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How To Build A Combat Robot |
| A few
years ago, Team Found Objects' Brandon Davis sat down
and put together a "How To" guide to help all new
builders learn the basics of combat robot design.
Hopefully, this will get you moving forward on the right
track. What This Is This is
a thrown together set of rules of thumb, suggestions,
hints and general officiousness, with the intent of
assisting in the construction of a CHEAP 12 pound robot
from more or less easily found bits & pieces. This was
created to supplement informal robot construction
seminars conducted after a robot fight. The idea goes
like this; have a robot fight and while watching folks
are drunk on mechanical destruction & carnage, show them
how easy it is to build their first bot. Right there,
right then (recognize the economic model? First taste is
free kiddo!). Give the folk a hand-out to take home for
reference. They come to the next fight with their
creations and a new group of ravenous mechanical
destroyers is born (BWAH_HAH_HAH_HA!... Sorry). Repeat.
And since this is being re-printed on the Robot Battles
website, here's
a link to a PDF version to print
out for yourself. This is targeted at folks who have never built a combat robot before. It is not a technical document. Folks who have built a combat robot before will be bored silly by this. This will not help folk who have access to mills, lathes, CNC machines and degrees in electronics (you don't need my help-go build something cool). Why Listen To Me? If you are asking yourself the above question, the answer is that you probably shouldn't. I am not a heavyweight in the robot combat world (or any other world). What I am is an intermediate level builder who really enjoys a hobby and would like to get others involved. I don't have lathes, mills, or CNC machines (OK, there is a degree in electronics but that isn't going to come into play here - promise). What Is A Combat Robot? For the purposes of this exercise, a combat robot is an R/C car in a very bad mood with the desire to find other R/C cars and kick them into scrap. Purists will tell you that to qualify as a robot, a machine must be autonomous. Fine. Good. Go read something else. WARNING This is one if the few times in this little article that I am not in any way kidding. Combat robots are inherently dangerous. You do this at your own risk - I accept NO liability for ANYTHING. This hobby, in both its construction and execution, has the potential for fire, explosion, trauma and other injury as well as death. Be smart, be safe. Read manuals. Read warning labels. Ask questions. THINK.
To get a combat robot to do anything (other than be an vaguely amusing sculpture) you need six fundamental elements (this is the order we'll be discussing things):
The
transmitter, receiver and the speed controller are the
items that most folks just can't do for themselves. (If
you are one of the folks that can build your own
electronics hooray for you! Now go bask in your own
superiority-QUIETLY, while the rest of us get on with
our pitiful ignorant lives.) The bad news is that these
items are relatively expensive and absolutely
indispensable. The good news is that in recent years
these items have become essentially commodities. You are
encouraged to spend your money here, buying for the
future. Investing in good quality radio equipment and
high quality speed controllers is not only less
frustration in the long haul, but much cheaper. With
care, these items will fight on in multiple different
chassis.
Especially the battery vs. motor priority portion can be the subject of disputes no less vicious than Mac vs. Wintel or any of the innumerable schisms that make religious studies such a side splitting (or slitting, these folk get SERIOUS) hoot. Well, I'm the one writing this, those are my priorities, and the rest of you can go schism among yourselves (again QUIETLY). Speed Controller The
Speed Controller (ESC) is really the beating heart of a
combat robot. It will probably be the most expensive
item on your shopping list. Do not skimp here. Many of
the items that can blow up or be damaged during a fight
can be often be borrowed from other competitors in the
pits (No really, one of the strange things about a robot
fight is that your opponents are almost as interested in
your bot being able to fight as you are. Otherwise, how
else can they beat you to scrap? Oh yeah, the pits are
where to find the bot builders who aren't fighting at
the moment. Look for tables off to one side that look
like a hardware store mated with an electronics shop &
then exploded.). There are frequently enough spares
floating around the pits to replace most of the items
that die during a fight-but the ESC is expensive &
consequently rare. Make protection of the ESC a basic
criterion of your design.
An important consideration in the ESC of your dreams could be number of channels. There are many ESCs available that will control 2 motors (Left & Right Channels) from the single board. This can simplify your layout considerably. Some ESCs allow for control of 3 channels, Left Right & Aux. This is very handy if you are interested (now or in the future) in having an active weapon on your robot. Mixing is a feature found on many ESCs. There are two steering techniques available to the combat robot; Tank & Mixed. In Tank steering, the left hand stick controls the left side motor(s), and the right hand stick controls the right side motor(s). Both sticks forward= forward, move one stick back and the other forward= a very fast turn. In Mixed steering, the ESC places Forward/Reverse on one stick axis (Y axis, up & down) & R/L on the X axis of the same stick. This results in a one handed drive, leaving the other hand and stick available for weapon control (BWAH_HAH_HAH_HA!... sorry). Once you
have an ESC- READ THE DOCUMENTATION! Keep it around.
Download a copy & store it in your hard drive (you know
you'll lose it one day). You need a Transmitter (TX) & a Receiver (RX) that match each other. A handy guide to concepts in R/C basics can be found here while a guide to R/C terminology can be found here. Radio System Types
A note on channels: If you decide on an FM or AM system, you will have to also purchase channel crystals (XTAL). Crystals cost anywhere from $7-15 each. You need matching XTALs for both TX & RX (example: a channel 65 for your TX AND a channel 65 for your RX). Plan on having at least 3 channels (more is better) that work with your system to go to a fight. The reason for this is that you want to control only your bot-not other folks'. Of course the reverse of this is true-you REALLY don't want somebody else to have control of your bot! Having multiple channels to select from is frequently a requirement of the rule sets. Be prepared for this; it is really disappointing to not be allowed to fight because of channel conflicts. It is also a very good idea to test each channel pair in your completed bot BEFORE you show up at the fight. Like anything else, XTALs break. To completely avoid channel conflicts, consider a 2.4 GHz spread spectrum system. While the initial investment is higher, these radios will bond with their receivers, creating a unique pair that that does not conflict with other systems. The result is fewer giblets to cart around and less scrambling in the pits to resolve radio issues. Another consideration is the NUMBER of channels a TX/RX pair can control. For example, the GWS system cited for a FM system will control 4 separate things; say Left Motor, Right Motor, and a Weapon motor, with a channel left over. The example cited for an AM Radio only has 2 Channels of control which will be generally used up by Left Motor/ Right Motor. Try to not only consider what you build today, but what you may wish to build tomorrow. If the
ESC you select does not have BEC, you will need to
provide a 5v source to the Receiver. You need at least two motors for your bot, one for Left side drive & one for Right side. The motors by themselves are not particularly useful; they spin too fast and with little real power. Some sort of transmission is also called for. For your first combat bot, allow me to recommend the quick "one-stop shopping" technique of the battery operated drill. This is a great inexpensive way to get both motor & transmission in a single fell swoop (there is an additional benefit to this that we'll discuss in the next section-multitasking baby!). The motors in the drill are the brushed type. Keep an eye open at the hardware or "home improvement" store for sales. Perhaps the easiest way to get hold of very inexpensive motors is to purchase on-line from a site like Harbor Freight. After I wrote that sentence, I found an 18v drill motor for $27 and a 4.8v for $15. An 18v drill motor would be delightfully adequate for a 12 lb to 30lb fighting robot (4.8v might be a bit anemic for a 12lb). Anything in the 9v and up range is a nice place to start. These drills cost less than most of the "specialty" motors alone. Once you have the drill, there is a bit of surgery required (we call it hacking). I am lazy, so this will not be covered in this document. Instead, I refer you to a nice web article by a builder of almost mythic stature in the Robot Battles family of fighter/ builders, Dale Heatherington (spend some time on this site; there is LOTS of good stuff for the geek here. There are lots of other drill motor hacks out there, as usual, Google is your friend). Pay careful attention to the July 2006 Update, those set screws are vital. What you have after the hack (and say $60, including shipping) is a pair of motors (transmission included) with a shaft already attached (the threads on that shaft are 3/8" 24, you can mount wheels directly to this), batteries to run them, and chargers for the batteries. This combo of materials, purchased separately, can easily cost (no kidding) hundreds of dollars. Battery/Charger You need something to power your bot. Many fights don't allow Internal Combustion Engines (a.k.a. IC or ICE) because they have an unreasoning fear of fire (silly, yes, but the times we live in require tolerance of many strange opinions). We won't be talking about IC. For most of us, this leaves the electric option; for the vast majority of this group it means a battery (you mad scientists out there can work out your own alternatives, again QUIETLY). So where
is your battery & charger for this project? You already
have it- it came with the drill guns you acquired and
hacked for their motors. The batteries are low-end
NiCads. You need a (possibly) new tool for this next
bit-the Multi-meter (a.k.a. DMM or just meter). This
will allow you to test the battery and all kinds of
electrical thingummies in a number of ways. You don't
need anything fancy (Though they are nice). Radio Shack,
Home Depot, any hardware store is a good place to look
for this item. Talk to the nice person at the store &
tell them what you are doing (you're gonna blow their
mind!). There are instructions in the box with your new
toy (and best diagnostic friend).
Battery Guidelines Here are some basic guidelines to the care & feeding of your battery and charger. Please note that items that include words in all capital letters (like NEVER & READ) are not suggestions; these have the potential of explosions, fire, injury and (I kid you not) death.
Chassis This is where you get to use as much imagination as you may possess. I have built robots that, aside from the electronics, were constructed entirely out of materials acquired from (multiple trips to) Home Depot. There are bots made from R/C Cars. There are bots made from wood. There are bots made from closed cell foam. There are bots made from exotic materials like Carbon Fiber & Titanium. The choice (and the skills & tools to implement that choice) is yours. Fair warning - odds are good that your first robot will� and there is no nice way to say this� suck (this is true for almost all of us. If you aren't one of US, then you are one of THEM. And you should know what happens to one of THEM that get mouthy. Remember, QUIETLY). Don't sweat it. Your next one will be better, and so on. Some guidelines to ease you into the process:
That's
all I have for you. - Brandon Davis, Team Found Objects
Sample List-12lb robot
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