the relative motion of the leg to the body makes the elbow/knee extend.
Before anyone asks, these legs are not in any way load rated! They will not be carrying the weight of the dragon, just providing some balance and making him look less like a glorified snake.