Presentation on theme: "Robot Recipes: How to cook-up a robot using COTS items Alan Federman Homebrew Robotics Club March, 2009 A short introduction to mobile platforms – mostly."— Presentation transcript:
Robot Recipes: How to cook-up a robot using COTS items Alan Federman Homebrew Robotics Club March, 2009 A short introduction to mobile platforms – mostly leaving controllers out.
Why present this talk? Hurdle (CTAG) between starter kits and a practical platform. Lots of skills, techniques(tricks) and some math needed. Most of these skills acquired over a lifetime: – Automotive bicycle mechanics/repair – Carpentry and cabinet making – Soldering and electronics fabrication (Heathkits) – Radio control models – HAM radio – Running scientific instruments/computer programming – Competition robotics (yes, Robogames counts) – Household appliance/plumbing repairs
What is a Robot?* (*not a trick question) A mechanism that performs a (useful)function normally performed by a biological organism (primate?). Why robots - The four Ds: – Dirty – Dangerous – Dull – Distant Also FUN - Geeks off the Streets!
Primate vs. Robot PrimateRobot Skeleton/jointsChassis/running gear MusclesEffectors SensesSensors Brain/nervesController/wires Knowledge/instinctPrograms Air/Food/Water/Power/Battery/wires circulatory system
Building a Robot is like Baking a Cake We have to acquire our ingredients/components. Heat up the oven/charge up or plug in the tools. Get out our utensils/lay out our tools. Make sure our hands are washed /work area is clean and safe! Creativity is great - but it helps to have a recipe. Follow the recipe / adjust modify to finish. Great cooks perfect recipes over time. Next reality TV: Iron Robot Chef War Survivor!
Is it a Robot? IMHO a true robot needs to be able to both move and react to changes in its environment. So: Traffic Lights, Vending machines, programmable thermostats, and RC cars with attached webcams are not robots. An I-bot may be a robot if it can operate after com is lost. The MERS are definitely robots. This lecture will concentrate on building an almost robot, since it wont be autonomous.
List of Ingredients 12 v rechargeable sealed lead/acid battery. 2 automotive geared motors 2 wheels 2 by 4 sheet ½ birch ply, 81 by 1 Casters Axle/bearings Fuse panel/fuses Relays/pwm / H-brdge Glue (wood, hot, epoxy, super), screws, fasteners. Aluminum/steel angle, sheet. Salvage, adapt, improvise, overcome.
Mechanical Chassis (Skeleton) Plywood box beam construction very strong, lightweight Glue/drywall screws make quick prototype possible. Plumbers tape good for motor mounts. Wheels mounted on axle securely. Off the shelf hardware available or you can modify what you have - example – a threaded rod can be heated and bent into a U-bolt. Attaching motors to chassis, and the to wheels is non-trivial Minimize weight/friction/inertia – maximize torque/power. Platform needs to move/deliver payload. Salvaged cable spool
Effectors DC motors, servos, steppers, linear actuators, pneumatics, etc. Wide variety – but for purposes of this platform – a couple of smaller automotive motors best - window or seat position motors are a good bet - starter motors a bad idea. Another benefit of these motors is they are already geared down for acceptable speeds. A six inch wheel at 60 rpm means about a foot and ½ per second on the floor which is faster than a Roomba. Easy to find 12v components for the drive-power chain. Consider how to attach motors to chassis, wheels to motors.
Power and Control 12v sealed lead acid battery heavy, but easy to charge. Components (wires connectors easy to obtain) Relays are cheap, but PWM probably better (expensive) Since an RC servo motor and PWM use the same signal easy to control. Relay(s) or H-bridge easier to implement. Benefit of DC motor is to reverse rotation, reverse current. In a perfect world Ohms Law rules: V= IR The VOM is your friend.
Power/Control Distribution Fuses and master CB/switch are always a good idea Fuse costs 50cents. PWM costs $100. New Globe motors also $100.
Practical Wiring 6 AWG in battery-to-Power Distribution Board path 12 AWG in circuits connected to 40A breaker 14 AWG in circuits connected to 30A breaker 18 AWG in circuits connected to 20A breaker 20 AWG to power the cRIO, wireless adapter and camera from the PD 20 AWG for attaching Breakouts and Sidecars to individual 20A breakers on + red white brown - black blue
Physics: Electric motors DC motors convert the V into F. Current in wire – resistance/inductance Force - friction/momentum Reverse the current, reverse the direction H-bridge uses switches* to control.
Sensors/Control Sensors can be divided into analog or digital Most measurements are analog (continuous) Digital – micro switch two states on/off – binary Analog – temperature or light sensor – continuous For digital electronics need to convert analog to digital. Converse for output – need to convert digital to analog. Servos use the same control D to A as PWMs Analog sensors typically convert a continuous 0 to 5v signal to a digital measurement – one byte 0-255 integer.