Page 49 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Before blindly picking one, you should look at how this selection will affect
each of the other systems at work in your robot design. For example, for a given
horsepower rating on the motors, a 24-volt motor will draw about half the current
as a 12-volt motor. That’s a good thing, right? Not necessarily, because running at
24-volts will require two 12-volt batteries—which increases the battery storage
area and robot weight. That’s a bad thing, right? Well, again, not necessarily. A
12-volt battery might not be able to deliver the current to drive a 12-volt motor,
but will have plenty of current for driving a 24-volt motor.
This is why you make the system interface drawings first. When you pick a
component to use, you update the interface requirements, such as weight, voltage,
current, spacing, the need to add new subcomponents or delete old components,
and so on.
A bigger part of the compromising process occurs when you build your bot
around existing parts. Obviously, life gets a little easier when you can build with
stuff you already have, but often this means getting a bot that’s less flashy than
you envisioned. For example, say you were planning to include heavy-duty motors
on your bot, but the ones you had in mind are hard to obtain, and you happen to
haveacoupleofwheelchairmotorslyingaroundthegarage(botbuilderstendtohave
this kind of stuff lying around). You may choose to use the motors you already
have, rather than going on a wild goose chase for the other motors. So, these mo-
tors now become a fixed specification, and you’ll need to compromise on your
bot’s performance goals. That 20-mph robot you were planning might only go
10 mph now, and can only push half the weight you originally wanted.
Probably the biggest area of compromise comes with cost considerations. Say you
found the ideal motors you want, but they cost $800 each and you need four of them
for your four-wheel-drive bot. Like most beginners, you can’t really justify spend-
ing $3,200 for motors. So you either find different motors, such as $100 cordless
drill motors, or change the design from a four-wheel-drive bot to a two-wheel-
drive bot.
Again, ideally, you should design the entire bot on paper or CAD before you
start constructing it, although this usually isn’t as much fun. Most people find de-
signing and building at the same time more enjoyable because it allows you to see
the progression of the bot from day one. Other people enjoy the design process
more than the actual building. If you enjoy building, team up with a good de-
signer. If designing is your thing, then find yourself a good builder to partner with.
When your bot is completed, you should create a new set of drawings showing
how the bot was actually built—especially all of the electrical wiring. These draw-
ings will come in handy when you need to repair or improve the bot at later dates.
It’s easy to remember everything that went into building the bot when we first fin-
ish building it. But we soon forget certain details, which can create problems when
maintenance is needed. These as-built drawings will save you a lot of headaches
down the road.