|
Building a competitive combat robot is not a simple task. The builder must consider the trade offs between armor, power, weapons, mobility and reliability, all the while remaining within the weight and technical requirements of the combat robot tournament. This article offers suggestions to help builders during the building and testing of a combat robot. It is possible that some of the recommendations may be requirements at some tournaments, or that a particular tournament may change its requirements in the future. Check with tournaments for their particular tournament rules, requirements and technical regulations.
Technical Regulations
Technical regulations are the requirements for combat robot design and construction. If your combat robot does not meet a tournament's technical regulations, it is unlikely to pass their safety or technical inspections. If you are unsure if any particular feature of your combat robot will pass the safety or technical inspection, then contact the tournament organizer for prior approval. This should be done well in advance of the tournament date.
Construction materials
Some materials should not be used in combat robot construction. Materials that are easily damaged or that tend to leave debris on the arena floor during bouts should be avoided. These are:
Wood, paper or cardboard.
Fabrics not bonded to a resin composite.
Clay-based materials or ceramics.
Polyurethane Foam
Polyurethane insulating foam, is commonly found in lumber yards and at building supply stores. When heated with a flame or hot metal, polyurethane foam gives off poisonous gasses. For this reason, most tournament organizers strongly recommend that you do not use polyurethane foam in your combat robot. Use open-cell PVC or polystyrene foam instead. Both of these materials have many properties that are superior to polyurethane.
Safety/Tech Inspection
If you don't have appropriate safety covers or restraints, most tournament safety inspectors won't inspect your combat robot. Don't risk failing the inspection because you didn't spend some time making your robot safe for those who are moving around and working on the combat robot.
Make safety covers
Making the safety covers does not need to be difficult or elaborate. Try using plastic, rubber, foam or metal. Another good method is to form a fiberglass/resin composite cover over the point or edge.
Make safety restraints
Pinch hazard and safety restraints can be as varied as robot designs. In some cases, a block of wood or chunk of rubber is enough to prevent a pinch hazard. In other situations, a snap ring/clip connecting to eyelets may work well.
Cover attachment
Covers may be attached using bungees cords, springs, a tied cord/rope or some other mechanical method. Friction attachment method and press fit covers are generally not allowed at many tournaments. Covers that use twist ties/wires to secure a cover are not likely to be approved, since they are not really "reusable". Instead, make a loop of wire that hooks over some part of your combat robot. Also, using adhesive/duct tape is not acceptable.
Test your covers and restraints
Most tournaments do not have specific requirements for measuring the effectiveness of a safety covers or restraint. Generally, a "hard" push or bump on a safety cover should not compromise the cover, and a "good pull" should not remove any safety cover or restraint. Safety covers and restraints will be obviously safe and secure by simple inspection. If there is a question or concern, safety/technical inspectors have the right to have you change or re-make your safety covers and restraints.
Weight limits
Most tournaments have specific weigh-in procedures described in their tournament procedures documents. Combat robot weight limits are strictly enforced at most tournaments. The tournament organizers will usually have an “Official Scale". The reading on the scale is your official weight.
Overweight combat robots
Overweight combat robots tend to be the most common problem at tournament. Many bathroom scales will usually read 3% to 5% low. Commercial scales, such as UPS and FedEx, frequently read low to reduce the risk of over charging customers. Many experienced competitors will build slightly underweight and add weight if necessary. At every tournament there are several entrants whose robots come in overweight. Builders will end up weakening trying to shave off a few pounds. Some will then spent hours trying to make the weight limits. Other will end up removing their weapon system to make the weight limit. If you think that your combat robot will "just barely" make the weight limit, it is most likely too heavy. Design your combat robot to be at 2% or 3% under the weight limit for its weight division.
Moving your combat robot at a tournament
Keep in mind that when you are working on your robot, you will need to support it with its wheels/tracks/legs off the ground, so that it cannot run away. When testing your combat robot or when having it inspected, it may be necessary to operate your robot without having it move along the ground. When you are moving your combat robot, most tournaments will require you to use a cart or dolly. Most tournaments will not allow you to drive your combat robot anywhere except within a testing area and inside the arena. Build a carrying cradle/dolly/cart specifically for your robot. This can be as simple as a wooden box with handles, or a plywood platform with castors.
Non-proportional control
In an effort to reduce costs, some builders make "On-Off" wheel motor controllers by connecting servos to switches. Generally these are unreliable and erratic. Also when your transmitter is shut off, some servos do not always return into the "Off" position, causing the combat robot to run away if transmitter signal is lost. At most tournaments this will guarantee that you will not pass the safety or technical inspection. Since servo designs are mechanical, hard impacts can cause switches to become stuck in the on or shut-off position. If you build such a system into your combat robot, construct it well, test it and then test it again. Make sure that your servos and switches will fail-safe if the transmitter signal is lost.
IF Controllers (Innovation First Controllers)
If you can manage it use an IF or similar 900 MHz radio controllers. IF controllers use multiple transmission codes, reducing the chance of frequency conflicts with other competitors. Labeled-packet data transmission greatly reduces the chance of radio interference. A built-in microprocessor will allow you to program the controller so you can perform functions at the flip of a switch such as, reverse controls allowing you to drive inverted. Frequently IF controllers come with a tether that will allow you to perform tests without radio transmission or radio interference.
Electrical drawings
Before building your combat robot, make a drawing of your electrical system. As you work on and test your combat robot, update the drawing as necessary. The drawing can be very useful when troubleshooting. At some tournaments it may also be useful for the safety and technical inspection.
Electrical safety
Batteries may look very safe, but they can store a lot of power. Ni-Cad and Ni-MH batteries, when short-circuited, can give off hazardous fumes, become very hot, or possibly explode. Wear safety glasses, and put an insulating cover on at least one of the battery terminals when working with a battery.
Lead-acid batteries
Tournament technical regulations almost always require that sealed-lead-acid batteries be "leak proof". There are many manufacturers and distributors of this type of battery. Some of the most popular batteries are the Hawker Genesis, the Panasonic LCR, and the Power Sonic PS series. Wet-cell lead-acid batteries are generally not allowed by any tournament. Also, there can be substantial differences in reliability, durability and performance between different battery brands. Beware that a cheap battery may not be worth the money.
Battery hold-downs
Batteries can become very hot during high-current discharge. Hold-downs for batteries should be made from materials capable of withstanding moderately high heat. Nylon and plastic tie-wraps are a very poor choice, as many rechargeable (Ni-cad, Li-ion and others) can melt them. A better method for battery hold-down is to use a plastic or other non-conductive box to contain the batteries. This will also help to protect and secure your batteries from impact shock. Screw clamps have also been used successfully. Using a small fan to help cool the batteries will help to extend a batteries life.
Wire gauge chart
A wire's voltage rating is determined by the type and thickness of the wire's insulation. The gauge or size of the electrical conductor determines how much amperage or current the wire can carry. If the size of the wire is too small the wire will heat up and power will be lost. If the wire is far too small for the current, the insulation may burn off or the wire itself may melt. The chart below shows values for various currents though copper wire. Note that smaller wires have larger gauge numbers. The actual wire gauge used can vary, depending on wire length, allowed heating, and so on.
Wiring
Wiring to the Master Switch has to be the multi-stranded (non-solid) type and should be insulated with a minimum insulation voltage rating of 300 volts. The wire should be sized such that at the maximum current, the temperature of the wire does not exceed 180ş F. In practice, most quality wiring has insulation that meets those voltage and temperature specifications. If you can find it, use Tefzelâ or Kaptonâ insulated wire. These insulation types are thinner, smoother, tougher and can withstand higher temperatures than the standard PVC insulated wire. All wiring in your combat robot should be stranded, not solid. In a typical application, there is no difference in current carrying capacity of solid versus stranded wires of the same gauge. Stranded wire is also much easier to work with.
Fuses
Fuses should be used in all of your primary and secondary electrical systems. If an electrical circuit uses multiple batteries in series, the optimum location of a fuse is between two of the batteries. Generally, your fuses should be rated for two times the expected maximum current.
Grounding the chassis/frame
Grounding a metallic robot chassis is not recommended. All electrical system grounding should be done with wires not connected to the chassis. Combat robots with High DC Voltages (over 48V nominal), cannot have a grounded chassis as per most technical regulations used at tournaments. Understandably, in some cases, grounding the chassis can reduce or eliminate some radio reception problems. If a grounded chassis is used, special care should be taken to insulate the positive battery voltages to avoid a short-circuit to the chassis, also contact the event organizer to get prior approval.
Electrical motor radio frequency suppression capacitors
Use capacitors to reduce the amount of radio interference caused by the arcing of the motor brushes. For each brush-type motor, it is a good idea to place .01 uF ceramic capacitors from each brush connection to the motor casing. The motor casing should itself be grounded or otherwise connected to ground through another .01 uF ceramic capacitor. Most electronic hobby stores or electric motor repair shops can help you with this if you're not sure what you need to do. Mounting a capacitor is inexpensive and well worth the few minutes it takes to do. Note that, if possible, the motor casing should be connected to a grounding wire, not to a grounded robot frame or chassis.
Motor cooling
Try to use some kind of cooling system for electric motors, as they can become very hot during competition. Some competitors will pre-cool electric motors prior to a bout using ice packs or even dry ice.
Starting fuel powered engines
Fuel powered engine starting has been a problem for many competitors. Break-in new engines for at least 30 minutes before going to a tournament. Test-start the engine after it is installed, some problems (fuel feed, etc.) don't always show up when the engine is run on a test stand.
Electric starters
Some competitors use electric starters for their engines. External starter motors may save weight, but engine-mounted starters, if properly wired to the receiver, will allow you to re-start your engine if it stalls because of a sudden jolt or blow from a competitor.
Spring-type throttle returns
A requirement of many technical regulations is that an internal combustion engine (ICE) must return too idle speed (or shut off) when transmitter signal is lost. Some builder's use throttle return springs to meet this requirement. This can prove to be ineffective. The spring must be weak enough to be overridden by the servo, yet strong enough to pull back the inactive servo. One solution is to use R/C equipment that allows you to set the servo's position when transmitter signal is lost. Another solution is to design your control system to shut the ignition off if transmitter signal is lost.
Pneumatic system drawings
Before you build a combat robot, make a drawing of the pneumatic system. Show system pressures in all of the pneumatic systems sections. As you work on and test your robot, make changes to the drawings as necessary. The drawings can be helpful when repairing or troubleshooting and may even be required for the safety and technical inspection. You may need this drawing if you are required to seek prior approval from the tournament to use high-pressure pneumatics.
Pneumatic component rating and mounting
If there are components in your pneumatic system that does not have a clear rating label or stamp, you may be required to provide documentation showing the rating for that component. Inspectors check the mounting of the pneumatic components to ensure that your components and mountings meet the requirements of the tournaments technical regulations.
Pressure bottle securing
There are lots of ways to mount a pneumatic/hydraulic pressure bottles that will satisfy the inspectors. Here are some suggestions for mounting the typical pressure bottle. There should be at least two (2) hold-down straps, each at least 1/2" wide, which connect directly to the robot's structure. The straps can be metal screw clamps or metal straps with over-center hold-down clamps. Electrical tape will not make the inspector happy. Don't use U-bolts, they create pressure points on the bottle. The hold-downs must be secured so that vibration, inertial shock or impact will not release the hold-down. This is especially important when using over-center hold-down clamps. The two outermost hold-downs should be separated by a distance greater than the diameter of the pressure bottle, and at least 1/2" from the "round" part of the container. A block should be mounted at the bottom of the pressure bottle. The block should be attached solidly to the combat robot frame or chassis. The clamps must be reusable, so that the bottle is always secured in place the same way each time it is put to use.
Pneumatic safety precautions
When developing and testing a pneumatic system always:
Wear approved safety glasses or better yet a full-face shield.
Use a protective shield or barrier.
Wear approved safety glasses or better yet a full-face shield.
Use a protective shield or barrier.
Perform initial tests using low system pressures.
Slowly increase pressures during testing.
Fully depressurize the pneumatic or hydraulic system after each test session.
Do not allow your pneumatic system to become contaminated with petroleum products or dirt.
Charging a pneumatic system
Charge your pneumatic system slowly. Rapidly charging a high-pressure air system can result in an explosion due to “dieseling" if contaminants are present in the system. Charge pressure bottles at a rate of no more than 600 psi per minute.
Hydraulic system drawings
Before you build a combat robot, make a drawing of the pneumatic system. Show system pressures in all of the pneumatic systems sections. As you work on and test your robot, make changes to the drawings as necessary. The drawings can be helpful when repairing or troubleshooting and may even be required for the safety and technical inspection. You may need this drawing if you are required to seek prior approval from the tournament organizer.
Hydraulic component rating and mounting
If there are components in your hydraulic system that does not have a clear rating label or stamp, you may be required to provide documentation showing the rating for that component. Inspectors check the mounting of the hydraulic components to ensure that your components and mountings meet the requirements of the tournaments technical regulations.
Hydraulic safety precautions
When working on or testing a hydraulic system, always:
Wear approved safety glasses or even better, a full-face shield.
Use a protective barrier when the hydraulic system is pressurized.
Perform initial tests of the system using low pressure.
Do not use contaminated hydraulic fluid.
Depressurized the hydraulic system after each testing session.
Note: Hydraulic fluids are considered hazardous waste and should be disposed of properly.
Large spring safety
Never position a stretched or compressed spring in such a way that it is pointing at you or at another person. Reduce the risk of injury by assuming that strong springs will break free from mounts.
Flywheel safety
If a rapidly spinning flywheel suddenly becomes unbalanced, or breaks apart, a great deal of energy can be released in an uncontrolled manner.
When testing flywheel operation always:
Wear approved safety glasses or even better, a full-face shield.
Restrain the combat robot securely, so that it will not move if the flywheel becomes unbalanced.
Remain behind a protective barrier when the flywheel is spinning.
Perform initial tests of the flywheel using low speeds.
Before approaching a combat robot, wait for the flywheel to come to a complete stop.
Your combat robot and team names
Although it's not a construction issue, you should do some research on the name you choose to give your combat robot and the name of your team. First of all, the name should not be offensive, vulgar or indecent. Many tournaments reserve the right to reject your entry if there is an issue with the name of your combat robot or team name. Obviously the name should be unique. If your combat robot does well, there is always the possibility of a toy manufacturer or commercial product that will want to use your name. If the name has already been copyrighted or trademarked, you will not be able to use your combat robot's name on any commercial product. At least do a search on the internet using Google and Yahoo. You can also research your name on the website Builders Data Base Check to see if the name of your team and/or combat robot conflicts with any existing trademarks or copyrights. This should include, entertainment services, toys, video games, books and so on. Even doing these searches is still not a guarantee, but it will significantly reduce the chance that someone else has the rights to the name you've chosen.
Now quit sitting around, put your brain in gear, get out there.....and kick some bot!
|
|
