BullyBot

By TheCowGod @ Mon, 2008-06-30 02:08

• Actuators / output devices: Tamiya dual gearbox, 2 servos for aiming gun
• CPU: Arduino Diecimilla
• Power source: 4 AA batteries for motors, 9V for logic
• Sensors / input devices: Sharp IR, IR detectors
• Target environment: Anywhere other robots are having a good time

By now I've built a few different robots, and they've had it pretty good so far. They get to spend their entire life going about their business, drumming on things or chasing light, with nobody to bother them. I think it's time that changed. They need to learn what it's like in the real world.

To that end, I've started building what I'm tentatively calling the BullyBot. It's going to be a tank-tread-based robot with an AirSoft machine gun mounted on top, and it will find the other robots in the room and shoot at them. It builds character.

2008/6/29

Initial construction. I bought a cheap, electric-powered Airsoft gun, took it apart, and figured out how it works. It's pretty simple -- the trigger operates a simple switch which closes the circuit between the 4 AA batteries and the electric motor that drives the mechanism. I cut off all the parts of the gun that the robot won't need (the handle, shoulder stock, etc), removed the trigger mechanism, and soldered my own wires to the motor. I then wired up a simple circuit to let the Arduino fire the gun by means of a relay. Works great, aside from the fact that there's no good way to fire a single shot. No big loss, I can just shoot 2 or 3 at a time.

Next I bought two torquey servos and set about building a 2-axis mount for the gun, to let the robot turn the gun left and right and aim it up and down, like a tank. I also started working on the main body of the robot (it'll be plywood-based, just like Little Drum Machine).

Extending the axles

Useless parts removed

Removed parts

Up/Down servo mounted

The robot's base (those axles will need some support)

Mounted on the second servo for left/right aiming

View from the other side

It might be a good idea to add a second up/down servo on the right, just to add some support so it's not hanging in space like that.

Over the last few days I've been working on the mobile base of the robot. I've got it basically all put together -- I guess the next step is to mount the gun turret servo on the base, breadboard up all the circuits, and then start working on the IR detection. I'm still not sure exactly what will be required to detect other robots, so obviously I don't want to solder anything together yet. I just received my Digikey order containing a bunch of Panasonic PNA4612's, which are IR detectors originally designed for use in electronics appliances like VCRs for detecting the remote control signal from across the room. The specified max range is "minimum 11m, typical 18m". I hope that those will do what I want -- all I'll have to do is modulate the IR LED on the other robots at 38 kHz so this sensor can detect them. I'll post them as a component once I've gotten familiar with them.

I'm already pretty clear on what the circuitry for the motors, servos, and gun firing will be, so I might go ahead and solder that up on one perfboard (sort of a 'motors control module'), and then just build a second circuit board for the IR circuits once that's finalized.

Pictures!

Lotsa holes drilled in the base

The lower half of the base assembled

The bottom of the base

Preparing to install the upper half of the base. Leftover aluminum tubing from Little Drum Machine's drumsticks make for pretty good DIY standoffs, except that if you overtighten the screws, the aluminum starts to crumple.

The assembled base.

Space between the platforms to mount the Arduino and all the other circuit boards. I plan to mount the batteries on top, to make them easy to remove for charging.

2008/7/7

I soldered up an 'output module' as I described earlier -- a PCB containing the circuitry for the Pololu Low Voltage Dual Serial Motor Controller, the relay and transtor for the gun firing circuit, and the header pins for the two aiming servos. Once I finalize the IR detection, I'll have a separate board for that circuitry.

With everything assembled (but with no input at all), I coded up a simple program to have him aim the gun around at random and shoot wildly into the air. I quickly noticed that the recoil affects his aim pretty significantly. Every time he fires, the gun moves up and to the left. I might have to modify the 'shoot()' routine to move the servos down and to the right while he's shooting, to try and balance that effect. We'll see how that goes.

I also did some work on the IR detection. Building the detector circuit was simple -- the sensors I ordered output a voltage that's high when no 38 kHz signal is detected, and low when it detects a signal. So for now, I just ran it through an LED -- later, I'll sample the output with a digital input. I tested it with a remote control, and the sensor picks it up with no problems, even when I'm 15' away on the other side of the room, around the corner, and pointing the remote AWAY from the sensor. Range isn't going to be a problem -- I think the real struggle will actually be LIMITING the sensor's sensitivity to make it more directional so I can actually use it to find WHERE the other robots are. But it's interesting to know that the communication is so reliable at such a distance -- these sensors were only about $1, so this might represent a good way for two robots to talk to each other (indoors) for less money than the EasyRadio modules.

With the detector circuit built and working in 2 minutes, I was optimistic about the IR emitter circuit that will be mounted on each of the other robots. I shouldn't have been. I've never used the 555 timer chip before, and I struggled for hours, researching and trying various combinations of resistors, capacitors, and wiring, before finally coming up with something that the detector could see. Man, I'd love to have an oscilloscope.

So finally I've got both parts of the circuit working, and as I suspected, it's way too sensitive. I epoxied on a length of aluminum tube to the front of the sensor to try and give it 'tunnel vision', and it did seem to help, but I think there's still a lot of leakage through the gaps in the sides of the metal case. I'll have to look into covering it with opaque paint or something. But I'm hopeful.

Now to the pictures!

The completed 'output module'. I'm pretty happy with how compact and orderly it turned out. Inputs from the Arduino are on the top, power connections are on the left, and outputs to the motors are on the bottom (along with the servo connections in the top left). The green PCB is the Pololu motor controller -- it fits perfectly and sits flush on top of the relay (pictured below). I worried about the magnetic field in the relay's coils affecting the operation of the motor controller, but I haven't noticed a problem so far.

Pololu controller removed from its socket, showing the rest of the components.

Underside, showing all the junctions. Maybe it's time to start looking into PCBs.

Everything wired up for testing, and working perfectly.

555-based 38kHz IR emitter circuit. The digicam actually sees the infrared light emitted by the LED, though in real life it's invisible.

Detector circuit -- much simpler.

All assembled.

Stick 'em up!!

Thought I'd give a little update. I've been having trouble getting BullyBot to move. The Pololu Low Voltage Motor Controller and Tamiya gearbox worked in testing, but when I assembled the whole robot, it wouldn't move. So I took it all apart again for troubleshooting, and I think I might have been overloading the batteries or something. But I think it doesn't matter, because it looks like I might have killed the low voltage motor controller while troubleshooting. Oops :) Fortunately, I have a spare Micro Dual Serial Motor Controller left over from LDM. The uDSMC can't run the toy motors in the Tamiya gearbox, as we learned in this thread, but as Ben from Pololu suggested in that same thread, you can replace the FA-130 motors with Solarbotics RM3's, which the uDSMC can control. So I ordered a bunch of those RM3s, and now I just need to desolder the capacitors and motor leads from the current motors and solder up the new ones in their place. I'm hoping that will take care of that problem, and then I can get back to troubleshooting the IR robot targeting.