September 30th, 2009
Ok, so that might be a stretch. It's not really a robot
since it doesn't sense or act on its own (yet) but it has some robotic qualities. But every project has to have a cool acronym whether it deserves it or not. So I chose RuFES (roo-fus). RuFES is simply a small servo hack I built just to get somethings going. I have been wanting to do something with some servos I had but just haven't got around to doing anything major. So I was messing around with a laser pointer (and my cat) and thought what not build a small servo assembly to move the laser around? RuFUS is made of 3-servos mounted in a Pan, Tilt, and Roll configuration only because I wanted to experiment with 3-axis of movement. At the end of the servo assembly is a small 5mW laser module. The servos are connected to a 4-channel RC receiver which I can control through an old RC transmitter I had for an RC helicopter I have. Through RC control I am able to operate and point the laser all over the room. You can imagine how entertaining this would be for any cat who loves to chase a laser pointer. My plans in the future are to add a small micro controller which can control each of the 3-servos, power to the laser module and randomly position itself. The micro controller would be able to be programmed so that it might wake up every hour or so, run for about 5 minutes, then turn itself off. But all that is for another day.
Hitec HS-47 Servo Motor
Various servo mounting hardware (screws, rivets, etc.)
Scrap 1/2" Birch Plywood (servo base)
Scrap 3/4" Birch Plywood (assembly base, bottom)
Scrap 3/4" Oak (Laser module holder)
Spare satellite speaker mount.
To construct the assembly I started with some servo brackets made by Lynxmotion. They are awesome brackets which make it super easy to construct any number of configurations with standard servos. It only took an evening to assemble the servos into a configuration which gave pretty free movement across 3-axis. I used the HS-425BB servo at the base (pan) because its slightly more heavy duty and contains a bearing. Same goes for the middle servo (roll). The HS-47 is lighter duty and is mounted on the end and provides tilt. Since it only needs to move the small laser module base and the module itself it is more than sufficient to handle the job.
Once I had the configuration worked out it was just a matter of connecting it to the Berg-4 RC receiver. Since the 4-Channel transmitter I have is for a Helicopter the receiver I had operates at 72 MHz. Typically this frequency is used for Aircraft and Helicopters but what the heck it's what I had and it works. Plus it's not like a need a whole lot of range.
A while back, I made a small PCB to accept the Berg-4 receiver. It was an ultra-simple design with just a few headers, power connector, led and a capacitor to smooth out the power supply. This project finally gave me an excuse to use it. It just takes an input of 5VDC and breaks-out the Berg-4's servo outputs to individual headers. It also has underside mounted headers so that it fits on top of a small piece of solder-less breadboard. If you like this PCB you can order it online from BatchPCB which I use for all my PCB designs.
To mount everything I made a small servo base from 1/2" Birch plywood. I cut a rectangular hole in the front to accept the Lynxmotion servo bracket. I left it long enough to allow for some prototyping space with some solder-less breadboards. For the base I cut a piece of 3/4" plywood and mounted a home entertainment satellite speaker mount to both the assembly base and servo base. This provided a fairly stable platform to mount the assembly. Lastly I made a small LED Laser module holder to mount on the end of the Lynxmotion "C" servo bracket.
This is the LED Laser Module I used. You can get these for about $5 on eBay.
This is the "recycled" transmitter I used to control the servos.
For now, it's kind of fun to play with and pretty easy to control. In the future I want to attach a micro controller which can control the servos without an RC transmitter. This way the servos can be operated autonomously. I might try to program it so that it just randomly positions the laser (slow, fast, crazy, whatever). I also might add the ability for it to sleep for a period of time, then wake up and begin "playing" with the cat. Might be a nice entertainment system for the cat while we are away.
Here are some videos of the RuFES in action.