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,
but it's far more annoying to have your robot suddenly and mysteriously stop dead while dominating a match than it is to lose to a worthy foe after putting up a good fight.
Here's a random compilation of some common self-destruction methods I've encountered in my robots, my friends' robots, and my opponents' robots, which can cause an otherwise good robot to fail.
 Nothing is as disappointing as having a battery or other electronic item come unplugged during an impact. Most sealed lead-acid gel cell batteries have spade terminals, which are hooked up to your robot's electronics via crimp-on connectors that slide over these spades.
 Sometimes these connectors can come loose and pull off easily. Take a pair of small pliers and squeeze the female connector so that it requires some effort to attach to and remove from the battery's male terminal.
 Put a piece of tape across the wire or connector as extra insurance that it won't go anywhere.
 Or better yet, use batteries that have secure screw-down terminals.
Make sure that your batteries can provide a full 3 minutes (or 5 minutes for a rumble) of run time under *extreme* conditions. Motors draw the most current when they are stalled (stopped) and trying to spin. This condition is met during a shoving match between the 2 bots. Often the winner of a match is decided by which robot can slowly and forcefully shove its opponent into the arena hazards. After you've put your bot together, run it at full throttle against a curb and see how long the batteries last--if it can do this for 3 minutes straight, you shouldn't need to worry about battery life during a match.
If you're using more than one battery (or battery pack) in your robot, wired either in series (for higher voltage) or in parallel (for longer battery life), make sure that all of the batteries are rated equally and charged equally. If the batteries are mismatched, you're asking for trouble. Have enough chargers & spare batteries to keep all of your bot's batteries in equal and peak condition.
Yet another battery failure that I experienced was internal battery breakage from a huge impact. A strong robot named Carnage, with a big axe, landed a blow to Missing Link's battery box, destroying the battery from the impact. The battery looked unscathed from the outside but no longer worked. It was right up against the panel that Carnage axed, so the shock of the blow was transmitted directly to the battery. After that loss, I added some low-tech shock-absorbing cushions (pieces of computer mouse pads).
 Electric wires that carry current through your bot are like its veins and arteries carrying around blood, the life of the bot. You must ensure that all connections are made securely. I used to put connectors in critical portions of the wiring system, for convenient swapping out of motors or speed controllers, but these just created unnecessary potential failure points in my wiring systems, which sometimes crippled my bots. Now, I solder every connection securely & use as few connectors as possible, meaning the only easy things to unplug are the batteries for swapping out after a fight.
Make sure your wires are thick enough to handle the current that your motors draw. In the past with Rampage and Bot Will Eat Itself, I used thin-gauge wire for a pair of high-current motor weapons. The heat generated in the wires melted the rubber insulation on them, shorted some together, and...poof! A short circuit which led to battery pack failure and a pretty cloud of smoke. Most speed controller instructions give a recommended wire gauge for the current values that they can handle--use this wire gauge or go even bigger just to be safe.
 The Missing Link started out with 6"-diameter spherical wheels with about 3/8" tread of vacuum cleaner belts attached. I originally just used epoxy and the belt tension to fasten the belts to the wheels.
 In one fight, a robot named Gator sawed through the belts, causing one to fall off & another to start to come apart. This led to 2 changes in Missing Link's wheel scheme: I replaced the soft belts with a taller 8" diameter pneumatic tire, cut open to fit around the spherical wheel; and I screwed down tire's sidewalls to the wheel so they would be more secure. While more durable than the vacuum cleaner belts, this new tire scheme posed 2 problems:  the uninflated tire was soft & would deform as the robot rolled, making the motors work harder to move the bot; and the increased diameter of the wheels gave Missing Link a higher top speed, but it lost some pushing power & taxed the motors more heavily. Result: I blew out 2 speed controllers in 2 different matches, after successfully shoving and beating the other robot around for a while, resulting in 2 disappointing losses. The motors were drawing more current with this new tire scheme, and the speed controller was now in over its head.
 After these losses, I switched back to the grippy old vacuum cleaner belts, but this time, I screwed them down with sheet metal screws. Even against a few killer blows from Ziggo's spinner, the majority of the tread was still attached & in place. |
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 Since I didn't finish Dr. Inferno Jr. in time for BotBash 2000, I entered his drivetrain in the 30lbs class, as Overpowered Box. His wheels were foam-filled large model airplane wheels. They were extremely grippy and gave him great traction, though they wore down a bit over the course of the event.
 With the extra 28lbs added for the lightweight class at BattleBots San Francisco 2000, in a tough pushing match against Alpha Raptor, 3 of Dr. Inferno Jr.'s 4 tires shredded to pieces on the rough BattleBox floor. This was a good lesson in showing that some components may work well for lighter robots but fail when they're used in heavier ones. The solution was to replace them with rugged rubber-on-plastic Colson caster wheels.
 Another wheel-related failure on Dr. Inferno Jr. was that his motor's gearbox came undone from the wheel axle a couple of times. The axle is a steel rod drilled & tapped so it screws down on the output shaft of the gearbox. To keep the assembly from unscrewing during operation, I drilled a hole through both shafts & stuck a mild steel cotter pin through & bent its arms so it wouldn't slide out. These pins snapped a few times under heavy use, sometimes not affecting the bot, but sometimes slowing it down considerably. After nearly losing a fight to this failure, I drilled the holes out slightly bigger & press-fit in some really tough steel dowel pins, with some threadlocker to make sure they wouldn't slip out. These pins should never break.
 Physics caused me to lose another Missing Link match. He had a gas-powered circular saw (created from a chain saw engine) that drove a 14" blade at *really* high RPMs. Originally, I used a light 1.5lb abrasive fibrous chop saw for a weapon. The robot handled & worked great with this attachment, but the blade itself proved to be ill-suited to high impacts and abuse. It's a great blade that can cut through all sorts of hard materials, but only if it's used properly and carefully.
 After I blew up that abrasive cutting disc, I replaced it with a 6.5lb carbide-chip steel emergency blade. The new weapon was formidable, but I found that, when it was spinning at top speed, Missing Link had lots of trouble turning left or right, and the shock-mounted blade & gas engine would tilt to the side during turns, sometimes enough to make gouges in the ground. And I even lost one match because the battery drained faster than normal with this new saw blade attached.
Thinking back to my physics classes, I recalled an experiment with a person sitting in an office chair, holding a spinning bicycle wheel--when he tilted the wheel, the chair started turning in circles. In short, a spinning mass doesn't like to change its orientation--a flywheel likes to keep spinning in the same plane. Watch videos of Backlash popping one of his drive wheels way up in the air while he's taking turns--same concept. A robot with a horizontal spinner weapon will not experience these same effects, since the disc will stay in the same orientation when the robot moves. It may even make your robot more difficult to flip over.
 One problem I had with Overpowered Box and Dr. Inferno Jr. was that I was screwing 1/4-28 bolts into threaded holes in thin, 1/8" aluminum pieces. The 1/4 means the bolt is 1/4" in diameter, and the 28 means that there are 28 threads per inch. Because aluminum is a relatively soft metal, and because I was using a fine thread pitch, and because I was screwing into thin metal, many of the threads on the aluminum stripped and the screws fell out. Fortunately, I had lots of redundant screws that kept the bot together. The morals I learned from these failures: use coarse threaded-bolts on softer materials (I should have used 1/4-20 bolts), and 1/8" of aluminum is not enough material in which to cut enough threads to avoid stripping--1/4" aluminum would've been better.
 My first bots, Rampage and Bot Will Eat Itself, had several parts joined with threaded rivets. When you don't have access to the inside of your robot and you're screwing on the outer panels, you can't hold a nut on the inside while you screw in a bolt from the outside. So, I drilled holes in the frame and used a riveting tool to squeeze in rivets that had threaded holes in the middle. Then, I'd attach the parts together and insert screws into these threaded rivets. I soon found out that, because some were installed improperly or because I put the screws in too forcefully, the rivets would break free and spin in their holes. Then it would be very difficult to put screws in or take them out, since the threaded portion was turning along with the bolt. I haven't used these fasteners since.
 Missing Link used several servo-driven cables to actuate its weapons. Both the chain saw and circular saw gas engines used an aircraft servo that pulled a cable or a linkage to control the throttle, while the pair of scuba spear guns used a pair of servos with cables to pull the triggers. These worked well, but, after storing the bot for a while and then running it, I noticed that the cables had developed considerable slack and I couldn't actuate the weapons properly. Moral of this story: if you're using cables to actuate something, check & double check that the connections are secure and that the line hasn't picked up any slack.
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