You must give careful thought to choosing the right batteries for your robot. The power supply system for the robot must be able to handle the voltage and current ratings of the motors, lighting system, sound system, and control circuitry.
It is a good idea to test each type of motor used on your robot to find out how much current is needed when they start up, when they are running under normal load conditions, and when they stall.
Most robot designs will require several different regulated voltage sources. The drive motors may require +12 or +24 volts at up to 30 amps. The electronic subsystems may require voltages such as +5, +6, +9, and +12 volts. Multiple voltages can be handled several different ways. The best method is to use separate battery supplies. One heavy-duty lead acid set of batteries to provide power for the drive motors and any other motors used on the robot such as: waist, neck, and arm motors. Another smaller set of gel-cell batteries should be used to power all the electronic subsystems.
The reasoning behind this is because motors generally distribute a lot of electrical noise throughout the power wires. Electronics can be extremely sensitive to electrical noise. Using two separate sets of batteries nearly eliminates these problems. However, other problems can occur due to the arcing of motor commutators, which can cause rf interference with remote control and wireless video/audio systems. Another reason is that in a one-battery system, the current surge that occurs when a motor is activated may zap all the juice from the electronics. This sudden dip in power might cause certain circuits to fail or become erratic causing the robot to lose control. Not good.
If all of the electronics in your robot are powered by the same batteries, make sure to add a filtering capacitor across the positive and negative power rails after the fuse. The capacitor helps to reduce electrical noise and current spikes often caused by motors. The value of the capacitor should be over 100uf and rated at the proper voltage for the system.
Be sure to place smaller capacitors such as 0.1uf across the power rails wherever power enters or exits each circuit board. These are used as “de-coupling” capacitors. Other “de-coupling” capacitors should be added as close as possible on the circuit boards across the power inputs for “clocked” logic IC’s, especially counters and flip-flops.
Batteries can deliver a large amount of current. If the leads of the battery accidentally touch each other or there is a short in the circuit somewhere, the wires may melt a start a fire! The smoke from such a fire is poisonous.
Batteries can explode. When a battery is charging, it gives off hydrogen gas. Hydrogen is flammable and will explode if there is a spark or ignition source near the battery. Always provide good ventilation when the batteries are charging.
ALWAYS wear safety chemical goggles and rubber gloves when handling or hooking up batteries. I even use a face shield. Lead-acid batteries contain sulfuric acid, which can burn you skin or eyes if any leaks out or is splashed in your face.
Always check that you have hooked up the battery with the correct polarity. Hooking up a battery backwards can damage the battery, charging system, and electronics.
Most rechargeable batteries are recharged about 20 percent higher than their specified rating. As an example, the 12-volt battery in your vehicle is charged to about 14 volts.
Most batteries are considered dead when their power rating reaches 80 % of their rated voltage. When you are testing your robot’s electrical systems, keep a careful eye on the condition of the batteries with a hand-held voltmeter. Make these tests while the batteries are in use. Otherwise, the test results may be erroneous.
The amp-hour rating for a battery is the amount of power, in amps or milliamps, that the battery can deliver in a specified time period.
Some people have been taught that amp-hour means that the battery will provide its rated current for 1 hour before going kaput. Some say if a battery is rated at 5 amp-hours, it can provide 5 amps continuously for 1 hour or 1 amp continuously for 5 hours. This is a misconception. The 5 Ah rating is actually taken at a 10 to 20 hour discharge interval. The battery is tested for 10 or 20 hours at a low or medium discharge rate. After the time period has finished, the battery is checked to see how much energy it has left. The rating of the battery is calculated by taking the difference between the discharge rate and the reserve power then multiplying it by the number of hours under test.
You should always choose a battery that has an amp-hour rating 20 to 40 percent more than what you need to power your robot.
Be sure to follow the manufacturer’s instructions for recharging your batteries.
If you are not sure of the specific charge rate you should limit the recharging level to 1/10th the amp-hour rating of the battery.
Another factor to keep in mind about batteries is their weight. Lead-acid batteries like the one in your vehicle can weigh 25 lbs. or more. You must plan for this by selecting drive motors with enough torque to propel your robot.
You must choose the correct type of fuse to protect you robot from major malfunctions. Fuses help to eliminate the problems caused by short circuits or power overloads. Remember how much blood, sweat and tears went into building all this. You don’t want it to go up in a puff of smoke.
Installing a fuse that is rated too far above your current requirements may not blow when a malfunction occurs. This could result in a fire!
Be extra careful when wiring you power supply system. Triple check your work. A mistake here will cost you dearly.
Install the main fuse in line with the positive rail of the battery, as near to the battery as practical. Choosing the right amp value requires that you know how much current you robot uses during normal and stalled motor conditions. (I will talk more about how to do this in a latter chapter). Add this to the current draw for each of the subsystems and then add 25%.
Recall that motors draw excessive current during start up so make sure your fuse is the slow-blow type. Unless you like changing the fuse each time the drive motors kick in.
You should also install a fuse for each of the separate regulated supplies required for your robot. Base the fuse size on the current needs of whatever subsystem they are supplying. Note : I am not responsible for any harm you cause to yourself, others or any damage you cause while attempting to replicate what is discussed in these or future articles. Please use good judgment and the proper personal protective equipment to protect yourself. If you feel that something I have posted is wrong or needs correcting please feel free to bring it up.
The three most popular types of locomotion for a robot are:
Wheels are usually the simplest and most versatile choice for robot mobility. Wheel size will depend on the size of your robot and the type of terrain it will travel over. Small wheels will have difficulty driving over items such as carpet, uneven flooring, thresholds that separate one room from another, small pebbles and rocks, etc. The larger the robot the larger the wheels;) Two other factors to consider are the weight of your robot and the type of material that the wheels are made of. If your robot will be considerably heavy, say over 100 lbs.; you should choose wheels that are made of a fairly dense rubber or plastic. Will they leave marks on floors like hardwood, tile or linoleum? Better be sure. You don’t want your robot to be an unwelcome guest. Surplus wheelchairs tend to be a good choice as they are engineered to carry a good amount of weight, the gearing and variable speed drive system is built in and you can hack the controls to suit your needs.
Very few people who attempt to build a large heavy robot take on the challenge of using legs for locomotion. Many questions come up such as:
How many legs will there need to be for good stability?
How do the legs need to move in order to propel the robot forward, backward or turn?
How many joints will the legs need to work smoothly?
How big do the legs need to be to support the robot?
The mechanical design and programming can be very tricky and complex. Four legged robots tend to be easier to balance but, steering and locomotion are harder to achieve. Hexapod robots are better equipped to walk at faster speeds without falling over and are better at making turns.
Tracks are my personal favorite mainly because they look so cool! They can be fairly hard to design and build but have some advantages over wheels or legs. Tracks act like giant wheels and provide terrific traction depending on what they are made of. Due to the way a track drive is constructed it can support quite a bit of weight and provide good stability (another reason I chose them). The length of each track is usually as long as the robots base. Their width will depend on the size and weight of your robot and will usually be 2 to 4 inches wide. The length of the robot base will determine how many idler wheels are needed. The idler wheels will generally travel in a channel that is formed into the tracks. Some tracks have one single fin-like protrusion in the center that requires the idler wheels to have a groove cut into them. Or the idler wheels can be doubled up with a small space between each set. Whether it is a channel or fin, either one helps keep the tracks from being thrown off as the robot moves or turns. Each track will also need a drive sprocket and some adjustable method to keep them at the correct tension. The Razor scooter wheels shown in the picture are mounted on an axle at the rear of the robot base. The axle can slide in a slot and is adjusted by a pair of bolts that push against it to tension the tracks. More details and pictures will be coming soon in future chapters. Tracked robots can travel over almost any type of surface. Even snow! However, the biggest drawback is the damage they can do to flooring and carpets especially when making turns. Tracked robots should usually be driven outside.
This project will satisfy a dream of mine that started almost as far back as I can remember. Basic Capabilities and Description:
goal is to build a large robot that will be totally remote controlled.
It will be approximately 6’ tall with a cylinder shaped torso, two arms
that each have a three finger claw, and a classic “bubble” head. This
robot will be built to impress, so it must look sharp. It must emanate a
presence when it enters a room.
1. It will have a tank tread drive system. 2. It will have wireless video so it can be steered even when it is not in my direct line of sight.
3. It will have sensors that will keep it from bumping into objects or
people. I still think it best to have an assistant that stays with the
robot to help with the demonstration, show, act (whatever you might want
to call it) and to keep people from touching it. 4. It will have two-way wireless audio communication so that I can carry on a conversation with others “through” the robot.
5. It will have a voice changer circuit or program that allows my voice
to sound more “robotic” to make it seem or appear that the robot is
operating on its own (with no one controlling it).
First stack-up. Can't wait to see how it will look with the final pait job.
Certain aspects of the robot need to be automatic to allow me to control it more easily.
Examples include: 1. After the torso has been rotated left or right, have it automatically return to the center straight-ahead position. 2. Also perform this auto centering for the robot’s head.
3. After moving the robot’s arms to a particular position, have them
“return to home” or a neutral position automatically. In some cases you
may want one command to move both arms in an identical manner at the
same time. 4. Collision avoidance should also be automatic. 5.
Certain other aspects of the robot’s behavior need to respond to sound
and motion stimuli in order to make its appearance more authentic.
6. The robot will have a “drop dead” feature if it gets out of radio
control range. (If operation of the robot becomes unstable for some
reason, it will have an emergency shut down feature that the assistant
or I can activate via push button. )
Base Platform with tread drive. Tested to 200 lb. payload.
Variable Speed Drive Panel.
:Sound and Lighting Effects
The robot will also have a number of special effects to enhance its presence. These will include: 1. Sound effects that give the impression that there are mechanical and electronic processes that are taking place inside the robot, a sort of low-level background noise. 2. Sound effects that enhance the movements of the robot's body, arms, head, etc. 3. Voice lights that modulate or flicker as the robot speaks. 4. Various flashing lights on different parts of the body. 5. The ominous “cylon” eye that strobes back and forth. 6. Other lights that respond to outside stimuli such as sound or motion. 7. Certain lights will actually be used to monitor or indicate real robot status items (such as battery charge level).
This is the first chapter of a long and rewarding “How To” article. This project is going to be very complex and time consuming. This is my ongoing build journal for a robot that I call Magnus. He is approximately 6 foot tall and will weigh somewhere around 300 lbs. This robot will be built mainly for entertainment purposes. However, it will serve as a testing platform for more advanced robot control later on. It is also intended to serve as an inspiration to others to enter the field of robotics. If you are planning to build a large robot similar to this one, follow along, I hope that you will be able to use the information to your benefit.
Building robots can be a very fun and rewarding experience. There’s a very special feeling you get when you see something that you made with your own hands come to life and scoot around performing the things you programmed it to do. However, it can also be very frustrating if you don’t have the proper skills to take on a project of this scope. I’ve been kicking this robot idea around for 40 years now. Three years ago I decided get serious and bring all my sketches and drawings to life. Even now I still find myself having to learn new skills. But, don’t be disheartened. Take it one step at a time. Seek out advice from others and be patient. If you find yourself up against a wall because you don’t know how to do something, realize this fact, it’s not always what you know… but what you can figure out. Listen to what your common sense is telling you. Go with your gut. And remember; nothing is so complex that it can’t be broken down into small enough pieces for it to be understood. Research and learn what is needed. Use the web. It’s a wonderful tool…Oh, and one more thing…remember to have fun!
Things You Will Need:
Desire- A burning desire to build robots. If you don’t have this there is a very good chance you will fail. Tools-Lots of tools or access to tools such as: hand tools, cordless drill, table saw, scroll saw, band saw, drill press, lathe, milling machine, belt sander, clamps, etc. Large Work Area- You need lots of storage space and elbow room. You are going to make quite a mess. Raw Materials- Wood, metal, plastic, etc. Money- I’m not saying you have to be rich but, when building something like this it takes quite a bit of money. Plan and work out a budget. Figure out what you need next and save up for it. Find ways to earn extra cash. Sell something you don’t need anymore. You’re clever. You’ll figure it out. Who knows, you may even find a sponsor willing to make a donation. Time- Understand that a project of this magnitude is going to take up much of your spare time. It could take years. Patience- The capacity to accept or tolerate delay, trouble, or suffering without getting angry or upset. Get some:) Information- You definitely need a computer with a good high speed connection to the web for research, obtaining parts and communicating with others that share your dream. Junk- Yes junk! Collect all kinds of stuff. Try to see the potential in everyday, ordinary items. People throw away tons of good stuff like old broken printers, copy machines, radios, TVs and computers that are full of usable parts. Also collect things such as PVC pipe and fittings, metal or plastic rods and tubes, wire, pieces of angle iron, ball bearings and brackets just to name a few. A Plan- You need to give some serious thought to what you want your robot to look like and what you want it to do. Break it down into systems, sub assemblies or sections and try to get an idea of what major components will be needed. How big will it be? What look or shape are you going for? What’s it going to made of? What type of locomotion will it need? Will it be remote controlled or autonomous or a little of both? What kind of sounds will it make? Does it need a wireless video and audio system? These are just a few of many things to ponder. Oh, one last thought… How are you going to transport it from place to place? Friends- Friends can be very helpful. There will be times when you need an extra set of hands. Some of your friends may have a certain tool you need borrow or they can perform a specific task such as turning something on a lathe, machining a part or welding. Encourage your friends to let you know before they throw out something useful. Determination- You must be determined to see this through. There will be times when you will feel like giving up. Don't lose site of your dream!